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Sample records for fe pt single

  1. Probing Single Pt Atoms in Complex Intermetallic Al13Fe4.

    Science.gov (United States)

    Yamada, Tsunetomo; Kojima, Takayuki; Abe, Eiji; Kameoka, Satoshi; Murakami, Yumi; Gille, Peter; Tsai, An Pang

    2018-03-21

    The atomic structure of a 0.2 atom % Pt-doped complex metallic alloy, monoclinic Al 13 Fe 4 , was investigated using a single crystal prepared by the Czochralski method. High-angle annular dark-field scanning transmission electron microscopy showed that the Pt atoms were dispersed as single atoms and substituted at Fe sites in Al 13 Fe 4 . Single-crystal X-ray structural analysis revealed that the Pt atoms preferentially substitute at Fe(1). Unlike those that have been reported, Pt single atoms in the surface layers showed lower activity and selectivity than those of Al 2 Pt and bulk Pt for propyne hydrogenation, indicating that the active state of a given single-atom Pt site is strongly dominated by the bonding to surrounding Al atoms.

  2. Pt-Fe catalyst nanoparticles supported on single-wall carbon nanotubes: Direct synthesis and electrochemical performance for methanol oxidation

    Science.gov (United States)

    Ma, Xiaohui; Luo, Liqiang; Zhu, Limei; Yu, Liming; Sheng, Leimei; An, Kang; Ando, Yoshinori; Zhao, Xinluo

    2013-11-01

    Single-wall carbon nanotubes (SWCNTs) supported Pt-Fe nanoparticles have been prepared by one-step hydrogen arc discharge evaporation of carbon electrode containing both Pt and Fe metal elements. The formation of SWCNTs and Pt-Fe nanoparticles occur simultaneously during the evaporation process. High-temperature hydrogen treatment and hydrochloric acid soaking have been carried out to purify and activate those materials in order to obtain a new type of Pt-Fe/SWCNTs catalyst for methanol oxidation. The Pt-Fe/SWCNTs catalyst performs much higher electrocatalytic activity for methanol oxidation, better stability and better durability than a commercial Pt/C catalyst according to the electrochemical measurements, indicating that it has a great potential for applications in direct methanol fuel cells.

  3. Magnetic Properties and Microstructure of FeOx/Fe/FePt and FeOx/FePt Films

    Directory of Open Access Journals (Sweden)

    Jai-Lin Tsai

    2013-01-01

    Full Text Available The Fe(6 nm/FePt film with perpendicular magnetization was deposited on the glass substrate. To study the oxygen diffusion effect on the coupling of Fe/FePt bilayer, the plasma oxidation with 0.5~7% oxygen flow ratio was performed during sputtered part of Fe layer and formed the FeOx(3 nm/Fe(3 nm/FePt trilayer. Two-step magnetic hysteresis loops were found in trilayer with oxygen flow ratio above 1%. The magnetization in FeOx and Fe/FePt layers was decoupled. The moments in FeOx layer were first reversed and followed by coupled Fe/FePt bilayer. The trilayer was annealed again at 500°C and 800°C for 3 minutes. When the FeOx(3 nm/Fe(3 nm/FePt trilayer was annealed at 500°C, the layers structure was changed to FeOx(6 nm/FePt bilayer due to oxygen diffusion. The hard-magnetic FeOx(6 nm/FePt film was coupled with single switching field. The FeOx/(disordered FePt layer structure was observed with further annealing at 800°C and presented soft-magnetic loop. In summary, the coupling between soft-magnetic Fe, FeOx layer, and hard-magnetic L10 FePt layer can be controlled by the oxygen diffusion behavior, and the oxidation of Fe layer was tuned by the annealing temperature. The ordered L10 FePt layer was deteriorated by oxygen and became disordered FePt when the annealed temperature was up to 800°C.

  4. A new type of FCT martensite phase in single-crystalline Fe{sub 3}Pt Invar alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, Masataka; Sekida, Sayaka [Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Fukuda, Takashi, E-mail: fukuda@mat.eng.osaka-u.ac.jp [Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Kakeshita, Tomoyuki [Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Takahashi, Kohki; Koyama, Keiichi; Nojiri, Hiroyuki [High-Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, 2-1-1 Sendai Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)

    2011-08-25

    Highlights: {center_dot} TEM observations at room temperature reveal that the specimen is a single phase of L1{sub 2}-type structure. {center_dot} The spontaneous magnetization and magnetic susceptibility curves of Fe{sub 3}Pt with S = 0.88 have bend points at 60 K. {center_dot} XRD measurements reveal that this alloy exhibits a martensitic transformation to FCT and the transformation temperature is 60 K. {center_dot} The tetragonality c/a is larger than unity in the FCT martensite. {center_dot} This tetragonality is in contrast to the tetragonality c/a < 1generally observed in the FCT martensite with S < 0.8. - Abstract: Martensitic transformation in a highly ordered Fe{sub 3}Pt has been investigated by magnetization and X-ray diffraction measurements. We confirmed that a new type of face-centered tetragonal (FCT) martensite phase appears below 60 K in Fe{sub 3}Pt with a degree of order S = 0.88. The tetragonality c/a gradually increases with decreasing temperature, and is approximately 1.005 at 10 K. This is in contrast to the tetragonality c/a < 1 generally observed in the FCT martensite with a degree of order less than 0.8. The spontaneous magnetization increases in association with the transformation.

  5. Stability investigation of a high number density Pt1/Fe2O3single-atom catalyst under different gas environments by HAADF-STEM.

    Science.gov (United States)

    Duan, Sibin; Wang, Rongming; Liu, Jingyue

    2018-05-18

    Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt 1 /Fe 2 O 3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water-gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe 2 O 3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H 2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H 2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H 2 O molecules to the CO or H 2 significantly accelerates the sintering of the Fe 2 O 3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal-support interaction.

  6. Influence of an Fe cap layer on the structural and magnetic properties of Fe49Pt51/Fe bi-layers

    International Nuclear Information System (INIS)

    Chao-Yang, Duan; Bin, Ma; Zong-Zhi, Zhang; Qing-Yuan, Jin; Fu-Lin, Wei

    2009-01-01

    The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L1 0 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe 49 Pt 51 /Fe bi-layers by their exchange coupling

  7. Solid-state phase equilibria in the Fe-Pt-Pr ternary system at 1173 K

    International Nuclear Information System (INIS)

    Ren Jing; Gu Zhengfei; Cheng Gang; Zhou Huaiying

    2005-01-01

    The solid-state phase equilibria in the Fe-Pt-Pr ternary system at 1173 K (Pr ≤ 70%) were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) techniques. The 1173 K isothermal section consists of 13 single-phase regions, 22 two-phase regions and 10 three-phase regions. At 1173 K, we have observed that the maximum solid solubility of Pt in α-Fe is below 1.5 at.% and the solid solution region of Pt in γ-Fe is from 2 to 35 at.%; the maximum solid solubility of Fe in Pt is 18 at.%. The maximum solubility of Fe in PrPt 5 , PrPt 3 , PrPt 2 , Pr 3 Pt 4 , PrPt, Pr 3 Pt 2 and Pr 7 Pt 3 is below 1 at.%. The maximum solubility of Pr in α-(Fe, Pt), γ-(Fe, Pt), FePt, FePt 3 and (Pt, Fe) (the solid solution of Fe in Pt) is 6, 2, 4, 4.5 and 1.5 at.%, respectively. In this work, it is found that the phase Pr 3 Pt 4 does not exist in the ternary system. The binary compounds Fe 7 Pr and Fe 2 Pr and any new ternary compounds were not observed

  8. High Temperature Magnetic Properties of Indirect Exchange Spring FePt/M(Cu,C/Fe Trilayer Thin Films

    Directory of Open Access Journals (Sweden)

    Anabil Gayen

    2013-01-01

    Full Text Available We report the investigation of temperature dependent magnetic properties of FePt and FePt(30/M(Cu,C/Fe(5 trilayer thin films prepared by using magnetron sputtering technique at ambient temperature and postannealed at different temperatures. L10 ordering, hard magnetic properties, and thermal stability of FePt films are improved with increasing postannealing temperature. In FePt/M/Fe trilayer, the formation of interlayer exchange coupling between magnetic layers depends on interlayer materials and interface morphology. In FePt/C/Fe trilayer, when the C interlayer thickness was about 0.5 nm, a strong interlayer exchange coupling between hard and soft layers was achieved, and saturation magnetization was enhanced considerably after using interlayer exchange coupling with Fe. In addition, incoherent magnetization reversal process observed in FePt/Fe films changes into coherent switching process in FePt/C/Fe films giving rise to a single hysteresis loop. High temperature magnetic studies up to 573 K reveal that the effective reduction in the coercivity decreases largely from 34 Oe/K for FePt/Fe film to 13 Oe/K for FePt/C(0.5/Fe film demonstrating that the interlayer exchange coupling seems to be a promising approach to improve the stability of hard magnetic properties at high temperatures, which is suitable for high-performance magnets and thermally assisted magnetic recording media.

  9. Interface structures in FePt/Fe3Pt hard-soft exchange-coupled magnetic nanocomposites

    International Nuclear Information System (INIS)

    Li Jing; Wang Zhonglin; Zeng Hao; Sun Shouheng; Ping Liu, J.

    2003-01-01

    Self-assembly of FePt and Fe 3 O 4 nanoparticles of different sizes led to various FePt-Fe 3 O 4 nanocomposites. Annealing the composite under reducing atmosphere at 650 and 700 deg. C induced magnetically hard FePt phase and magnetically soft Fe 3 Pt phase. The FePt and Fe 3 Pt phases were either linked by a common interface or coexisted within one grain as domains with sizes <10 nm. This ensures the effective exchange coupling of magnetically hard and soft phases. High-resolution transmission electron microscopy studies provide detailed structural characterization for the FePt based nanocomposites

  10. Hybrid materials based on polymethylsilsesquioxanes containing Fe, Pt, and Fe-Pt metallic nanoparticles

    Science.gov (United States)

    Vasil'kov, A. Yu.; Migulin, D. A.; Naumkin, A. V.; Zubavichus, Ya. V.; Budnikov, A. V.; Ellert, O. G.; Maksimov, Yu. V.; Muzafarov, A. M.

    2017-11-01

    New hybrid materials based on Pt, Fe, and Pt-Fe nanoparticles stabilized in a matrix of polymethylsilsesquioxane nanogel and ultrahigh molecular weight polyethylene (UHMWPE) were prepared. Metal vapor synthesis was used to produce mono- and bimetallic nanoparticles. It was shown that organosilicon nanogel effectively stabilizes Pt nanoparticles with an average size of 0.9 nm. Using the nanogel results in the formation of superparamagnetic Fe particles 3-5 nm in size that consist of ferromagnetic Fe0 core and antiferromagnetic shells of Fe oxides. It is established that using an organosilicon matrix in the formation of Pt-Fe/UHMWPE systems helps reduce the average particle size of Fe in the material from 6.5 to 4.5 nm and narrow their particle size distribution. The composition, magnetic and electronic characteristics of the nanocomposites are studied via transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, XANES, and EXAFS.

  11. Rapid thermal annealing of FePt and FePt/Cu thin films

    Energy Technology Data Exchange (ETDEWEB)

    Brombacher, Christoph

    2011-01-10

    Chemically ordered FePt is one of the most promising materials to reach the ultimate limitations in storage density of future magnetic recording devices due to its high uniaxial magnetocrystalline anisotropy and a corrosion resistance superior to rare-earth based magnets. In this study, FePt and FePt/Cu bilayers have been sputter deposited at room temperature onto thermally oxidized silicon wafers, glass substrates and self-assembled arrays of spherical SiO{sub 2} particles with diameters down to 10 nm. Millisecond flash lamp annealing, as well as conventional rapid thermal annealing was employed to induce the phase transformation from the chemically disordered A1 phase into the chemically ordered L1{sub 0} phase. The influence of the annealing temperature, annealing time and the film thickness on the ordering transformation and (001) texture evolution of FePt films with near equiatomic composition was studied. Whereas flash lamp annealed FePt films exhibit a polycrystalline morphology with high chemical L1{sub 0} order, rapid thermal annealing can lead to the formation of chemically ordered FePt films with (001) texture on amorphous SiO{sub 2}/Si substrates. The resultant high perpendicular magnetic anisotropy and large coercivities up to 40 kOe are demonstrated. Simultaneously to the ordering transformation, rapid thermal annealing to temperatures exceeding 600 C leads to a break up of the continuous FePt film into separated islands. This dewetting behavior was utilized to create regular arrays of FePt nanostructures on SiO{sub 2} particle templates with periods down to 50 nm. The addition of Cu improves the (001) texture formation and chemical ordering for annealing temperatures T{sub a} {<=}600 C. In addition, the magnetic anisotropy and the coercivity of the ternary FePtCu alloy can be effectively tailored by adjusting the Cu content. The prospects of FePtCu based exchange spring media, as well as the magnetic properties of FePtCu nanostructures fabricated

  12. Doping effect on the physical properties of Ca10Pt3As8(Fe2As2)5 single crystals

    Science.gov (United States)

    Pan, Jiayun; Karki, Amar; Plummer, E. W.; Jin, Rongying

    2017-12-01

    Ca10Pt3As8(Fe2As2)5 is a unique parent compound for superconductivity, which consists of both semiconducting Pt3As8 and metallic FeAs layers. We report the observation of superconductivity induced via chemical doping in either Ca site using rare-earth (RE) elements (RE  =  La, Gd) or Fe site using Pt. The interlayer distance and the normal-state physical properties of the doped system change correspondingly. The coupled changes include (1) superconducting transition temperature T c increases with increasing both doping concentration and interlayer distance, (2) our T c value is higher than previously reported maximum value for Pt doping in the Fe site, (3) both the normal-state in-plane resistivity and out-of-plane resistivity change from non-metallic to metallic behavior with increasing doping concentration and T c, and (4) the transverse in-plane magnetoresistance (MRab) changes from linear-field dependence to quadratic behavior upon increasing T c. For La-doped compound with the highest T c (~35 K), upper critical fields (Hc2ab , Hc2c ), coherence lengths (ξ ab, ξ c), and in-plane penetration depth (λ ab) are estimated. We discuss the relationship between chemical doping, interlayer distance, and physical properties in this system.

  13. Nano-stuctured Pt-Fe/C as cathode catalyst in direct methanol fuel cell

    International Nuclear Information System (INIS)

    Li Wenzhen; Zhou Weijiang; Li Huanqiao; Zhou Zhenhua; Zhou Bing; Sun Gongquan; Xin Qin

    2004-01-01

    Pt-Fe/C catalysts were prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution, and then were heat-treated under H 2 /Ar (10 vol.%) at moderate temperature (300 deg. C, Pt-Fe/C300) or high temperature (900 deg. C, Pt-Fe/C900). As comparison, Pt-Fe/C alloy catalyst was prepared by a two-step method (Pt-Fe/C900B). X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that particles size of the catalyst increases with the increase of treatment temperatures. Pt-Fe/C300 catalyst has a mean particle size of 2.8 nm (XRD), 3.6 nm (TEM) and some Pt-Fe alloy was partly formed in this sample. Pt-Fe/C900B catalyst has the biggest particle size of 6.2 nm (XRD) and the best Pt-Fe alloy form. Cyclicvoltammetry (CV) shows that Pt-Fe/C300 has larger electrochemical surface area than other Pt-Fe/C and the highest utilization ratio of 76% among these Pt-based catalysts. Rotating disk electrode (RDE) cathodic curves show that Pt-Fe/C300 has the highest oxygen reduction reaction (ORR) mass activity (MA) and specific activity (SA), as compared with Pt/C catalyst in 1.0 M HClO 4 . However, Pt-Fe/C catalyst does not appears to be a more active catalyst than Pt/C for ORR in 1.0 M HClO 4 + 0.1 M CH 3 OH. Pt-Fe/C300 exhibits higher ORR activity and better performance than other Pt-Fe/C or Pt/C catalysts when employed for cathode in direct methanol single cell test, the enhancement of the cell performance is logically attributed to its higher ORR activity, which is probably attributed to more Pt 0 species existing and Fe ion corrosion from the catalyst

  14. Magnetism of FePt Thin Films

    Science.gov (United States)

    Alqhtany, Norah H.

    Materials with large magnetic anisotropy have received significant attention from the scientific community due to its advantages in technological applications. Equiatomic FePt has been identified as such a material which could possibly be a potential candidate for ultra- high density magnetic recording and other applications like permanent magnets. FePt thin films exhibit ordered L10 texture with high magnetocrystalline anisotropy and high saturation magnetization which seem lucrative for technological applications. This thesis presents an investigation of structural and magnetic properties of granular and epitaxial FePt films with L10 phase prepared by DC sputtering on different substrates (SrTiO3 and glass). X-ray Diffraction (XRD), Atomic Force Microscopy/Magnetic Force Microscopy (AFM/MFM) and Vibrating Sample Magnetometer (VSM) were employed in characterization process. The measurements obtained from these equipment were significant in establishing the relationship between the microstructure and the magnetic properties of these films. The symmetry and magnitude of magnetic anisotropy has also been analyzed and discussed in detail.

  15. Seed-mediated synthesis of core/shell FePtM/FePt (M = Pd, Au) nanowires and their electrocatalysis for oxygen reduction reaction.

    Science.gov (United States)

    Guo, Shaojun; Zhang, Sen; Su, Dong; Sun, Shouheng

    2013-09-18

    We report a new seed-mediated growth of FePt over 2.5 nm wide FePtM (M = Pd, Au) nanowires (NWs) into core/shell FePtM/FePt NWs with controlled FePt shell thickness from 0.3 to 1.3 nm. These FePtM/FePt NWs show shell thickness and core composition-dependent electrocatalytic activity for oxygen reduction reaction (ORR) in 0.1 M HClO4. These core/shell FePtM/FePt NWs are generally more active and durable than the corresponding alloy NWs. Among FePtM/FePt NWs, FePt NWs, FePtPd NWs, and commercial Pt studied, the FePtPd/FePt NWs (0.8 nm shell) show the specific activity of 3.47 mA·cm(-2) and the mass activity of 1.68 A/mg Pt at 0.5 V (vs. Ag/AgCl), superior to all other NWs (less than 1.59 mA/cm(2) and 0.82 A/mg Pt for FePtAu/FePt and FePt) as well as the commercial Pt (0.24 mA/cm(2) and 0.141 A/mg Pt). The FePtM/FePt (0.8 nm shell) NWs are also stable in the ORR condition and show no activity decrease after 5000 potential sweeps between 0.4 and 0.8 V (vs Ag/AgCl). They are the most efficient nanocatalyst ever reported for ORR.

  16. L10 FePtCu bit patterned media

    International Nuclear Information System (INIS)

    Brombacher, C; Albrecht, M; Grobis, M; Hellwig, O; Lee, J; Fidler, J; Eriksson, T; Werner, T

    2012-01-01

    Chemically ordered 5 nm-thick L1 0 FePtCu films with strong perpendicular magnetic anisotropy were post-patterned by nanoimprint lithography into a dot array over a 3 mm-wide circumferential band on a 3 inch Si wafer. The dots with a diameter of 30 nm and a center-to-center pitch of 60 nm appear as single domain and reveal an enhanced switching field as compared to the continuous film. We demonstrate successful recording on a single track using shingled writing with a conventional hard disk drive write/read head.

  17. On the Relationship of Magnetocrystalline Anisotropy and Stoichiometry in Epitaxial L1{sub 0} CoPt(001) and FePt(001) Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Barmak, K

    2004-08-10

    Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 C. In the second series the substrate temperature was kept constant at 704 C for CoPt and 620 C for FePt, while the alloy stoichiometry was varied in the nominalrange of 40-60 at% Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the L1{sub 0} phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering occurring more readily in FePt when compared with CoPt. A perpendicular anisotropy developed in CoPt for substrate temperatures above 534 C and in FePt above 321 C. The structure and width of the magnetic domains in CoPt and FePt, as seen by magnetic force microscopy, also demonstrated an increase in magnetic anisotropy with increasing temperature. For the films deposited at the highest temperatures (704 C for CoPt and 620 C for FePt), the order parameter reached a maximum near the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the concentration of Co or Fe was increased from below to slightly above the equiatomic composition. It is concluded that non-stoichiometric L1{sub 0} CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies.

  18. Surface-effect enhanced magneto-electric coupling in FePt/PMN-PT multiferroic heterostructures

    Science.gov (United States)

    Yang, Y. T.; Li, J.; Peng, X. L.; Hong, B.; Wang, X. Q.; Ge, H. L.; Wang, D. H.; Du, Y. W.

    2017-05-01

    A series of FePt films with different film thickness are deposited on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrates. A standard symmetric `Butterfly' shaped Δ M /M -Ed c loops is obtained in 8 nm FePt/PMN-PT heterostrucuture via strain mediated magnetoelectric coupling. For the 3 nm FePt/PMN-PT heterostructure, the loop-like in-plane magnetization (M) -E curve shares a similar shape with the electric polarization of PMN-PT as a function of electric field. The value of MS shows a dramatic change of 30.9% with Edc changing from 0 to 8 kV/cm, this giant magnetoelectric effect in 3 nm FePt/PMN-PT heterostructure results from the remnant polarization induced charge on FePt/PMN-PT interface via the screening charge effect. The enhanced magnetoelectric coupling in thin magnetic/ferroelectric heterostructures opens a promising avenue for the design of ultralow power magnetoelectric devices and information storage devices.

  19. Thermal treatment effects in the self-assembly of FePt nanoparticle arrays

    International Nuclear Information System (INIS)

    Simeonidis, K.; Mourdikoudis, S.; Tsiaoussis, I.; Dendrinou-Samara, C.; Angelakeris, M.; Kalogirou, O.

    2008-01-01

    This work concentrates on the influence of synthetic mechanisms of FePt nanoparticles on their self-arrangement and some structural and magnetic properties as studied by means of different electron microscopy techniques and SQUID magnetometry. High-reflux points associated with long boiling durations seem adequate to increase the iron precursor's decomposition yield and facilitate the simultaneous cubic to tetragonal FePt transformation, in single-phase FePt nanoparticles. Nevertheless, such conditions also result in the loss of long-range arrangement and in the appearance of coalescence effects. A core-shell structure comprising of FePt and Fe 3 O 4 is favored under mild thermal conditions during synthesis, which seems to confront the undesirable atomic diffusion. Additionally, particle isolation due to the surfactant coating leads in an hcp-symmetry self-assembly. Moreover, working at lower temperatures allows a homogeneous mixture between different phases producing binary composite arrays

  20. Magnetism of FePt Nanoclusters in Polyimide

    Directory of Open Access Journals (Sweden)

    Mircea Chipara

    2015-01-01

    Full Text Available FePt nanoclusters have been implanted onto polyimide films and subjected to thermal annealing in order to obtain a special magnetic phase (L10 dispersed within the polymer. SQUID measurements quantified the magnetic features of the as-prepared and annealed hybrid films. As-implanted FePt nanoparticles in polyimide films exhibited a blocking temperature of 70 ± 5 K. Thermal annealing in zero and 10 kOe applied magnetic field increased the magnetic anisotropy and coercivity of the samples. Wide Angle X-Ray Scattering confirmed the presence of FePt and L10 phase. All samples (as deposited and annealed exhibited electron spin resonance spectra consisting of two overlapping lines. The broad line was a ferromagnetic resonance originating from FePt nanoparticles. Its angular dependence indicated the magnetic anisotropy of FePt nanoparticles. SEM micrographs suggest a negligible coalescence of FePt nanoparticles, supporting that the enhancement of the magnetic properties is a consequence of the improvement of the L10 structure. The narrow ESR line was assigned to nonmagnetic (paramagnetic impurities within the samples consistent with graphite-like structures generated by the local degradation of the polymer during implantation and annealing. Raman spectroscopy confirmed the formation of graphitic structures in annealed KHN and in KHN-FePt.

  1. Surface Modification and Heat Generation of FePt Nanoparticles

    Directory of Open Access Journals (Sweden)

    Da-Hua Wei

    2017-02-01

    Full Text Available The chemical reduction of ferric acetylacetonate (Fe(acac3 and platinum acetylacetonate (Pt(acac2 using the polyol solvent of phenyl ether as an agent as well as an effective surfactant has successfully yielded monodispersive FePt nanoparticles (NPs with a hydrophobic ligand and a size of approximately 3.8 nm. The present FePt NPs synthesized using oleic acid and oleylamine as the stabilizers under identical conditions were achieved with a simple method. The surface modification of FePt NPs by using mercaptoacetic acid (thiol as a phase transfer reagent through ligand exchange turned the NPs hydrophilic, and the FePt NPs were water-dispersible. The hydrophilic NPs indicated slight agglomeration which was observed by transmission electron microscopy images. The thiol functional group bond to the FePt atoms of the surface was confirmed by Fourier transform infrared spectroscopy (FTIR spectra. The water-dispersible FePt NPs employed as a heating agent could reach the requirement of biocompatibility and produce a sufficient heat response of 45 °C for magnetically induced hyperthermia in tumor treatment fields.

  2. FePt magnetic particles prepared by surfactant-assisted ball milling

    Energy Technology Data Exchange (ETDEWEB)

    Velasco, V., E-mail: vvjimeno@fis.ucm.es [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, P.O. Box 155, Las Rozas 28230 (Spain); Departamento de Física de Materiales, Universidad Complutense de Madrid, Madrid 28040 (Spain); Hernando, A.; Crespo, P. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, P.O. Box 155, Las Rozas 28230 (Spain); Departamento de Física de Materiales, Universidad Complutense de Madrid, Madrid 28040 (Spain)

    2013-10-15

    High-energy ball milling of Fe and Pt elemental powders has been carried out under dry and wet (in presence of solvent and surfactants) conditions. Dry milling leads to the formation of the disordered FCC-FePt alloy whereas by the wet milling procedure the main process is the decrease of Fe and Pt particle size, although some dissolution of Pt into Fe grains cannot be ruled out, and no hint of the formation of the FCC-FePt phase is observed even to milling times up to 20 h, as X-ray diffraction, electron microscopy and Mössbauer spectroscopy indicates. The as-milled particles were annealed at 600 °C for 2 h under Ar atmosphere. It is noticed that the disordered fcc-FePt phase observed in particles milled under dry conditions transform to ordered fct phase characterized by a hard magnetic behavior with a coercive field up to 10,000 Oe. However, those particles milled in the surfactant/solvent medium exhibit a soft magnetic behavior with a coercive field of 600 Oe. These results indicate that wet high-energy ball milling is not an adequate technique for obtaining single-phase FePt particles. - Highlights: • FePt particles have been obtained by high-energy ball milling. • In the presence of surfactants and solvents, almost no alloying process takes place. • After annealing, the coercive field of the FePt alloy particles increases from 150 Oe to 10,000 Oe.

  3. Single crystalline PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices.

    Science.gov (United States)

    Lin, Yung-Chen; Lu, Kuo-Chang; Wu, Wen-Wei; Bai, Jingwei; Chen, Lih J; Tu, K N; Huang, Yu

    2008-03-01

    We report the formation of PtSi nanowires, PtSi/Si/PtSi nanowire heterostructures, and nanodevices from such heterostructures. Scanning electron microscopy studies show that silicon nanowires can be converted into PtSi nanowires through controlled reactions between lithographically defined platinum pads and silicon nanowires. High-resolution transmission electron microscopy studies show that PtSi/Si/PtSi heterostructure has an atomically sharp interface with epitaxial relationships of Si[110]//PtSi[010] and Si(111)//PtSi(101). Electrical measurements show that the pure PtSi nanowires have low resistivities approximately 28.6 microOmega.cm and high breakdown current densities>1x10(8) A/cm2. Furthermore, using single crystal PtSi/Si/PtSi nanowire heterostructures with atomically sharp interfaces, we have fabricated high-performance nanoscale field-effect transistors from intrinsic silicon nanowires, in which the source and drain contacts are defined by the metallic PtSi nanowire regions, and the gate length is defined by the Si nanowire region. Electrical measurements show nearly perfect p-channel enhancement mode transistor behavior with a normalized transconductance of 0.3 mS/microm, field-effect hole mobility of 168 cm2/V.s, and on/off ratio>10(7), demonstrating the best performing device from intrinsic silicon nanowires.

  4. Low Temperature Transformation of Fe-Pd and Fe-Pt Invar Alloys

    OpenAIRE

    Masaaki, Matsui; Kengo, Adachi; Hidefumi, Asano; Department of Iron and Steel Engineering, Faculty of Engineering Nagoya University; Department of Iron and Steel Engineering, Faculty of Engineering Nagoya University; Department of Iron and Steel Engineering, Faculty of Engineering Nagoya University

    1981-01-01

    Low temperature structures of Fe-Pd and Fe-Pt alloys in the Invar region have been determined by means of low temperature X-ray diffraction experiment. The phase diagrams are obtained. A new fct phase is found in the ordered and disordered Fe-Pt and the disordered Fe-Pd systems. An effect of the degree of order for Fe_3Pt to the structural transformations are examined. The lattice instability of Fe-based fcc Invar alloys are discussed from the low temperature structures with the lattice softe...

  5. Correlating Structure and Oxygen Reduction Activity on Y/Pt(111) and Gd/Pt(111) Single Crystals

    DEFF Research Database (Denmark)

    Ulrikkeholm, Elisabeth Therese; Pedersen, Anders Filsøe; Johansson, Tobias Peter

    2015-01-01

    of this technology. Improving the activity of Pt by alloying it with other metals could decrease the loading of Pt at the cathode to a level comparable to Pt-group metal loading in internal combustion engines. PtxY and PtxGd exhibit exceptionally high activity for oxygen reduction, both in the polycrystalline form...... and the nanoparticulate form. [1,2,3,4]. Moreover, their negative alloying energy may make them inherently less prone to degradation via dealloying than the more commonly investigated alloys of Pt and late transition metals such as Ni, Co, Fe and Cu. In order to understand the origin of the enhanced activity...... of these alloys, we have investigated Y/Pt(111) [5] and Gd/Pt(111) single crystals, formed by depositing large amounts of Y and Gd on Pt(111) single crystals under Ultra-High Vacuum (UHV) conditions and annealing to high temperatures. We subsequently characterised the surface using low energy electron diffraction...

  6. Fe Stabilization by Intermetallic L10-FePt and Pt Catalysis Enhancement in L10-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells.

    Science.gov (United States)

    Li, Junrui; Xi, Zheng; Pan, Yung-Tin; Spendelow, Jacob S; Duchesne, Paul N; Su, Dong; Li, Qing; Yu, Chao; Yin, Zhouyang; Shen, Bo; Kim, Yu Seung; Zhang, Peng; Sun, Shouheng

    2018-02-28

    We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L1 0 -MPt alloy nanoparticle (NP) structure and how to surround the L1 0 -MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L1 0 -FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Pt shell, especially the two atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO 4 solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L1 0 -FePt/Pt catalyst has a mass activity of 0.7 A/mg Pt from the half-cell ORR test and shows no obvious mass activity loss after 30 000 potential cycles between 0.6 and 0.95 V at 80 °C in the MEA, meeting the DOE 2020 target (fuel cell applications.

  7. Nanocrystalline Fe-Pt alloys. Phase transformations, structure and magnetism

    Energy Technology Data Exchange (ETDEWEB)

    Lyubina, J.V.

    2006-12-21

    This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometersized grains. Nanocrystalline Fe{sub 100-x}Pt{sub x} (x=40-60) alloys have been prepared by mechanical ball milling of elemental Fe and Pt powders at liquid nitrogen temperature. The as-milled Fe-Pt alloys consist of {proportional_to} 100 {mu}m sized particles constituted by randomly oriented grains having an average size in the range of 10-40 nm. Depending on the milling time, three major microstructure types have been obtained: samples with a multilayer-type structure of Fe and Pt with a thickness of 20-300 nm and a very thin (several nanometers) A1 layer at their interfaces (2 h milled), an intermediate structure, consisting of finer lamellae of Fe and Pt (below approximately 100 nm) with the A1 layer thickness reaching several tens of nanometers (4 h milled) and alloys containing a homogeneous A1 phase (7 h milled). Subsequent heat treatment at elevated temperatures is required for the formation of the L1{sub 0} FePt phase. The ordering develops via so-called combined solid state reactions. It is accompanied by grain growth and thermally assisted removal of defects introduced by milling and proceeds rapidly at moderate temperatures by nucleation and growth of the ordered phases with a high degree of the long-range order. In a two-particle interaction model elaborated in the present work, the existence of hysteresis in recoil loops has been shown to arise from insufficient coupling between the low- and the high-anisotropy particles. The model reveals the main features of magnetisation reversal processes observed experimentally in exchange-coupled systems. Neutron diffraction has been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. (orig.)

  8. The investigation of electrochemical properties for Fe3O4@Pt nanocomposites and an enhancement sensing for nitrite

    International Nuclear Information System (INIS)

    Liu, Yang; Zhou, Jie; Gong, Jin; Wu, Wei-Ping; Bao, Ning; Pan, Zhong-Qin; Gu, Hai-Ying

    2013-01-01

    Highlights: •Electrochemical characteristics on nanoparticles and nanocomposites were compared. •The reasons for superior electrochemical activity of Fe 3 O 4 @Pt were discussed. •We report an excellent nitrite biosensor based on Fe 3 O 4 @Pt. •Electro-analytical parameters of nitrite at Fe 3 O 4 @Pt were evaluated in detail. -- Abstract: The electrochemical differences (such as charge transfer resistivity, electroactive surface, standard electron transfer rate constant, adsorption amount and analytical performance of nitrite sensor) between Fe 3 O 4 @Pt nanocomposites with two elements and core–shell structure and NPs (Fe 3 O 4 nanoparticles and Pt nanoparticles) with single component and simple structure were investigated in detail. Above those investigations, it is believed that for the Fe 3 O 4 @Pt core–shell nanocomposites, Pt shell could provide more electro-catalytic activity while magnetic Fe 3 O 4 core could provide larger surface area and facilitate the purification of nanocomposites. After that, Fe 3 O 4 @Pt nanocomposites modified GCE served as a nitrite sensor. Electrochemical parameters of nitrite at Fe 3 O 4 @Pt nanocomposites such as electron transfer number, electron transfer coefficient, standard heterogeneous rate constant and electron diffusion coefficient were evaluated. With the proposed electrochemical sensors, nitrite in tap water and orange juice could be detected. This investigation suggested that core–shell nanocomposites were superior for the fabrication of electrochemical sensors

  9. Novel Nanohybrids Derived from the Attachment of FePt Nanoparticles on Carbon Nanotubes

    NARCIS (Netherlands)

    Tsoufis, Theodoros; Tomou, Aphrodite; Gournis, Dimitrios; Douvalis, Alexios P.; Panagiotopoulos, Ioannis; Kooi, Bart; Georgakilas, Vasilios; Arfaoui, Imad; Bakas, Thomas

    2008-01-01

    Multiwalled carbon nanotubes (MWCNTs) were used as nanotemplates for the dispersion and stabilization of FePt nanoparticles (NPs). Pre-formed capped FePt NPs were connected to the MWCNTs external surface via covalent binding through organic linkers. Free FePt NPs and MWCNTs-FePt hybrids were

  10. Relaxor-PT Single Crystal Piezoelectric Sensors

    Directory of Open Access Journals (Sweden)

    Xiaoning Jiang

    2014-07-01

    Full Text Available Relaxor-PbTiO3 piezoelectric single crystals have been widely used in a broad range of electromechanical devices, including piezoelectric sensors, actuators, and transducers. This paper reviews the unique properties of these single crystals for piezoelectric sensors. Design, fabrication and characterization of various relaxor-PT single crystal piezoelectric sensors and their applications are presented and compared with their piezoelectric ceramic counterparts. Newly applicable fields and future trends of relaxor-PT sensors are also suggested in this review paper.

  11. Infrared-active quadruple contrast FePt nanoparticles for multiple scale molecular imaging.

    Science.gov (United States)

    Chou, Shang-Wei; Liu, Chien-Liang; Liu, Tzu-Ming; Shen, Yu-Fang; Kuo, Lun-Chang; Wu, Cheng-Ham; Hsieh, Tsung-Yuan; Wu, Pei-Chun; Tsai, Ming-Rung; Yang, Che-Chang; Chang, Kai-Yao; Lu, Meng-Hua; Li, Pai-Chi; Chen, Shi-Ping; Wang, Yu-Hsin; Lu, Chen-Wen; Chen, Yi-An; Huang, Chih-Chia; Wang, Churng-Ren Chris; Hsiao, Jong-Kai; Li, Meng-Lin; Chou, Pi-Tai

    2016-04-01

    A single nanomaterial with multiple imaging contrasts and functions is highly desired for multiscale theragnosis. Herein, we demonstrate single 1-1.9 μm infrared-active FePt alloy nanoparticles (FePt NPs) offering unprecedented four-contrast-in-one molecular imaging - computed tomography (CT), magnetic resonance imaging (MRI), photoacoustic (PA) imaging, and high-order multiphoton luminescence (HOMPL) microscopy. The PA response of FePt NPs outperforms that of infrared-active gold nanorods by 3- to 5.6-fold under identical excitation fluence and particle concentrations. HOMPL (680 nm) of an isolated FePt NP renders spatial full-width-at-half-maximum values of 432 nm and 300 nm beyond the optical diffraction limit for 1230-nm and 920-nm excitation, respectively. The in vivo targeting function was successfully visualized using HOMPL, PA imaging, CT, and MRI, thereby validating FePt as a single nanomaterial system covering up to four types (Optical/PA/CT/MRI) of molecular imaging contrast, ranging from the microscopic level to whole-body scale investigation. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Splitting of the ultraviolet plasmon resonance from controlling FePt nanoparticles morphology

    Science.gov (United States)

    Yu, Jian; Xiao, Tingting; Wang, Xuemin; Zhao, Yan; Li, Xiaojia; Xu, Xibin; Xiong, Zhengwei; Wang, Xinming; Peng, Liping; Wang, Jin; Yin, Hongbu; Chen, Jie; Meng, Gang; Li, Yifan; Wu, Weidong

    2018-03-01

    We show a designed FePt nanoparticles for embedding in a single crystal MgO matrix and demonstrate plasmon resonance absorption can appear in the ultraviolet region. The state of the FePt alloy is confirmed by X-ray photoelectron spectroscopy and selected area electron diffraction. By increasing the laser energy density from 4 to 6 J/cm2, the shape of the FePt nanoparticles is changed from quasi-spherical to quasi-elliptical. Compared with pure MgO, a single plasmon resonance peak at 234 nm was found in the ultraviolet region for the embedded FePt. Increasing the laser energy density induces peak splitting into two peaks, located at 225 and 262 nm, respectively. With a high laser energy density, a red-shift and a blue-shift are observed for the two peaks, respectively. These results are accordance with the theoretical calculations. The ultraviolet plasmon resonance absorption for FePt NPs can be tuned by changing the shape of the nanoparticles.

  13. Catalyzed hydrogenation of nitrogen and ethylene on metal (Fe, Pt) single crystal surfaces and effects of coadsorption: A sum frequency generation vibrational spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Westerberg, Staffan Per Gustav [Univ. of California, Berkeley, CA (United States)

    2004-01-01

    High-pressure catalytic reactions and associated processes, such as adsorption have been studied on a molecular level on single crystal surfaces. Sum Frequency Generation (SFG) vibrational spectroscopy together with Auger Electron Spectroscopy (AES), Temperature Programmed Desorption (TPD) and Gas Chromatography (GC) were used to investigate the nature of species on catalytic surfaces and to measure the catalytic reaction rates. Special attention has been directed at studying high-pressure reactions and in particular, ammonia synthesis in order to identify reaction intermediates and the influence of adsorbates on the surface during reaction conditions. The adsorption of gases N2, H2, O2 and NH3 that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by sum frequency generation vibrational spectroscopy using an integrated Ultra-High Vacuum (UHV)/high-pressure system. SFG spectra are presented for the dissociation intermediates, NH2 (~3325 cm-1) and NH (~3235 cm-1) under high pressure of ammonia (200 Torr) on the clean Fe(111) surface. Addition of 0.5 Torr of oxygen to 200 Torr of ammonia does not significantly change the bonding of dissociation intermediates to the surface. However, it leads to a phase change of nearly 180° between the resonant and non-resonant second order non-linear susceptibility of the surface, demonstrated by the reversal of the SFG spectral features. Heating the surface in the presence of 200 Torr ammonia and 0.5 Torr oxygen reduces the oxygen coverage, which can be seen from the SFG spectra as another relative phase change of 180°. The reduction of the oxide is also supported by Auger electron spectroscopy. The result suggests that the phase change of the spectral features could serve as a sensitive indicator of the chemical environment of the adsorbates.

  14. Preparation and properties of ferromagnetic FePt dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Sato, K. [Dowa Mining Company, Daiichi Takko building. 1-8-2, Marunouchi Chiyada ku, Tokyo 100-8282 (Japan); Jeyadevan, B. [Graduate School of Environmental Studies, Tohoku University, Aoba 20, Aramaki Aza Aoba ku, Sendai 980-8579 (Japan)]. E-mail: jeya@mail.kankyo.tohoku.ac.jp; Tohji, K. [Graduate School of Environmental Studies, Tohoku University, Aoba 20, Aramaki Aza Aoba ku, Sendai 980-8579 (Japan)

    2005-03-15

    FePt nanoparticles were prepared via the coreduction of platinum and iron acetyl acetonate precursors in tetraethylene glycol at various temperatures. The X-ray diffractogram of the as-synthesized FePt nanoparticles at temperatures above 573 K exhibited (0 0 1) and (1 1 0) superlattice reflections. TEM-EDX studies revealed that the average particle diameter was 5 nm with nearly equiatomic composition. The saturation magnetization and coercivity at room temperature (RT) were found to be 50 emu/g and 2.1 kOe, respectively. The high anisotropy field of about 32 kOe and magnetic ordering at RT revealed the presence of the highly anisotropic L1{sub 0} phase. These particles were partially dispersed in an organic solvent using oleyl amine as surfactant. The dispersed FePt nanoparticles will be useful in future technological applications.

  15. Double MgO-based Perpendicular Magnetic-Tunnel-Junction Spin-valve Structure with a Top Co2Fe6B2Free Layer using a Single SyAF [Co/Pt]nLayer.

    Science.gov (United States)

    Choi, Jin-Young; Lee, Dong-Gi; Baek, Jong-Ung; Park, Jea-Gun

    2018-02-01

    A new perpendicular spin-transfer-torque magnetic-tunnel-junction (p-MTJ) spin-valve was developed to achieve a high tunneling magnetoresistance (TMR) ratio. It had a double MgO-based spin-valve structure with a top Co 2 Fe 6 B 2 free layer and incorporated a single SyAF [Co(0.4 nm)/Pt(0.3 nm)] 3 layer and a new buffer layer of Co(0.6)/Pt(0.3)/Co(0.4). It had a TMR ratio of 180% and anisotropy exchange field (H ex ) of 3.44 kOe after ex-situ annealing of 350 °C for 30 min under a vacuum below 10 -6 torr and a perpendicular magnetic field of 3 tesla, thereby ensuring a memory margin and avoiding read disturbance failures. Its high level of performance was due to the face-center-cubic crystallinity of the MgO tunneling barrier being significantly improved by decreasing its surface roughness (i.e., peak-to-valley length of 1.4 nm).

  16. SELECTIVE HYDROGENATION OF CINNAMALDEHYDE WITH Pt AND Pt-Fe CATALYSTS: EFFECTS OF THE SUPPORT

    Directory of Open Access Journals (Sweden)

    A.B. da Silva

    1998-06-01

    Full Text Available Low-temperature reduced TiO2-supported Pt and Pt-Fe catalysts are much more active and selective for the liquid–phase hydrogenation of cinnamaldehyde to unsaturated cinnamyl alcohol than the corresponding carbon-supported catalysts. High-temperature reduced catalysts, where the SMSI effect should be present, are almost inactive for this reaction. There is at present no definitive explanation for this effect but an electronic metal-support interaction is most probably involved.

  17. Self-suspended permanent magnetic FePt ferrofluids

    KAUST Repository

    Dallas, Panagiotis

    2013-10-01

    We present the synthesis and characterization of a new class of self-suspended ferrofluids that exhibit remanent magnetization at room temperature. Our system relies on the chemisorption of a thiol-terminated ionic liquid with very low melting point on the surface of L10 FePt nanoparticles. In contrast, all types of ferrofluids previously reported employ either volatile solvents as the suspending media or superparamagnetic iron oxide nanoparticles (that lacks permanent magnetization) as the inorganic component. The ferrofluids do not show any sign of flocculation or phase separation, despite the strong interactions between the magnetic nanoparticles due to the strong chemisorption of the ionic liquid as evidenced by Raman spectroscopy and thermal analysis. Composites with high FePt loading (40 and 70. wt%) exhibit a pseudo solid-like rheological behavior and high remanent magnetization values (10.1 and 12.8. emu/g respectively). At lower FePt loading (12. wt%) a liquid like behavior is observed and the remanent and saturation magnetization values are 3.5 and 6.2. emu/g, respectively. The magnetic and flow properties of the materials can be easily fine tuned by controlling the type and amount of FePt nanoparticles used. © 2013 Elsevier Inc.

  18. Magnetocrystalline anisotropy of FePt: a detailed view

    Czech Academy of Sciences Publication Activity Database

    Khan, S.A.; Blaha, P.; Ebert, H.; Minár, J.; Šipr, Ondřej

    2016-01-01

    Roč. 94, č. 14 (2016), 1-10, č. článku 144436. ISSN 2469-9950 Institutional support: RVO:68378271 Keywords : magnetocrystalline anisotropy * FePt * LDA Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016

  19. Preparation and characterization of Fe3O4-Pt nanoparticles

    Science.gov (United States)

    Andrade, Ângela Leão; Cavalcante, Luis Carlos Duarte; Fabris, José Domingos; Pereira, Márcio César; Ardisson, José Domingos; Domingues, Rosana Zacarias

    2017-11-01

    Pt and Pt-based nanomaterials are active anticancer drugs for their ability to inhibit the division of living cells. Nanoparticles of magnetite containing variable proportions of platinum were prepared in the laboratory. The magnetite nanoparticles with platinum (Pt-Fe3O4) were obtained by reducing the Fe3+ of the maghemite ( γ Fe2O3) mixed with platinum (II) acetylacetonate and sucrose in two inversely coupled ceramic crucibles and heated in a furnace at 400 °C for 20 min. The formed carbon during this preparation acts to chemically reduce the ferric iron in maghemite. Moreover, its residual layer on the particle surface prevents the forming magnetite from oxidizing in air and helps retain the platinum in the solid mixture. The produced Pt-magnetite samples were characterized by 57Fe-Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, and magnetization measurements. Measurements of AC magnetic-field-induced heating properties of the obtained nanocomposites, in aqueous solution, showed that they are suitable as a hyperthermia agent for biological applications.

  20. Nanoporous PtFe alloys as highly active and durable electrocatalysts for oxygen reduction reaction

    Science.gov (United States)

    Duan, Huimei; Hao, Qin; Xu, Caixia

    2014-12-01

    Nanoporous PtFe alloys with two different bimetallic ratios are fabricated by selectively dealloying PtFeAl ternary alloys, characterized by nanoscaled bicontinuous network skeleton with interconnected hollow channels extending in all three dimensions. The reactive components in PtFeAl ternary alloy were sequentially leached out in a highly controllable manner, generating nanoporous architecture with different bimetallic ratios and the typical ligament size as small as 5 nm. These nanoporous PtFe alloys exhibit much enhanced electrocatalytic activity for oxygen reduction reaction compared with the PtFe/C and Pt/C catalysts. The specific and mass activities for oxygen reduction follow the order of nanoporous Pt75Fe25 > nanoporous Pt55Fe45 > PtFe/C > Pt/C. In the absence of any catalyst support, the structure stability of nanoporous PtFe alloys is greatly enhanced with less loss of the electrochemical surface area and the oxygen reduction activity upon long-term potential scan tests compared with PtFe/C and Pt/C catalysts. The as-made nanoporous PtFe alloys thus hold great application potential as promising cathode electrocatalyst in proton exchange membrane fuel cells with the advantages of easy preparation along with superior oxygen reduction activity and durability.

  1. Magnetic and structural characterizations on nanoparticles of FePt, FeRh and their composites

    International Nuclear Information System (INIS)

    Ko, Hnin Yu Yu; Suzuki, Takao; Nam, Nguyen T.; Phuoc, Nguyen N.; Cao Jiangwei; Hirotsu, Yoshihiko

    2008-01-01

    The various compositions of FePt and FeRh nanoparticles, and their composite particles have been fabricated by the solution-phase chemical method and their magnetic properties characterized. High-resolution transmission electron microscopic observations indicate that mono-dispersed FeRh and FePt/FeRh nanoparticles are fabricated with the average size of 3-5 nm. However, larger size particles are distributed in the annealed state. From X-ray diffraction results, the as-deposited FeRh nanoparticles reveal a chemically disordered fcc structure which can be transformed into CsCl-type structure through thermal annealing. Similarly, the annealed FePt nanoparticles show the L1 0 -phase fct structure although the fcc structure is apparent in the as-deposited state. It is also found that the first time in the exchange bias effect in the composite of ferromagnetic (FePt) and anti-ferromagnetic (FeRh) nanoparticles; result in a shift of the hysteresis loop after field cooling process

  2. Environmental transmission electron microscopy investigations of Pt-Fe2O3 nanoparticles for nucleating carbon nanotubes

    DEFF Research Database (Denmark)

    He, Maoshuai; Jin, Hua; Zhang, Lili

    2016-01-01

    Elucidating the evolution of bimetallic catalyst for nucleating carbon nanotube has been challenging. In this work, acorn-like Pt-Fe2O3 nanoparticles are developed for the growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition. Using in situ environmental transmission...... electron microscopy, restructuring of the acorn-like Pt-Fe2O3 nanoparticles at reaction conditions is investigated. Upon heating to reaction temperature, ε-Fe2O3 is converted to β-Fe2O3, which can be subsequently reduced to metallic Fe once introducing CO. As Pt promotes the carburization of Fe, part...

  3. Chemical synthesis, phase transformation and magnetic proprieties of FePt and FePd nanoparticles

    International Nuclear Information System (INIS)

    Delattre, Anastasia

    2010-01-01

    This work aims at understanding the chemical synthesis of FePt and FePd nanoparticles (NPs), and at exploring how to implement the phase transformation from the chemically disordered to the L10 phase, without coalescence. Using hexadecanenitrile instead of oleylamine, we obtain NPs with a more homogenous internal composition, instead of core-shell NPs. Through a systematic study (designed experiment relying on Taguchi tables), we developed the FePd synthesis, while evidencing the role of each ligand and of the reductor. To induce the crystalline phase transformation while avoiding coalescence, we explored two ways. In the first one, atomic vacancies are introduced in the NPs through light ion irradiation, atomic mobility being ensured by annealing at moderate temperature (300 C). As a result, the blocking temperature is multiplied by 4, due to anisotropy enhancement. However, strong chemical ordering in the L10 phase cannot be achieved. The second approach relies on the dispersion of the NPs in a salt (NaCl) matrix, prior to annealing at 700 C: high chemical ordering is achieved, and the blocking temperature is beyond 400 C. We then developed a single-step process to remove the salt by dissolution in water and to re-disperse NPs in stable aqueous or organics solutions. These high magnetic anisotropy NPs are then readily available for further chemical or manipulation steps, with applied perspectives in areas such as data storage, or biology. (author)

  4. Role of Pt(0) in bimetallic (Pt,Fe)-FER catalysts in the N2O decomposition

    Czech Academy of Sciences Publication Activity Database

    Tabor, Edyta; Jíša, Kamil; Nováková, Jana; Bastl, Zdeněk; Vondrová, Alena; Závěta, K.; Sobalík, Zdeněk

    2013-01-01

    Roč. 165, JAN 2013 (2013), s. 40-47 ISSN 1387-1811 R&D Projects: GA ČR GA203/09/1627 Institutional support: RVO:61388955 Keywords : bimetallic Pt,Fe-FER * Pt-FER * Pt(0) clusters Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.209, year: 2013

  5. Thermal stability, thermal expansion and grain-growth in exchange-coupled Fe-Pt-Ag-B bulk nanocomposite magnets

    International Nuclear Information System (INIS)

    Nicula, R.; Crisan, O.; Crisan, A.D.; Mercioniu, I.; Stir, M.; Vasiliu, F.

    2015-01-01

    Highlights: • Formation of the L10 FePt hard-magnetic phase (>90%) directly in the as-cast state. • Specific alternating hard/soft nanostructure is stable to 600 °C without grain growth. • Anisotropic and non-linear thermal expansion effects. • The FePtAgB alloy behaves like a single magnetic phase (full exchange coupling). - Abstract: Rare-earth free (RE-free) exchange coupling nanocomposite magnets are intensively studied nowadays due to their potential use in applications demanding stable high-temperature operation and corrosion resistance. In this respect, the FePt alloy system is one of the most actively addressed potential permanent magnet solutions. In FePt alloys, promising magnetic features arise from the co-existence of hard magnetic L1 0 FePt and soft magnetic L1 2 Fe 3 Pt phases emerged from the same metastable precursor. The present work deals with an in-situ temperature-resolved synchrotron radiation study of the thermal stability, thermal expansion and microstructure evolution in exchange-coupled FePtAgB alloys. The as-cast microstructural state as well as the optimized magnetic behavior are given as reference and correlated to the observed microstructural evolution with temperature. The melt-spun Fe 48 Pt 28 Ag 6 B 18 alloy ribbons were examined in situ by synchrotron X-ray powder diffraction from ambient temperature up to 600 °C. The FePt-Fe 3 Pt exchange-coupled microstructure achieved by rapid solidification is not significantly altered during the high temperature exposure. The thermal expansion of the FePt L1 0 unit cell has been found to be strongly anisotropic, being essentially an in-plane expansion which may be seen as an anisotropic invar effect. For the FePt L1 0 phase, a significant deviation from linear thermal expansion is observed at the Curie temperature T C = 477 °C. This non-linear behavior above T C is tentatively linked to a diffusion/segregation mechanism of Ag. The promising hard magnetic properties as well as the

  6. Thermal stability, thermal expansion and grain-growth in exchange-coupled Fe-Pt-Ag-B bulk nanocomposite magnets

    Energy Technology Data Exchange (ETDEWEB)

    Nicula, R., E-mail: radu.nicula@empa.ch [Empa, Swiss Federal Laboratories for Materials Science and Technology, Advanced Materials Processing, Feuerwerkerstr. 39, CH-3602 Thun (Switzerland); Crisan, O.; Crisan, A.D.; Mercioniu, I. [National Institute for Materials Physics, P.O. Box MG-7, 077125 Bucharest-Magurele (Romania); Stir, M. [University of Berne, Department of Chemistry and Biochemistry, Freiestrasse 3, CH-3012 Berne (Switzerland); Vasiliu, F. [National Institute for Materials Physics, P.O. Box MG-7, 077125 Bucharest-Magurele (Romania)

    2015-02-15

    Highlights: • Formation of the L10 FePt hard-magnetic phase (>90%) directly in the as-cast state. • Specific alternating hard/soft nanostructure is stable to 600 °C without grain growth. • Anisotropic and non-linear thermal expansion effects. • The FePtAgB alloy behaves like a single magnetic phase (full exchange coupling). - Abstract: Rare-earth free (RE-free) exchange coupling nanocomposite magnets are intensively studied nowadays due to their potential use in applications demanding stable high-temperature operation and corrosion resistance. In this respect, the FePt alloy system is one of the most actively addressed potential permanent magnet solutions. In FePt alloys, promising magnetic features arise from the co-existence of hard magnetic L1{sub 0} FePt and soft magnetic L1{sub 2} Fe{sub 3}Pt phases emerged from the same metastable precursor. The present work deals with an in-situ temperature-resolved synchrotron radiation study of the thermal stability, thermal expansion and microstructure evolution in exchange-coupled FePtAgB alloys. The as-cast microstructural state as well as the optimized magnetic behavior are given as reference and correlated to the observed microstructural evolution with temperature. The melt-spun Fe{sub 48}Pt{sub 28}Ag{sub 6}B{sub 18} alloy ribbons were examined in situ by synchrotron X-ray powder diffraction from ambient temperature up to 600 °C. The FePt-Fe{sub 3}Pt exchange-coupled microstructure achieved by rapid solidification is not significantly altered during the high temperature exposure. The thermal expansion of the FePt L1{sub 0} unit cell has been found to be strongly anisotropic, being essentially an in-plane expansion which may be seen as an anisotropic invar effect. For the FePt L1{sub 0} phase, a significant deviation from linear thermal expansion is observed at the Curie temperature T{sub C} = 477 °C. This non-linear behavior above T{sub C} is tentatively linked to a diffusion/segregation mechanism of Ag

  7. Shape-dependent surface magnetism of Co-Pt and Fe-Pt nanoparticles from first principles

    Science.gov (United States)

    Liu, Zhenyu; Wang, Guofeng

    2017-12-01

    In this paper, we have performed the first-principles density functional theory calculations to predict the magnetic properties of the CoPt and FePt nanoparticles in cuboctahedral, decahedral, and icosahedral shapes. The modeled alloy nanoparticles have a diameter of 1.1 nm and consist of 31 5 d Pt atoms and 24 3 d Co (or Fe) atoms. For both CoPt and FePt, we found that the decahedral nanoparticles had appreciably lower surface magnetic moments than the cuboctahedral and icosahedral nanoparticles. Our analysis indicated that this reduction in the surface magnetism was related to a large contraction of atomic spacing and high local Co (or Fe) concentration in the surface of the decahedral nanoparticles. More interestingly, we predicted that the CoPt and FePt cuboctahedral nanoparticles exhibited dramatically different surface spin structures when noncollinear magnetism was taken into account. Our calculation results revealed that surface anisotropy energy decided the fashion of surface spin canting in the CoPt and FePt nanoparticles, confirming previous predictions from atomistic Monte Carlo simulations.

  8. Design and Micromagnetic Simulation of Fe/L10-FePt/Fe Trilayer for Exchange Coupled Composite Bit Patterned Media at Ultrahigh Areal Density

    Directory of Open Access Journals (Sweden)

    Warunee Tipcharoen

    2015-01-01

    Full Text Available Exchange coupled composite bit patterned media (ECC-BPM are one candidate to solve the trilemma issues, overcome superparamagnetic limitations, and obtain ultrahigh areal density. In this work, the ECC continuous media and ECC-BPM of Fe/L10-FePt/Fe trilayer schemes are proposed and investigated based on the Landau-Lifshitz-Gilbert equation. The switching field, Hsw, of the hard phase in the proposed continuous ECC trilayer media structure is reduced below the maximum write head field at interlayer exchange coupling between hard and soft phases, Aex, higher than 20 pJ/m and its value is lower than that for continuous L10-FePt single layer media and L10-FePt/Fe bilayer. Furthermore, the Hsw of the proposed ECC-BPM is lower than the maximum write head field with exchange coupling coefficient between neighboring dots of 5 pJ/m and Aex over 10 pJ/m. Therefore, the proposed ECC-BPM trilayer has the highest potential and is suitable for ultrahigh areal density magnetic recording technology at ultrahigh areal density. The results of this work may be gainful idea for nanopatterning in magnetic media nanotechnology.

  9. Growth mechanisms and size control of FePt nanoparticles synthesized using Fe(CO)x (x < 5)-oleylamine and platinum(ii) acetylacetonate.

    Science.gov (United States)

    Bian, Baoru; Xia, Weixing; Du, Juan; Zhang, Jian; Liu, J Ping; Guo, Zhaohui; Yan, Aru

    2013-03-21

    By using Fe(CO)x-OAm (oleylamine, x analyses indicated that the NPs with isotropic shape were single crystalline throughout the synthesis and were formed by a diffusion-controlled Ostwald-ripening (OR) growth mechanism. The nanorod particles were first formed via joining of arbitrarily oriented single crystals and the two crystals formed a uniform particle afterwards, as described by the oriented-attachment (OA) mechanism. The ratio of OAm to Fe(CO)5 used in the preparation of Fe(CO)x-OAm has a significant influence on the growth process, and subsequently the shape, size and size distribution of the FePt NPs. By adjusting the ratio and its complexing temperature, single-crystal FePt NPs with controllable size and isotropic shape were obtained. The insight into the exploration of the specific roles of the reaction conditions and the formation mechanisms provided important information for controlling the morphology of the nanoparticles.

  10. Structural and magnetic properties of FePt nanoparticles from the gas phase; Strukturelle und magnetische Eigenschaften von FePt-Nanopartikeln aus der Gasphase

    Energy Technology Data Exchange (ETDEWEB)

    Dmitrieva, O.

    2007-09-21

    In this work, we present the structural and magnetic characterization of FePt nanoparticles. The nanoparticles with mean size of about 6 nm were prepared by sputtering in the gas and subsequent inert gas condensation. The particles are annealed in the furnace during their flight prior to deposition on a substrate. The aim of this work is to prepare magnetically hard FePt nanoparticles in the L1{sub 0}-ordered phase. The structure of the particles was investigated by high-resolution transmission electron microscopy, and the investigations were supported by contrast simulations. The morphology of the particles varies with the sputter-gas pressure and with the annealing temperature. At a pressure of 0.5 mbar, the FePt-nanoparticles are multiply-twinned with an icosahedral structure and exhibit no formation of the L1{sub 0}-ordered phase. At a higher pressure of 1 mbar and an annealing temperature of 1000 C, the particles are partially single-crystalline. About 36 % of the particles are found to be in the L1{sub 0}-ordered state as was estimated by statistical counting supported by simulations. In order to activate the volume diffusion in the particles and to stabilize the formation of the L1{sub 0}-ordered state, the addition of nitrogen was used during the sputtering phase. In this phase, atomic nitrogen is incorporated interstitially into the structure of the primary particles. After annealing nitrogen effuses out of the particles and, thereby, increases the volume diffusion of the Fe and Pt atoms. The incorporation of nitrogen atoms during nucleation and their effusion at an annealing temperature of 1000 C was verified by electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS). Structural investigations on particles prepared in the presence of nitrogen shows that most of the particles are single-crystalline and about 70 % of them are L1{sub 0}-ordered. Detailed structural analysis of the nanoparticles was done by the exit wave

  11. First-principles calculations on Fe-Pt nanoclusters of various morphologies.

    Science.gov (United States)

    Platonenko, Alexander; Piskunov, Sergei; Bocharov, Dmitry; Zhukovskii, Yuri F; Evarestov, Robert A; Bellucci, Stefano

    2017-09-05

    Bimetallic FePt nanoparticles with L1 0 structure are attracting a lot of attention due to their high magnetocrystalline anisotropy and high coercivity what makes them potential material for storage of ultra-high density magnetic data. FePt nanoclusters are considered also as nanocatalysts for growth of carbon nanotubes of different chiralities. Using the DFT-LCAO CRYSTAL14 code, we have performed large-scale spin-polarized calculations on 19 different polyhedral structures of FePt nanoparticles in order to estimate which icosahedral or hcp-structured morphology is the energetically more preferable. Surface energy calculations of all aforementioned nanoparticles indicate that the global minimum corresponds to the nanocluster possessing the icosahedron "onion-like" structure and Fe 43 Pt 104 morphology where the outer layer consists of Pt atoms. The presence of the Pt-enriched layer around FePt core explains high oxidation resistance and environmental stability, both observed experimentally.

  12. Electronic structure of ordered and disordered Fe3Pt

    Science.gov (United States)

    Major, Zs; Dugdale, S. B.; Jarlborg, T.; Bruno, E.; Ginatempo, B.; Staunton, J. B.; Poulter, J.

    2003-06-01

    The electronic structure of invar alloys (i.e. materials in which the near absence of thermal expansion is observed) has been the focus of much study, owing both to the technological applications of these materials and interest in the fundamental mechanism that is responsible for the effect. Here, calculations of the magnetic Compton profiles are presented for ordered and disordered Fe3Pt alloys. Using linear muffin-tin orbital and KKR methods, the latter incorporating the coherent potential approximation to describe the substitutional disorder, the electronic band structure and measurable quantities such as the Fermi surface topology are presented.

  13. Electronic structure of ordered and disordered Fe sub 3 Pt

    CERN Document Server

    Major, Z; Jarlborg, T; Bruno, E; Ginatempo, B; Staunton, J B; Poulter, J

    2003-01-01

    The electronic structure of invar alloys (i.e. materials in which the near absence of thermal expansion is observed) has been the focus of much study, owing both to the technological applications of these materials and interest in the fundamental mechanism that is responsible for the effect. Here, calculations of the magnetic Compton profiles are presented for ordered and disordered Fe sub 3 Pt alloys. Using linear muffin-tin orbital and KKR methods, the latter incorporating the coherent potential approximation to describe the substitutional disorder, the electronic band structure and measurable quantities such as the Fermi surface topology are presented.

  14. Effect of magnetic field annealing on microstructure and magnetic properties of FePt films

    International Nuclear Information System (INIS)

    Li, Y.B.; Lou, Y.F.; Zhang, L.R.; Ma, B.; Bai, J.M.; Wei, F.L

    2010-01-01

    FePt (20 nm) films were annealed in a magnetic field (along the normal direction of the films) at a temperature around the Curie temperature of L1 0 FePt. The influence of magnetic filed annealing on texture and magnetic properties of FePt films were investigated. The results indicate that preferential (0 0 1) orientation and perpendicular anisotropy can be obtained in L1 0 FePt films by using magnetic field annealing around the Curie temperature of L1 0 FePt. This is one of the potential methods to obtain (0 0 1) orientation and thus to improve the perpendicular anisotropy in FePt films.

  15. High Field Linear Magnetoresistance Sensors with Perpendicular Anisotropy L10-FePt Reference Layer

    Directory of Open Access Journals (Sweden)

    X. Liu

    2016-01-01

    Full Text Available High field linear magnetoresistance is an important feature for magnetic sensors applied in magnetic levitating train and high field positioning measurements. Here, we investigate linear magnetoresistance in Pt/FePt/ZnO/Fe/Pt multilayer magnetic sensor, where FePt and Fe ferromagnetic layers exhibit out-of-plane and in-plane magnetic anisotropy, respectively. Perpendicular anisotropy L10-FePt reference layer with large coercivity and high squareness ratio was obtained by in situ substrate heating. Linear magnetoresistance is observed in this sensor in a large range between +5 kOe and −5 kOe with the current parallel to the film plane. This L10-FePt based sensor is significant for the expansion of linear range and the simplification of preparation for future high field magnetic sensors.

  16. Anomalous magnetic moments in Fe-Pt and Fe-Pd Invar alloys under high pressure

    CERN Document Server

    Matsushita, M; Endo, S; Ishizuka, M; Kindo, K; Ono, F

    2002-01-01

    Magnetization measurements have been carried out for disordered Fe sub 7 sub 2 Pt sub 2 sub 8 , Fe sub 6 sub 6 Pd sub 3 sub 4 , and Fe sub 6 sub 8 Pd sub 3 sub 2 Invar alloys under high pressure using a technique combining a pressure-clamp-type Drickamer cell and a pulse magnet. In Fe sub 7 sub 2 Pt sub 2 sub 8 at room temperature, the magnetization decreased rapidly with increasing pressure up to 2.5 GPa, but above 2.5 GPa the rate of decrease became small and remained at a small value up to 5.6 GPa. In Fe-Pd Invar alloys at room temperature, the magnetization decreased linearly with increasing pressure. But, at 4.2 K, the change of magnetization with pressure was small in Fe sub 6 sub 6 Pd sub 3 sub 4 , which means that Fe sub 6 sub 6 Pd sub 3 sub 4 behaves as a strong ferromagnet.

  17. Observation of high coercive fields in chemically synthesized coated Fe-Pt nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Dalavi, Shankar B.; Panda, Rabi N., E-mail: rnp@goa.bits-pilani.ac.in

    2017-04-15

    Nanocrystalline Fe-Pt alloys have been synthesized via chemical reduction route using various capping agents; such as: oleic acid/oleylamine (route-1) and oleic acid/CTAB (route-2). We could able to synthesize Fe50Pt and Fe54Pt alloys via route 1 and 2, respectively. As-prepared Fe-Pt alloys crystallize in disordered fcc phase with crystallite sizes of 2.3 nm and 6 nm for route-1 and route-2, respectively. Disordered Fe-Pt alloys were transformed to ordered fct phase after annealing at 600 °C. SEM studies confirm the spherical shape morphologies of annealed Fe-Pt nanoparticles with SEM particle sizes of 24.4 nm and 21.2 nm for route-1 and route-2, respectively. TEM study confirms the presence of 4.6 nm particles for annealed Fe50Pt alloys with several agglomerating clusters of bigger size and appropriately agrees well with the XRD study. Room temperature magnetization studies of as-prepared Fe-Pt alloys (fcc) show ferromagnetism with negligible coercivities. Average magnetic moments per particle for as-prepared Fe-Pt alloys were estimated to be 753 μ{sub B} and 814 μ{sub B}, for route 1 and 2, respectively. Ordered fct Fe-Pt alloys show high values of coercivities of 10,000 Oe and 10,792 Oe for route-1 and route-2, respectively. Observed magnetic properties of the fct Fe-Pt alloys nps were interpreted with the basis of order parameters, size, surface, and composition effects. - Highlights: • Synthesis of capped nanocrystalline Fe-Pt alloys via chemical routes. • Ordered fct phase were obtained at 600 °C. • Microstructural studies were carried out using SEM and TEM. • Investigation on evolution of magnetic properties from fcc to fct state. • Maximum values of coercivities up to 10,792 Oe were observed.

  18. Weathering of PGE sulfides and Pt-Fe alloys in the Freetown Layered Complex, Sierra Leone

    Science.gov (United States)

    Bowles, John F. W.; Suárez, Saioa; Prichard, Hazel M.; Fisher, Peter C.

    2017-12-01

    Fresh and weathered rocks and saprolite from Horizon B of the Freetown Layered Complex contain platinum-group minerals (PGM). The PGM in the fresh rocks are 1-7 μm across, including cooperite (PtS), isoferroplatinum (Pt3Fe), minor tetraferroplatinum (PtFe), tulameenite (Pt2FeCu), Os-bearing laurite (RuS2), and other base metal-sulfide (BMS)-bearing PGM. The weathered rocks contain fewer of those PGM but a high proportion of disordered Cu-(±Pd)-bearing Pt-Fe alloys. The saprolite hosts scarce, smaller (1-3 μm) ordered PtFe and disordered PtFe3. The Pt-Fe alloys became increasingly Fe rich as weathering proceeded. Pt-Fe oxides appeared during weathering. Copper sulfides associated with the primary PGM and cooperite (with <3% Pd) were destroyed to provide the minor Cu and Pd found in some of the disordered Pt-Fe alloys. Platinum- and Pd-bearing saprolites have retained the original rock fabric and, to a depth of about 2 m, surround residual rocks that show progressive weathering (corestones). Ground water passing through the saprolite has transported Pt and Pd (and probably Au) in solution down slope into saprolite over unmineralized rocks. Transport is marked by changes in the Pt/Pd ratio indicating that the metals have moved independently. Palladium is present in marginally higher concentrations in the deeper saprolite than in the corestones suggesting some retention of Pd in the deeper saprolite. Platinum and Pd are less concentrated in the upper saprolite than the deeper saprolite indicating surface leaching. Alteration occurred over a long period in an organic and microbial rich environment that may have contributed to the leaching and transport of PGE.

  19. Observation of high coercive fields in chemically synthesized coated Fe-Pt nanostructures

    Science.gov (United States)

    Dalavi, Shankar B.; Panda, Rabi N.

    2017-04-01

    Nanocrystalline Fe-Pt alloys have been synthesized via chemical reduction route using various capping agents; such as: oleic acid/oleylamine (route-1) and oleic acid/CTAB (route-2). We could able to synthesize Fe50Pt and Fe54Pt alloys via route 1 and 2, respectively. As-prepared Fe-Pt alloys crystallize in disordered fcc phase with crystallite sizes of 2.3 nm and 6 nm for route-1 and route-2, respectively. Disordered Fe-Pt alloys were transformed to ordered fct phase after annealing at 600 °C. SEM studies confirm the spherical shape morphologies of annealed Fe-Pt nanoparticles with SEM particle sizes of 24.4 nm and 21.2 nm for route-1 and route-2, respectively. TEM study confirms the presence of 4.6 nm particles for annealed Fe50Pt alloys with several agglomerating clusters of bigger size and appropriately agrees well with the XRD study. Room temperature magnetization studies of as-prepared Fe-Pt alloys (fcc) show ferromagnetism with negligible coercivities. Average magnetic moments per particle for as-prepared Fe-Pt alloys were estimated to be 753 μB and 814 μB, for route 1 and 2, respectively. Ordered fct Fe-Pt alloys show high values of coercivities of 10,000 Oe and 10,792 Oe for route-1 and route-2, respectively. Observed magnetic properties of the fct Fe-Pt alloys nps were interpreted with the basis of order parameters, size, surface, and composition effects.

  20. Study of microstructure and magnetic properties of L10 FePt/SiO2 thin films

    Directory of Open Access Journals (Sweden)

    Giannopoulos G.

    2014-07-01

    Full Text Available Achieving magnetic recording densities in excess of 1Tbit/in2 requires not only perpendicular media with anisotropies larger than 7 MJ/m3, making FePt alloys an ideal choice, but also a narrow distribution below 10 nm for a reduced S/N ratio. Such grain size reduction and shape control are crucial parameters for high density magnetic recording, along with high thermal stability. Previous work has shown that the L10 FePt grain size can be controlled by alloying FePt with materials such as C, Ag, and insulators such as AlOx, MgO. Au and Al2O3 also act to segregate and magnetically decouple the FePt grains. Better results were obtained with C with respect to the uniformity of grains and SiO2 with respect to the shape. We present our results on co-sputtering FePt with C or SiO2 (up to 30 vol % on MgO (001 single crystal substrates at 350 and 500 oC. With C or SiO2 addition we achieved grain size reduction, shape control and isolated structure formation, producing continuous films with high uniformity and a narrow grain size distribution. These additions thus allow us to simultaneously control the coercivity and the S/N ratio. We also will report structural and microstructural properties.

  1. Dense-plasma-driven ultrafast formation of FePt organization on ...

    Indian Academy of Sciences (India)

    Keywords. Nanostructures; chemical synthesis; magnetic materials; phase transition. ... The irradiation of energetic H + ions on FePt nanoparticles clearly resulted in enhanced structural and magnetic behaviour of the FePt nanoparticles as a function ofplasma focused irradiation shots. Transmission electron microscopy ...

  2. Dense-plasma-driven ultrafast formation of FePt organization on ...

    Indian Academy of Sciences (India)

    The gradual removal of organic capping over chemically synthesized FePt nanoparticles with increasing plasma focus shots exposure is confirmed usingRaman spectroscopy. A uniform 2D organization of bimetallic FePt nanoparticles over 1 cm × 1 cm silicon substrate is obtained with three plasma focus shots with better ...

  3. Structural and Magnetic model of self-assembled FePt nanoparticle arrays

    International Nuclear Information System (INIS)

    Thomson, T

    2004-01-01

    Chemically ordered, self-assembled FePt nanoparticle arrays with high magnetic anisotropy are considered a candidate medium for data storage beyond 1 Tbit/in 2 . We report comprehensive structural and magnetic studies on thin (3 layer) assemblies of polyethylenimine (PEI) and 4 nm Fe 58 Pt 42 nanoparticles using X-ray diffraction, small angle neutron scattering and magnetometry. We show that prior to annealing FePt nanoparticles in the PEI-FePt assembly consist of a metallic, magnetic core surrounded by a weakly magnetic or non-magnetic shell. High temperature annealing creates the desired L1 0 chemical ordering and results in high coercivity FePt nanoparticles. However, we find that the high temperatures necessary to establish full chemical ordering leads to particle sintering and agglomeration. Understanding the magnetic and physical properties of these assemblies allows future research directions to be clarified for nanoparticle arrays as data storage media

  4. Fabrication of superhydrophobic Pt3Fe/Fe surface for its application

    Science.gov (United States)

    Cui, Shuo; Lu, Shixiang; Xu, Wenguo; Wu, Bei

    2017-10-01

    Well-defined Pt3Fe/Fe superhydrophobic materials on iron sheet with special properties, such as corrosion resistance, superhydrophobicity and superoleophilicity, was fabricated. The fabrication process involved etching in hydrochloric acid aqueous solution and simple replacement deposition process without using any seed and organic solvent, and then annealing. The electrochemical measurements show that the resultant surface in 3.5% sodium chloride solution displays good corrosion resistance. Also, it is proved that the obtained surface has better mechanical abrasion resistance via scratch test. The superoleophilicity and low water adhesion force of the obtained surface endow it high oil/water separation capacity. The as-prepared nanocomposites display enhanced catalytic activity and kinetics toward degradation of methyl orange. In particular, it possesses the most efficient degradation capacity (95%) towards methyl orange at a high concentration (17.5 mg/L) in 80 min. The improved stability and excellent catalytic activity of the Pt3Fe/Fe nanocomposites promise new opportunities for the development of waste water treatment.

  5. Electric Field Manipulated Multilevel Magnetic States Storage in FePt/(011) PMN-PT Heterostructure.

    Science.gov (United States)

    Zhao, Xiaoyu; Wen, Jiahong; Yang, Bo; Zhu, Huachen; Cao, Qingqi; Wang, Dunhui; Qian, Zhenghong; Du, Youwei

    2017-10-18

    In the current information society, the realization of a magnetic storage technique with energy-efficient design and high storage density is greatly desirable. Here, we demonstrate that, without bias magnetic field, different values of remanent magnetization (M r ) can be obtained in a FePt/0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (PMN-PT) heterostructure by applying a unipolar electric field across the substrate. These multilevel magnetic signals can serve as writing data bits in a storage device, which remarkably increases the storage density. As for the data reading, these multilevel M r values can be read nondestructively and distinguishably using a commercial giant magnetoresistance magnetic sensor by converting the magnetic signal to voltage signal. Furthermore, these multilevel voltage signals show good retention and switching property, which enables promising applications in electric-writing magnetic-reading memory devices with low power consumption and high storage density.

  6. Post-treatment Method for the Synthesis of Monodisperse Binary FePt-Fe3O4 Nanoparticles

    Science.gov (United States)

    Liu, Zhilu; Wu, Chun; Niu, Liang; Yang, Ganting; Wang, Kai; Pei, Wenli; Wang, Qiang

    2017-09-01

    To obtain the optimal 1:1 composition of FePt alloy nanomaterials by polyol synthesis, the iron precursor (iron pentacarbonyl, Fe(CO)5) must be used in excess, because the Fe(CO)5 exists in the vapor phase at the typical temperatures used for FePt synthesis and cannot be consumed completely. Fabrication of Fe3O4 nanoparticles by consuming the excess iron precursor was an effective strategy to make full use of the iron precursor. In this paper, a facile post-treatment method was applied to consume the excess iron, which was oxidized to Fe3O4 after post-treatment at 150 and 200 °C, and a monodisperse binary FePt-Fe3O4 nanoparticle system was generated. The post-treatment method did not affect the crystal structure, grain size, or composition of the FePt nanoparticles. However, the content and grain size of the fcc-Fe3O4 nanoparticles can be increased simply by increasing the post-treatment temperature from 150 to 200 °C.

  7. In situ investigation of ordering phase transformations in FePt magnetic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Wittig, James E., E-mail: j.wittig@vanderbilt.edu [Interdisciplinary Materials Science, Vanderbilt University, PMB 351683, 2301 Vanderbilt Place, Nashville, TN 37232 (United States); Bentley, James, E-mail: bentleyj48@gmail.com [Materials Science and Technology Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6376 (United States); Allard, Lawrence F., E-mail: allardlfjr@ornl.gov [Materials Science and Technology Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6376 (United States)

    2017-05-15

    In situ high-resolution electron microscopy was used to reveal information at the atomic level for the disordered-to-ordered phase transformation of equiatomic FePt nanoparticles that can exhibit outstanding magnetic properties after transforming from disordered face-centered-cubic into the tetragonal L1{sub 0} ordered structure. High-angle annular dark-field imaging in the scanning transmission electron microscope provided sufficient contrast between the Fe and Pt atoms to readily monitor the ordering of the atoms during in situ heating experiments. However, during continuous high-magnification imaging the electron beam influenced the kinetics of the transformation so annealing had to be performed with the electron beam blanked. At 500 °C where the reaction rate was relatively slow, observation of the transformation mechanisms using this sequential imaging protocol revealed that ordering proceeded from (002) surface facets but was incomplete and multiple-domain particles were formed that contained anti-phase domain boundaries and anti-site defects. At 600 and 700 °C, the limitations of sequential imaging were revealed as a consequence of increased transformation kinetics. Annealing for only 5 min at 700 °C produced complete single-domain L1{sub 0} order; such single-domain particles were more spherical in shape with (002) facets. The in situ experiments also provided information concerning nanoparticle sintering, coalescence, and consolidation. Although there was resistance to complete sintering due to the crystallography of L1{sub 0} order, the driving force from the large surface-area-to-volume ratio resulted in considerable nanoparticle coalescence, which would render such FePt nanoparticles unsuitable for use as magnetic recording media. Comparison of the in situ data acquired using the protocol described above with parallel ex situ annealing experiments showed that identical behavior resulted in all cases. - Highlights: • HAADF STEM imaging reveals the

  8. Phase relations in the metal-rich portions of the phase system Pt-Ir-Fe-S at 1000 degrees C and 1100 degrees C

    DEFF Research Database (Denmark)

    Makovicky, E.; Karup-Møller, Sven

    2000-01-01

    with gamma-(Pt,Fe), Pt3Fe and PtFe which dissolve respectively at least 5.1, 29.3 and 24.0 at.% Ir at 1100 degreesC (2.2, 23.6 and less than or equal to 17.2 at.% Ir at 1000 degreesC). Gaps between the nearly Ir-free Pt-Fe alloys gamma (Pt,Fe), Pt3Fe s.s., PtFe s.s. and gamma (Fe,Pt) were estimated as 20...

  9. Direct synthesis of water dispersible superparamagnetic TGA capped FePt nanoparticles: One pot, one shot

    Energy Technology Data Exchange (ETDEWEB)

    Jha, Deepak K. [Department of Physics, Tezpur University (Central University), Tezpur 784028 (India); Varadarajan, Komanduri S.; Patel, Anant B. [Center for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007 (India); Deb, Pritam, E-mail: pdeb@tezu.ernet.in [Department of Physics, Tezpur University (Central University), Tezpur 784028 (India)

    2015-04-15

    Thioglycolic acid (TGA) capped hydrophilic fcc-FePt magnetic nanoparticles (MNPs) were directly synthesized by a facile one pot polyol method. Thioglycolic acid (TGA) was used to functionalize the nanoparticles by incorporating thiol group onto the surface. It helped in the preparation of highly stable dispersions of nanoparticles with spherical morphology. A possible formation mechanism for these FePt MNPs, depending on the role of TGA, was proposed. The as-prepared FePt MNPs possessed a face centered cubic structure with an average size of 6 ± 1 nm and superparamagnetic property at room temperature. MRI study showed that these MNPs exhibited a transverse relaxivity of ∼600 mg{sup −1} ml s{sup −1}, superior to that of reported iron oxide nanoparticles. - Highlights: • One pot synthesis of TGA capped hydrophilic FePt superparamagnetic nanoparticles. • Role of TGA molecules in the formation of FePt nanoparticles. • EDX reveals the equiatomic ratio of Fe and Pt atoms in FePt nanoparticles. • The HR-TEM exhibits spherical nanoparticles with a narrow size distribution. • High transverse relaxivity suggesting as potential MRI contrast agent.

  10. Structural Investigation of Rapidly Quenched FeCoPtB Alloys

    International Nuclear Information System (INIS)

    Grabias, A.; Kopcewicz, M.; Latuch, J.; Oleszak, D.

    2011-01-01

    Two sets of Fe 52-x Co x Pt 28 B 20 (x = 0-26 at.%) and Fe 60-x Co x Pt 25 B 15 (x = 0-40 at.%) alloys were prepared in the form of ribbons by the rapid quenching technique. Structure of the samples was characterized by Moessbauer spectroscopy and X-ray diffraction. In the as-quenched alloys the amorphous phase coexisted with the fcc-(Fe,Co)Pt disordered solid solution. Differential scanning calorimetry measurements performed in the range 50-720 ± C revealed one or two exothermal peaks. The magnetically hard ordered L1 0 (Fe,Co)Pt and magnetically soft (Fe,Co) 2 B nanocrystalline phases were formed due to thermal treatment of the alloys. The influence of Co content on the structure of the as-quenched and heated alloys was studied. (authors)

  11. Magnetic properties and structure of FePt/FeMn multilayers

    International Nuclear Information System (INIS)

    Phuoc, Nguyen N.; Suzuki, Takao

    2007-01-01

    A systematic study of the magnetic properties by ion beam sputter-deposition system, was conducted in conjunction with the structure of FePt/FeMn multilayers fabricated onto MgO(0 0 1) substrates. Both parallel and perpendicular exchange biases were observed in the multilayers and were found to decrease drastically, as the deposition temperature is higher than 350 deg. C, which is evidently due to the interdiffusion at the interface. The thickness dependence study shows that the perpendicular magnetic anisotropy observed in the multilayers originates from surface anisotropy, being consistent with the decrease of perpendicular magnetic anisotropy as the deposition temperature is increased. The difference between parallel and perpendicular blocking temperatures that was clearly observed, is possibly due to the spin canting out of plane at the interface

  12. Asymmetry of nucleation density and its variation with Pt spacer thickness in exchange-biased [Pt/Co]5/Pt/FeMn multilayers

    Science.gov (United States)

    Fassatoui, Aymen; Belhi, Rachid; Vogel, Jan; Pizzini, Stefania; David, Philippe; Abdelmoula, Kahena

    2018-03-01

    The magnetization reversal of perpendicular exchange-biased [Pt/Co]5/Pt/FeMn multilayers was investigated by magneto-optical Kerr microscopy. The effect of varying the Pt interlayer thickness between the topmost Co layer and the FeMn layer was studied. Our measurements reveal that coercivity (HC) and exchange bias field (HEB) vary with Pt spacer thickness, and have a maximum for a Pt thickness of 0.4 nm. Magnetization reversal measurements show that, for the unbiased multilayer, the reversal is dominated by domain wall propagation starting from a few nucleation centers. For the exchange-biased multilayers, magnetization reversal occurs by nucleation and domain wall propagation with a variation in the nucleation density. For 0 and 0.2 nm Pt spacer, no difference is observed in the nucleation density of the ascending and descending branches unlike for 0.4 and 0.6 nm Pt spacer where the measurements reveal a larger density of nucleation centers in the descending branch.

  13. FePt/Co core/shell nanoparticle-based anisotropic nanocomposites and their exchange spring behavior.

    Science.gov (United States)

    Li, Deyao; Wang, Hui; Ma, Zhenhui; Liu, Xin; Dong, Ying; Liu, Zhiqi; Zhang, Tianli; Jiang, Chengbao

    2018-02-22

    Anisotropic exchange-coupled nanocomposites provide us a salient candidate for the new generation of permanent magnets owing to their huge predicted maximum energy product. However, previous research basically focused on thin films or bulk materials and the impact of easy-axis alignment on the exchange coupling behavior is not clear. Herein, strongly coupled FePt/Co core/shell nanoparticles with single-phase-like hysteresis loops were synthesized by the seed mediated method. Then, these nanoparticles were successfully aligned by the external magnetic field and fixed in an acrylic binder, so that FePt/Co core/shell nanoparticle-based anisotropic nanocomposites were obtained. The nanocomposites exhibited high degree of orientation as indicated by the increased remanence ratio from 0.62 for isotropic nanoparticles to 0.78 for anisotropic nanocomposites. However, a visible kink in the demagnetization curve was observed around the zero field, implying the exchange spring behavior. This result suggests that the aligned FePt cores impose a stronger overall dipolar field in Co shells and finally, force the Co shells to reverse at a low field before the switch of FePt cores. Our research extends the preparation methods of anisotropic hard/soft-phase nanocomposites and might be helpful for the design of high-performance anisotropic exchange-coupled nanocomposites.

  14. Annealing effect on magnetic property and recording performance of [FePt/MgO]n perpendicular magnetic recording media

    International Nuclear Information System (INIS)

    Suzuki, Takao; Zhang, Zhengang; Singh, Amarendra K.; Yin, Jinhua; Perumal, A.; Osawa, Hiroshi

    2005-01-01

    Granular-type FePt perpendicular magnetic recording media with (001)-texture, obtained by annealing FePt/MgO multilayer films, are fabricated onto 2.5-in glass discs. For the sake of spin-stand testing, the coercivity of FePt films is carefully modulated by controlling the annealing conditions. With annealing, exchange coupling between FePt grains is decreased, indicated by the reductions in α value and activation volume. FePt ordering process is dependent on initial FePt/MgO multilayer structures, which governs the optimum annealing condition regarding coercivities and α(=4π(dM/dH)H=Hc). The SNR ratio exhibits a sensitive dependence on initial FePt/MgO multilayer structures as well as annealing conditions

  15. Atomistic computer simulations of FePt nanoparticles. Thermodynamic and kinetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, M.

    2007-12-20

    In the present dissertation, a hierarchical multiscale approach for modeling FePt nanoparticles by atomistic computer simulations is developed. By describing the interatomic interactions on different levels of sophistication, various time and length scales can be accessed. Methods range from static quantum-mechanic total-energy calculations of small periodic systems to simulations of whole particles over an extended time by using simple lattice Hamiltonians. By employing these methods, the energetic and thermodynamic stability of non-crystalline multiply twinned FePt nanoparticles is investigated. Subsequently, the thermodynamics of the order-disorder transition in FePt nanoparticles is analyzed, including the influence of particle size, composition and modified surface energies by different chemical surroundings. In order to identify processes that reduce or enhance the rate of transformation from the disordered to the ordered state, the kinetics of the ordering transition in FePt nanoparticles is finally investigated by assessing the contributions of surface and volume diffusion. (orig.)

  16. Tunable magnetotransport in Fe/hBN/graphene/hBN/Pt(Fe) epitaxial multilayers

    Science.gov (United States)

    Magnus Ukpong, Aniekan

    2018-03-01

    Theoretical and computational analysis of the magnetotransport properties and spin-transfer torque field-induced switching of magnetization density in vertically-stacked multilayers is presented. Using epitaxially-capped free layers of Pt and Fe, atom-resolved magnetic moments and spin-transfer torques are computed at finite bias. The calculations are performed within linear response approximation to the spin-density reformulation of the van der Waals density functional theory. Dynamical spin excitations are computed as a function of a spin-transfer torque induced magnetic field along the magnetic easy axis, and the corresponding spin polarization perpendicular to the easy axis is obtained. Bias-dependent giant anisotropic magnetoresistance of up to 3200% is obtained in the nonmagnetic-metal-capped Fe/hBN/graphene/hBN/Pt multilayer architecture. Since this specific heterostructure is not yet fabricated and characterized, the predicted high performance has not been demonstrated experimentally. Nevertheless, similar calculations performed on the Fe/hBN/Co stack show that the tunneling magnetoresistance obtained at the Fermi-level is in excellent agreement with results of recent magnetotransport measurements on magnetic tunnel junctions that contain the monolayer hBN tunnel region. The magnitude of the spin-transfer torque is found to increase as the tunneling spin current increases, and this activates the magnetization switching process due to increased charge accumulation. This mechanism causes substantial spin backflow, which manifests as rapid undulations in the bias-dependent tunneling spin currents. The implication of these findings on the design of nanoscale spintronic devices with spin-transfer torque tunable magnetization density is discussed. Insights derived from this study are expected to enhance the prospects for developing and integrating artificially assembled van der Waals multilayer heterostructures as the preferred material platform for efficient

  17. A general strategy for synthesizing high-coercivity L10-FePt nanoparticles.

    Science.gov (United States)

    Lei, Wenjuan; Yu, Yongsheng; Yang, Weiwei; Feng, Ming; Li, Haibo

    2017-09-14

    It is extremely desirable but challenging to develop a facile solution phase synthesis to directly prepare well-dispersed L1 0 -FePt nanoparticles (NPs) to meet the requirements of advanced magnets in modern industry and information technology. Here, we report a novel strategy to synthesize hard magnetic L1 0 -FePt NPs via controlled co-reduction of Fe(acac) 3 and K 2 PtCl 6 in the presence of oleylamine, in which effective control of the magnetic properties and chemical ordering of L1 0 -FePt NPs was achieved by tuning the mole ratio of the precursors, reaction time and temperature. The highest coercivity of 10.5 kOe can be obtained for the NPs synthesized at 350 °C for 8 h, which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt NPs without annealing or the third elemental additive. The reported one-pot synthesis of L1 0 -FePt NPs may provide an ideal class of building blocks for magnetic energy applications.

  18. Magnetic Properties of FePt Nanoparticles Prepared by a Micellar Method

    Directory of Open Access Journals (Sweden)

    Gao Y

    2009-01-01

    Full Text Available Abstract FePt nanoparticles with average size of 9 nm were synthesized using a diblock polymer micellar method combined with plasma treatment. To prevent from oxidation under ambient conditions, immediately after plasma treatment, the FePt nanoparticle arrays were in situ transferred into the film-growth chamber where they were covered by an SiO2 overlayer. A nearly complete transformation of L10 FePt was achieved for samples annealed at temperatures above 700 °C. The well control on the FePt stoichiometry and avoidance from surface oxidation largely enhanced the coercivity, and a value as high as 10 kOe was obtained in this study. An evaluation of magnetic interactions was made using the so-called isothermal remanence (IRM and dc-demagnetization (DCD remanence curves and Kelly–Henkel plots (ΔM measurement. The ΔM measurement reveals that the resultant FePt nanoparticles exhibit a rather weak interparticle dipolar coupling, and the absence of interparticle exchange interaction suggests no significant particle agglomeration occurred during the post-annealing. Additionally, a slight parallel magnetic anisotropy was also observed. The results indicate the micellar method has a high potential in preparing FePt nanoparticle arrays used for ultrahigh density recording media.

  19. Effect of hexane on magnetic blocking behavior of FePt nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Simsek, Telem, E-mail: telem@hacettepe.edu.tr [SNTG Laboratory, Department of Physics Engineering, Hacettepe University, 06800 Beytepe Ankara (Turkey); Akansel, Serkan, E-mail: akansel@hacettepe.edu.tr [SNTG Laboratory, Department of Physics Engineering, Hacettepe University, 06800 Beytepe Ankara (Turkey); Oezcan, Sadan, E-mail: sadan@hacettepe.edu.tr [SNTG Laboratory, Department of Physics Engineering, Hacettepe University, 06800 Beytepe Ankara (Turkey)

    2012-11-15

    In this work effect of the carrier fluid, hexane, on the magnetic properties of 4.7 nm sized FePt nanoparticles is investigated. Nanoparticles are synthesized by chemical method. Structural and magnetic characterizations confirmed that samples are monodispersed with disordered face centered cubic (fcc) crystal structure and, magnetically, exhibit two blocking behaviors; the first is at 27 K and second at 110 K. Carrier fluid of particles, hexane, is found to influence the blocking of 7% of the total magnetic moments in the system by freezing at low temperatures resulting in a two blocking phenomena even for nanoparticles that are monodispersed with narrow particle size distribution. - Highlights: Black-Right-Pointing-Pointer We investigate the effect of excess hexane on spin relaxation mechanism of single domain FePt nanoparticles. Black-Right-Pointing-Pointer We report that uncomplete evaporation of carrier fluid hexane blocks 7% of total magnetic moment to relax above blocking temperature. Black-Right-Pointing-Pointer This kind of systems could be further used as magnetic switches by controlling.

  20. Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

    Energy Technology Data Exchange (ETDEWEB)

    Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei; Ball, Madelyn; Huber, George W.; Zanchet, Daniela; Dumesic, James A.

    2018-03-01

    FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. The catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H2O activation on FeOx species at or near the Pt surface, mostly in the (II) oxidation state.

  1. Growth and Characterization on PMN-PT-Based Single Crystals

    Directory of Open Access Journals (Sweden)

    Jian Tian

    2014-07-01

    Full Text Available Lead magnesium niobate—lead titanate (PMN-PT single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity. To obtain high quality and relatively low cost single crystals for commercial production, PMN-PT single crystals were grown with modified Bridgman method, by which crystals were grown directly from stoichiometric melt without flux. For ultrasound imaging application, [001] crystal growth is essential to provide uniform composition and property within a crystal plate, which is critical for transducer performance. In addition, improvement in crystal growth technique is under development with the goals of improving the composition homogeneity along crystal growth direction and reducing unit cost of crystals. In recent years, PIN-PMN-PT single crystals have been developed with higher de-poling temperature and coercive field to provide improved thermal and electrical stability for transducer application.

  2. Phosphorescent Decanuclear Bimetallic Pt6M4(M = Zn, Fe) Tetrahedral Cages.

    Science.gov (United States)

    Zhang, Yuzhen; Crawley, Matthew R; Hauke, Cory E; Friedman, Alan E; Cook, Timothy R

    2017-04-17

    Coordination-driven self-assembly delivers discrete, nanoscopic architectures that may preserve or enhance the physicochemical properties of their parent building blocks. Herein, we report the syntheses, characterization, and photophysical properties of two tetrahedral cages, [Zn II 4 L 6 ](PF 6 ) 8 (C1) and [Fe II 4 L 6 ](OTf) 8 (C2), where L = Pt II (PEt 3 ) 2 (C≡C-bpy) 2 (PEt 3 = triethylphosphine; C≡C-bpy = 5-ethynyl-2,2'-bipyridine) and OTf = trifluoromethanesulfonate. C1 and C2 were assembled in isolated yields of 72% and 81% by treating 2 equiv of Zn(NO 3 ) 2 ·6H 2 O or Fe(OTf) 2 with 3 equiv of L, respectively. Both cages were fully characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction (SCXRD). The local D 3 symmetry at each polypyridyl metal node raises the possibility of a number of isomeric cages; however, only the homochiral enantiomers (ΔΔΔΔ and ΛΛΛΛ) are formed based on 1 H NMR and SCXRD. C1 exhibits phosphorescence centered at 545 nm with a quantum yield of 10% in N 2 -degassed acetonitrile at 25 °C. The quantum yield of C2 is significantly lower due to a nonradiative relaxation from 5 MC (MC = metal-centered) states introduced by the Fe II nodes.

  3. Temperature Dependent Magnetic Anisotropy in Metallic Magnets from an Ab Initio Electronic Structure Theory: L10-Ordered FePt

    Science.gov (United States)

    Staunton, J. B.; Ostanin, S.; Razee, S. S.; Gyorffy, B. L.; Szunyogh, L.; Ginatempo, B.; Bruno, Ezio

    2004-12-01

    Using a first-principles, relativistic electronic structure theory of finite temperature metallic magnetism, we investigate the variation of magnetic anisotropy K with magnetization M in metallic ferromagnets. We apply the theory to the high uniaxial K material, L10-ordered FePt, and find its magnetic easy axis perpendicular to the Fe/Pt layers for all M and K to be proportional to M2 for a broad range of values of M. For small M, near the Curie temperature, the calculations pick out the easy axis for the onset of magnetic order. Our abinitio results for this important magnetic material agree well with recent experimental measurements, whereas the single-ion anisotropy model fails to give the correct qualitative behavior.

  4. Magnetic properties of the alloy system Fe-Pt. Bulk materials and nanoparticles; Magnetische Eigenschaften des Legierungssystems Fe-Pt. Volumenmaterialien und Nanopartikel

    Energy Technology Data Exchange (ETDEWEB)

    Antoniak, C.

    2007-12-14

    Besides the determination of magnetic properties of epitaxial grown Fe{sub x}Pt{sub 1-x} films like e.g. the magnetic anisotropy, effective magnetisation, exchange length and damping as reference data, wet-chemically synthesised spherical Fe{sub x}Pt{sub 1-x} nanoparticles with different sizes, compositions and crystal structures were examined systematically after the reduction of Fe oxides by a hydrogen plasma treatment. Organic ligands surrounding the particles after the synthesis, were removed as well during this procedure. These ligands prevent the agglomeration of the nanoparticles when deposited onto a substrate, but do not have any measurable effect on the oxide formation under air exposure and do not change the magnetic properties of oxidised nanoparticles within experimental error bars. Static and dynamic magnetic properties were determined using the ferromagnetic resonance technique and themeasurement of the x-ray absorption, especially the analysis of the X-ray circular dichroism. The analysis of the element-specific magnetic moments shows that the effective magnetic spin moment ({mu}{sup eff}{sub s}) of the Fe{sub x}Pt{sub 1-x} nanoparticles is reduced by 20.30% with respect to the one of the corresponding Fe{sub x}Pt{sub 1-x} film due to the inhomogeneous composition within the nanoparticles which was found by the analysis of the extended X-ray absorption fine structure. With decreasing particle size, {mu}{sup eff}{sub s} is further decreasing while the ratio of orbital-to-effective-spin magnetic moment ({mu}{sub l}/{mu}{sup eff}{sub s}) increases. Annealing at 600 C of a sample consisting of Fe{sub 0.50}Pt{sub 0.50} nanoparticles with a mean diameter around 6 nm yields a strong increase of the {mu}{sub l}/{mu}{sup eff}{sub s} ratio at the Fe sites: it reaches a value of about 9% and is as large as the value at the Pt sites. This is accompanied by an enhancement of the coercive field from (36{+-}5) mT to (292{+-}8) mT after annealing that can be

  5. Growth, structure and magnetic properties of magnetron sputtered FePt thin films

    Energy Technology Data Exchange (ETDEWEB)

    Cantelli, Valentina

    2010-07-01

    The L1{sub 0} FePt phase belongs to the most promising hard ferromagnetic materials for high density recording media. The main challenges for thin FePt films are: (i) to lower the process temperature for the transition from the soft magnetic A1 to the hard magnetic L1{sub 0} phase, (ii) to realize c-axes preferential oriented layers independently from the substrate nature and (iii) to control layer morphology supporting the formation of FePt-L1{sub 0} selforganized isolated nanoislands towards an increase of the signal-to-noise ratio. In this study, dc magnetron sputtered FePt thin films on amorphous substrates were investigated. The work is focused on the correlation between structural and magnetic properties with respect to the influence of deposition parameters like growth mode (cosputtering vs. layer - by - layer) and the variation of the deposition gas (Ar, Xe) or pressure (0.3-3 Pa). In low-pressure Ar discharges, high energetic particle impacts support vacancies formation during layer growth lowering the phase transition temperature to (320{+-}20) C. By reducing the particle kinetic energy in Xe discharges, highly (001) preferential oriented L1{sub 0}-FePt films were obtained on a-SiO{sub 2} after vacuum annealing. L1{sub 0}-FePt nano-island formation was supported by the introduction of an Ag matrix, or by random ballistic aggregation and atomic self shadowing realized by FePt depositions at very high pressure (3 Pa). The high coercivity (1.5 T) of granular, magnetic isotropic FePt layers, deposited in Ar discharges, was measured with SQUID magnetometer hysteresis loops. For non-granular films with (001) preferential orientation the coercivity decreased (0.6 T) together with an enhancement of the out-of- plane anisotropy. Nanoislands show a coercive field close to the values obtained for granular layers but exhibit an in-plane easy axis due to shape anisotropy effects. An extensive study with different synchrotron X-ray scattering techniques, mainly

  6. Effect of sputter pressure on magnetotransport properties of FePt nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Mi, Shu, E-mail: mishu@buaa.edu.cn; Liu, Rui, E-mail: liurui1987@buaa.edu.cn; Li, Yuanyuan, E-mail: buaaliyuan@163.com; Ye, Jun, E-mail: yejun@iphy.ac.cn; Xie, Yong, E-mail: xiey@buaa.edu.cn; Chen, Ziyu, E-mail: chenzy@buaa.edu.cn

    2016-04-01

    FePt films were prepared by magnetron sputtering deposition using Ar as the sputtering gas under different working pressures (0.3–0.7 Pa). The effect of sputtering gas pressure on the microstructure, magnetic, and magnetoresistance properties has been investigated. The results show that the crystallization of FePt films is strongly dependent on the Ar sputter pressure. With the decrease of Ar working pressures, the fct phase forms and the coercivity (Hc) of FePt films rises under the same annealing temperature. As a result, the giant magnetoresistance (GMR) increases by 20% at the room temperature. At 0.7 Pa, the anisotropy magnetoresistance (AMR) can be observed clearly at a low field. However, as the Ar pressure decreases, the increase of GMR leads to a degradation of AMR effect. We believe that the improvement of GMR effect results from the increase of magnetic anisotropy and spin polarization in the process of transformation from the soft magnetic fcc phase to the hard magnetic fct phase. - Highlights: • FePt films were sputtered under different Ar working pressures. • The low Ar pressure promotes the formation of L1{sub 0} phase. • The Hc of FePt films enlarges with the reduction of Ar pressure. • As the Ar pressure decreases, the MR increases by 20%. • The total MR results from the competition of GMR and AMR.

  7. Effect of sputter pressure on magnetotransport properties of FePt nanocomposites

    International Nuclear Information System (INIS)

    Mi, Shu; Liu, Rui; Li, Yuanyuan; Ye, Jun; Xie, Yong; Chen, Ziyu

    2016-01-01

    FePt films were prepared by magnetron sputtering deposition using Ar as the sputtering gas under different working pressures (0.3–0.7 Pa). The effect of sputtering gas pressure on the microstructure, magnetic, and magnetoresistance properties has been investigated. The results show that the crystallization of FePt films is strongly dependent on the Ar sputter pressure. With the decrease of Ar working pressures, the fct phase forms and the coercivity (Hc) of FePt films rises under the same annealing temperature. As a result, the giant magnetoresistance (GMR) increases by 20% at the room temperature. At 0.7 Pa, the anisotropy magnetoresistance (AMR) can be observed clearly at a low field. However, as the Ar pressure decreases, the increase of GMR leads to a degradation of AMR effect. We believe that the improvement of GMR effect results from the increase of magnetic anisotropy and spin polarization in the process of transformation from the soft magnetic fcc phase to the hard magnetic fct phase. - Highlights: • FePt films were sputtered under different Ar working pressures. • The low Ar pressure promotes the formation of L1 0 phase. • The Hc of FePt films enlarges with the reduction of Ar pressure. • As the Ar pressure decreases, the MR increases by 20%. • The total MR results from the competition of GMR and AMR.

  8. Fabrication, morphological, structural and magnetic properties of electrodeposited Fe{sub 3}Pt nanowires and nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Khan, U. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Adeela, N. [Centre for High Energy Physics, University of the Punjab, Lahore 54000 (Pakistan); Li, Wenjing; Irfan, M.; Javed, K.; Riaz, S. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Han, X.F., E-mail: xfhan@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2017-02-15

    Highly ordered Fe{sub 3}Pt nanowires (NWs) and nanotubes (NTs) embedded in anodic aluminum oxide (AAO) template have been fabricated by dc electrodeposition method. Response of heat treatment on structural and magnetic properties of the samples has been studied with and without the presence of magnetic field (1 T). X-Ray Diffraction analysis shows chemically ordered L1{sub 2} face centered cubic (FCC) as the dominant phase for Fe{sub 3}Pt NWs and heat treatment improves crystallinity with retained its phase. Whereas, Fe{sub 3}Pt NTs show amorphous behavior with and without magnetic field annealing. Furthermore, magnetic properties of the samples have been investigated by vibrating sample magnetometer (VSM). Magnetic parameters of Fe{sub 3}Pt including magnetic coercivity, saturation magnetization, squareness and shape of MH-loops have been investigated as a result of simple and MF annealing. - Highlights: • Fe{sub 3}Pt NWs and NTs embedded into anodic alumina templates have been synthesized by dc electrodeposition method. • Structural analysis (XRD) confirmed the formation of fcc structure. • Magnetic properties have been measured as a function of simple and magnetic field annealing.

  9. Structure, magnetic and magneto-optical properties, and 57Fe Moessbauer effect in a new variety of Heusler alloy: PtFeSb

    International Nuclear Information System (INIS)

    Buschow, K.H.J.; Vucht, J.H.N. van; Engen, P.G. van; Mooij, D.B. de

    1983-01-01

    The compounds PtFeSb and PtCrSb are found to form a new variety of Heusler alloy. A structure determination on the former compound shows that the crystal structure is closely related to the Cl/sub b/ type. The magnetic properties of both compounds are determined, revealing that the Fe moment in PtFeSb equals to 2.54 μ/sub B/ while Cr is non-magnetic in PtCrSb. X-ray diffraction and 57 Fe Moessbauer effect spectroscopy in PtFeSb show that there is a partial exchange in site occupation of the Pt and Fe atoms. This leads to a situation where the net magnetization tends to vanish in PtFeSb even though there is a strong hyperfine splitting. A study of the magneto-optical properties of PtFeSb reveals that in the whole energy range (0.6 to 4.4 eV) the polar Kerr rotation angle 2phi/sub K/ is rather low compared to that found in PtMnSb. (author)

  10. Synthesis and characterization of FePt/Au core-shell nanoparticles

    International Nuclear Information System (INIS)

    Presa, P. de la; Multigner, M.; Morales, M.P.; Rueda, T.; Fernandez-Pinel, E.; Hernando, A.

    2007-01-01

    In this work, the structural and magnetic properties of the gold-coated FePt nanoparticles synthesized from high-temperature solution phase are presented. The amount of gold was optimized to obtain most of the FePt particles coated. The particle diameter increases from 4 to 10 nm as observed by TEM. The magnetic properties are largely affected by the coating. At low temperature, the coercive field Hc of the coated nanoparticles decreases about three times respect to the uncoated and the blocking temperature reduces to the half. The changes of the magnetic behavior are discussed in terms of the effect of the gold atoms at the FePt core surface

  11. Frequency dispersion of flexoelectricity in PMN-PT single crystal

    Science.gov (United States)

    Shu, Longlong; Wan, Meiqian; Jiang, Xiaoning; Li, Fei; Zhou, Naigen; Huang, Wenbin; Wang, Tong

    2017-01-01

    The mechanism of the recent discovered enhanced flexoelectricity in perovskites has brought about numerous controversies which still remain unclear. In this paper, we employed relaxor 0.68Pb(Mg2/3Nb1/3)O3 -0.32PbTiO3 (PMN-PT) single crystals for study. The observed flexoelectric coefficient in PMN-PT single crystal reaches up to 100 μ C /m , and in a relative low frequency range, exhibits an abnormal frequency dispersion phenomenon with a positive relationship with frequency. Such frequency dispersion regulation is different from the normal relaxation behavior that usually occur a time delay, and hence proves the flexoelectricity acting more like bulk effect rather than surface effect in this kind of materials.

  12. Frequency dispersion of flexoelectricity in PMN-PT single crystal

    Directory of Open Access Journals (Sweden)

    Longlong Shu

    2017-01-01

    Full Text Available The mechanism of the recent discovered enhanced flexoelectricity in perovskites has brought about numerous controversies which still remain unclear. In this paper, we employed relaxor 0.68Pb(Mg2/3Nb1/3O3 -0.32PbTiO3 (PMN-PT single crystals for study. The observed flexoelectric coefficient in PMN-PT single crystal reaches up to 100 μC/m, and in a relative low frequency range, exhibits an abnormal frequency dispersion phenomenon with a positive relationship with frequency. Such frequency dispersion regulation is different from the normal relaxation behavior that usually occur a time delay, and hence proves the flexoelectricity acting more like bulk effect rather than surface effect in this kind of materials.

  13. Control of magnetic anisotropy field of (001) oriented L1{sub 0}-Fe(Pd{sub x}Pt{sub 1-x}) films for MRAM application

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimura, Satoru; Omiya, Shogo; Egawa, Genta; Saito, Hitoshi [Center for Geo-environmental Science, Faculty of Engineering and Resource Science, Akita University, Tegatagakuen-machi 1-1, Akita, 010-8502 (Japan); Bai Jianmin, E-mail: syoshi@gipc.akita-u.ac.jp [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, TianShui Road, S 222, LanZhou, GanSu, 730000 (China)

    2011-01-01

    L1{sub 0}-Fe(Pd,Pt) films which are expected to have tunable perpendicular magnetic anisotropy and lower ordering temperature compared with the L1{sub 0}-FePt films were fabricated and investigated in order to realize high-performance Magnetic Random Access Memory (MRAM) with spin-transfer magnetization switching method and Magnetic Domain-Wall Racetrack Memory with current-driven domain wall motion. The main results are as follows: (1) The long-range chemical order degree S for the L1{sub 0}-Fe(Pd,Pt) films with the optimized thermal treatment temperature fabricated on MgO(001) substrate was about 0.8. (2) The perpendicular coercive force and magnetic anisotropy field for the L1{sub 0}-FePd film with the thermal treatment temperature of 600 {sup 0}C were 300 Oe and 14 kOe respectively, whereas the L1{sub 0}-FePt film with the thermal treatment temperature of 800 {sup 0}C were 2000 Oe and 102 kOe, respectively. (3) The optimized ordering temperature to obtain L1{sub 0} single phase decreased continuously from 800{sup 0}C to 600{sup 0}C with the increasing Pd content for the Fe(Pd,Pt) films. (4) The perpendicular magnetic anisotropy field for the L1{sub 0}-Fe(Pd,Pt) films decreased continuously from 102 kOe to 14 kOe with the increasing Pd content. It is found that the Fe(Pd,Pd) films which have tunable perpendicular magnetic anisotropy field is one of suitable ferromagnetic material for high-performance magnetic recording devices.

  14. Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

    International Nuclear Information System (INIS)

    Kisielewski, J.; Kurant, Z.; Sveklo, I.; Tekielak, M.; Maziewski, A.; Wawro, A.

    2016-01-01

    Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

  15. Patterned FePt nanostructures using ultrathin self-organized templates

    Science.gov (United States)

    Deng, Chen Hua; Zhang, Min; Wang, Fang; Xu, Xiao Hong

    2018-02-01

    Patterned magnetic thin films are both scientifically interesting and technologically useful. Ultrathin self-organized anodic aluminum oxide (AAO) template can be used to fabricate large area nanodot and antidot arrays. The magnetic properties of these nanostructures may be tuned by the morphology of the AAO template, which in turn can be controlled by synthetic parameters. In this work, ultrathin AAO templates were used as etching masks for the fabrication of both FePt nanodot and antidot arrays with high areal density. The perpendicular magnetic anisotropy of L10 FePt thin films are preserved in the nanostructures.

  16. Lowering of the L10 ordering temperature of FePt nanoparticles by He+ ion irradiation

    International Nuclear Information System (INIS)

    Wiedwald, U.; Klimmer, A.; Kern, B.; Han, L.; Boyen, H.-G.; Ziemann, P.; Fauth, K.

    2007-01-01

    Arrays of FePt particles (diameter 7 nm) with mean interparticle distances of 60 nm are prepared by a micellar technique on Si substrates. The phase transition of these magnetic particles towards the chemically ordered L1 0 phase is tracked for 350 kV He + ion irradiated samples and compared to a nonirradiated reference. Due to the large separation of the magnetically decoupled particles the array can be safely annealed without any agglomeration as usually observed for more densely packed colloidal FePt nanoparticles. The He + ion exposure yields a significant reduction of the ordering temperature by more than 100 K

  17. In-Situ Liquid Hydrogenation of m-Chloronitrobenzene over Fe-Modified Pt/Carbon Nanotubes Catalysts

    Directory of Open Access Journals (Sweden)

    Feng Li

    2018-02-01

    Full Text Available In-situ liquid-phase hydrogenation of m-chloronitrobenzene (m-CNB based on aqueous-phase reforming (APR of ethanol and catalytic hydrogenation was carried out over Fe-modified Pt/carbon nanotubes (CNTs catalysts. The effects of Pt loading over CNTs and Fe modification on the catalytic performance of Pt/CNTs catalysts were studied. In-tube loading of Pt particles, compared with out-tube loading, considerably improved the catalytic activity. With in-tube loading, Fe-modified Pt/CNTs catalysts further improved the m-CNB in-situ hydrogenation performance. After Fe modification, Pt–Fe/CNTs catalysts formed, inside CNTs, a Pt–Fe alloy and iron oxides, which both improved catalytic hydrogenation performance and significantly enhanced ethanol APR hydrogen producing performance, thereby increasing the m-CNB in-situ hydrogenation reactivity.

  18. Structure, magnetism, and interface properties of epitactical thin Fe and FePt films on GaAs(001) substrates; Struktur, Magnetismus und Grenzflaecheneigenschaften epitaktischer duenner Fe- und FePt-Filme auf GaAs(001)-Substraten

    Energy Technology Data Exchange (ETDEWEB)

    Schuster, Ellen Ursula

    2007-12-17

    The research in this thesis is focused on the study of the Fe spin structure and interface magnetism of thin epitaxial Fe layers or epitaxial FePt alloy films with chemical L1{sub 0} order on GaAs(001) surfaces. The main method of investigation was isotope-specific conversion electron Moessbauer spectroscopy (CEMS) combined with the {sup 57}Fe probe-layer technique in the temperature range of 4.2-300 K. The film structure was studied using electron diffraction (RHEED) and X-ray diffraction (XRD). The chemical order parameter S determined by XRD was found to increase with rising growth temperature, T{sub S}, to a maximum value of 0.71, until long range order is destroyed at T{sub S}>350 C by alloying with the substrate. As an important result a linear correlation between short-range order (revealed by the relative spectral area of the L1{sub 0} phase) and long-range order S was observed. The observed perpendicular Fe spin texture, characterized by the mean tilting angle left angle {theta} right angle of the Fe spins (relative to the film normal direction), was found to correlate with the L1{sub 0} phase content and with S. Furthermore, epitaxial Fe(001) films on GaAs(001)-(4 x 6) and on GaAs(001)-LED surfaces were grown successfully. In the initial stage of Fe film growth non-monotonous behavior of the in-plane lattice parameter was observed by RHEED. The magnetic hyperfine field distributions P(B{sub hf}) at the Fe/GaAs interface extracted from CEMS spectra for T{sub S}=-140 C or room temperature (RT) were found to be very similar. The observed large mean hyperfine fields of left angle B{sub hf} right angle {approx}25-27 T at the interface indicate the presence of high average Fe moments of 1.7-1.8 {mu}{sub B}. Nonmagnetic interface layers either can be excluded (Fe/GaAs) or are very thin (0.5 ML,Fe/GaAs-LED). Owing to its island structure an ultrathin (1.9 ML thick) uncoated Fe(001) film on GaAs(001)-(4 x 6) shows superparamagnetism with a blocking temperature of

  19. Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

    Science.gov (United States)

    Lohrasbi, Elaheh; Javanbakht, Mehran; Mozaffari, Sayed Ahmad

    2017-06-01

    The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO3sbnd groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1 mg cm-2 Pt) reaches to a maximum of 530 mW cm-2 at 75 °C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

  20. Ni3FeN-Supported Fe3Pt Intermetallic Nanoalloy as a High-Performance Bifunctional Catalyst for Metal-Air Batteries.

    Science.gov (United States)

    Cui, Zhiming; Fu, Gengtao; Li, Yutao; Goodenough, John B

    2017-08-07

    Electrocatalysts for both the oxygen reduction and evolution reactions (ORR and OER) are vital for the performances of rechargeable metal-air batteries. Herein, we report an advanced bifunctional oxygen electrocatalyst consisting of porous metallic nickel-iron nitride (Ni 3 FeN) supporting ordered Fe 3 Pt intermetallic nanoalloy. In this hybrid catalyst, the bimetallic nitride Ni 3 FeN mainly contributes to the high activity for the OER while the ordered Fe 3 Pt nanoalloy contributes to the excellent activity for the ORR. Robust Ni 3 FeN-supported Fe 3 Pt catalysts show superior catalytic performance to the state-of-the-art ORR catalyst (Pt/C) and OER catalyst (Ir/C). The Fe 3 Pt/Ni 3 FeN bifunctional catalyst enables Zn-air batteries to achieve a long-term cycling performance of over 480 h at 10 mA cm -2 with high efficiency. The extraordinarily high performance of the Fe 3 Pt/Ni 3 FeN bifunctional catalyst makes it a very promising air cathode in alkaline electrolyte. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Strained lattice with persistent atomic order in Pt3Fe2 intermetallic core-shell nanocatalysts.

    Science.gov (United States)

    Prabhudev, Sagar; Bugnet, Matthieu; Bock, Christina; Botton, Gianluigi A

    2013-07-23

    Fine-tuning nanocatalysts to enhance their catalytic activity and durability is crucial to commercialize proton exchange membrane fuel cells. The structural ordering and time evolution of ordered Pt3Fe2 intermetallic core-shell nanocatalysts for the oxygen reduction reaction that exhibit increased mass activity (228%) and an enhanced catalytic activity (155%) compared to Pt/C has been quantified using aberration-corrected scanning transmission electron microscopy. These catalysts were found to exhibit a static core-dynamic shell regime wherein, despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity and the ordered Pt3Fe2 core remained virtually intact while the Pt shell suffered a continuous enrichment. The existence of this regime was further confirmed by X-ray diffraction and the compositional analyses using energy-dispersive spectroscopy. With atomic-scale two-dimensional (2-D) surface relaxation mapping, we demonstrate that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to noncycled catalysts. With 2-D lattice strain mapping, we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.

  2. Preparation and characterization of Fe{sub 3}O{sub 4}-Pt nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Andrade, Ângela Leão, E-mail: angelala01@hotmail.com [Federal University of Ouro Preto (UFOP), Department of Chemistry, ICEB (Brazil); Cavalcante, Luis Carlos Duarte [Federal University of Piauí (UFPI), Center of Natural Sciences (Brazil); Fabris, José Domingos [Federal University of Minas Gerais (UFMG), Department of Chemistry, ICEx (Brazil); Pereira, Márcio César [Federal University of the Jequitinhonha and Mucuri Valleys (UFVJM), Institute of Science, Engineering and Technology (Brazil); Ardisson, José Domingos [Center for the Development of the Nuclear Technology (CDTN), Laboratory of Applied Physics (Brazil); Domingues, Rosana Zacarias [Federal University of Minas Gerais (UFMG), Department of Chemistry, ICEx (Brazil)

    2017-11-15

    Pt and Pt-based nanomaterials are active anticancer drugs for their ability to inhibit the division of living cells. Nanoparticles of magnetite containing variable proportions of platinum were prepared in the laboratory. The magnetite nanoparticles with platinum (Pt-Fe{sub 3}O{sub 4}) were obtained by reducing the Fe{sup 3+} of the maghemite (γ Fe{sub 2}O{sub 3}) mixed with platinum (II) acetylacetonate and sucrose in two inversely coupled ceramic crucibles and heated in a furnace at 400 °C for 20 min. The formed carbon during this preparation acts to chemically reduce the ferric iron in maghemite. Moreover, its residual layer on the particle surface prevents the forming magnetite from oxidizing in air and helps retain the platinum in the solid mixture. The produced Pt-magnetite samples were characterized by {sup 57}Fe-Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, and magnetization measurements. Measurements of AC magnetic-field-induced heating properties of the obtained nanocomposites, in aqueous solution, showed that they are suitable as a hyperthermia agent for biological applications.

  3. Galvanomagnetic properties of partially ordered L1.sub.0./sub. FePt alloys

    Czech Academy of Sciences Publication Activity Database

    Kudrnovský, Josef; Drchal, Václav; Turek, I.

    2014-01-01

    Roč. 89, č. 22 (2014), "224422-1"-"224422-8" ISSN 1098-0121 R&D Projects: GA ČR(CZ) GAP204/11/1228 Institutional support: RVO:68378271 Keywords : anomalous Hall effect * long-range order * FePt alloys * spin disorder Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  4. Analysis of grain size in FePt films fabricated using remote plasma deposition

    Science.gov (United States)

    Huskisson, D.; Zygridou, S.; Haigh, S. J.; Barton, C. W.; Nutter, P. W.; Thomson, T.

    2017-12-01

    Remote plasma sputtering (RPS) offers a high degree of control over the sputtering parameters used to deposit thin metallic films and has demonstrated a capability to control the media grain size distribution. Narrow grain size distributions remain a key requirement for future magnetic media. Here we report a comprehensive magnetometry, X-ray diffraction and transmission electron microscopy study of how RPS affects the grain size distribution of continuous, non-segregated L10 FePt thin films. These provide a model medium for heat-assisted magnetic recording and more generally for spintronic devices such as magnetoresistive random access memory and spin torque oscillators, where very high perpendicular magnetocrystalline anisotropy is required. Varying the target DC bias voltage, which in RPS can be tuned independently of the plasma generation, produces no meaningful, statistical change in average grain size, 6.5 ± 0.1 nm, for as-deposited, disordered FePt. Annealing at 800 °C creates the well-ordered L10 phase but results in an increased average grain size of 8.3-13.6 nm, and a significantly wider grain size distribution of 6.4-8.5 nm. These results show that whilst RPS is capable of producing well-ordered L10 FePt thin films, it does not offer an advantage in controlling the grain size of FePt, as reported in other thin film systems.

  5. Monolayer-directed Assembly and Magnetic Properties of FePt Nanoparticles on Patterned Aluminum Oxide

    NARCIS (Netherlands)

    Yildirim, O.; Gang, T.; Kinge, S.S.; Reinhoudt, David; Blank, David H.A.; van der Wiel, Wilfred Gerard; Rijnders, Augustinus J.H.M.; Huskens, Jurriaan

    2010-01-01

    FePt nanoparticles (NPs) were assembled on aluminum oxide substrates, and their ferromagnetic properties were studied before and after thermal annealing. For the first time, phosph(on)ates were used as an adsorbate to form self-assembled monolayers (SAMs) on alumina to direct the assembly of NPs

  6. Perpendicular Magnetic Anisotropy in FePt Patterned Media Employing a CrV Seed Layer

    Directory of Open Access Journals (Sweden)

    Chun Dong

    2011-01-01

    Full Text Available Abstract A thin FePt film was deposited onto a CrV seed layer at 400°C and showed a high coercivity (~3,400 Oe and high magnetization (900–1,000 emu/cm3 characteristic of L10 phase. However, the magnetic properties of patterned media fabricated from the film stack were degraded due to the Ar-ion bombardment. We employed a deposition-last process, in which FePt film deposited at room temperature underwent lift-off and post-annealing processes, to avoid the exposure of FePt to Ar plasma. A patterned medium with 100-nm nano-columns showed an out-of-plane coercivity fivefold larger than its in-plane counterpart and a remanent magnetization comparable to saturation magnetization in the out-of-plane direction, indicating a high perpendicular anisotropy. These results demonstrate the high perpendicular anisotropy in FePt patterned media using a Cr-based compound seed layer for the first time and suggest that ultra-high-density magnetic recording media can be achieved using this optimized top-down approach.

  7. Dense-plasma-driven ultrafast formation of FePt organization on ...

    Indian Academy of Sciences (India)

    Plasma-based etching is one of the best and fastest tools to clean the organic capping of FePt nanoparticles in ambient atmosphere. In the plasma processing, the energetic ion beam has been extensively used for the modification and synthesis of nanoscale structures. The surface modifications of the nanostructures due to ...

  8. Dense-plasma-driven ultrafast formation of FePt organization on ...

    Indian Academy of Sciences (India)

    the log normal distribution, as shown in the inset of figure 1c. The change in morphology and reduction in the clustering of organic-matrix-embedded FePt was studied as an effect of the hydrogen ions/plasma exposure shots using the DPF. The specimen was exposed to varying hydrogen ions/plasma doses by varying ...

  9. The effect of growth surface morphology on the crystal structure and magnetic property of L1{sub 0} order PtFe layers deposited by magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Ding Wanyu, E-mail: dwysd_2000@163.com [Graduate School of Saitama Institute of Technology, Fukaya, Saitama 369-0293 (Japan) and School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028 (China); Ishiguro, Satoshi; Ogatsu, Ryo [Graduate School of Saitama Institute of Technology, Fukaya, Saitama 369-0293 (Japan); Ju, Dongying, E-mail: dyju@sit.ac.jp [Graduate School of Saitama Institute of Technology, Fukaya, Saitama 369-0293 (Japan)

    2012-08-01

    The Fe/Pt/Fe/Pt layers (Pt/Fe multilayer) were deposited on general glass substrate at room temperature by magnetron sputtering technique. Varying the deposition and post-annealing treatment parameters, the PtFe alloy (PtFe) layer with different crystal structures and magnetic properties were obtained at the interface between Fe and Pt layer. The characterization by X-ray diffraction (XRD) showed that the as-deposited Pt/Fe multilayer only contained pure Fe and Pt with body-centered and face-centered cubic structures, respectively. As-deposited Pt layer displayed (2 0 0) preferred orientation, and the columnar grains structure could be observed by the scanning electron microscopy. The PtFe layers with L1{sub 0} face-centered cubic structure could be formed at the interface between Pt and Fe layers by post-annealing the multilayers at 500 Degree-Sign C. In case of Pt/Fe multilayer deposited on smooth substrate, the larger columnar grains in Pt layer resulted in L1{sub 0} PtFe layers without any preferred orientation. While in case of Pt/Fe multilayer deposited on the rough substrate, the thinner columnar grains in Pt layer could induce L1{sub 0} PtFe layers with (2 0 0) preferred orientation. In this case, the vibrating sample magnetometer results indicated that, the magnetic coercivity in plane and out-of-plane model could reach 3.72 and 2.32 kOe, respectively. Based on above results, the L1{sub 0} structure Pt/Fe multilayer with satisfied magnetic properties could be prepared at low temperature by our simple route.

  10. Electron impact excitation of Fe2+. Pt. 1

    International Nuclear Information System (INIS)

    Berrington, K.A.; Eissner, W.; Burke, P.G.

    1991-01-01

    A Breit-Pauli R-matrix calculation for the electron impact collision strengths of Fe 2+ is reported involving transitions among the lowest 17 levels corresponding to the 3d 6 5 D, 3 H, 3 P, 3 F and 3 G terms. Resonance structures are elucidated for the first time. The calculated collision strengths at impact energies above the resonance region show some disagreements with those from an earlier five-term R-matrix calculation. (author)

  11. Strength of FePd/MgO and FePt/MgO interfaces from first principles

    Science.gov (United States)

    Černý, M.

    2018-04-01

    Cleavage characteristics such as the cleavage energy and the cleavage stress of FePd/MgO and FePt/MgO interfaces are computed from first principles. Considering several possible cleavage planes, the weakest link in these systems is found as the plane with the lowest cleavage stress. This weakest plane is identified in both systems with the interface plane, where the cohesion is reduced by 30% compared to the MgO bulk. Two distinct models of tensile test are employed to verify the results and convergence of computed values with respect to size of the simulation cell is discussed.

  12. Electric-field tunable spin diode FMR in patterned PMN-PT/NiFe structures

    Energy Technology Data Exchange (ETDEWEB)

    Ziętek, Slawomir, E-mail: zietek@agh.edu.pl; Skowroński, Witold; Stobiecki, Tomasz [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); Ogrodnik, Piotr, E-mail: piotrogr@if.pw.edu.pl [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); Faculty of Physics, Warsaw University of Technology, ul. Koszykowa 75, 00-662 Warszawa (Poland); Stobiecki, Feliks [Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznań (Poland); Dijken, Sebastiaan van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Barnaś, Józef [Faculty of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań (Poland); Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznań (Poland)

    2016-08-15

    Dynamic properties of NiFe thin films on PMN-PT piezoelectric substrate are investigated using the spin-diode method. Ferromagnetic resonance (FMR) spectra of microstrips with varying width are measured as a function of magnetic field and frequency. The FMR frequency is shown to depend on the electric field applied across the substrate, which induces strain in the NiFe layer. Electric field tunability of up to 100 MHz per 1 kV/cm is achieved. An analytical model based on total energy minimization and the Landau-Lifshitz-Gilbert equation, taking into account the magnetostriction effect, is used to explain the measured dynamics. Based on this model, conditions for optimal electric-field tunable spin diode FMR in patterned NiFe/PMN-PT structures are derived.

  13. Elaboration et propriétés de nanofils de CoPt et FePt électrodéposés

    OpenAIRE

    Dahmane , Yasmina

    2007-01-01

    The main purpose of this work is to prepare CoPt and FePt nanowires by electrodeposition in nanoporous aluminum membranes. The electrochemical bath was composed of only two salts (chlorides), one for the cobalt (CoCl2, 6H2O) and one for platinum (K2PtCl6). We succeeded preparing networks of CoPt nanowires with diameters of about 70-80 nm and a coercivity of 1.1 Tesla at room temperature. These magnetically hard materials present the tetragonal phase L10 obtained after annealing at 700 °C the ...

  14. Magnetic properties and inhomogeneous phase transition in (Fe sub x Co sub 0 sub . sub 5 sub - sub x)Pt sub 0 sub . sub 5 films

    CERN Document Server

    Jang, P W; Na, J G; Lee, S R

    1999-01-01

    (Fe sub x Co sub 0 sub . sub 5 sub - sub x)Pt sub 0 sub . sub 5 ternary thin films were deposited on glass substrates by using a dc sputtering method at room temperature and were subsequently annealed at 700 .deg. C in a high vacuum. A high degree of the (111) preferred orientation could be obtained in all the as-deposited films and was not destroyed, even though post annealing. The CoPt and the FePt binary alloys were completely mixed and had a L1 sub o -type ordered structure, as confirmed by single (222) peaks and by the linear variation of the lattice constant a sub o. The ordered structure of the FePt alloy was thought to have formed from the disordered structure by an inhomogeneous process, which was confirmed by the asymmetric peak shapes. The lattice parameter a sub o varied linearly with the Fe content while the coercivity showed a minimum value at the equiatomic composition of the Fe and the Co atoms.

  15. Magnetic proximity effect in Pt /CoFe2O4 bilayers

    Science.gov (United States)

    Amamou, Walid; Pinchuk, Igor V.; Trout, Amanda H.; Williams, Robert E. A.; Antolin, Nikolas; Goad, Adam; O'Hara, Dante J.; Ahmed, Adam S.; Windl, Wolfgang; McComb, David W.; Kawakami, Roland K.

    2018-01-01

    We observe the magnetic proximity effect (MPE) in Pt /CoFe2O4 bilayers grown by molecular beam epitaxy. This is revealed through angle-dependent magnetoresistance measurements at 5 K, which isolate the contributions of induced ferromagnetism (i.e., anisotropic magnetoresistance) and the spin Hall effect (i.e., the spin Hall magnetoresistance) in the Pt layer. The strong evidence for induced ferromagnetism in Pt via the anisotropic magnetoresistance is supported further by density functional theory calculations and various control measurements including the insertion of a Cu spacer layer to suppress the induced ferromagnetism. In addition, anomalous Hall effect measurements show an out-of-plane magnetic hysteresis loop of the induced ferromagnetic phase with larger coercivity and larger remanence than the bulk CoFe2O4 . By demonstrating the MPE in Pt /CoFe2O4 , these results establish the spinel ferrite family as a promising material for the MPE and spin manipulation via proximity exchange fields.

  16. Work function mediated by deposition of ultrathin polar FeO on Pt(111)

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Shuangzan; Qin, Zhihui; Guo, Qinmin; Cao, Gengyu, E-mail: gycao@wipm.ac.cn

    2017-01-15

    Highlights: • Growth of FeO layers on Pt(111) is found to consecutively reduce the work function of the system. • The electrostatic compression effect and the structural relaxation make major contributions to the reductions. • Significant rectifying effect observed in the FeO layer is induced by band alignment shift as work function changing. - Abstract: Significant work function changes from bare Pt(111) surface to 1 monolayer and 2 monolayers of ultrathin iron oxide (FeO) films on it are investigated by means of scanning tunneling microscopy/spectroscopy (STM/STS). With FeO layer-by-layer growth, a continuous reduction of the work function along with the surface vacuum level (VL) shifting is observed. We found that the compression of the electron spill-out at the metal-oxide interface and the substantial reconstruction of 2 ML FeO film, respectively, make major contributions to the first and the second reductions of the work function. The rectifying effect in FeO films is also observed, which is attributed to the downward shift of band alignment imposed by the total change in surface dipole. Our work shows that the polar oxide films play an important role to adjust surface electronic structures for enhancing device functionality.

  17. Influence of cobalt content on the structure and hard magnetic properties of nanocomposite (Fe,Co)-Pt-B alloys

    Energy Technology Data Exchange (ETDEWEB)

    Grabias, A., E-mail: agnieszka.grabias@itme.edu.pl [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); Kopcewicz, M. [Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw (Poland); Latuch, J.; Oleszak, D. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland); Pękała, M. [Department of Chemistry, University of Warsaw, Al. Żwirki i Wigury 101, 02-089 Warsaw (Poland); Kowalczyk, M. [Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw (Poland)

    2017-07-15

    Highlights: • Nanocomposite alloys were formed by annealing of the rapidly quenched alloys. • Magnetically hard L1{sub 0} (Fe,Co)Pt and soft (Fe,Co){sub 2}B or (Fe,Co)B were formed. • Mössbauer spectra revealed Co substitution for Fe in L1{sub 0} FePt, FeB and Fe{sub 2}B phases. • Annealed alloys exhibit hard magnetic properties which depend on phase compositions. • Co addition was found to decrease the magnetization and the energy product. - Abstract: The influence of Co content on the structural and hard magnetic properties of two sets of nanocrystalline Fe{sub 52−x}Co{sub x}Pt{sub 28}B{sub 20} (x = 0–26) and Fe{sub 60−y}Co{sub y}Pt{sub 25}B{sub 15} (y = 0–40) alloys was studied. The alloys were prepared as ribbons by the rapid quenching technique. The nanocomposite structure in the alloys was obtained by annealing at 840–880 K for 30 min. Structural characterization of the samples was performed using the Mössbauer spectroscopy and X-ray diffraction. Magnetic properties of the samples were studied by the measurements of the hysteresis loops and of the magnetization at increasing temperatures. An amorphous phase prevailed in the as-quenched Fe{sub 52−x}Co{sub x}Pt{sub 28}B{sub 20} alloys while a disordered solid solution of fcc-(Fe,Co)Pt was a dominating phase in the Fe{sub 60−y}Co{sub y}Pt{sub 25}B{sub 15} ribbons. Differential scanning calorimetry measurements revealed one or two exothermic peaks at temperatures up to 993 K, depending on the composition of the alloys. Thermal treatment of the samples led to the formation of the magnetically hard ordered L1{sub 0} tetragonal (Fe,Co)Pt nanocrystallites and magnetically softer phases of (Fe,Co)B (for Fe{sub 52−x}Co{sub x}Pt{sub 28}B{sub 20}) or (Fe,Co){sub 2}B (for Fe{sub 60−y}Co{sub y}Pt{sub 25}B{sub 15}). Detailed Mössbauer spectroscopy studies revealed that cobalt substituted for iron in both the L1{sub 0} phase and in iron borides. The nanocomposite Fe{sub 60−y}Co{sub y}Pt

  18. Photovoltaic effect in an indium-tin-oxide/ZnO/BiFeO3/Pt heterostructure

    International Nuclear Information System (INIS)

    Fan, Zhen; Yao, Kui; Wang, John

    2014-01-01

    We have studied the photovoltaic effect in a metal/semiconductor/ferroelectric/metal heterostructure of In 2 O 3 -SnO 2 /ZnO/BiFeO 3 /Pt (ITO/ZnO/BFO/Pt) multilayer thin films. The heterolayered structure shows a short-circuit current density (J sc ) of 340 μA/cm 2 and an energy conversion efficiency of up to 0.33% under blue monochromatic illumination. The photovoltaic mechanism, specifically in terms of the major generation site of photo-excited electron-hole (e-h) pairs and the driving forces for the separation of e-h pairs, is clarified. The significant increase in photocurrent of the ITO/ZnO/BFO/Pt compared to that of ITO/BFO/Pt is attributed to the abundant e-h pairs generated from ZnO. Ultraviolet photoelectron spectroscopy reveals the energy band alignment of ITO/ZnO/BFO/Pt, where a Schottky barrier and an n + -n junction are formed at the BFO/Pt and ZnO/BFO interfaces, respectively. Therefore, two built-in fields developed at the two interfaces are constructively responsible for the separation and transport of photo-excited e-h pairs.

  19. Impact of ultrafast demagnetization process on magnetization reversal in L10 FePt revealed using double laser pulse excitation

    Science.gov (United States)

    Shi, J. Y.; Tang, M.; Zhang, Z.; Ma, L.; Sun, L.; Zhou, C.; Hu, X. F.; Zheng, Z.; Shen, L. Q.; Zhou, S. M.; Wu, Y. Z.; Chen, L. Y.; Zhao, H. B.

    2018-02-01

    Ultrafast laser induced magnetization reversal in L10 FePt films with high perpendicular magnetic anisotropy was investigated using single- and double-pulse excitations. Single-pulse excitation beyond 10 mJ cm-2 caused magnetization (M) reversal at the applied fields much smaller than the static coercivity of the films. For double-pulse excitation, both coercivity reduction and reversal percentage showed a rapid and large decrease with the increasing time interval (Δt) of the two pulses in the range of 0-2 ps. In this Δt range, the maximum demagnetization (ΔMp) was also strongly attenuated, whereas the integrated demagnetization signals over more than 10 ps, corresponding to the average lattice heat effect, showed little change. These results indicate that laser induced M reversal in FePt films critically relies on ΔMp. Because ΔMp is determined by spin temperature, which is higher than lattice temperature, utilizing an ultrafast laser instead of a continuous-wave laser in laser-assisted M reversal may reduce the overall deposited energy and increase the speed of recording. The effective control of M reversal by slightly tuning the time delay of two laser pulses may also be useful for ultrafast spin manipulation.

  20. Unipolar resistive switching in planar Pt/BiFeO3/Pt structure

    Directory of Open Access Journals (Sweden)

    Rajesh K. Katiyar

    2015-03-01

    Full Text Available We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO3 thin films in planar electrode configuration with non-overlapping Set and Reset voltages, On/Off resistance ratio of ∼104 and good data retention (verified for up to 3,000 s. We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of ∼100 mW/cm2. Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical model.

  1. Tip-Dependent Scanning Tunneling Microscopy Imaging of Ultrathin FeO Films on Pt(111)

    DEFF Research Database (Denmark)

    Merte, Lindsay Richard; Grabow, Lars C.; Peng, Guowen

    2011-01-01

    High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen......-vacancy dislocation loops in the FeO moiré structure. The experimental STM results are compared with the results of electronic structure calculations within the DFT+U scheme for a realistic (sqrt(91)xsqrt(91)R5.2 moiré unit cell supported on Pt(111) as well as with the results from previous studies. We find that one...

  2. High-coercivity FePt nanoparticle assemblies embedded in silica thin films

    International Nuclear Information System (INIS)

    Yan, Q; Purkayastha, A; Singh, A P; Li, H; Ramanath, G; Li, A; Ramanujan, R V

    2009-01-01

    The ability to process assemblies using thin film techniques in a scalable fashion would be a key to transmuting the assemblies into manufacturable devices. Here, we embed FePt nanoparticle assemblies into a silica thin film by sol-gel processing. Annealing the thin film composite at 650 deg. C transforms the chemically disordered fcc FePt phase into the fct phase, yielding magnetic coercivity values H c >630 mT. The positional order of the particles is retained due to the protection offered by the silica host. Such films with assemblies of high-coercivity magnetic particles are attractive for realizing new types of ultra-high-density data storage devices and magneto-composites.

  3. Effect of atomic composition on the compressive strain and electrocatalytic activity of PtCoFe/sulfonated graphene

    Energy Technology Data Exchange (ETDEWEB)

    Lohrasbi, Elaheh [Department of Chemistry, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Javanbakht, Mehran, E-mail: mehranjavanbakht@gmail.com [Department of Chemistry, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Fuel and Solar Cell Lab, Renewable Energy Research Center, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Mozaffari, Sayed Ahmad [Fuel and Solar Cell Lab, Renewable Energy Research Center, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Thin Layer and Nanotechnology Laboratory, Department of Chemical Technology, Iranian Research Organization for Science and Technology (IROST), Tehran (Iran, Islamic Republic of)

    2017-06-15

    Highlights: • SO{sub 3}H-graphene supported PtFeCo alloy nanoparticles were prepared. • Co:Fe atomic ratio plays important role in the electrocatalytic performance. • PtCoFe/SG with 7:3 Co:Fe atomic ratio is optimized for PEMFCs. • Power density of 530 mW cm{sup −2} with 0.1 mg cm{sup −2} Pt loading was obtained at 75 °C. - Abstract: The aim of this work is improvement of the stability and durability of sulfonated graphene supported PtCoFe electrocatalyst (PtCoFe/SG) for application in proton exchange membrane fuel cells (PEMFCs). The durability investigation of PtCoFe/SG is evaluated by a repetitive potential cycling test. The compressive strain in the lattice of PtCoFe/SG towards the electrocatalytic oxygen reduction reaction is studied. The synthesized electrocatalysts are examined physically and electrochemically for their structure, morphology and electrocatalytic performance. It is shown that presence of SO{sub 3}− groups on the graphene cause better adsorption of PtCoFe nanoparticles on the support and increase stability of electrocatalysts. Also, it is shown that Co:Fe atomic ratio in the synthesized electrocatalysts plays important role in their electrocatalytic performance. In the optimum Co:Fe atomic ratio, the compressive strain goes through the ideal value of the binding energy; further increase in Co/Fe atomic fraction introduces the excessive compressive strain and the activity of electrocatalyst decreases. The electrocatalyst synthesized in the optimum conditions is utilized as cathode in PEMFC. The power density of the PEMFC in low metal loading (0.1 mg cm{sup −2} Pt) reaches to a maximum of 530 mW cm{sup −2} at 75 °C. It suggests that PtCoFe/SG with 7:3 Co:Fe atomic ratio promises to improve the power density of PEMFCs.

  4. Stabilization of Pt nanoparticles by single stranded DNA and the binary assembly of Au and Pt nanoparticles without hybridization

    International Nuclear Information System (INIS)

    Yang, J.; Lee, Jim Yang; Too, Heng-Phon; Chow, Gan-Moog; Gan, Leong M.

    2006-01-01

    The non-specific interaction between single stranded DNA (ssDNA) and 12 nm Pt nanoparticles is investigated in this work. The data show a strong and non-specific interaction between the two which can be exploited for the stabilization of Pt nanoparticles in aqueous solutions. Based on the experimental findings, a non-hybridization based protocol to assemble 17 nm Au and Pt nanoparticles (12 nm cubic and 3.6 nm spherical) by single-stranded DNA was developed. Transmission electron microscopy (TEM) and UV-visible spectroscopy confirmed that Au and Pt nanoparticles could be assembled by the non-specific interaction in an orderly manner. The experimental results also caution against the potential pitfalls in using DNA melting point analysis to infer metal nanoparticle assembly by DNA hybridization

  5. Velocity dependence of transient hyperfine field at Pt ions rapidly recoiling through magnetized Fe

    International Nuclear Information System (INIS)

    Stuchbery, A.E.; Ryan, C.G.; Bolotin, H.H.

    1981-01-01

    The velocity-dependence of the transient hyperfine magnetic field acting at nuclei of 196 Pt ions rapidly recoiling through thin magnetized Fe was investigated at a number of recoil velocities. The state of interest (2 1 + ) was populated by Coulomb excitation using beams of 80- and 120-MeV 32 S and 150- and 220-MeV 58 Ni ions. The 2 1 + →0 1 + γ-ray angular distribution precession measurements were carried out in coincidence with backscattered projectiles. From these results, the strength of the transient field acting on Pt ions recoiling through magnetized Fe with average velocities in the extended range 2.14<=v/vsub(o)<=4.82 (vsub(o) = c/137) was found to be consistent with a linear velocity dependence and to be incompatible with the specific vsup(0.45+-0.18) dependence which has been previously reported to account well for all ions in the mass range from oxygen through samarium. This seemingly singular behaviour for Pt and other ions in the Pt mass vicinity is discussed

  6. Double-layered perpendicular magnetic recording media of granular-type FePt-MgO films

    International Nuclear Information System (INIS)

    Zhang Zhengang; Singh, Amarendra K.; Yin Jinhua; Perumal, A.; Suzuki, Takao

    2005-01-01

    The recording performance of double-layered granular-type FePt-MgO perpendicular magnetic recording media fabricated onto glass discs by sputtering is investigated. The (0 0 1)-textured FePt granular films are obtained by annealing FePt/MgO multilayers. Three different multilayer structures are compared in their magnetic properties and recording SNR performances. To evaluate thermal stability property of these granular-type FePt disks, the time-dependent magnetic force microscope (MFM) signal from the written bits on one of these disks is recorded in the temperature range 25-200 degree sign C. The signal decay at high observation temperature is interpreted based on the temperature dependence of magnetic anisotropy (K u )

  7. Mn doping effect on structure and magnetism of epitaxial (FePt)1-xMnx films

    International Nuclear Information System (INIS)

    Huang, J.C.A.; Chang, Y.C.; Yu, C.C.; Yao, Y.D.; Hu, Y.M.; Fu, C.M.

    2003-01-01

    We study the structure and perpendicular magnetism of molecular beam epitaxy grown (FePt) 1-x Mn x films with doping concentration x=0, 1%, 2%, 3%, 4%, and 5%. The (FePt) 1-x Mn x films were made by multilayers growth of [Fe/Pt/Mn]xN at 100 deg. C and annealed at 600 deg. C. X-ray diffraction scans indicate that relatively better L1 0 ordered structure for low Mn doping (x 3%. The perpendicular magnetic anisotropy effect of the (FePt) 1-x Mn x films tends to decrease with the increase of Mn doping for x>1%. However, the x=1% doped films possess slightly better perpendicular magnetic anisotropy effect than the zero doped film. The perpendicular magnetic anisotropy constant are of about 1.3x10 7 and 1.6x10 7 erg/cm 3 for x=0% and x=1%, respectively

  8. Atomic structure and thermal stability of Pt-Fe bimetallic nanoparticles: from alloy to core/shell architectures.

    Science.gov (United States)

    Huang, Rao; Wen, Yu-Hua; Shao, Gui-Fang; Sun, Shi-Gang

    2016-06-22

    Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt-Fe alloy and core-shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt-Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure-property relationships of Pt-Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts.

  9. FePt nanoparticles as a potential X-ray activated chemotherapy agent for HeLa cells

    Directory of Open Access Journals (Sweden)

    Zheng Y

    2015-10-01

    Full Text Available Yanhong Zheng,1 Yunlan Tang,2 Zhirong Bao,1 Hui Wang,1 Feng Ren,1 Mingxiong Guo,2 Hong Quan,1 Changzhong Jiang11Key Laboratory of Artificial Micro- and Nano-structures of the Ministry of Education and Center for Electronic Microscopy and Department of Physics, Wuhan University; 2College of Life Sciences, Wuhan University, Wuhan, People’s Republic of ChinaAbstract: Nanomaterials have an advantage in “personalized” therapy, which is the ultimate goal of tumor treatment. In order to investigate the potential ability of FePt nanoparticles (NPs in the diagnosis and chemoradiotherapy treatment of malignant tumors, superparamagnetic, monodispersed FePt (~3 nm alloy NPs were synthesized, using cysteamine as a capping agent. The NPs were characterized by means of X-ray diffraction; transmission electron microscopy, Physical Property Measurement System, and Fourier transform infrared spectroscopy. The cytotoxicity of FePt NPs on Vero cells was assessed using an MTT assay, and tumor cell proliferation inhibited by individual FePt NPs and FePt NPs combined with X-ray beams were also collected using MTT assays; HeLa human cancer cell lines were used as in vitro models. Further confirmation of the combined effect of FePt NPs and X-rays was verified using HeLa cells, after which, the cellular uptake of FePt NPs was captured by transmission electron microscopy. The results indicated that the growth of HeLa cells was significantly inhibited by FePt NPs in a concentration-dependent manner, and the growth was significantly more inhibited by FePt NPs combined with a series of X-ray beam doses; the individual NPs did not display any remarkable cytotoxicity on Vero cells at a concentration <250 µg/mL. Meanwhile, the FePt NPs showed negative/positive contrast enhancement for MRI/CT molecule imaging at the end of the study. Therefore, the combined results implied that FePt NPs might potentially serve as a promising nanoprobe for the integration of tumor

  10. Spin-photo-currents generated by femtosecond laser pulses in a ferrimagnetic GdFeCo/Pt bilayer

    Science.gov (United States)

    Huisman, T. J.; Ciccarelli, C.; Tsukamoto, A.; Mikhaylovskiy, R. V.; Rasing, Th.; Kimel, A. V.

    2017-02-01

    Using THz emission spectroscopy, we detect spin-photo-currents from a ferrimagnetic amorphous alloy GdFeCo to an adjacent Pt capping layer. The currents are generated upon excitation of a GdFeCo/Pt heterostructure with femtosecond laser pulses. It is found that the polarization of the spin-polarized current is determined by magnetic sublattice sensitivity rather than the total magnetization, allowing for spin-polarized current generation when the net magnetization is zero.

  11. Growth, structure and magnetic properties of FePt nanostructures on NaCl(001) and MgO(001)

    International Nuclear Information System (INIS)

    Liscio, F; Maret, M; Doisneau-Cottignies, B; Makarov, D; Albrecht, M; Roussel, H

    2010-01-01

    A comparison of the structural and magnetic properties of FePt nanostructures grown at different temperatures on NaCl(001) and MgO(001) substrates is presented. A strong influence of the deposition temperature on the epitaxial growth as well as on the size distribution of FePt nanostructures grown on NaCl substrates is observed. In spite of a large lattice mismatch between FePt and NaCl, a 'cube-over-cube' growth of nanostructures with a narrow size distribution was achieved at 520 K. Moreover, the growth of FePt nanostructures on NaCl(001) is not preceded by the formation of a wetting layer as observed on MgO(001). The higher degree of L1 0 chemical ordering in FePt nanostructures grown on MgO(001) accompanied by the absence of L1 0 variants with an in-plane tetragonal c-axis indicates that the tensile epitaxial stress induced by the MgO substrate is a key factor in the formation of the L1 0 phase with an out-of-plane c-axis. Superparamagnetic behavior is revealed for the FePt nanostructures grown on NaCl(001) due to their small size and relatively poor chemical order.

  12. Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

    Science.gov (United States)

    Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

    2018-02-01

    It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Exchange bias effect in L10-ordered FePt and FeCo-based bilayer structure: effect of increasing applied field

    Science.gov (United States)

    Singh, Sadhana; Kumar, Dileep; Bhagat, Babli; Choudhary, R. J.; Reddy, V. R.; Gupta, Ajay

    2018-02-01

    The applied magnetic field (H APP) dependence of the exchange bias (EB) is studied in an exchange-coupled thin-film bilayer composed of a hard ferromagnetic FePt layer in the proximity of a soft ferromagnetic FeCo layer. FePt/FeCo structure is deposited in an ultra-high vacuum chamber, where the FePt layer was first annealed at 823 K for 30 min and subsequently cooled to room temperature in the presence of an in-plane magnetic field, H MAX ~ 1.5 kOe to promote L10-ordered hard magnetic phase with magnetic moments aligned in one of the in-plane directions in the FePt layer. In-situ magneto-optical Kerr effect measurements during different stages of bilayer growth and detailed ex-situ superconducting quantum interference device-vibrating sample magnetometer measurements jointly revealed that due to the interplay between exchange coupling at the interface and dipolar energies of the saturated hard FePt layer, a hysteresis loop of FeCo layer shifts along the magnetic field axis. A clear dependence of EB field (H EB) on increasing maximum value of the H APP during the hysteresis loop measurement is understood in terms of the magnetic state of soft and hard magnetic layers, where EB increases with increasing H APP until the hard layer moment remains undisturbed in its remanence state. As soon as the field was sufficient to rotate the spins of the FePt layer, the loop became symmetric with respect to the field axis.

  14. FePt and CoPt nanoparticles prepared by micellar method. Effects of A1{yields}L1{sub 0} transition on oxidation resistance and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Han, Luyang

    2011-02-15

    In this thesis FePt and CoPt alloy nanoparticles are prepared with reverse micelles. The metallic nanoparticles with diameters of 2-12 nm and interparticle distances of 20-140 nm are obtained on Si substrates. The magnetic properties of FePt and CoPt nanoparticles as well as oxidation behavior of FePt nanoparticles are investigated. X-ray magnetic circular dichroism (XMCD) measurements on 5.8 nm FePt nanoparticles after hydrogen plasma reduction at 300 C reveals that the magnetic moment per Fe atom and magnetic anisotropy energy match chemically disordered FePt in A1 phase. Annealing at 650 C transform portion of FePt particles to chemically ordered L1{sub 0} phase. The presense of nanoparticles in L1{sub 0} phase is identified by high-resolution transmission electronmicroscopy (HRTEM) investigation, where it is also observed that large fraction of the particles contain defects such as twin boundaries and stacking faults. By increasing the annealing temperature or prolonging annealing time, ratio of transformed particles increases. The average magnetic anisotropy energy of the transformed particles is below 30% of the value of bulk FePt in L1{sub 0} phase. Annealing at above 750 C, however, decreases the average magnetic anisotropy in the sample. Similar A1 {yields} L1{sub 0} transition is observed in FePt nanoparticles with different diameters as well as in CoPt nanoparticles. The spin moment of Fe in FePt nanoparticles decreases with smaller particle diameter, while the orbital moment stays almost constant. Magnetic moments at room temperature are significantly reduced compared to those at low temperature, suggesting the Curie temperatures in FePt and CoPt nanoparticles are significantly lower than in the bulk. The annealing also induces Pt segregation towards the surface in FePt nanoparticles, which is identified by the decreased apparent Fe content measured by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The segregation of Pt

  15. Influence of MgO underlayers on the structure and magnetic properties of FePt-C nanogranular films for heat-assisted magnetic recording media

    Directory of Open Access Journals (Sweden)

    T. Shiroyama

    2016-10-01

    Full Text Available In order to optimize the nanogranular structure of FePt-C for heat-assisted magnetic recording media, we investigated the influence of MgO underlayers on the growth of FePt grains in the FePt-C layer. The FePt-C layer was deposited by using the alternating sputtering method, by which FePt and FePt-C layers were alternately deposited. To understand the growth mechanism of the FePt-C layer on the MgO underlayers deposited under various conditions, detailed plan-view and cross sectional transmission electron microscopy observations were made for different film thicknesses. We found that columnar FePt grains grow only when the deposition conditions of the MgO underlayer are optimal. Direct TEM observation of the growth process of the FePt-C layer revealed that the number density of nuclei is sufficient in the initial stage of the film deposition; however, coarsening of the grains after grain impingement causes a substantial decrease in the number density of the FePt grains.

  16. Origin of (0 0 1) orientation and superlattice structure identification in L10-FePt/B4C multilayer thin films

    Science.gov (United States)

    Zhang, Jun; Xie, Jian; Wang, Yi; Wang, Hanbin; Liu, Xiang; Ye, Cong; Wang, Hao

    2015-12-01

    (0 0 1) textured L10 FePt/B4C multilayer thin films have been prepared on amorphous substrates by magnetron sputtering. High resolution transmission electron microscopy investigation indicates that the Fe and Pt atoms stacked alternately along the c-axis of L10 FePt, confirming the formation of the superlattice structure of L10-ordered FePt. The internal stress calculation and geometrical phase analysis confirm the existence of the in-plane tensile strain in the L10 FePt thin films. The diffusion of the B and C atoms into the FePt layers results in expansion of the FePt unit cells in the interfaces, which induces an in-plane tensile strain in the adjacent deep parts of FePt layer. Such an in-plane tensile strain creates a favorable condition for the FePt films to stabilize the (0 0 1) texture because it relaxes the ordering strain energy of FePt during phase transformation.

  17. Electronic modification effects induced by Fe in Pt-Ru-Fe ternary catalyst on the electrooxidation of CO/H₂ and methanol.

    Science.gov (United States)

    Kim, Taeyoon; Kobayashi, Koichi; Take, Tetsuo; Nagai, Masayuki

    2012-01-01

    Electro-oxidation of CO/H₂ and methanol was performed over a carbon supported Pt-Ru-Fe ternary alloy catalyst prepared via the conventional NaBH₄ reduction method. Physicochemical and electrochemical measurements were used to elucidate the respective roles of Ru and Fe in the ternary catalyst, revealing synergistic effects in the Pt-Ru-Fe catalyst on the electro-oxidation of CO/H₂ and methanol. The methanol oxidation activity of Pt₃Ru₂Fe/C was ca. 2.5 times higher than that of PtRu/C at 0.45 V vs. RHE as a result of enhanced CO tolerance. The enhanced CO tolerance of the Pt-Ru-Fe ternary alloy catalysts was derived from the reaction between the high mobility, weakly adsorbed CO on the Pt site that was electronically modified by alloying with Fe and adsorbed water species on the Ru site. This combination of features produced an improvement in the electro-oxidation of CO/H₂ and methanol at lower potential. On the basis of the data, it was proposed that the addition of a water activator such as Ru is indispensible in the design of multicomponent alloy catalysts for methanol oxidation, and the additional effect derived from an electronic modifier is an important factor for improving the CO and methanol oxidation activity of the catalyst containing the water activator.

  18. Dependence on composition of electronic properties and stability of Pt-Fe/C catalysts for oxygen reduction

    Energy Technology Data Exchange (ETDEWEB)

    Malheiro, A.R.; Perez, J.; Villullas, H.M. [Departamento de Fisico-Quimica, Instituto de Quimica, Universidade Estadual Paulista - UNESP, Caixa Postal 355, R. Francisco Degni, s/n, CEP 14801-970, Araraquara, SP (Brazil)

    2010-11-01

    This work presents studies of electronic characteristics and alloy stability carried out for Pt-Fe/C catalysts of different compositions (10-50% Fe, in atoms) and same particle size. The electronic properties are characterized by in situ dispersive X-ray absorption spectroscopy (DXAS). The results show a steady decrease in Pt d-band occupancy as the amount of Fe in the alloy increases. The alloy stability is evaluated by prolonged potential cycling up to 1.0 V. Catalysts with Fe content up to 30% show good stabilities and keep their activities for oxygen reduction after prolonged cycling. In contrast, catalysts with Fe content above 30% suffer pronounced Fe leaching. (author)

  19. Fabrication and magnetic properties of FePt/Al2O3 composite film by atomic-layer-deposition

    International Nuclear Information System (INIS)

    Kong, Ji-Zhou; Gao, Mo-Yun; Zhai, Hai-Fa; Yan, Qing-Yu; Li, Ai-Dong; Li, Hui; Wu, Di

    2013-01-01

    Self-assembled face-centered cubic FePt nanoparticles were capped by a amorphous Al 2 O 3 capping layer with the thickness of 10 nm using the atomic layer deposition (ALD) technology, and transmission electron microscopy indicates that the FePt nanocrystals are well-separated. After annealing the composite film at 700 °C, well-monodispersed face-centered tetragonal FePt particles can be obtained, yielding a coercivity value Hc=5.9 kOe with the magnetocrystalline anisotropy of 3.86 MJ/m 3 . The thermal factor for the composite film is 68.5, meeting the industry requirement (K u V/k B T ≥ 50). The protection of amorphous Al 2 O 3 matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L1 0 ordering transition. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a new potential approach to fabricate patterned magnetic recording media with ultrahigh areal density. - Highlights: • Well-monodispersed fcc-FePt NPs were prepared via chemical reduction. • Self-assembled fcc-FePt NPs were capped by Al 2 O 3 layer via ALD. • Al 2 O 3 capping layer can prevent particles from agglomerating and sintering. • A coercivity of 5.9 kOe with the magnetocrystalline anisotropy of 3.86 MJ/m 3 was obtained. • The thermal factor of the composite film is 68.5, meeting the industry requirement

  20. Monatomic Fe and Co wires at the Pt surface step edge: theory of the unconventional magnetic anisotropy

    International Nuclear Information System (INIS)

    Shick, Alexander B.; Maca, Frantisek; Oppeneer, Peter M.

    2005-01-01

    We report a first-principles investigation of the anomalous magnetic anisotropy of quasi-one-dimensional ferromagnetic Fe and Co chains decorating the Pt(111) step edge. Our calculations for both Fe and Co wires show that the easy magnetization is always confined in the plane perpendicular to the wire. The symmetry breaking at the step leads to an easy magnetization axis of the Co wire at an odd angle of ∼ 20 deg. towards the Pt step, in agreement with the experiment. This canting becomes more pronounced for the Fe wire, for which we obtain an easy axis at 30 deg. towards the Pt step. Also, the Fe and Co spin and orbital moments become noncollinear, even in the case of a collinear ferromagnetic spin arrangement

  1. Invar behavior of NANOPERM-type amorphous Fe-(Pt)-Zr-Nb-Cu-B alloys

    Science.gov (United States)

    Gondro, J.; Świerczek, J.; Rzącki, J.; Ciurzyńska, W.; Olszewski, J.; Zbroszczyk, J.; Błoch, K.; Osyra, M.; Łukiewska, A.

    2013-09-01

    Transmission Mössbauer spectra of amorphous Fe86Zr7Nb1Cu1B5, Fe81Zr7Nb1Cu1B10 and Fe81Pt5Zr7Nb1Cu1B5 alloys in the as-quenched state and subjected to the accumulative annealing for 15 min in the temperature range from 573 K up to 750 K are presented. After these heat treatments the alloys remain in the amorphous state. The accumulative annealing for 15 min at 573 K and then 600 K of the Fe86Zr7Nb1Cu1B5 and Fe81Zr7Nb1Cu1B10 alloys causes the narrowing of the transmission Mössbauer spectra as compared to the as-quenched state and the decrease of the average hyperfine field induction which is connected with the invar effect. For similar behavior in Fe81Pt5Zr7Nb1Cu1B5 alloy the accumulative annealing up to 700 K is needed. With further increase of the annealing temperature up to 750 K the broadening of the Mössbauer spectra and the increase of the average hyperfine field induction occur. The lowest value of the average hyperfine field induction of amorphous samples is accompanied by the lowest value of the Curie temperature. The investigated amorphous alloys do not reach the magnetic saturation up to the magnetizing field of 2 T and the coefficient in Holstein-Primakoff term is about one order in magnitude larger than in other classical FeCo-based amorphous alloys due to the non-collinear magnetic structure. The Mössbauer spectra and hysteresis loops of the amorphous Fe86Zr7Nb1Cu1B5 alloy in the as-quenched state and after the accumulative annealing at 573+620 K for 15 min are sensitive to the tensile stresses subjected to the sample. Such behavior is ascribed to the invar anomalies.

  2. Precursors of thermoelastic Fcc-Fct martensite transformation of Fe3Pt alloys

    International Nuclear Information System (INIS)

    Oshima, R.; Takahashi, M.

    2000-01-01

    Precursor phenomena of thermoelastic martensite transformations of Fe 3 Pt have been studied by mechanical tests, X-ray diffractometry, transmission electron microscopy and neutron inelastic scattering measurements. The ordered austenite with an Ll 2 structure becomes soft markedly at temperatures below 200 K. It was also confirmed that the TA mode along [011] directions of the alloy became soft at zone boundaries of the reciprocal space with approaching to the transition temperature. The observed precursor phenomena are considered to be related to the thermoelastic fcc-fct martensite transformation. (orig.)

  3. Effect of hexane on magnetic blocking behavior of FePt nanoparticles

    Science.gov (United States)

    Şimşek, Telem; Akansel, Serkan; Özcan, Şadan

    2012-11-01

    In this work effect of the carrier fluid, hexane, on the magnetic properties of 4.7 nm sized FePt nanoparticles is investigated. Nanoparticles are synthesized by chemical method. Structural and magnetic characterizations confirmed that samples are monodispersed with disordered face centered cubic (fcc) crystal structure and, magnetically, exhibit two blocking behaviors; the first is at 27 K and second at 110 K. Carrier fluid of particles, hexane, is found to influence the blocking of 7% of the total magnetic moments in the system by freezing at low temperatures resulting in a two blocking phenomena even for nanoparticles that are monodispersed with narrow particle size distribution.

  4. Irreversible magnetization process and switching mechanism in L10 FePt thin films

    Directory of Open Access Journals (Sweden)

    A. Lisfi

    2017-05-01

    Full Text Available The irreversible characteristics of the magnetization and the switching mechanism have been investigated in granular FePt films with L10 phase prepared by sputtering on a polymer substrate. The films display an extremely large magnetic anisotropy with a random distribution of the magnetization easy axis. The magnetic instabilities and the irreversible magnetization are found to be controlled by domain wall, which is responsible for the magnetization reversal. Through remanence curves and ΔM plot, the nature of magnetic interactions was revealed to be positive exchange coupling.

  5. Self-assembled FePt nanodot arrays with mono-dispersion and -orientation

    Energy Technology Data Exchange (ETDEWEB)

    Gai, Prof. Zheng [Peking University; Howe, Jane Y [ORNL; Guo, Jiandong [University of Tennessee, Knoxville (UTK); Blom, Douglas Allen [ORNL; Plummer, E Ward [ORNL; Shen, Jian [ORNL

    2005-01-01

    For self-assembled nanodots, the ultimate dream is to simultaneously achieve tunable uniformity in size, spatial distribution, chemical composition, and crystallographic orientation. By utilizing the Volmer-Weber growth mode in thin film epitaxy, we have grown self-assembled two-dimensional arrays of FePt alloy nanodots that are uniform in size, chemical composition, and are all crystallgraphically aligned. These dot assemblies are ferromagnetic at room temperature and can be easily transferred onto other templates without destroying the size and orientation uniformity.

  6. Giant magnetoimpedance effect in sputtered single layered NiFe film and meander NiFe/Cu/NiFe film

    International Nuclear Information System (INIS)

    Chen, L.; Zhou, Y.; Lei, C.; Zhou, Z.M.; Ding, W.

    2010-01-01

    Giant magnetoimpedance (GMI) effect on NiFe thin film is very promising due to its application in developing the magnetic field sensors with highly sensitivity and low cost. In this paper, the single layered NiFe thin film and NiFe/Cu/NiFe thin film with a meander structure are prepared by the MEMS technology. The influences of sputtering parameters, film structure and conductor layer width on GMI effect in NiFe single layer and meander NiFe/Cu/NiFe film are investigated. Maximum of the GMI ratio in single layer and sandwich film is 5% and 64%, respectively. The results obtained are useful for developing the high-performance magnetic sensors based on NiFe thin film.

  7. Single-Crystalline cooperite (PtS): Crystal-Chemical characterization, ESR spectroscopy, and {sup 195}Pt NMR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rozhdestvina, V. I., E-mail: veronika@ascnet.ru; Ivanov, A. V.; Zaremba, M. A. [Far East Division, Russian Academy of Sciences, Institute of Geology and Nature Management (Russian Federation); Antsutkin, O. N.; Forsling, W. [Lulea University of Technology (Sweden)

    2008-05-15

    Single-crystalline cooperite (PtS) with a nearly stoichiometric composition was characterized in detail by X-ray diffraction, electron-probe X-ray microanalysis, and high-resolution scanning electron microscopy. For the first time it was demonstrated that {sup 195}Pt static and MAS NMR spectroscopy can be used for studying natural platinum minerals. The {sup 195}Pt chemical-shift tensor of cooperite was found to be consistent with the axial symmetry and is characterized by the following principal values: {delta}{sub xx} = -5920 ppm, {delta}{sub yy} = -3734 ppm, {delta}{sub zz} = +4023 ppm, and {delta}{sub iso} = -1850 ppm. According to the ESR data, the samples of cooperite contain copper(II), which is adsorbed on the surface during the layer-by-layer crystal growth and is not involved in the crystal lattice.

  8. Control of Microstructure and Magnetic Properties of FePt Thin Films with TiN-MgO Intermediate Layer.

    Science.gov (United States)

    Dong, Kai-Feng; Jin, Fang; Mo, Wen-Qin; Song, Jun-Lei; Cheng, Wei-Ming

    2018-04-01

    The effects of TiN-MgO intermediate layer on the microstructure and magnetic properties of FePt-SiNx-C films were investigated. With doping MgO into TiN, three components were formed, including titanium dioxide, titanium nitride and titanium oxynitride. This caused the decrease of the surface energy and the increase of the interface energy, and further induced the promotion of island growth of FePt, thus the improvement of the isolation and the decrease of FePt grains. On the other hand, the decrease of surface energy and the forming of some titanium dioxide with doping MgO would accompany the deterioration of epitaxial growth and thus the deterioration of the perpendicular magnetic anisotropy of FePt films in a certain degree. By optimizing the concentration of TiN and MgO, the FePt-SiNx-C films with small grain size of 5.86±1.03 nm and good perpendicular anisotropy would be obtained.

  9. Synthesis and characterization of FePt nanoparticles by high energy ball milling with and without surfactant

    International Nuclear Information System (INIS)

    Velasco, V.; Martinez, A.; Recio, J.; Hernando, A.; Crespo, P.

    2012-01-01

    Highlights: ► Fe and Pt powders in the presence of surfactants don’t alloyed by HEBM technique. ► FePt alloys obtained by dry milling exhibit particle sizes of around 10 μm. ► FePt alloys obtained by dry milling exhibit soft magnetic behavior. ► A thermal treatment induces a phase transformation from FCC to FCT. - Abstract: FePt nanoparticles were prepared by high energy ball milling (HEBM) in two different ways. In the first one, elemental powders were mixed and milled whereas in the second one the milling was performed in the presence of oleyl amine and oleic acid as surfactants and hexane as a solvent. X-ray diffraction shows that when the milling is performed in dry conditions, Fe and Pt are alloyed after 5 h, whereas in the wet milling procedure alloying does not take place. In the first case, the diffraction pattern corresponds to the disordered FCC phase. This behavior is also corroborated by the evolution of the magnetic characteristics. In the case of the alloy obtained in dry conditions, the powder was heat treated in order to induce the transformation to the ordered phase. Coercivities of 2.5 kOe are obtained after 650 °C for 2 h.

  10. Synthesis and characterization of FePt nanoparticles by high energy ball milling with and without surfactant

    Energy Technology Data Exchange (ETDEWEB)

    Velasco, V., E-mail: vvjimeno@fis.ucm.es [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Martinez, A.; Recio, J. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Hernando, A.; Crespo, P. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Dpto. de Fisica de Materiales, UCM, 28040 Madrid (Spain)

    2012-09-25

    Highlights: Black-Right-Pointing-Pointer Fe and Pt powders in the presence of surfactants don't alloyed by HEBM technique. Black-Right-Pointing-Pointer FePt alloys obtained by dry milling exhibit particle sizes of around 10 {mu}m. Black-Right-Pointing-Pointer FePt alloys obtained by dry milling exhibit soft magnetic behavior. Black-Right-Pointing-Pointer A thermal treatment induces a phase transformation from FCC to FCT. - Abstract: FePt nanoparticles were prepared by high energy ball milling (HEBM) in two different ways. In the first one, elemental powders were mixed and milled whereas in the second one the milling was performed in the presence of oleyl amine and oleic acid as surfactants and hexane as a solvent. X-ray diffraction shows that when the milling is performed in dry conditions, Fe and Pt are alloyed after 5 h, whereas in the wet milling procedure alloying does not take place. In the first case, the diffraction pattern corresponds to the disordered FCC phase. This behavior is also corroborated by the evolution of the magnetic characteristics. In the case of the alloy obtained in dry conditions, the powder was heat treated in order to induce the transformation to the ordered phase. Coercivities of 2.5 kOe are obtained after 650 Degree-Sign C for 2 h.

  11. Unusually sharp paramagnetic phase transition in thin film Fe3Pt invar

    Science.gov (United States)

    Drisko, Jasper; Cumings, John

    2013-03-01

    Invar alloys, typically 3d transition metal rich systems, are most commonly known for their extremely low coefficients of thermal expansion (CTE) over a wide range of temperatures close to room temperature. This anomalous behavior in the CTE lends Invar to a variety of important applications in precision mechanical devices, scientific instruments, and sensors, among others. Many theoretical models of Invar have been proposed over the years, the most promising of which is a system described by two coexisting phases, one high-spin high-volume and the other low-spin low-volume, that compete to stabilize the volume of the material as the temperature is changed. However, no theory has yet been able to explain all experimental observations across the range of Invar alloys, especially at finite temperature. We have fabricated thin films of a Fe3Pt Invar alloy and investigate them using Lorentz Transmission Electron Microscopy (TEM). 23nm films are deposited onto SiN membrane substrates via radio-frequency magnetron sputtering from a pure Fe target decorated with Pt pieces. We observe novel magnetic domain structures and an unusually sharp phase transition between ferromagnetic (FM) and paramagnetic (PM) regions of the film under a temperature gradient. This sharp transition suggests that the FM-to-PM transition may be first order, perhaps containing a structural-elastic component to the order parameter. However, electron diffraction reveals that both the FM and PM regions have the same FCC crystal structure.

  12. Understanding the Oxygen Reduction Reaction on a Y/Pt(111) Single Crystal

    DEFF Research Database (Denmark)

    Ulrikkeholm, Elisabeth Therese; Johansson, Tobias Peter; Malacrida, Paolo

    2014-01-01

    was significantly different from our initial expectations. In order to understand this phenomenon, we investigated a Y/Pt(111) single crystal, formed by depositing large amounts of Y om Pt(111) under ultra-high vacuum (UHV) conditions and annealing to high temperatures. We subsequently characterised the surface...

  13. Biological fate of a single administration of 191Pt in rats following different routes of exposure

    International Nuclear Information System (INIS)

    Moore, W. Jr.; Hysell, D.; Crocker, W.; Stara, J.

    1975-01-01

    The retention, tissue distribution, and excretion of 191 Pt in adult rats was determined following oral, intravenous (IV), and intratracheal administration. The highest retention was obtained following IV dosing, and lowest retention (less than 0.5 percent) occurred after oral dosing. Tissues containing the highest concentrations of 191 Pt following IV administration were the kidney, adrenal, spleen, and liver. Following a single oral dose, almost all of the 191 Pt was excreted in the feces due to nonabsorption, whereas after IV dosing, similar quantities were excreted in both the urine and feces. Following IV dosing of pregnant rats, 191 Pt was found in all the fetuses; however, the amount was small

  14. Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer

    Science.gov (United States)

    Ishikawa, S.; Sato, H.; Yamanouchi, M.; Ikeda, S.; Fukami, S.; Matsukura, F.; Ohno, H.

    2013-05-01

    Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer were investigated and the structure was adopted as a recording layer in magnetic tunnel junctions (MTJs) with perpendicular magnetic easy-axis to attain a high thermal stability. Perpendicular easy-axis was obtained with the Pt thickness range of 0.6-1.2 nm and the CoFeB thickness range of 0.6-1.5 nm. As-made MTJs employing the CoFeB-[Co/Pt] multilayer structure as a recording layer showed tunnel magnetoresistance of 40% on average. A high thermal stability factor over 200 was obtained in the MTJs with the size of 25 nm in diameter.

  15. Supergene neoformation of Pt-Ir-Fe-Ni alloys: multistage grains explain nugget formation in Ni-laterites

    Science.gov (United States)

    Aiglsperger, Thomas; Proenza, Joaquín A.; Font-Bardia, Mercè; Baurier-Aymat, Sandra; Galí, Salvador; Lewis, John F.; Longo, Francisco

    2017-10-01

    Ni-laterites from the Dominican Republic host rare but extremely platinum-group element (PGE)-rich chromitites (up to 17.5 ppm) without economic significance. These chromitites occur either included in saprolite (beneath the Mg discontinuity) or as `floating chromitites' within limonite (above the Mg discontinuity). Both chromitite types have similar iridium-group PGE (IPGE)-enriched chondrite normalized patterns; however, chromitites included in limonite show a pronounced positive Pt anomaly. Investigation of heavy mineral concentrates, obtained via hydroseparation techniques, led to the discovery of multistage PGE grains: (i) Os-Ru-Fe-(Ir) grains of porous appearance are overgrown by (ii) Ni-Fe-Ir and Ir-Fe-Ni-(Pt) phases which are overgrown by (iii) Pt-Ir-Fe-Ni mineral phases. Whereas Ir-dominated overgrowths prevail in chromitites from the saprolite, Pt-dominated overgrowths are observed within floating chromitites. The following formation model for multistage PGE grains is discussed: (i) hypogene platinum-group minerals (PGM) (e.g. laurite) are transformed to secondary PGM by desulphurization during serpentinization; (ii) at the stages of serpentinization and/or at the early stages of lateritization, Ir is mobilized and recrystallizes on porous surfaces of secondary PGM (serving as a natural catalyst) and (iii) at the late stages of lateritization, biogenic mediated neoformation (and accumulation) of Pt-Ir-Fe-Ni nanoparticles occurs. The evidence presented in this work demonstrates that in situ growth of Pt-Ir-Fe-Ni alloy nuggets of isometric symmetry is possible within Ni-laterites from the Dominican Republic.

  16. Crystal structure of the coordination polymer [FeIII2{PtII(CN4}3

    Directory of Open Access Journals (Sweden)

    Maksym Seredyuk

    2015-01-01

    Full Text Available The title complex, poly[dodeca-μ-cyanido-diiron(IIItriplatinum(II], [FeIII2{PtII(CN4}3], has a three-dimensional polymeric structure. It is built-up from square-planar [PtII(CN4]2− anions (point group symmetry 2/m bridging cationic [FeIIIPtII(CN4]+∞ layers extending in the bc plane. The FeII atoms of the layers are located on inversion centres and exhibit an octahedral coordination sphere defined by six N atoms of cyanide ligands, while the PtII atoms are located on twofold rotation axes and are surrounded by four C atoms of the cyanide ligands in a square-planar coordination. The geometrical preferences of the two cations for octahedral and square-planar coordination, respectively, lead to a corrugated organisation of the layers. The distance between neighbouring [FeIIIPtII(CN4]+∞ layers corresponds to the length a/2 = 8.0070 (3 Å, and the separation between two neighbouring PtII atoms of the bridging [PtII(CN4]2− groups corresponds to the length of the c axis [7.5720 (2 Å]. The structure is porous with accessible voids of 390 Å3 per unit cell.

  17. Magnetoresistance in Hybrid Pt/CoFe2O4 Bilayers Controlled by Competing Spin Accumulation and Interfacial Chemical Reconstruction.

    Science.gov (United States)

    Vasili, Hari Babu; Gamino, Matheus; Gàzquez, Jaume; Sánchez, Florencio; Valvidares, Manuel; Gargiani, Pierluigi; Pellegrin, Eric; Fontcuberta, Josep

    2018-04-11

    Pure spin currents have potential for use in energy-friendly spintronics. They can be generated by a flow of charge along a nonmagnetic metal with large spin-orbit coupling. This produces a spin accumulation at the surfaces, controllable by the magnetization of an adjacent ferromagnetic layer. Paramagnetic metals typically used are close to ferromagnetic instability and thus magnetic proximity effects can contribute to the observed angular-dependent magnetoresistance (ADMR). As interface phenomena govern the spin conductance across the metal/ferromagnetic-insulator heterostructures, unraveling these distinct contributions is pivotal for a full understanding of spin current conductance. Here, we report X-ray absorption and magnetic circular dichroism (XMCD) at Pt M and (Co, Fe) L absorption edges and atomically resolved energy electron loss spectroscopy (EELS) data of Pt/CoFe 2 O 4 bilayers, where CoFe 2 O 4 layers have been capped by Pt grown at different temperatures. It was found that the ADMR differs dramatically, dominated either by spin Hall magnetoresistance (SMR) associated with the spin Hall effect or by anisotropic magnetoresistance. The XMCD and EELS data indicate that the Pt layer grown at room temperature does not display any magnetic moment, whereas when grown at a higher temperature, it becomes magnetic due to interfacial Pt-(Co, Fe) alloying. These results enable differentiation of spin accumulation from interfacial chemical reconstructions and tailoring of the angular-dependent magnetoresistance.

  18. First-principles study on surface reconstruction and magnetic phase stability of an FePt3 film on a Pt(110) substrate

    Science.gov (United States)

    Kim, Hanchul; Kim, Miyoung

    2016-01-01

    The FePt3 alloy is one of the most investigated materials for high density storage applications due to its rich variety of magnetic structures which transform sensitively depending on change in its local structure. Here, we present the ab-initio total energy and electronic structure calculations within the framework of density functional theory for an FePt3 film of 0.5 nm in thickness on a Pt (110) surface. The results show that a missing-row surface reconstruction along the [1overline 1 0] direction is energetically more stable over the unreconstructed clean surface, which is attributed to the energy gain by the spill out of p-electron charge to the large facet area from Pt atoms at the second and third atomic layers. The missing-row reconstruction is found to enhance the stability of the ferromagnetic phase over the antiferromagnetic bulk ground-state phase and to induce possible concurrence of a meta-stable atomic structure with an in-plane anti-phase boundary along the orientation of missing-row in addition to the conventional L12 surface, implying the observation of various magnetic phases.

  19. Room temperature magnetism of few-nanometers-thick Fe3O4(111) films on Pt(111) and Ru(0001) studied in ambient conditions

    International Nuclear Information System (INIS)

    Lewandowski, M.; Miłosz, Z.; Michalak, N.; Ranecki, R.; Sveklo, I.; Kurant, Z.; Maziewski, A.; Mielcarek, S.; Luciński, T.; Jurga, S.

    2015-01-01

    Few-nanometers-thick Fe 3 O 4 (111) films were epitaxially grown on Pt(111) and Ru(0001) single crystal supports by sequential iron deposition and oxidation in an ultra-high vacuum chamber. The growth of well-ordered magnetite films was confirmed by low energy electron diffraction. The films were covered with a protective Au layer and subjected to magnetic and structural studies in ambient conditions. Magnetic hysteresis loops, recorded using magneto-optical Kerr effect apparatus, confirmed magnetic ordering in both films at room temperature. The Kerr measurements indicated in-plane orientation of magnetization, which was supported by the lack of magnetic contrast in magnetic force microscopy images. Atomic force microscopy revealed significant differences in morphology of the films, tentatively attributed to different lattice mismatch with Pt(111) and Ru(0001) single crystal supports. - Highlights: • Few-nanometers-thick Fe 3 O 4 (111) films were grown on Pt(111) and Ru(0001). • Magnetic properties were studied using MOKE and AFM/MFM in ambient conditions. • The films exhibited in-plane magnetic ordering at room temperature. • Differences in magnetic properties were tentatively assigned to structural differences.

  20. Spin Crossover in Fe(II)-M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2-Substituted Pyrazines.

    Science.gov (United States)

    Kucheriv, Olesia I; Shylin, Sergii I; Ksenofontov, Vadim; Dechert, Sebastian; Haukka, Matti; Fritsky, Igor O; Gural'skiy, Il'ya A

    2016-05-16

    Discovery of spin-crossover (SCO) behavior in the family of Fe(II)-based Hofmann clathrates has led to a "new rush" in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe(2+), square planar tetracyanometalates M(II)(CN)4(2-) (M(II) = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fe(II) ion has a pseudo-octahedral coordination environment supported by four μ4-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M(II) = Ni (1), Pd (2), Pt (3); X = Me and M(II) = Ni (4), Pd (5)) or one 2X-pyrazine and one water molecule (X = I and M(II) = Ni (7), Pd (8), Pt (9)), or, alternatively, two distinct Fe(II) positions with either two pyrazines or two water molecules (X = Me and M(II) = Pt (6)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN6 units (1-6) display cooperative spin transition, while Fe(II) ions in N5O or N4O2 surrounding are high spin (HS). Structural changes in the nearest Fe(II) environment upon low-spin (LS) to HS transition, which include ca. 10% Fe-N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of 1-9 (see abstract figure). Effects of a pyrazine substituent and M(II) nature on the hyperfine parameters in both spin states are established.

  1. Anisotropy-graded magnetic media obtained by ion irradiation of L10 FePt

    International Nuclear Information System (INIS)

    Bona, A. di; Luches, P.; Albertini, F.; Casoli, F.; Lupo, P.; Nasi, L.; D’Addato, S.; Gazzadi, G.C.; Valeri, S.

    2013-01-01

    We show that Ar + irradiation can be used effectively to transform a chemically ordered FePt L1 0 homogeneous thin film into an anisotropy-graded composite media with tunable magnetic response. This can be exploited to produce magnetic media with high thermal stability and moderate coercivity with potential in high-density magnetic recording applications. The depth distribution of the chemical order parameter, which controls the magnetic switching mechanism of the system, has been determined by high-resolution transmission electron microscopy. The irradiation-induced modifications of the material have been modeled using Monte Carlo simulations for ion transport in solids. The magnetic properties and coupling regimes of the resulting exchange-coupled systems are discussed

  2. Tunable room-temperature magnetic skyrmions in Ir/Fe/Co/Pt multilayers

    Science.gov (United States)

    Soumyanarayanan, Anjan; Raju, M.; Gonzalez Oyarce, A. L.; Tan, Anthony K. C.; Im, Mi-Young; Petrović, A. P.; Ho, Pin; Khoo, K. H.; Tran, M.; Gan, C. K.; Ernult, F.; Panagopoulos, C.

    2017-09-01

    Magnetic skyrmions are nanoscale topological spin structures offering great promise for next-generation information storage technologies. The recent discovery of sub-100-nm room-temperature (RT) skyrmions in several multilayer films has triggered vigorous efforts to modulate their physical properties for their use in devices. Here we present a tunable RT skyrmion platform based on multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy, magnetic force microscopy and Hall transport techniques. By varying the ferromagnetic layer composition, we can tailor the magnetic interactions governing skyrmion properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. The skyrmions exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of two and ten, respectively. We thus establish a platform for investigating functional sub-50-nm RT skyrmions, pointing towards the development of skyrmion-based memory devices.

  3. Desorption of Furfural from Bimetallic Pt-Fe Oxides/Alumina Catalysts

    Directory of Open Access Journals (Sweden)

    Gloria Lourdes Dimas-Rivera

    2014-01-01

    Full Text Available In this work, the desorption of furfural, which is a competitive intermediate during the production of biofuel and valuable aromatic compounds, was studied using pure alumina, as well as alumina impregnated with iron and platinum oxides both individually and in combination, using thermogravimetric analysis (TGA. The bimetallic sample exhibited the lowest desorption percentage for furfural. High-resolution transmission electron microscopy (HRTEM imaging revealed the intimate connection between the iron and platinum oxide species on the alumina support. The mechanism of furfural desorption from the Pt-Fe/Al2O3 0.5%-0.5% sample was determined using physisorbed furfural instead of chemisorbed furfural; this mechanism involved the oxidation of the C=O group on furfural by the catalyst. The oxide nanoparticles on γ-Al2O3 support helped to stabilize the furfural molecule on the surface.

  4. Effect of TiN-ZrO{sub 2} intermediate layer on the microstructure and magnetic properties of FePt and FePt-SiO{sub 2}-C thin films

    Energy Technology Data Exchange (ETDEWEB)

    Dong, K.F., E-mail: dongkf1981@163.com; Mo, W.Q.; Jin, F.; Song, J.L.

    2017-06-15

    Highlights: • The TiN-ZrO{sub 2} consisted of solid solution of Ti(Zr)ON segregated by amorphous ZrO{sub 2}. • With doping ZrO{sub 2} into TiN layer, grain size of FePt films significantly decreased. • By introducing TiN-ZrO{sub 2}/TiN combined layer, the magnetic properties were improved. - Abstract: The microstructures and magnetic properties of FePt based thin films grown on TiN-ZrO{sub 2} and TiN-ZrO{sub 2}/TiN intermediate layers were systematically investigated. The TiN-ZrO{sub 2} intermediate layer was granular consisting of grains of solid solution of Ti(Zr)ON segregated by amorphous ZrO{sub 2}. It was found with doping ZrO{sub 2} into TiN intermediate layer, grain size of FePt-SiO{sub 2}-C films significantly decreased. Simultaneously, the isolation was obviously improved and grain size distribution became more uniform. However, the magnetic properties of the FePt-SiO{sub 2}-C films grown on TiN-ZrO{sub 2} intermediate layers were slowly deteriorated, which was due to the disturbance of the epitaxial growth of FePt by amorphous ZrO{sub 2} in TiN-ZrO{sub 2} intermediate layer. In order to improve the TiN-ZrO{sub 2} (0 0 2) texture and the crystallinity of TiN-ZrO{sub 2}, TiN-ZrO{sub 2}/TiN combined intermediate layer was introduced. And the magnetic properties were improved, simultaneously, achieving the benefit of grain size reduction. For the FePt 4 nm-SiO{sub 2} 40 vol%-C 20 vol% film grown on TiN/TiN-ZrO{sub 2} 30 vol% combined intermediate layer, well isolated FePt (0 0 1) granular films with coercivity higher than 17.6 kOe and an average size as small as 6.5 nm were achieved.

  5. Measurement of magnetic property of FePt granular media at near Curie temperature

    Energy Technology Data Exchange (ETDEWEB)

    Yang, H.Z., E-mail: YANG_Hongzhi@dsi.a-star.edu.sg; Chen, Y.J.; Leong, S.H.; An, C.W.; Ye, K.D.; Hu, J.F.

    2017-02-01

    The characterization of the magnetic switching behavior of heat assisted magnetic recording (HAMR) media at near Curie temperature (T{sub c}) is important for high density recording. In this study, we measured the magnetic property of FePt granular media (with room temperature coercivity ~25 kOe) at near T{sub c} with a home built HAMR testing instrument. The local area of HAMR media is heated to near T{sub c} by a flat-top optical heating beam. The magnetic property in the heated area was in-situ measured by a magneto-optic Kerr effect (MOKE) testing beam. The switching field distribution (SFD) and coercive field (H{sub c}) of the FePt granular media and their dependence on the optical heating power at near T{sub c} were studied. We measured the DC demagnetization (DCD) signal with pulsed laser heating at different optical powers. We also measured the T{sub c} distribution of the media by measuring the AC magnetic signal as a function of optical heating power. In a summary, we studied the SFD, H{sub c} of the HAMR media at near T{sub c} in a static manner. The present methodology will facilitate the HAMR media testing. - Highlights: • A flat-top optical beam homogeneously heats up HAMR media to near T{sub c}. • When H{sub c} of media drops to 5 kOe with optical heating, SFD is measured to be 0.6. • H{sub c}, SFD, M{sub s} of HAMR media at near T{sub c} are measured with the methodology.

  6. Beneficial Role of Copper in the Enhancement of Durability of Ordered Intermetallic PtFeCu Catalyst for Electrocatalytic Oxygen Reduction.

    Science.gov (United States)

    Arumugam, Balamurugan; Tamaki, Takanori; Yamaguchi, Takeo

    2015-08-05

    Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 °C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 °C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to

  7. L1{sub 0} stacked binaries as candidates for hard-magnets. FePt, MnAl and MnGa

    Energy Technology Data Exchange (ETDEWEB)

    Matsushita, Yu-ichiro [Max-Planck Institut fuer Microstrukture Physics, Halle (Germany); Department of Applied Physics, The University of Tokyo (Japan); Madjarova, Galia [Max-Planck Institut fuer Microstrukture Physics, Halle (Germany); Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University (Bulgaria); Flores-Livas, Jose A. [Department of Physics, Universitaet Basel (Switzerland); Dewhurst, J.K.; Gross, E.K.U. [Max-Planck Institut fuer Microstrukture Physics, Halle (Germany); Felser, C. [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Sharma, S. [Max-Planck Institut fuer Microstrukture Physics, Halle (Germany); Department of Physics, Indian Institute of Technology, Roorkee, Uttarkhand (India)

    2017-08-15

    We present a novel approach for designing new hard magnets by forming stacks of existing binary magnets to enhance the magneto crystalline anisotropy. This is followed by an attempt at reducing the amount of expensive metal in these stacks by replacing it with cheaper metal with similar ionic radius. This strategy is explored using examples of FePt, MnAl and MnGa. In this study a few promising materials are suggested as good candidates for hard magnets: stacked binary FePt{sub 2}MnGa{sub 2} in structure where each magnetic layer is separated by two non-magnetic layers, FePtMnGa and FePtMnAl in hexagonally distorted Heusler structures and FePt{sub 0.5}Ti{sub 0.5}MnAl. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Comparing and Optimizing Nitrate Adsorption from Aqueous Solution Using Fe/Pt Bimetallic Nanoparticles and Anion Exchange Resins

    International Nuclear Information System (INIS)

    Daud, M.; Khan, Z.; Ashgar, A.; Danish, M. I.; Qazi, I. A.

    2015-01-01

    This research work was carried out for the removal of nitrate from raw water for a drinking water supply. Nitrate is a widespread ground water contaminant. Methodology employed in this study included adsorption on metal based nanoparticles and ion exchange using anionic resins. Fe/Pt bimetallic nanoparticles were prepared in the laboratory, by the reduction of their respective salts using sodium borohydride. Scanning electron microscope, X-ray diffraction, energy dispersive spectrometry, and X-ray florescence techniques were utilized for characterization of bimetallic Fe/Pt nanoparticles. Optimum dose, ph, temperature, and contact time were determined for removal through batch tests, both for metal based nanoparticles and anionic exchange resin. Adsorption data fitted well the Langmuir isotherm and conformed to the pseudo first-order kinetic model. Results indicated 97% reduction in nitrate by 0.25 mg/L of Fe/Pt nanoparticles at ph 7 and 83% reduction in nitrate was observed using 0.50 mg/L anionic exchange resins at ph 4 and contact time of one hour. Overall, Fe/Pt bimetallic nanoparticles demonstrated greater removal efficiency due to the small particle size, extremely large surface area (627 m 2 /g), and high adsorption capacity.

  9. Growth and structure of L1 sub 0 ordered FePt films on GaAs(001)

    CERN Document Server

    Nefedov, A; Theis-Broehl, K; Zabel, H; Doi, M; Schuster, E; Keune, W

    2002-01-01

    The structural properties of epitaxial L1 sub 0 ordered FePt(001) films, grown by molecular beam epitaxy (alternating deposition of Fe and Pt atomic layers) on buffer-Pt/seed-Fe/GaAs(001) have been studied by in situ reflection high-energy electron diffraction and by ex situ x-ray scattering as a function of the growth conditions. Reflection high-energy electron diffraction intensity oscillations measured during FePt layer growth provide evidence for island growth at T sub s = 200 deg. C and quasi layer-by-layer growth at T sub s = 350 deg. C. From small-angle and wide-angle x-ray scattering it was found that the degree of epitaxy depends critically on morphology of the seed layer and the substrate roughness. X-ray diffraction analysis showed that the long-range order parameter increases from near zero for films grown at 200 deg. C to 0.65 for films grown at 350 deg. C. This confirms the fact that the order parameter is mainly determined by the surface mobility of the atoms which is controlled experimentally ...

  10. Direct synthesis of L1{sub 0} FePt nanoparticles within carbon nanotubes by wet chemical procedure

    Energy Technology Data Exchange (ETDEWEB)

    Capobianchi, A; Laureti, S; Fiorani, D [Consiglio Nazionale delle Ricerche (CNR), Istituto di Struttura della Materia (ISM), Rome (Italy); Foglia, S [Consiglio Nazionale delle Ricerche (CNR), Istituto di Fotonica e Nanotecnologie, Rome (Italy); Palange, E, E-mail: aldo.capobianchi@ism.cnr.i [Universita degli Studi dell' Aquila, Dipartimento di Ingegneria Elettrica e dell' Informazione, L' Aquila (Italy)

    2010-12-01

    This paper reports on the low temperature synthesis of L1{sub 0} iron-platinum (FePt) particles within multiwall carbon nanotubes using a novel wet chemical method that allows the filling of the nanotube cavity keeping clean its external wall. In the proposed procedure, nanotubes are filled with a precursor salt of hexaaquairon(II) hexachloroplatinate, ([Fe(H{sub 2}O){sub 6}][PtCl{sub 6}]) and nanoparticles of the magnetically hard phase are directly obtained by heating at 400 {sup 0}C in a reductive atmosphere. The advantage of such a precursor, allowing one to obtain at low temperature the L1{sub 0} phase without passing through the soft fcc phase, is due to its structure, where the Fe and Pt atoms are arranged in alternating planes, as in the fct FePt structure. Morphological, structural and magnetic properties of the filled nanotubes have been investigated by transmission electron microscopy, x-ray diffraction and magnetization measurements. The results show the coexistence of nanoparticles in the superparamagnetic and blocked state, depending on the temperature, due to the particle size distribution.

  11. Hydrothermal Synthesis of Pt-, Fe-, and Zn-doped SnO2 Nanospheres and Carbon Monoxide Sensing Properties

    Directory of Open Access Journals (Sweden)

    Weigen Chen

    2013-01-01

    Full Text Available Pure and M-doped (M = Pt, Fe, and Zn SnO2 nanospheres were successfully synthesized via a simple and facile hydrothermal method and characterized by X-ray powder diffraction, field-emission scanning electron microscopy, and energy dispersive spectroscopy. Chemical gas sensors were fabricated based on the as-synthesized nanostructures, and carbon monoxide sensing properties were systematically measured. Compared to pure, Fe-, and Zn-doped SnO2 nanospheres, the Pt-doped SnO2 nanospheres sensor exhibits higher sensitivity, lower operating temperature, more rapid response and recovery, better stability, and excellent selectivity. In addition, a theoretical study based on the first principles calculation was conducted. All results demonstrate the potential of Pt dopant for improving the gas sensing properties of SnO2-based sensors to carbon monoxide.

  12. Effects of Au content on the structure and magnetic properties of L1{sub 0}-FePt nanoparticles synthesized by the sol–gel method

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yang [Institute of Condensed State Physics, Jilin Normal University, Siping 136000 (China); Institute of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Jiang, Yuhong [Institute of Condensed State Physics, Jilin Normal University, Siping 136000 (China); Kadasala, Naveen [Department of Chemistry, Purdue University, West Lafayette, IN 47907 (United States); Zhang, Xiaolong [Institute of Condensed State Physics, Jilin Normal University, Siping 136000 (China); Mao, Chenyi [Department of Chemistry, Purdue University, West Lafayette, IN 47907 (United States); Wang, Yaxin; Liu, Huilian; Liu, Yanqing [Institute of Condensed State Physics, Jilin Normal University, Siping 136000 (China); Yang, Jinghai, E-mail: jhyang1@jlnu.edu.cn [Institute of Condensed State Physics, Jilin Normal University, Siping 136000 (China); Yan, Yongsheng, E-mail: yanyongsheng215@126.com [Institute of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China)

    2014-07-01

    (FePt){sub 100−x}Au{sub x} (x=0, 5, 10, and 20) nanoparticles were synthesized by the sol–gel method, and effects of Au content on the structural and magnetic properties of samples were investigated. Au doping reduced the phase transition temperature from face-centered cubic (FCC) to face-centered tetragonal (FCT) structure. In addition, additive Au promotes the chemical ordering of L1{sub 0} FePt NPs and increases the grain size of L1{sub 0} FePt NPs. When Au content increased from 0 to 10 at%, the coercivity (H{sub c}) increased due to the increase in degree of ordering S and grain size of L1{sub 0} FePt NPs. By increasing the Au content to 20 at%, H{sub c} decreased. - Graphical abstract: (FePt){sub 100}Au{sub 0} NPs are the coexistence of FCT and FCC phases. However, no hints of FCC phase were found for the (FePt){sub 100−x}Au{sub x} NPs (x=5, 10 and 20), which indicates that addition of gold greatly promotes the FCC to FCT phase transition. - Highlights: • (FePt){sub 100−x}Au{sub x} (x=0, 5, 10 and 20) nanoparticles (NPs) were synthesized. • Au addition promotes the chemical ordering of L1{sub 0} FePt NPs. • Au addition reduces ordering temperature of L1{sub 0} FePt NPs from FCC to FCT phase. • (FePt){sub 90}Au{sub 10} NPs show a high coercivity of 9585 Oe at room temperature.

  13. DFT calculations of strain and interface effects on electronic structures and magnetic properties of L10-FePt/Ag heterojunction of GMR applications

    Science.gov (United States)

    Pramchu, Sittichain; Jaroenjittichai, Atchara Punya; Laosiritaworn, Yongyut

    2018-03-01

    In this work, density functional theory (DFT) was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001)/Ag(001), that is, interface between Fe and Ag layers (Fe/Ag) and between Pt and Ag layers (Pt/Ag), were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of "interfacial" Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS) analysis suggests that interaction between Fe (Pt) and Ag near Fe/Ag (Pt/Ag) interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt atoms reduce because of the increase in the electronic states near the Fermi level of the minority-spin electrons. In addition, the significant enhancements of the LDOS near the Fermi levels of the minority-spin electrons signify the boosting of the transport properties of the minority-spin electrons and hence the spin-dependent electron transport at this ferromagnet/metal interface. From this work, it is expected that this clarification of the interfacial magnetism may inspire new innovation on how to improve spin-dependent electron transport for enhancing the giant magnetoresistance (GMR) ratio of potential GMR-based spintronic devices.

  14. DFT calculations of strain and interface effects on electronic structures and magnetic properties of L10-FePt/Ag heterojunction of GMR applications

    Directory of Open Access Journals (Sweden)

    Sittichain Pramchu

    2018-03-01

    Full Text Available In this work, density functional theory (DFT was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001/Ag(001, that is, interface between Fe and Ag layers (Fe/Ag and between Pt and Ag layers (Pt/Ag, were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of “interfacial” Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS analysis suggests that interaction between Fe (Pt and Ag near Fe/Ag (Pt/Ag interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt atoms reduce because of the increase in the electronic states near the Fermi level of the minority-spin electrons. In addition, the significant enhancements of the LDOS near the Fermi levels of the minority-spin electrons signify the boosting of the transport properties of the minority-spin electrons and hence the spin-dependent electron transport at this ferromagnet/metal interface. From this work, it is expected that this clarification of the interfacial magnetism may inspire new innovation on how to improve spin-dependent electron transport for enhancing the giant magnetoresistance (GMR ratio of potential GMR-based spintronic devices.

  15. Magnetically actuated bi-directional microactuators with permalloy and Fe/Pt hard magnet

    International Nuclear Information System (INIS)

    Pan, C.T.; Shen, S.C.

    2005-01-01

    Bi-directional polyimide (PI) electromagnetic microactuator with different geometries are designed, fabricated and tested. Fabrication of the electromagnetic microactuator consists of 10 μm thick Ni/Fe (80/20) permalloy deposition on the PI diaphragm by electroplating, high aspect ratio electroplating of copper planar coil with 10 μm in thickness, bulk micromachining, and excimer laser selective ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems during wafer etching. A mathematical model is created by ANSYS software to analyze the microactuator. The external magnetic field intensity (H ext ) generated by the planar coil is simulated by ANSYS software. ANSYS software is used to predict the deflection angle of the microactuator. Besides, to provide bi-directional and large deflection angle of microactuator, hard magnet Fe/Pt is deposited at a low temperature of 300 deg. C by sputtering onto the PI diaphragm to produce a perpendicular magnetic anisotropic field. This magnetic field can enhance the interaction with H ext to induce attractive and repulsive bi-directional force to provide large displacement. The results of magnetic microactuator with and without hard magnets are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one

  16. Synthesis of Fe3O4/Pt Nanoparticles Decorated Carbon Nanotubes and Their Use as Magnetically Recyclable Catalysts

    Directory of Open Access Journals (Sweden)

    Hongkun He

    2011-01-01

    Full Text Available We report a facile approach to prepare Fe3O4/Pt nanoparticles decorated carbon nanotubes (CNTs. The superparamagnetic Fe3O4 nanoparticles with average size of 4∼5 nm were loaded on the surfaces of carboxyl groups functionalized CNTs via a high-temperature solution-phase hydrolysis method from the raw material of FeCl3. The synthesis process of magnetic CNTs is green and readily scalable. The loading amounts of Fe3O4 nanopartilces and the magnetizations of the resulting magnetic CNTs show good tunability. The Pt nanopaticles with average size of 2.5 nm were deposited on the magnetic CNTs through a solution-based method. It is demonstrated that the Fe3O4/Pt nanoparticles decorated CNTs have high catalytic activity in the reduction reaction of 4-nitrophenol and can be readily recycled by a magnet and reused in the next reactions with high efficiencies for at least fifteen successive cycles. The novel CNTs-supported magnetically recyclable catalysts are promising in heterogeneous catalysis applications.

  17. Synthesis of Fe3O4/Pt Nanoparticles Decorated Carbon Nano tubes and Their Use as Magnetically Recyclable Catalysts

    International Nuclear Information System (INIS)

    He, H.; Gao, C.

    2011-01-01

    We report a facile approach to prepare Fe 3 O 4 /Pt nanoparticles decorated carbon nano tubes (CNTs). The superparamagnetic Fe 3 O 4 nanoparticles with average size of 45 nm were loaded on the surfaces of carboxyl groups functionalized CNTs via a high-temperature solution-phase hydrolysis method from the raw material of FeCl 3 . The synthesis process of magnetic CNTs is green and readily scalable. The loading amounts of Fe 3 O 4 nanoparticles and the magnetizations of the resulting magnetic CNTs show good tunability. The Pt nanoparticles with average size of 2.5 nm were deposited on the magnetic CNTs through a solution-based method. It is demonstrated that the Fe 3 O 4 /Pt nanoparticles decorated CNTs have high catalytic activity in the reduction reaction of 4-nitrophenol and can be readily recycled by a magnet and reused in the next reactions with high efficiencies for at least fifteen successive cycles. The novel CNTs-supported magnetically recyclable catalysts are promising in heterogeneous catalysis applications.

  18. Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

    Science.gov (United States)

    DeRita, Leo; Dai, Sheng; Lopez-Zepeda, Kimberly; Pham, Nicholas; Graham, George W; Pan, Xiaoqing; Christopher, Phillip

    2017-10-11

    Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO 2 . In these structures, isolated Pt atoms, Pt iso , remain stable through various conditions, and spectroscopic evidence suggests Pt iso species exist in homogeneous local environments. Comparing Pt iso to ∼1 nm preoxidized (Pt ox ) and prereduced (Pt metal ) Pt clusters on TiO 2 , we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt iso ≪ Pt metal atoms bonded to TiO 2 and that Pt iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO 2 . This approach should be generally useful for studying the behavior of supported precious metal atoms.

  19. Co/Pt multilayer-based magnetic tunnel junctions with a CoFeB/Ta insertion layer

    Science.gov (United States)

    Ishikawa, S.; Sato, H.; Yamanouchi, M.; Ikeda, S.; Fukami, S.; Matsukura, F.; Ohno, H.

    2014-05-01

    We investigate properties of magnetic tunnel junctions (MTJs) having a Co/Pt multilayer as a recording layer. A CoFeB layer is inserted between MgO barrier and the recording layer in order to enhance the tunnel magnetoresistance ratio. We show that an additional layer of Ta inserted between CoFeB and Co/Pt multilayer is effective in improving the MTJ properties after annealing. A high effective magnetic anisotropy energy per unit area over 1.2 mJ/m2 is obtained after annealing at 300 °C. Using a 1.6 nm-thick CoFeB insertion layer, both high thermal stability factor of 92 and high tunnel magnetoresistance ratio of 91% are achieved in a MTJ with 17 nm in diameter.

  20. Electric field poling induced self-biased converse magnetoelectric response in PMN-PT/NiFe2O4 nanocomposites

    Science.gov (United States)

    Ahlawat, Anju; Satapathy, S.; Deshmukh, Pratik; Shirolkar, M. M.; Sinha, A. K.; Karnal, A. K.

    2017-12-01

    In this letter, studies on structural transitions and the effect of electric field poling on magnetoelectric (ME) properties in 0.65Pb (Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT)/NiFe2O4 (NFO) nanocomposites are reported. The composite illustrates dramatic changes in the NFO crystal structure across ferroelectric transition temperature [Curie temperature (Tc) ˜ 450 K] of PMN-PT, while pure NFO does not exhibit any structural change in the temperature range (300 K-650 K). Synchrotron based X-ray diffraction analysis revealed the splitting of NFO peaks across the Tc of PMN-PT in the PMN-PT/NFO composite. Consequently, the anomalies are observed in temperature dependent magnetization of the NFO phase at the Tc of PMN-PT, establishing ME coupling in the PMN-PT/NFO composite. Furthermore, the composite exhibits drastic modification in ME coupling under electrically poled and unpoled conditions. A large self-biased ME effect characterized by non-zero ME response at zero Hbias was observed in electrically poled composites, which was not observed in unpoled PMN-PT/NFO. These results propose an alternative mechanism for intrinsic converse ME effects. The maximum magnetoelectric output was doubled after electrical poling. The observed self-biased converse magnetoelectric effect at room temperature provides potential applications in electrically controlled memory devices and magnetic flux control devices.

  1. Understanding the Oxygen Reduction Reaction on a Y/Pt(111) Single Crystal

    DEFF Research Database (Denmark)

    Ulrikkeholm, Elisabeth Therese; Johansson, Tobias Peter; Malacrida, Paolo

    2014-01-01

    Polymer electrolyte membrane fuel cells (PEMFC) hold promise as a zero-emission source of power, particularly suitable for automotive vehicles. However, the high loading of Pt required to catalyse the oxygen reduction reaction (ORR) at the PEMFC cathode, prevents the commercialisation of this tec......Polymer electrolyte membrane fuel cells (PEMFC) hold promise as a zero-emission source of power, particularly suitable for automotive vehicles. However, the high loading of Pt required to catalyse the oxygen reduction reaction (ORR) at the PEMFC cathode, prevents the commercialisation...... of this technology. Improving the activity of Pt by alloying it with other metals could decrease the loading of Pt. An earlier theoretical study conducted at our laboratory identified PtxY as an active and stable catalyst for oxygen reduction. Experiments conducted on sputter-cleaned polycrystalline Pt3Y confirmed...... was significantly different from our initial expectations. In order to understand this phenomenon, we investigated a Y/Pt(111) single crystal, formed by depositing large amounts of Y om Pt(111) under ultra-high vacuum (UHV) conditions and annealing to high temperatures. We subsequently characterised the surface...

  2. Electric-regulated enhanced in-plane uniaxial anisotropy in FeGa/PMN-PT composite using oblique pulsed laser deposition

    Science.gov (United States)

    Zhang, Yi; Huang, Chaojuan; Turghun, Mutellip; Duan, Zhihua; Wang, Feifei; Shi, Wangzhou

    2018-04-01

    The FeGa film with in-plane uniaxial magnetic anisotropy was fabricated onto different oriented single-crystal lead magnesium niobate-lead titanate using oblique pulsed laser deposition. An enhanced in-plane uniaxial magnetic anisotropy field of FeGa film can be adjusted from 18 Oe to 275 Oe by tuning the oblique angle and polarizing voltage. The competitive relationship of shape anisotropy and strain anisotropy has been discussed, which was induced by oblique angle and polarizing voltage, respectively. The (100)-oriented and (110)-oriented PMN-PT show completely different characters on voltage-dependent magnetic properties, which could be attributed to various anisotropy directions depended on different strain directions.

  3. Single-Atom Pt as Co-Catalyst for Enhanced Photocatalytic H2 Evolution.

    Science.gov (United States)

    Li, Xiaogang; Bi, Wentuan; Zhang, Lei; Tao, Shi; Chu, Wangsheng; Zhang, Qun; Luo, Yi; Wu, Changzheng; Xie, Yi

    2016-03-23

    Isolated single-atom platinum (Pt) embedded in the sub-nanoporosity of 2D g-C3 N4 as a new form of co-catalyst is reported. The highly stable single-atom co-catalyst maximizes the atom efficiency and alters the surface trap states of g-C3 N4 , leading to significantly enhanced photocatalytic H2 evolution activity, 8.6 times higher than that of Pt nanoparticles and up to 50 times that for bare g-C3 N4 . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Strength anomaly in B2 FeAl single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimi, K.; Hanada, S.; Yoo, M.H. [Oak Ridge National Lab., TN (United States); Matsumoto, N. [Tohoku Univ. (Japan). Graduate School

    1994-12-31

    Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). The orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.

  5. In Situ FTIR Analysis of CO-Tolerance of a Pt-Fe Alloy with Stabilized Pt Skin Layers as a Hydrogen Anode Catalyst for Polymer Electrolyte Fuel Cells

    Directory of Open Access Journals (Sweden)

    Yoshiyuki Ogihara

    2016-12-01

    Full Text Available The CO-tolerance mechanism of a carbon-supported Pt-Fe alloy catalyst with two atomic layers of stabilized Pt-skin (Pt2AL–PtFe/C was investigated, in comparison with commercial Pt2Ru3/C (c-Pt2Ru3/C, by in situ attenuated total reflection Fourier transform infrared (ATR-FTIR spectroscopy in 0.1 M HClO4 solution at 60 °C. When 1% CO (H2-balance was bubbled continuously in the solution, the hydrogen oxidation reaction (HOR activities of both catalysts decreased severely because the active sites were blocked by COad, reaching the coverage θCO ≈ 0.99. The bands in the IR spectra observed on both catalysts were successfully assigned to linearly adsorbed CO (COL and bridged CO (COB, both of which consisted of multiple components (COL or COB at terraces and step/edge sites. The Pt2AL–PtFe/C catalyst lost 99% of its initial mass activity (MA for the HOR after 30 min, whereas about 10% of the initial MA was maintained on c-Pt2Ru3/C after 2 h, which can be ascribed to a suppression of linearly adsorbed CO at terrace sites (COL, terrace. In contrast, the HOR activities of both catalysts with pre-adsorbed CO recovered appreciably after bubbling with CO-free pure H2. We clarify, for the first time, that such a recovery of activity can be ascribed to an increased number of active sites by a transfer of COL, terrace to COL, step/edge, without removal of COad from the surface. The Pt2AL–PtFe/C catalyst showed a larger decrease in the band intensity of COL, terrace. A possible mechanism for the CO-tolerant HOR is also discussed.

  6. Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: Experiment and micromagnetic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Ziȩtek, Slawomir, E-mail: zietek@agh.edu.pl [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); Chȩciński, Jakub [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Kraków (Poland); Frankowski, Marek; Skowroński, Witold; Stobiecki, Tomasz [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland)

    2017-04-15

    We present a comprehensive theoretical and experimental study of voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe multiferroic heterostructures patterned into microstrips. A spin-diode technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in NiFe strip mechanically coupled with a piezoelectric substrate. Application of an electric field to a PMN-PT creates a strain in permalloy and thus shifts the FMR and SSWR fields due to the magnetostriction effect. The experimental results are compared with micromagnetic simulations and a good agreement between them is found for dynamics of FMR and SSWR with and without electric field. Moreover, micromagnetic simulations enable us to discuss the amplitude and phase spatial distributions of FMR and SSWR modes, which are not directly observable by means of spin diode detection technique.

  7. A Highly Stable and Magnetically Recyclable Nanocatalyst System: Mesoporous Silica Spheres Embedded with FeCo/Graphitic Shell Magnetic Nanoparticles and Pt Nanocatalysts.

    Science.gov (United States)

    Kim, Da Jeong; Li, Yan; Kim, Yun Jin; Hur, Nam Hwi; Seo, Won Seok

    2015-12-01

    We have developed a highly stable and magnetically recyclable nanocatalyst system for alkene hydrogenation. The materials are composed of mesoporous silica spheres (MSS) embedded with FeCo/graphitic shell (FeCo/GC) magnetic nanoparticles and Pt nanocatalysts (Pt-FeCo/GC@MSS). The Pt-FeCo/GC@MSS have superparamagnetism at room temperature and show type IV isotherm typical for mesoporous silica, thereby ensuring a large enough inner space (surface area of 235.3 m(2)  g(-1), pore volume of 0.165 cm(3)  g(-1), and pore diameter of 2.8 nm) to undergo catalytic reactions. We have shown that the Pt-FeCo/GC@MSS system readily converts cyclohexene into cyclohexane, which is the only product isolated and Pt-FeCo/GC@MSS can be seperated very quickly by an external magnetic field after the catalytic reaction is finished. We have demonstrated that the recycled Pt-FeCo/GC@MSS can be reused further for the same hydrogenation reaction at least four times without loss in the initial catalytic activity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Development of novel FePt/nanodiamond hybrid nanostructures: L1{sub 0} phase size-growth suppression and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Douvalis, A. P., E-mail: adouval@uoi.gr; Bourlinos, A. B. [University of Ioannina, Physics Department (Greece); Tucek, J.; Čépe, K. [Palacký University Olomouc, Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science (Czech Republic); Bakas, T. [University of Ioannina, Physics Department (Greece); Zboril, R. [Palacký University Olomouc, Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science (Czech Republic)

    2016-05-15

    A new type of hybrid nanomaterial composed of magnetic FePt nanoparticles grown on the surface of nanodiamond nanotemplate assemblies is described for the first time. Post annealing in vacuum of the as-made nanomaterial bearing cubic A1 soft magnetic FePt nanoparticles leads to the development of FePt nanoparticles with tetragonal L1{sub 0} hard, magnetic-phase characteristics, leaving untouched the nanodiamond nanotemplate assemblies. X-ray diffraction, high-resolution transmission electron microscopy including chemical mapping (HRTEM/HAADF), magnetization measurements, and {sup 57}Fe Mössbauer spectroscopy data show that the magnetic FePt nanoparticles, with average sizes of 3 and 8 nm in the as-made and annealed hybrids, respectively, are homogenously distributed within the nanodiamond template in both nanomaterials. As a consequence, their structural, morphological, and magnetic properties differ significantly from the corresponding properties of the nonsupported (free) as-made and annealed FePt nanoparticles with average sizes of 6 and 32 nm, respectively, developed by the same methods. This spatial isolation suppresses the size-growth of the FePt nanoparticles during the post-annealing procedure, triggering superparamagnetic relaxation phenomena, which are exposed as a combination of hard and soft magnetic-phase characteristics.

  9. Light Illuminated α−Fe2O3/Pt Nanoparticles as Water Activation Agent for Photoelectrochemical Water Splitting

    Science.gov (United States)

    Li, Xiaodong; Wang, Zhi; Zhang, Zemin; Chen, Lulu; Cheng, Jianli; Ni, Wei; Wang, Bin; Xie, Erqing

    2015-01-01

    The photoelectrochemical (PEC) water splitting is hampered by strong bonds of H2O molecules and low ionic conductivity of pure water. The photocatalysts dispersed in pure water can serve as a water activation agent, which provides an alternative pathway to overcome such limitations. Here we report that the light illuminated α−Fe2O3/Pt nanoparticles may produce a reservoir of reactive intermediates including H2O2, ·OH, OH− and H+ capable of promoting the pure water reduction/oxidation half−reactions at cathode and highly photocatalytic−active TiO2/In2S3/AgInS2 photoanode, respectively. Remarkable photocurrent enhancement has been obtained with α−Fe2O3/Pt as water activation agent. The use of α−Fe2O3/Pt to promote the reactivity of pure water represents a new paradigm for reproducible hydrogen fuel provision by PEC water splitting, allowing efficient splitting of pure water without adding of corrosive chemicals or sacrificial agent. PMID:25773684

  10. Light illuminated α-Fe2O3/Pt nanoparticles as water activation agent for photoelectrochemical water splitting.

    Science.gov (United States)

    Li, Xiaodong; Wang, Zhi; Zhang, Zemin; Chen, Lulu; Cheng, Jianli; Ni, Wei; Wang, Bin; Xie, Erqing

    2015-03-16

    The photoelectrochemical (PEC) water splitting is hampered by strong bonds of H2O molecules and low ionic conductivity of pure water. The photocatalysts dispersed in pure water can serve as a water activation agent, which provides an alternative pathway to overcome such limitations. Here we report that the light illuminated α-Fe2O3/Pt nanoparticles may produce a reservoir of reactive intermediates including H2O2, ·OH, OH(-) and H(+) capable of promoting the pure water reduction/oxidation half-reactions at cathode and highly photocatalytic-active TiO2/In2S3/AgInS2 photoanode, respectively. Remarkable photocurrent enhancement has been obtained with α-Fe2O3/Pt as water activation agent. The use of α-Fe2O3/Pt to promote the reactivity of pure water represents a new paradigm for reproducible hydrogen fuel provision by PEC water splitting, allowing efficient splitting of pure water without adding of corrosive chemicals or sacrificial agent.

  11. Decoration of carbon nanotube with size-controlled L10-FePt nanoparticles for storage media

    Science.gov (United States)

    Moradi, Reza; Sebt, Seyed Ali; Arabi, Hadi; Larijani, Majid Mojtahedzadeh

    2013-10-01

    In this work, first multi-wall carbon nanotubes (MWCNTs) with outer diameter about 20-30 nm are synthesized by a CVD method; they have been purified and functionalized with a two-step process. The approach consists of thermal oxidation and subsequent chemical oxidation. Then, monosize FePt nanoparticles along carbon nanotubes surface are synthesized by a Polyol process. The synthesized FePt nanoparticles are about 2.5 nm in size and they have superparamagnetic behavior with fcc structure. The CNTs surfaces as a substrate prevent the coalescence of particles during thermal annealing. Annealing at the temperature higher than 600 ∘C for 2 h under a reducing atmosphere (90 % Ar + 10 % H2) leads to phase transition from fcc to fct-L10 structure. So, the magnetic behavior changes from the superparamagnetic to the ferromagnetic. Furthermore, after the phase transition, the FePt nanoparticles have finite size with an average of about 3.5 nm and the coercivity of particles reaches 5.1 kOe.

  12. Silicide induced surface defects in FePt nanoparticle fcc-to-fct thermally activated phase transition

    International Nuclear Information System (INIS)

    Chen, Shu; Lee, Stephen L.; André, Pascal

    2016-01-01

    Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density information storage and magnetic resonance imaging to name but a few. Among the materials available to prepare MnPs, FePt is attracting growing attention. However, to harvest the strongest magnetic properties of FePt MnPs, a thermal annealing is often required to convert face-centered cubic as synthesized nPs into its tetragonal phase. Rarely addressed are the potential side effects of such treatments on the magnetic properties. In this study, we focus on the impact of silica shells often used in strategies aiming at overcoming MnP coalescence during the thermal annealing. While we show that this shell does prevent sintering, and that fcc-to-fct conversion does occur, we also reveal the formation of silicide, which can prevent the stronger magnetic properties of fct-FePt MnPs from being fully realised. This report therefore sheds lights on poorly investigated and understood interfacial phenomena occurring during the thermal annealing of MnPs and, by doing so, also highlights the benefits of developing new strategies to avoid silicide formation.

  13. Magnetic properties in the vortex state of Pr1-xNdxPt4Ge12 and PrPt3.88Fe0.12Ge12 superconductors

    Science.gov (United States)

    Chandra, L. S. Sharath; Chattopadhyay, M. K.

    2018-03-01

    We report the temperature and magnetic field dependence of magnetization of Pr1-xNdxPt4Ge12 (x = 0, 0.05 and 0.1) and PrPt3.88Fe0.12Ge12 below 10 K and up to 2 T magnetic field. When compared to the parent PrPt4Ge12, while the critical current density and flux pinning properties are enhanced in the Pr1-xNdxPt4Ge12 samples, they are considerably diminished in the PrPt3.88Fe0.12Ge12 sample. We argue that the observed changes are related to the way the substituting atoms at different crystallographic sites influence the superconductivity in these Germanide skutterudites.

  14. Single-step synthesis of PtRu/N-doped graphene for methanol electrocatalytic oxidation

    International Nuclear Information System (INIS)

    Xu, Xiao; Zhou, Yingke; Lu, Jiming; Tian, Xiaohui; Zhu, Hongxi; Liu, Jiangbo

    2014-01-01

    In this work, a single-step route was applied to achieve the reduction of graphene oxide, functional doping of graphene with nitrogen, and deposition of well-dispersed PtRu alloy nanoparticles on the doped graphene simultaneously in the solvent mixture of ethylene glycol and N-methyl-2-pyrrolidone. Transmission electron microscopy, X-ray powder diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and microstructure, while cyclic voltammetry, chronoamperometry and electrochemical impedance techniques were carried out to evaluate the electrocatalytic methanol oxidation activity and durability of the obtained PtRu/nitrogen-doped graphene catalysts. Compared to undoped PtRu/graphene, the nitrogen-doped PtRu/graphene catalyst presented better particle size distribution and improved activity and durability of methanol electrocatalytic oxidation, which could be further improved by optimization of the reaction time, temperature, as well as the composition of the reaction medium. The convenient single-step synthesis process for the PtRu/nitrogen-doped graphene catalysts is promising for the potential application of direct methanol fuel cells

  15. Microstructure and magnetic properties of FePt film with combined MoC/(Mg–X)O (X=Cu, Ni, Co) intermediate layers

    International Nuclear Information System (INIS)

    Tsai, Jai-Lin; Tzeng, Jie-Lin; Hu, Keng-Chun; Li, Hsu-Kang; Pan, Zu-Yu; Chang, Yuan-Shuo; Liao, Chang-Chun

    2017-01-01

    The magnetic properties and microstructure of FePt films grown on MoC layer and MoC/(Mg–X)O (X=Cu, Ni, Co) combined intermediate layers were studied. The (Mg–X)O (X=Cu, Ni, Co) layer with thickness of 5 nm was deposited on CrRu seed layer at 395 °C. The CrRu (200) texture was enhanced which may due to well grains growth in specific orientation and small lattice mismatch with (Mg–X)O (X=Cu, Ni, Co). Finally, the FePt/MoC layers were deposited on (Mg–X)O layer at 425 °C. Using MoC/MgCuO combined intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were changed from 7.1° to 6.1°, and 5.7° to 3.8°, respectively. For MoC/MgCoO dual intermediate layers, the rocking width of FePt (001) and CrRu (200) diffraction peak were 6.7° and 4.1°. The FePt/MoC/MgCoO film illustrates perpendicular magnetic anisotropy with out-of plane coercivity of 9.3 kOe which is higher than FePt film deposited on MoC layer (8.5 kOe) and the in-plane loops is linear. From microstructure, the FePt grains were more separated on MoC/(Mg–X)O (X=Cu, Ni, Co) combined intermediate layers. - Highlights: • The MgCoO intermediate layer was resisted the Cr diffusion. • The MgCoO capped layer promote the CrRu(200) texture. • The FePt film shows high perpendicular magnetization on MoC/MgCoO layer.

  16. Trends in the magnetic properties of Fe, Co, and Ni clusters and monolayers on Ir(111), Pt(111), and Au(111)

    Science.gov (United States)

    Bornemann, S.; Šipr, O.; Mankovsky, S.; Polesya, S.; Staunton, J. B.; Wurth, W.; Ebert, H.; Minár, J.

    2012-09-01

    We present a detailed theoretical investigation on the magnetic properties of small single-layered Fe, Co, and Ni clusters deposited on Ir(111), Pt(111), and Au(111). For this, a fully relativistic ab initio scheme based on density functional theory has been used. We analyze the element, size, and geometry specific variations of the atomic magnetic moments and their mutual exchange interactions as well as the magnetic anisotropy energy in these systems. Our results show that the atomic spin magnetic moments in the Fe and Co clusters decrease almost linearly with increasing coordination number on all three substrates, while the corresponding orbital magnetic moments appear to be much more sensitive to the local atomic environment. The isotropic exchange interaction among the cluster atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is, in general, one or two orders of magnitude smaller when compared to the isotropic one. For the magnetic properties of Ni clusters, the magnetic properties can show quite a different behavior, and we find in this case a strong tendency towards noncollinear magnetism.

  17. Ab initio studies on electronic and magnetic properties of X2PtGa (X=Cr, Mn, Fe, Co) Heusler alloys

    International Nuclear Information System (INIS)

    Roy, Tufan; Chakrabarti, Aparna

    2017-01-01

    Using first-principles calculations based on density functional theory, we probe the electronic and magnetic properties of X 2 PtGa (X being Cr, Mn, Fe, Co) Heusler alloys. Our calculations predict that all these systems possess inverse Heusler alloy structure in the respective ground states. Application of tetragonal distortion leads to lowering of energy with respect to their cubic phase. The equilibrium volumes of both the phases are nearly the same. These indicate that the materials studied here are prone to undergo martensite transition, as has been recently shown theoretically for Mn 2 PtGa in the literature. Ground state with a tetragonal symmetry is corroborated by the observation of soft tetragonal shear constants in the cubic phase. By comparing the energies of various types of magnetic configurations we predict that Cr 2 PtGa and Mn 2 PtGa possess ferrimagnetic configuration whereas Fe 2 PtGa and Co 2 PtGa possess ferromagnetic configuration in their respective ground states. - Highlights: • We predict stable martensitic phase of X 2 PtGa (X=Cr, Mn, Fe, Co). • Co 2 PtGa possesses least inherent brittleness among all the materials. • Martensite transitions are possible for the investigated materials. • A tetragonal ground state with high spin polarization is predicted for Co 2 PtGa.

  18. Electrocatalytic oxidation behavior of NADH at Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids modified glassy carbon electrode and its determination

    Energy Technology Data Exchange (ETDEWEB)

    Roushani, Mahmoud, E-mail: mahmoudroushani@yahoo.com [Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, 69315516 (Iran, Islamic Republic of); Hoseini, S. Jafar [Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj, 7591874831 (Iran, Islamic Republic of); Azadpour, Mitra [Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, 69315516 (Iran, Islamic Republic of); Heidari, Vahid; Bahrami, Mehrangiz; Maddahfar, Mahnaz [Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj, 7591874831 (Iran, Islamic Republic of)

    2016-10-01

    We have developed Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids modified glassy carbon (Pt/Fe{sub 3}O{sub 4}/RGO/GC) electrode as a novel system for the preparation of electrochemical sensing platform. Characterization of as-made composite was determined using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy-dispersive analysis of X-ray (EDAX) where the Pt, Fe, Si, O and C elements were observed. The Pt/Fe{sub 3}O{sub 4}/RGO/GC electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effect between Pt, Fe{sub 3}O{sub 4} and RGO, the nanohybrid exhibited excellent performance toward dihydronicotinamide adenine dinucleotide (NADH) oxidation in 0.1 M phosphate buffer solution, pH 7.0, with a low detection limit of 5 nM. - Highlights: • Preparation of a novel electrochemical sensing platform system • Excellent performance of Pt/Fe{sub 3}O{sub 4}/reduced-graphene oxide nanohybrids • Dihydronicotinamide adenine dinucleotide oxidation with a low detection limit of 5 nM.

  19. Room temperature biogenic synthesis of multiple nanoparticles (Ag, Pd, Fe, Rh, Ni, Ru, Pt, Co, and Li) by Pseudomonas aeruginosa SM1

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Sarvesh Kumar; Constanti, Magda, E-mail: magdalena.constanti@urv.cat [Universitat Rovira i Virgili, Departament d' Enginyeria Quimica (Spain)

    2012-03-15

    Room temperature biosynthesis of Ag, Pd, Fe, Rh, Ni, Ru, Pt, Co, and Li nanoparticles was achieved using Pseudomonas aeruginosa SM1 without the addition of growth media, electron donors, stabilizing agents, preparation of cell/cell-free extract or temperature, and pH adjustments. The resulting nanoparticles were characterized by Transmission electron microscopy and X-ray diffraction. It was observed that P. aeruginosa SM1 is capable of producing both intracellular (Co and Li) and extracellular (Ag, Pd, Fe, Rh, Ni, Ru, and Pt) nanoparticles in both crystalline and amorphous state. The FT-IR spectra clearly showed the presence of primary and secondary amines which may be responsible for the reduction and subsequent stabilization of the resulting extracellular nanoparticles which were obtained as a one-step process. This suggests toward an unknown 'selection mechanism' that reduces certain metal ions and allows others to enter the cell membrane. Finally, in this first of its kind study, single strain of bacteria was used to produce several different mono-metallic nanoparticles.

  20. Effect of magnetism and atomic order on static atomic displacements in the Invar alloy Fe-27 at.% Pt

    Science.gov (United States)

    Sax, C. R.; Schönfeld, B.; Ruban, A. V.

    2015-08-01

    Fe-27 at.% Pt was aged at 1123 K and quenched to room temperature (RT) to set up a state of thermal equilibrium. The local atomic arrangement was studied by diffuse x-ray scattering above (at 427 K) and below (at RT) the Curie temperature as well as at RT under a saturating magnetic field. The separated short-range order scattering remained unchanged for all three states, with maxima at 100 positions. Effective pair interaction parameters determined by the inverse Monte Carlo method gave an order-disorder transition temperature of about 1088 K, close to direct experimental findings. The species-dependent static atomic displacements for the first two shells show large differences, with a strong increase in magnitude from the state at 427 K over RT to the state under saturating magnetic field. This outcome is in agreement with an increase in atomic volume of Fe with increasing local magnetic moment. Electronic-structure calculations closely reproduce the values for the static atomic displacements in the ferromagnetic state, and predict their dependence on the atomic configuration. They also reveal a strong dependence of the magnetic exchange interactions in Fe-Pt on the atomic configuration state and lattice parameter. In particular, the increase of the Curie temperature in a random state relative to that in the ordered one is demonstrated to be related to the corresponding change of the magnetic exchange interactions due to the different local atomic chemical environment. There exists a similar strong concentration dependence of the chemical interactions as in the case of magnetic exchange interactions. Theoretical effective interactions for Fe-27 at.% Pt alloy are in good agreement with experimental results, and they also reproduce well the L1 2-A1 transition temperature.

  1. Reducción catalítica de NOx con Pt soportado sobre zeolitas MFI modificadas con Cu, Co, Fe, Mn.

    Directory of Open Access Journals (Sweden)

    Sarah Briceño

    2008-05-01

    Full Text Available The selective catalytic reduction of NO by propane in the presence of excess oxygen has been studied over catalysts based on Pt supported on Fe-ZSM-5, Co-ZSM-5, Cu- ZSM-5 and MnZSM-5. Pure Pt based catalysts are highly active, but produce large amounts of N2O. The bimetallic catalyst was found to offer wider temperature window than that of monocatalysts, and show a synergistic effect by combining high stability and activity of Pt catalysts with the high N2 selectivity of Fe, Co, Cu, Mn supported on MFI catalysts.

  2. Synergistically Enhanced Electrochemical Performance of Ni3S4-PtX (X = Fe, Ni) Heteronanorods as Heterogeneous Catalysts in Dye-Sensitized Solar Cells.

    Science.gov (United States)

    Huang, Shoushuang; Ma, Dui; Hu, ZhangJun; He, Qingquan; Zai, Jiantao; Chen, Dayong; Sun, Huai; Chen, Zhiwen; Qiao, Qiquan; Wu, Minghong; Qian, Xuefeng

    2017-08-23

    Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I - /I 3 - and Co 2+ /Co 3+ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott-Schottky (M-S) effect at the metal-semiconductor interface, we successfully strategize a low-Pt-based M-S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M-S electrocatalyst of Ni 3 S 4 -Pt 2 X 1 (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni 3 S 4 to Pt 2 X 1 at their interface under the Mott-Schottky effect result in the concentration of electrons onto Pt 2 X 1 domains, which subsequently accelerates the regeneration of both I - /I 3 - and Co 2+ /Co 3+ redox shuttles in DSSCs. As a result, the DSSC with Ni 3 S 4 -Pt 2 Fe 1 manifests an impressive power conversion efficiency (PCE) of 8.79% and 5.56% for iodine and cobalt-based electrolyte under AM1.5G illumination, respectively. These PCEs are obviously superior over those with Ni 3 S 4 -Pt, PtFe, Ni 3 S 4 , and pristine Pt electrodes. The strategy reported here is able to be further expanded to fabricate other low-Pt-alloyed M-S catalysts for wider applications in the fields of photocatalysis, water splitting, and heterojunction solar cells.

  3. Nano-structure formation of Fe-Pt perpendicular magnetic recording media co-deposited with MgO, Al{sub 2}O{sub 3} and SiO{sub 2} additives

    Energy Technology Data Exchange (ETDEWEB)

    Safran, G. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary)]. E-mail: safran@mfa.kfki.hu; Suzuki, T. [Akita Research Institute of Advanced Technology (AIT), 4-21 Sanuki, Araya, Akita 010-1623 (Japan); Ouchi, K. [Akita Research Institute of Advanced Technology (AIT), 4-21 Sanuki, Araya, Akita 010-1623 (Japan); Barna, P.B. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary); Radnoczi, G. [Research Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences 1121 Budapest, Konkoly-Thege ut 29-33 (Hungary)

    2006-02-21

    Perpendicular magnetic recording media samples were prepared by sputter deposition on sapphire with a layer sequence of MgO seed-layer/Cr under-layer/FeSi soft magnetic under-layer/MgO intermediate layer/FePt-oxide recording layer. The effects of MgO, Al{sub 2}O{sub 3} and SiO{sub 2} additives on the morphology and orientation of the FePt layer were investigated by transmission electron microscopy. The samples exhibited (001) orientation of the L1 FePt phase with the mutual orientations of sapphire substrate//MgO(100)[001]//Cr(100)[11-bar0]//FeSi(100)[11-bar0]//MgO(100) [001]//FePt(001)[100]. The morphology of the FePt films varied due to the co-deposited oxides: The FePt layers were continuous and segmented by stacking faults aligned at 54{sup o} to the surface. Films with SiO{sub 2} addition, beside the oriented columnar FePt grains, exhibited a fraction of misoriented crystallites due to random repeated nucleation. Al{sub 2}O{sub 3} addition resulted in a layered structure, i.e. an initial continuous epitaxial FePt layer covered by a secondary layer of FePt-Al{sub 2}O{sub 3} composite. Both components (FePt and MgO) of the MgO-added samples were grown epitaxially on the MgO intermediate layer, so that a nano-composite of intercalated (001) FePt and (001) MgO was formed. The revealed microstructures and formation mechanisms may facilitate the improvement of the structural and magnetic properties of the FePt-oxide composite perpendicular magnetic recording media.

  4. Stretching dependence of the vibration modes of a single-molecule Pt-H-2-Pt bridge

    DEFF Research Database (Denmark)

    Djukic, D.; Thygesen, Kristian Sommer; Untiedt, C.

    2005-01-01

    isotope substitution is obtained. The stretching dependence for each of the modes allows uniquely classifying them as longitudinal or transversal modes. The interpretation of the experiment in terms of a Pt-H-2-Pt bridge is verified by density-functional theory calculations for the stability, vibrational...

  5. Structural and magnetic properties of Fe{sub 7−n}Pt{sub n} with n = 0, 1, 2, . . . 7, bimetallic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ponce-Tadeo, A. P.; Morán-López, J. L., E-mail: joseluis.moran@ipicyt.edu.mx [Instituto Potosino de Investigación Científica y Tenológica, División de Materiales Avanzados (Mexico); Ricardo-Chavez, J. L. [Benemérita Universidad Autónoma de Puebla, Laboratorio Nacional de Supercómputo (Mexico)

    2016-11-15

    An exhaustive study of the structural and magnetic properties of Fe{sub 7−n}Pt{sub n} with n = 0, 1, 2, …7, bimetallic clusters is presented. Based on ab initio density functional theory that includes spin-orbit coupling (SOC) and graph theory, the ground state geometry, the local chemical order, and the orbital and spin magnetic moments are calculated. We show how the systems evolves from the 3-d Fe to the quasi-planar Pt clusters. These calculations show that SOC are necessary to describe correctly the composition dependence of the binding energy of these nanoalloys. We observe that the ground state geometries on the Fe rich side resemble the fcc structure adopted by bulk samples. Furthermore, we observe how the spin and orbital magnetic moments depend on the chemical concentration and chemical order. Based on these results, we estimated the magnetic anisotropy energy and found that the largest values correspond to some of the most symmetric structures, Fe{sub 5}Pt{sub 2} and FePt{sub 6}. To determine the degree of non-collinearity, we define an index that shows that in FePt{sub 6} the total magnetic moments, on each atom, are the less collinear.

  6. Flexoelectric behavior in PIN-PMN-PT single crystals over a wide temperature range

    Science.gov (United States)

    Shu, Longlong; Li, Tao; Wang, Zhiguo; Li, Fei; Fei, Linfeng; Rao, Zhenggang; Ye, Mao; Ke, Shanming; Huang, Wenbin; Wang, Yu; Yao, Xi

    2017-10-01

    Flexoelectricity couples strain gradient to polarization and usually exhibits a large coefficient in the paraelectric phase of the ferroelectric perovskites. In this study, we employed the relaxor 0.3Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PIN-PMN-PT) single crystals to study the relationship between flexoelectric coefficients and the crystal structure. The flexoelectric coefficients in PIN-PMN-PT single crystal are found to vary from 57 μC/m at orthorhombic/monoclinic phase to 135 μC/m at tetragonal phase, and decreases to less than 27 μC/m in the temperature above Tm. This result discloses that ferroelectricity can significantly enhance the flexoelectricity in this kind of perovskite.

  7. Tuning anomalous Hall conductivity in L1[sub 0] FePt films by long range chemical ordering

    KAUST Repository

    Chen, M.

    2011-02-24

    For L10 FePt films, the anomalous Hall conductivity σ xy=-a σxx-b, where a=a0f(T), b=b 0f(T), and f (T) is the temperature dependence factor of the spontaneous magnetization. With increasing chemical long range ordering S, a0 changes its sign accompanied by a reduction of its magnitude and b0 increases monotonically. The spin-orbit coupling strength is suggested to increase with increasing S. As an approach, the long range chemical ordering can be used to control the anomalous Hall effect in ferromagnetic alloy films. © 2011 American Institute of Physics.

  8. Interfacial effects on the electrical properties of multiferroic BiFeO3/Pt/Si thin film heterostructures

    International Nuclear Information System (INIS)

    Yakovlev, S.; Zekonyte, J.; Solterbeck, C.-H.; Es-Souni, M.

    2005-01-01

    Polycrystalline BiFeO 3 thin films of various thickness were fabricated on (111)Pt/Ti/SiO 2 /Si substrates via chemical solution deposition. The electrical properties were investigated using impedance and leakage current measurements. X-ray photoelectron spectroscopy (XPS) combined with Ar ion milling (depth profiling) was used to investigate elemental distribution near the electrode-film interface. It is shown that the dielectric constant depends on film thickness due to the presence of an interfacial film-electrode layer evidenced by XPS investigation. Direct current conductivity is found to be governed by Schottky and/or Poole-Frenkel mechanisms

  9. Microstructure and magnetic properties of FePt:Ag nanocomposite films on SiO2/Si(1 0 0)

    International Nuclear Information System (INIS)

    Wang Hao; Yang, F.J.; Wang, H.B.; Cao, X.; Xue, S.X.; Wang, J.A.; Gao, Y.; Huang, Z.B.; Yang, C.P.; Chiah, M.F.; Cheung, W.Y.; Wong, S.P.; Li, Q.; Li, Z.Y.

    2006-01-01

    FePt:Ag nanocomposite films were prepared by pulsed filtered vacuum arc deposition system and subsequent rapid thermal annealing on SiO 2 /Si(1 0 0) substrates. The microstructure and magnetic properties were investigated. A strong dependence of coercivity and ordering of the face-central tetragonal structure on both Ag concentration and annealing temperature was observed. With Ag concentration of 22% in atomic ratio, the coercivity got to 6.0 kOe with a grain size of 6.7 nm when annealing temperature was 400 deg. C

  10. Isotropic superconducting gap structure in BaFe1.90Pt0.10As2 from low temperature thermal conductivity

    Science.gov (United States)

    Kirshenbaum, Kevin; Saha, Shanta; Ziemak, Steven; Hu, Rongwei; Reid, Jean-Philippe; Gordon, Ryan; Taillefer, Louis; Paglione, Johnpierre

    2013-03-01

    In this study we present measurements of thermal transport down to 50 mK in single crystals of the iron-based superconductor BaFe1.90Pt0.10As2 with Tc = 23 K. Magnetic fields up to 15 T were applied along the c-axis of the crystal as well as along the basal plane direction to probe the anisotropy of the superconducting gap. The lack of any significant residual electronic term in thermal conductivity for all field directions and values confirms the absence of nodes and places limits on the depth of gap minima in this system. This work was supported by AFOSR-MURI FA9550-09-1-0603 and by an ICMR fellowship.

  11. Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions

    Energy Technology Data Exchange (ETDEWEB)

    Gangineni, R. B., E-mail: rameshg.phy@pondiuni.edu.in [Department of Physics, School of Physical, Chemical and Applied Sciences, Pondicherry University, R. V. Nagar, Kalapet, Pondicherry 605 014 (India); SPINTEC, UMR 8191 CEA/CNRS/UJF-Grenoble 1/Grenoble INP, INAC, 17 rue des Martyrs, F-38054 Grenoble Cedex (France); Bellouard, C., E-mail: christine.bellouard@ijl.nancy-universite.fr; Duluard, A. [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); Negulescu, B. [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); UFR de Sciences et Techniques, Matériaux, microélectronique, acoustique, nanotechnologies (GREMAN), University François Rabelais, Parc de Grandmont, 37200 Tours (France); Baraduc, C.; Gaudin, G. [SPINTEC, UMR 8191 CEA/CNRS/UJF-Grenoble 1/Grenoble INP, INAC, 17 rue des Martyrs, F-38054 Grenoble Cedex (France); Tiusan, C., E-mail: coriolan.tiusan@phys.utcluj.ro [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); Department of Physics and Chemistry, Center of Superconductivity, Spintronics and Surface Science, Technical University of Cluj Napoca, Str. Memorandumului No. 28, RO-400114 Cluj-Napoca (Romania)

    2014-05-05

    Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2 eV) interfacial resonance states: a mixture of Δ{sub 1}-like and Δ{sub 5}-like symmetries.

  12. Ionic Liquid Gating Control of RKKY Interaction in FeCoB/Ru/FeCoB and (Pt/Co)2/Ru/(Co/Pt)2 Multilayers.

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Qu; Wang, Lei; Zhou, Ziyao; Wang, Liqian; Zhang, Yijun; Zhao, Shishun; Dong, Guohua; Cheng, Yuxin; Min, Tai; Hu, Zhongqiang; Chen, Wei; Xia, Ke; Liu, Ming

    2018-03-07

    To overcome the fundamental challenge of the weak natural response of antiferromagnetic materials under a magnetic field, voltage manipulation of antiferromagnetic interaction is developed to realize ultrafast, high-density, and power efficient antiferromagnetic spintronics. Here, we report a low voltage modulation of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction via ionic liquid gating in synthetic antiferromagnetic multilayers of FeCoB/Ru/FeCoB and (Pt/Co)2/Ru/(Co/Pt)2. At room temperature, the distinct voltage control of transition between antiferromagnetic and ferromagnetic ordering is realized and up to 80% of perpendicular magnetic moments manage to switch with a small-applied voltage bias of 2.5 V. We related this ionic liquid gating-induced RKKY interaction modification to the disturbance of itinerant electrons inside synthetic antiferromagnetic heterostructure and the corresponding change of its Fermi level. Voltage tuning of RKKY interaction may enable the next generation of switchable spintronics between antiferromagnetic and ferromagnetic modes with both fundamental and practical perspectives.

  13. On the advantages of spring magnets compared to pure FePt: Strategy for rare-earth free permanent magnets following a bottom-up approach

    Energy Technology Data Exchange (ETDEWEB)

    Pousthomis, M.; Garnero, C. [Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Marcelot, C.G. [Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Centre d’Elaboration de Matériaux et d’Etudes Structurales, CEMES-CNRS, 29 rue Jeanne Marvig, B.P. 94347, 31055 Toulouse (France); Blon, T.; Cayez, S. [Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Cassignol, C.; Du, V.A.; Krispin, M. [Siemens AG, Corporate Technology, Munich (Germany); Arenal, R. [Transpyrenean Advanced Laboratory for Electron Microscopy (TALEM), INSA - INA, CNRS - Universidad de Zaragoza, 30155 Toulouse (France); Laboratorio de Microscopias Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA), U. Zaragoza, C/Mariano Esquillor s/n, 50018 Zaragoza (Spain); Fundacion ARAID, 50018 Zaragoza (Spain); Soulantica, K.; Viau, G. [Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Lacroix, L.-M., E-mail: lmlacroi@insa-toulouse.fr [Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Transpyrenean Advanced Laboratory for Electron Microscopy (TALEM), INSA - INA, CNRS - Universidad de Zaragoza, 30155 Toulouse (France)

    2017-02-15

    Nanostructured magnets benefiting from efficient exchange-coupling between hard and soft grains represent an appealing approach for integrated miniaturized magnetic power sources. Using a bottom-up approach, nanostructured materials were prepared from binary assemblies of bcc FeCo and fcc FePt nanoparticles and compared with pure L1{sub 0}-FePt materials. The use of a bifunctional mercapto benzoic acid yields homogeneous assemblies of the two types of particles while reducing the organic matter amount. The 650 °C thermal annealing, mandatory to allow the L1{sub 0}-FePt phase transition, led to an important interdiffusion and thus decreased drastically the amount of soft phase present in the final composites. The analysis of recoil curves however evidenced the presence of an efficient interphase exchange coupling, which allows obtaining better magnetic performances than pure L1{sub 0} FePt materials, energy product above 100 kJ m{sup −3} being estimated for a Pt content of only 33%. These results clearly evidenced the interest of chemically grown nanoparticles for the preparation of performant spring-magnets, opening promising perspective for integrated subcentimetric magnets with optimized properties.

  14. Anomalous metamagnetic-like transition in a FeRh/Fe3Pt interface occurring at T ≈ 120 K in the field-cooled-cooling curves for low magnetic fields

    Directory of Open Access Journals (Sweden)

    S. Salem-Sugui Jr.

    2012-09-01

    Full Text Available We report on the magnetic properties of a special configuration of a FeRh thin film. An anomalous behavior on the magnetisation vs. temperature was observed when low magnetic fields are applied in the plane of a thin layer of FeRh deposited on ordered Fe3Pt. The anomalous effect resembles a metamagnetic transition and occur only in the field-cooled-cooling magnetisation curve at temperatures near 120 K in samples without any heat treatment.

  15. Hydrogen spillover in Pt-single-walled carbon nanotube composites: formation of stable C-H bonds.

    Science.gov (United States)

    Bhowmick, Ranadeep; Rajasekaran, Srivats; Friebel, Daniel; Beasley, Cara; Jiao, Liying; Ogasawara, Hirohito; Dai, Hongjie; Clemens, Bruce; Nilsson, Anders

    2011-04-13

    Using in situ electrical conductivity and ex situ X-ray photoelectron spectroscopy (XPS) measurements, we have examined how the hydrogen uptake of single-walled carbon nanotubes (SWNTs) is influenced by the addition of Pt nanoparticles. The conductivity of platinum-sputtered single-walled carbon nanotubes (Pt-SWNTs) during molecular hydrogen exposure decreased more rapidly than that of the corresponding pure SWNTs, which supports a hydrogenation mechanism facilitated by "spillover" of dissociated hydrogen from the Pt nanoparticles. C 1s XPS spectra indicate that the Pt-SWNTs store hydrogen by means of chemisorption, that is, covalent C-H bond formation: molecular hydrogen charging at elevated pressure (8.27 bar) and room temperature yielded Pt-SWNTs with up to 16 ± 1.5 at. % sp(3)-hybridized carbon atoms, which corresponds to a hydrogen-storage capacity of 1.2 wt % (excluding the weight of Pt nanoparticles). Pt-SWNTs prepared by the Langmuir-Blodgett (LB) technique exhibited the highest Pt/SWNT ratio and also the best hydrogen uptake. © 2011 American Chemical Society

  16. An in-situ X-ray diffraction study on the electrochemical formation of PtZn alloys on Pt(1 1 1) single crystal electrode

    Energy Technology Data Exchange (ETDEWEB)

    Drnec, J., E-mail: drnec@esrf.fr [ESRF, Grenoble (France); Bizzotto, D. [Department of Chemistry, AMPEL, University of British Columbia, Vancouver, BC (Canada); Carlà, F. [ESRF, Grenoble (France); Fiala, R. [Charles University, Faculty of Mathematics and Physics, Prague (Czech Republic); Sode, A. [Ruhr-Universität Bochum, Bochum (Germany); Balmes, O.; Detlefs, B.; Dufrane, T. [ESRF, Grenoble (France); Felici, R., E-mail: felici@esrf.fr [ESRF, Grenoble (France)

    2015-11-01

    Highlights: • PtZn electrochemical alloying is observed on single crystal Pt electrodes. • In-situ X-ray characterization during alloy formation and dissolution is provided. • Structural model of the surface during alloying and dissolution is discussed. • X-ray based techniques can be used in in-operando studies of bimetallic fuel cell catalysts. - Abstract: The electrochemical formation and dissolution of the oxygen reduction reaction (ORR) PtZn catalyst on Pt(1 1 1) surface is followed by in-situ X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements. When the crystalline Pt surface is polarized to sufficiently negative potential values, with respect to an Ag/AgCl|KCl reference electrode, the electrodeposited zinc atoms diffuse into the bulk and characteristic features are observed in the X-ray patterns. The surface structure and composition during deposition and dissolution is determined from analysis of XRR curves and measurements of crystal truncation rods. Thin Zn-rich surface layer is present during the alloy formation while a Zn-depleted layer forms during dissolution.

  17. Surface structure of MgO underlayer with Ti diffusion for (002) oriented L10 FePt-based heat assisted magnetic recording media

    Science.gov (United States)

    Hinata, Sintaro; Jo, Shin; Saito, Shin

    2018-05-01

    Surface morphology of the MgO layer and magnetic properties of FePt-C layer deposited on the MgO were investigated for the FePt-based heat assisted magnetic recording media. Stacking structure of the underlayer for the FePt-C layer was MgO (0-5 nm)/Cr80Mn20 (0-30 nm)/Cr50Ti50 (0-50 nm)/glass sub.. Surface observation result for the MgO film by using an atomic force microscope revealed the existence of nodules with a height of about 2 nm and a network-like convex structure with a height difference of about sub nm (boundary wall, BW) on the MgO crystal grain boundary. Density of the nodules largely depends on the surface roughness of the CrTi layer, RaCrTi and it is suppressed from 10 to 2/0.5 μm2 by reducing RaCrTi from 420 to 260 pm. Height of the BW depends on thickness of the MgO layer, tMgO and it can be suppressed by reducing tMgO to less than 4 nm. From the cross-sectional energy dispersive x-ray mapping, it is clarified that the BW is formed by atomic diffusion of Ti atoms from CrTi layer due to the substrate heating process, and a compound consists of Mg, Ti and O atoms. This BW can be used as a template to magnetically isolate the FePt column in the FePt-based granular film, such as FePt-SiO2, if the size of the BW is reduced to less than 10 nm. M-H loop of the FePt-C granular film deposited on the underlayer showed that the nodule and BW induce oxidation of the FePt grains, and reduction of intergranular exchange coupling.

  18. Structure and magnetic properties of Co/Pt single- and bi-crystal multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Yu, C.C. E-mail: yucc@phys.sinica.edu.tw; Chu, Y.C.; Chang, F.L.; Wei, D.H.; Chou, S.C.; Liou, Y.; Yao, Y.D.; Cheng, W.C.; Chin, T.S

    2004-11-01

    Both FCC(1 1 1) single- and bi-crystal [Co(3 A)]/Pt(10 A)]{sub 23} multilayers have been successfully grown on sapphire (0 0 0 1) and yttria-stabilized cubic zirconia (1 0 0) substrates, respectively, by molecular-beam epitaxial technique. The coercivity of single crystal films decreased monotonically as elevating post-annealing temperature. However, bicrystal films displayed a larger coercivity than the other. Moreover, the coercivity of bicrystal films did not decrease until the annealing temperature >400 deg. C. The difference in magnetic behavior between single- and bi-crystal multilayers could be originated from the demagnetizing factors resulted by different grain and surface structures.

  19. Dielectric behavior and phase transition in [111]-oriented PIN–PMN–PT single crystals under dc bias

    Directory of Open Access Journals (Sweden)

    Yuhui Wan

    2014-01-01

    Full Text Available Temperature and electric field dependences of the dielectric behavior and phase transition for [111]-oriented 0.23PIN–0.52PMN–0.25PT (PIN-PMN–0.25PT and 0.24PIN–0.43PMN–0.33PT (PIN–PMN–0.33PT single crystals were investigated over a temperature range from -100°C to 250°C using field-heating (FH dielectric measurements. The transition phenomenon from ferroelectric microdomain to macrodomain was found in rhombohedra (R phase region in the single crystals under dc bias. This transition temperature Tf of micro-to-macrodomain is sensitive to dc bias and move quickly to lower temperature with increasing dc bias. The phase transition temperatures in the two single crystals shift toward high temperature and the dielectric permittivities at the phase transition temperature decrease with increasing dc bias. Especially, the phase transition peaks are gradually broad in PIN–PMN–0.33PT single crystal with the increasing dc bias. Effects of dc bias on the dielectric behavior and phase transition in PIN–PMN–PT single crystals are discussed.

  20. Growth of Ti or Fe doped lithium niobate single crystals

    International Nuclear Information System (INIS)

    Lee, J.H.; Kim, J.N.; Ro, J.H.; Kim, J.W.; Jeen, G.S.; Kim, Y.C.; Lee, H.S.

    1982-01-01

    This paper reprots a study of the growth of Ti or Fe doped LiNbO 3 single crystals by Czochralski method and its physical properties. On the basis of this study we have developed a growth procedure that produces a high yield of twin-free boules. The quality is better for crystals that are lightly doped with Ti than for those of high concentrations. However there are no significant quality differences among the crystals with concentrations of less than 0.5wt% of Fe. The crystals are characterized by optical absorption and magnetic susceptibility. Undoped crystals show the magnetic susceptibility of -10x10 -6 cgs, which is diamagnetic. The crystals with 0.01wt% and 0.5wt% of ferromagnetic susceptibilities of 2.6x1a -6 cgs, and 80x10 -6 cgs, respectively. Therefore, Fe-doped crystals are paramagnetic. Very small changes of magnetic susceptibilities have been observed in the Ti-doped crystals. (Author)

  1. Room temperature magnetism of few-nanometers-thick Fe{sub 3}O{sub 4}(111) films on Pt(111) and Ru(0001) studied in ambient conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lewandowski, M., E-mail: lewandowski@amu.edu.pl [NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland); Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Miłosz, Z.; Michalak, N.; Ranecki, R. [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Sveklo, I.; Kurant, Z.; Maziewski, A. [Faculty of Physics, University of Białystok, Lipowa 41, 15-424 Białystok (Poland); Mielcarek, S. [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland); Luciński, T. [Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań (Poland); Jurga, S. [NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland)

    2015-09-30

    Few-nanometers-thick Fe{sub 3}O{sub 4}(111) films were epitaxially grown on Pt(111) and Ru(0001) single crystal supports by sequential iron deposition and oxidation in an ultra-high vacuum chamber. The growth of well-ordered magnetite films was confirmed by low energy electron diffraction. The films were covered with a protective Au layer and subjected to magnetic and structural studies in ambient conditions. Magnetic hysteresis loops, recorded using magneto-optical Kerr effect apparatus, confirmed magnetic ordering in both films at room temperature. The Kerr measurements indicated in-plane orientation of magnetization, which was supported by the lack of magnetic contrast in magnetic force microscopy images. Atomic force microscopy revealed significant differences in morphology of the films, tentatively attributed to different lattice mismatch with Pt(111) and Ru(0001) single crystal supports. - Highlights: • Few-nanometers-thick Fe{sub 3}O{sub 4}(111) films were grown on Pt(111) and Ru(0001). • Magnetic properties were studied using MOKE and AFM/MFM in ambient conditions. • The films exhibited in-plane magnetic ordering at room temperature. • Differences in magnetic properties were tentatively assigned to structural differences.

  2. Effects of non-magnetic phase and deposition temperature on magnetic properties of FePt–MgO granular thin films on single-crystal MgO substrate

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Z.G. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zhongshan R& D Center for Materials Surface and Thin Films Technology of the South China University of Technology, Gent Materials Surface Technology (Guangdong) Co., Ltd, Zhongshan 528437 (China); Zeng, D.C., E-mail: medczeng@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zhongshan R& D Center for Materials Surface and Thin Films Technology of the South China University of Technology, Gent Materials Surface Technology (Guangdong) Co., Ltd, Zhongshan 528437 (China); Zhao, L.Z.; Wang, J. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Yu, H.Y. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zhongshan R& D Center for Materials Surface and Thin Films Technology of the South China University of Technology, Gent Materials Surface Technology (Guangdong) Co., Ltd, Zhongshan 528437 (China); Liu, Z.W. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Liu, J.P., E-mail: pliu@uta.edu [Department of Physics, University of Texas at Arlington, Arlington 76019 (United States); Zhou, K.S. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China)

    2016-11-01

    (FePt){sub 100−x}(MgO){sub x} granular thin films were fabricated by using co-sputtering on single crystal MgO substrate at different deposition temperatures followed by a high-temperature annealing. The adding MgO was found to have the following effects: 1) high fraction of MgO phase (70 vol%) degraded the L1{sub 0} phase transformation; 2) FePt grains embedded in MgO matrix were well separated, leading to minimized exchange interaction between the FePt grains; 3) 55 vol% fraction of MgO was optimal for the L1{sub 0}-FePt phase formation with highest coercivity, due to the formation of granular structure, which was also verified by comparing the structure and properties of FePt/MgO bilayer films. Deposition temperature has also effect on the magnetic properties of FePt–MgO films. Room temperature deposition did not result in the L1{sub 0} phase even after annealing at 800 °C. However, the magnetic properties of the films deposited at 200 °C were better than those deposited at 300 °C. The low coercivity resulted from elevated deposition temperature was attributed to the thermal expansion and competitively growth among FePt and MgO grains. The results revealed that adding appropriate amount of MgO (55 vol%) can be achieved by finding a proper deposition temperature (200 °C), well-defined granular L1{sub 0}-FePt films with fine grain distribution, high coercivity and small domain size.

  3. Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

    Directory of Open Access Journals (Sweden)

    R. Ramos

    2016-10-01

    Full Text Available We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.

  4. The memory effect of magnetoelectric coupling in FeGaB/NiTi/PMN-PT multiferroic heterostructure

    Science.gov (United States)

    Zhou, Ziyao; Zhao, Shishun; Gao, Yuan; Wang, Xinjun; Nan, Tianxiang; Sun, Nian X.; Yang, Xi; Liu, Ming

    2016-01-01

    Magnetoelectric coupling effect has provided a power efficient approach in controlling the magnetic properties of ferromagnetic materials. However, one remaining issue of ferromagnetic/ferroelectric magnetoelectric bilayer composite is that the induced effective anisotropy disappears with the removal of the electric field. The introducing of the shape memory alloys may prevent such problem by taking the advantage of its shape memory effect. Additionally, the shape memory alloy can also “store” the magnetoelectric coupling before heat release, which introduces more functionality to the system. In this paper, we study a FeGaB/NiTi/PMN-PT multiferroic heterostructure, which can be operating in different states with electric field and temperature manipulation. Such phenomenon is promising for tunable multiferroic devices with multi-functionalities. PMID:26847469

  5. Probing the A1 to L10 transformation in FeCuPt using the first order reversal curve method

    Directory of Open Access Journals (Sweden)

    Dustin A. Gilbert

    2014-08-01

    Full Text Available The A1-L10 phase transformation has been investigated in (001 FeCuPt thin films prepared by atomic-scale multilayer sputtering and rapid thermal annealing (RTA. Traditional x-ray diffraction is not always applicable in generating a true order parameter, due to non-ideal crystallinity of the A1 phase. Using the first-order reversal curve (FORC method, the A1 and L10 phases are deconvoluted into two distinct features in the FORC distribution, whose relative intensities change with the RTA temperature. The L10 ordering takes place via a nucleation-and-growth mode. A magnetization-based phase fraction is extracted, providing a quantitative measure of the L10 phase homogeneity.

  6. Mechanical confinement for tuning ferroelectric response in PMN-PT single crystal

    Science.gov (United States)

    Patel, Satyanarayan; Chauhan, Aditya; Vaish, Rahul

    2015-02-01

    Ferroelectrics form an important class of materials and are employed for a variety of applications. However, specific applications dictate the need of tailored ferroelectric response. This creates a requirement to obtain ferroelectric materials with tunable properties. Generally, chemical modifications or domain engineering are employed to this effect. This study attempts to shed light on the use of compressive pre-stresses for tuning and enhancing the ferroelectric properties. For the purpose, polarization versus electric field hysteresis data for 68Pb(Mn1/3Nb2/3)O3-32PbTiO3 (PMN-PT) single crystals were obtained as a function of uniaxial compressive stresses and operating temperatures. These data were utilized to investigate the effects of mechanical confinement for four individual case studies of electrocaloric effect, electrical energy storage, pyroelectric, and piezoelectric effect. A significant improvement was obtained for all case studies. The adiabatic temperature change was improved by ≈80% (28 MPa, 353 K); energy storage density increased by a factor of five (28 MPa, 353 K); pyroelectric figure of merits improved by an order of magnitude (21 MPa) and the piezoelectric coefficient was tailored (variable stress). The results offer promising insight into the use of directional confinement for improving application specific ferroelectric properties in PMN-PT single crystal.

  7. Size-dependent effects in supported highly dispersed Fe2O3 catalysts, doped with Pt and Pd

    International Nuclear Information System (INIS)

    Cherkezova-Zheleva, Zara; Shopska, Maya; Mitov, Ivan; Kadinov, Georgi

    2010-01-01

    Series of Fe and Fe–Me (Me = Pt or Pd) catalyst supported on γ-Al 2 O 3 , TiO 2 (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

  8. Thermally stable single atom Pt/m-Al2O3 for selective hydrogenation and CO oxidation

    KAUST Repository

    Zhang, Zailei

    2017-07-27

    Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al2O3, likely stabilized by coordinatively unsaturated pentahedral Al3+ centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al2O3 and control samples, this system exhibits significantly enhanced stability and performance for n-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period.

  9. Role of Ta-spacer layer on tuning the tilt angle magnetic anisotropy of L1{sub 1}-CoPt/Ta/NiFe exchange springs

    Energy Technology Data Exchange (ETDEWEB)

    Saravanan, P., E-mail: psdrdo@gmail.com [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Talapatra, A.; Mohanty, J. [Department of Physics, Indian Institute of Technology Hyderabad, Hyderabad 502285 (India); Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Kamat, S.V. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India)

    2017-06-15

    Highlights: • Role of Ta-spacer layer in L1{sub 1}-CoPt(10 nm)/Ta//NiFe(4 nm) trilayers was investigated. • Domain size increased at the expense of magnetic phase contrast with increasing t{sub Ta}. • Tilt angle magnetization increased from 43° to 77° upon increasing t{sub Ta} (0–2.5 nm). • Micromagnetic studies confirmed the existence of tilted magnetic anisotropy. • Ta-spacer is effective in preserving competing anisotropies of CoPt and NiFe-layers. - Abstract: L1{sub 1}-CoPt/Ta/NiFe trilayers are chosen as model films for probing the role of spacer layer on tuning the tilt angle magnetization (θ{sub M}) in such exchange springs. For this purpose, a non-magnetic layer (Ta) with varying thickness (t{sub Ta}) from 0 to 2.5 nm was inserted between 10-nm thick CoPt film exhibiting strong perpendicular magnetic anisotropy (PMA) and 4-nm thick NiFe film having in-plane magnetic anisotropy (IMA). With the insertion of Ta-spacer, the magnetic hysteresis loops become more and more tilted as t{sub Ta} increases. Upon increasing the t{sub Ta} from 0 to 2.5 nm, the estimated SQR{sub ⊥} (=M{sub r⊥}/M{sub s⊥}) from the M–H loops is found to decrease moderately; while the θ{sub M} increases significantly from 43° to 77°. MFM images revealed maze-like domain patterns and the domain size tends to increase at the expense of magnetic phase contrast with increasing t{sub Ta}. Micro-magnetic simulation of tilt in the anisotropy axis with respect to the bare CoPt-layer showed a trend similar to that of those observed with the M–H loops obtained by VSM measurements. The results of present study suggest that the insertion of Ta-spacer is not only beneficial in terms of preserving the competing anisotropies such as PMA and IMA of CoPt and NiFe-layers respectively through weakened exchange coupling; but also, act as an appropriate means for realizing tunable tilted magnetic anisotropy in the L1{sub 1}-CoPt/NiFe exchange springs.

  10. Large pyramid shaped single crystals of BiFeO{sub 3} by solvothermal synthesis method

    Energy Technology Data Exchange (ETDEWEB)

    Sornadurai, D.; Ravindran, T. R.; Paul, V. Thomas; Sastry, V. Sankara [Condensed Matter Physics Division, Materials Science Group, Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu (India); Condensed Matter Physics Division, Materials Science Group (India)

    2012-06-05

    Synthesis parameters are optimized in order to grow single crystals of multiferroic BiFeO{sub 3}. 2 to 3 mm size pyramid (tetrahedron) shaped single crystals were successfully obtained by solvothermal method. Scanning electron microscopy with EDAX confirmed the phase formation. Raman scattering spectra of bulk BiFeO3 single crystals have been measured which match well with reported spectra.

  11. Probing adsorption phenomena on a single crystal Pt-alloy surface under oxygen reduction reaction conditions

    DEFF Research Database (Denmark)

    Bondarenko, Alexander S.; Stephens, Ifan E.L.; Bech, Lone

    2012-01-01

    The adsorption dynamics of *OH and *O species at Pt(111) and Cu/Pt(111) near-surface alloy (NSA) surfaces in oxygen-free and O2-saturated 0.1M HClO4 was investigated. Subsurface Cu modifies the electronic structure at the Pt(111) surface resulting in weaker bonding to adsorbates like *OH, *H or *...

  12. Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$

    CERN Document Server

    Adolph, C; Alexeev, M G; Alexeev, G D; Amoroso, A; Andrieux, V; Anosov, V; Augustyniak, W; Austregesilo, A; Azevedo, C D R; Badełek, B; Balestra, F; Barth, J; Beck, R; Bedfer, Y; Bernhard, J; Bicker, K; Bielert, E R; Birsa, R; Bisplinghoff, J; Bodlak, M; Boer, M; Bordalo, P; Bradamante, F; Braun, C; Bressan, A; Büchele, M; Burtin, E; Chang, W-C; Chiosso, M; Choi, I; Chung, S U; Cicuttin, A; Crespo, M L; Curiel, Q; Dalla Torre, S; Dasgupta, S S; Dasgupta, S; Denisov, O Yu; Dhara, L; Donskov, S V; Doshita, N; Duic, V; Dünnweber, W; Dziewiecki, M; Efremov, A; Eversheim, P D; Eyrich, W; Faessler, M; Ferrero, A; Finger, M; Finger jr , M; Fischer, H; Franco, C; du Fresne von Hohenesche, N; Friedrich, J M; Frolov, V; Fuchey, E; Gautheron, F; Gavrichtchouk, O P; Gerassimov, S; Giordano, F; Gnesi, I; Gorzellik, M; Grabmüller, S; Grasso, A; Grosse Perdekamp, M; Grube, B; Grussenmeyer, T; Guskov, A; Haas, F; Hahne, D; von Harrach, D; Hashimoto, R; Heinsius, F H; Herrmann, F; Hinterberger, F; Horikawa, N; d'Hose, N; Hsieh, C-Y; Huber, S; Ishimoto, S; Ivanov, A; Ivanshin, Yu; Iwata, T; Jahn, R; Jary, V; Joosten, R; Jörg, P; Kabuß, E; Ketzer, B; Khaustov, G V; Khokhlov, Yu A; Kisselev, Yu; Klein, F; Klimaszewski, K; Koivuniemi, J H; Kolosov, V N; Kondo, K; Königsmann, K; Konorov, I; Konstantinov, V F; Kotzinian, A M; Kouznetsov, O; Krämer, M; Kremser, P; Krinner, F; Kroumchtein, Z V; Kuchinski, N; Kuhn, R; Kunne, F; Kurek, K; Kurjata, R P; Lednev, A A; Lehmann, A; Levillain, M; Levorato, S; Lichtenstadt, J; Longo, R; Maggiora, A; Magnon, A; Makins, N; Makke, N; Mallot, G K; Marchand, C; Marianski, B; Martin, A; Marzec, J; Matoušek, J; Matsuda, H; Matsuda, T; Meshcheryakov, G; Meyer, W; Michigami, T; Mikhailov, Yu V; Miyachi, Y; Montuenga, P; Nagaytsev, A; Nerling, F; Neyret, D; Nikolaenko, V I; Nový, J; Nowak, W-D; Nukazuka, G; Nunes, A S; Olshevsky, A G; Orlov, I; Ostrick, M; Panzieri, D; Parsamyan, B; Paul, S; Peng, J-C; Pereira, F; Pešek, M; Peshekhonov, D V; Platchkov, S; Pochodzalla, J; Polyakov, V A; Pretz, J; Quaresma, M; Quintans, C; Ramos, S; Regali, C; Reicherz, G; Riedl, C; Rossiyskaya, N S; Ryabchikov, D I; Rychter, A; Samoylenko, V D; Sandacz, A; Santos, C; Sarkar, S; Savin, I A; Sbrizzai, G; Schiavon, P; Schmidt, K; Schmieden, H; Schönning, K; Schopferer, S; Selyunin, A; Shevchenko, O Yu; Silva, L; Sinha, L; Sirtl, S; Slunecka, M; Sozzi, F; Srnka, A; Stolarski, M; Sulc, M; Suzuki, H; Szabelski, A; Szameitat, T; Sznajder, P; Takekawa, S; Tessaro, S; Tessarotto, F; Thibaud, F; Tosello, F; Tskhay, V; Uhl, S; Veloso, J; Virius, M; Weisrock, T; Wilfert, M; ter Wolbeek, J; Zaremba, K; Zavertyaev, M; Zemlyanichkina, E; Ziembicki, M; Zink, A

    2016-01-01

    We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\\it c$ to 4 GeV/$\\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\\it c$ or 200 GeV/$\\it c$ impinging on polarised $\\mathrm{{}^6LiD}$ or $\\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$.

  13. Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pT

    Directory of Open Access Journals (Sweden)

    C. Adolph

    2016-02-01

    Full Text Available We measured the longitudinal double spin asymmetries ALL for single hadron muoproduction off protons and deuterons at photon virtuality Q2<1(GeV/c2 for transverse hadron momenta pT in the range 1 GeV/c to 4 GeV/c. They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/c or 200 GeV/c impinging on polarised 6LiD or NH3 targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation ΔG inside the nucleon in the range of the nucleon momentum fraction carried by gluons 0.05

  14. Two-dimensional iron-phthalocyanine (Fe-Pc) monolayer as a promising single-atom-catalyst for oxygen reduction reaction: a computational study

    Science.gov (United States)

    Wang, Yu; Yuan, Hao; Li, Yafei; Chen, Zhongfang

    2015-07-01

    Searching for low-cost non-Pt catalysts for oxygen reduction reaction (ORR) has been a key scientific issue in the development of fuel cells. In this work, the potential of utilizing the experimentally available two-dimensional (2D) Fe-phthalocyanine (Fe-Pc) monolayer with precisely-controlled distribution of Fe atoms as a catalyst of ORR was systematically explored by means of comprehensive density functional theory computations. The computations revealed that O2 molecules can be sufficiently activated on the surface of the Fe-Pc monolayer, and the subsequent ORR steps prefer to proceed on the Fe-Pc monolayer through a more efficient 4e pathway with a considerable limiting potential of 0.68 V. Especially, the Fe-Pc monolayer is more stable than the Fe-Pc molecule in acidic medium, and can present good catalytic performance for ORR on the addition of axial ligands. Therefore, the Fe-Pc monolayer is quite a promising single-atom-catalyst with high efficiency for ORR in fuel cells.Searching for low-cost non-Pt catalysts for oxygen reduction reaction (ORR) has been a key scientific issue in the development of fuel cells. In this work, the potential of utilizing the experimentally available two-dimensional (2D) Fe-phthalocyanine (Fe-Pc) monolayer with precisely-controlled distribution of Fe atoms as a catalyst of ORR was systematically explored by means of comprehensive density functional theory computations. The computations revealed that O2 molecules can be sufficiently activated on the surface of the Fe-Pc monolayer, and the subsequent ORR steps prefer to proceed on the Fe-Pc monolayer through a more efficient 4e pathway with a considerable limiting potential of 0.68 V. Especially, the Fe-Pc monolayer is more stable than the Fe-Pc molecule in acidic medium, and can present good catalytic performance for ORR on the addition of axial ligands. Therefore, the Fe-Pc monolayer is quite a promising single-atom-catalyst with high efficiency for ORR in fuel cells. Electronic

  15. DFT calculations of the charged states of N@C60 and Fe4 single molecule magnets investigated in tunneling spectroscopy

    Science.gov (United States)

    Nossa, Javier; Islam, Fhokrul; Canali, Carlo; Pederson, Mark

    2012-02-01

    For device applications of single molecule magnets (SMMs) in high-density information storage and quantum-state control it is essential that the magnetic properties of the molecules remain stable under the influence of metallic contacts or surface environment. Recent tunneling experiments [1, 2] on N@C60 and Fe4 SMM have shown that these molecules preserve their magnetic characteristics when they are used as the central island of single-electron transistors. Although quantum spin models have been used extensively to study theoretically tunneling spectroscopy of SMMs, it has been shown recently that the orbital degrees of freedom, which is absent in spin models, can significantly affect the tunneling conductance [3]. In this work we present first-principles calculations of the neutral and charged states of N@C60 and Fe4 SMMs, and discuss a strategy to include their properties into a theory of quantum transport. We also present results of the magnetic anisotropy for the different charge states of Fe4 and discuss their relevance for experiments [2] in the sequential tunneling and cotunnelling regimes. [4pt] [1]. N. Roch et al., Phys. Rev. B 83, 081407 (2011). [0pt] [2]. A.S. Zyazin et al., Nano Lett. 10, 3307 (2010). [0pt] [3]. L. Michalak et al., Phys. Rev. Lett. 104, 017202 (2010).

  16. Pt atoms stabilized on hexagonal boron nitride as efficient single-atom catalysts for CO oxidation: A first-principles investigation

    KAUST Repository

    Liu, Xin

    2015-01-01

    Taking CO oxidation as a probe, we investigated the electronic structure and reactivity of Pt atoms stabilized by vacancy defects on hexagonal boron nitride (h-BN) by first-principles-based calculations. As a joint effect of the high reactivity of both a single Pt atom and a boron vacancy defect (PtBV), the Pt-N interaction is -4.40 eV and is already strong enough to prohibit the diffusion and aggregation of the stabilized Pt atom. Facilitated by the upshifted Pt-d states originated from the Pt-N interaction, the barriers for CO oxidation through the Langmuir-Hinshelwood mechanism for formation and dissociation of peroxide-like intermediate and the regeneration are as low as 0.38, 0.10 and 0.04 eV, respectively, suggesting the superiority of PtBV as a catalyst for low temperature CO oxidation.

  17. Fracture mechanics behavior of a Ni-Fe superalloy sheath for superconducting fusion magnets. Pt. 2. Magnet life analysis model

    International Nuclear Information System (INIS)

    Kim, J.H.

    1997-01-01

    For pt.1 see ibid., p.251-67,(1997). From previous results of fatigue crack growth and fracture toughness measurements for a Ni-Fe base superalloy, a primary candidate for the International Thermonuclear Experimental Reactor (ITER) central solenoid (CS) conduit, we derive an improved magnet life analysis model from the framework of Newman and Raju. For the superalloy conduit with an initial semielliptical surface crack in its thickness direction, the model predicts the evolution of crack aspect ratio for a wide range of initial crack geometries under pure tension and bending fatigue. The prediction of final fracture due to fatigue crack growth using the linear elastic fracture mechanics approach is shown to be underconservative. An alternative model based on Newman's elastic-plastic fracture toughness parameter is derived for the base metal with nearly semicircular cracks. The improved life analysis model taking into account the fatigue and fracture behavior is applied to the ITER CS magnet and the results are compared with those from earlier models. Accounting for the crack shape evolution leads to significantly longer life compared to assuming a constant aspect ratio. For the superalloy base metal we find that the expected fatigue life of engineering design activity design of the CS magnet is about eight times the design requirement. Even the conceptual design activity design with a free-standing CS meets the life requirement when analyzed by the improved model. (orig.)

  18. Magnetic-field-induced decrease of the spin Peltier effect in Pt/Y3Fe5O12 system at room temperature

    Science.gov (United States)

    Itoh, Ryuichi; Iguchi, Ryo; Daimon, Shunsuke; Oyanagi, Koichi; Uchida, Ken-ichi; Saitoh, Eiji

    2017-11-01

    We report the observation of magnetic-field-induced decrease of the spin Peltier effect (SPE) in a junction of a paramagnetic metal Pt and a ferrimagnetic insulator Y3Fe5O12 (YIG) at room temperature. For driving the SPE, spin currents are generated via the spin Hall effect from applied charge currents in the Pt layer, and injected into the adjacent thick YIG film. The resultant temperature modulation is detected by a commonly used thermocouple attached to the Pt/YIG junction. The output of the thermocouple shows sign reversal when the magnetization is reversed and linearly increases with the applied current, demonstrating the detection of the SPE signal. We found that the SPE signal decreases with the magnetic field. The observed decreasing rate was found to be comparable to that of the spin Seebeck effect (SSE), suggesting the dominant and similar contribution of the low-energy magnons in the SPE as in the SSE.

  19. Four-state memory based on a giant and non-volatile converse magnetoelectric effect in FeAl/PIN-PMN-PT structure.

    Science.gov (United States)

    Wei, Yanping; Gao, Cunxu; Chen, Zhendong; Xi, Shibo; Shao, Weixia; Zhang, Peng; Chen, Guilin; Li, Jiangong

    2016-07-15

    We report a stable, tunable and non-volatile converse magnetoelectric effect (ME) in a new type of FeAl/PIN-PMN-PT heterostructure at room temperature, with a giant electrical modulation of magnetization for which the maximum relative magnetization change (ΔM/M) is up to 66%. The 109° ferroelastic domain switching in the PIN-PMN-PT and coupling with the ferromagnetic (FM) film via uniaxial anisotropy originating from the PIN-PMN-PT (011) surface are the key roles in converse ME effect. We also propose here a new, four-state memory through which it is possible to modify the remanent magnetism state by adjusting the electric field. This work represents a helpful approach to securing electric-writing magnetic-reading with low energy consumption for future high-density information storage applications.

  20. One-step synthesis of L10 FePt particles through spray pyrolysis: the impacts of post annealing on product morphology and magnetic properties

    Science.gov (United States)

    You, Junhua; Guo, Yaozu

    2018-02-01

    One step synthesis of L10-FePt particles was reported in this paper. The particles were synthesized through high temperature spray pyrolysis. The as-synthesized particles were characterized by Transmitting Electron Microscopy (TEM), and corresponding results confirmed the polycrystalline and hollow structure of the products, with average size of ∼800 nm. The TEM Energy Dispersive x-ray (EDX) spectrum characterization showed that both Fe and Pt were homogenously distributed at nanoscale. The magnetic properties and crystal structure were investigated by Vibrating Sample Magnetometer (VSM) and x-ray Diffraction (XRD), respectively, and confirmed the high coercivity and L10 phase of the products. A post annealing was applied to the as-synthesized particles, and the results show that post annealing has little impact on the particle morphology, but could improve the magnetic properties.

  1. Growth of single crystals of BaFe12O19 by solid state crystal growth

    Science.gov (United States)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-10-01

    Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

  2. Spin-orbit driven phenomena in the isoelectronic L1.sub.0./sub.-Fe(Pd,Pt) alloys from first principles

    Czech Academy of Sciences Publication Activity Database

    Kudrnovský, Josef; Drchal, Václav; Turek, Ilja

    2017-01-01

    Roč. 96, č. 21 (2017), s. 1-7, č. článku 214437. ISSN 2469-9950 R&D Projects: GA ČR GA15-13436S Institutional support: RVO:68378271 ; RVO:68081723 Keywords : anomalous Hall effect * Gilbert damping * partial order * first- principles * Fe(Pd,Pt) alloys Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.836, year: 2016

  3. X-ray diffraction and Moessbauer studies of structural changes and L10 ordering kinetics during annealing of polycrystalline Fe51Pt49 thin films

    International Nuclear Information System (INIS)

    Spada, F.E.; Parker, F.T.; Platt, C.L.; Howard, J.K.

    2003-01-01

    Room-temperature x-ray diffraction and Moessbauer effect techniques have been used to characterize the structural features and local atomic environments of sputtered Fe 51 Pt 49 thin films following various isothermal treatments. Both techniques show that no significant changes occur in the chemically ordered L1 0 tetragonal phase after it has formed. In contrast, changes in the disordered face-centered-cubic (fcc) phase are observed prior to the transformation into the ordered tetragonal phase. Moessbauer measurements indicate the development of increasing short-range order in the disordered fcc phase with increasing annealing temperature. Asymmetries in the fcc x-ray diffraction profiles also suggest the presence of lattice distortions caused by atomic size differences commonly found in the quenched disordered fcc phase of materials that form ordered structures. Quasi-real-time kinetic measurements of the disorder→order transformation in sputtered Fe 51 Pt 49 thin films within the temperature range 300 deg. C≤T≤400 deg. C have also been conducted using high-temperature x-ray diffraction techniques. Significant differences are observed between the kinetic parameters determined in this study and those of previous reports. It is proposed that these differences arise from the lower temperature range investigated in the present work, where the gradual changes occurring in the fcc phase can influence the rate of the ordering transformation. Furthermore, because the initial state of disorder in Fe ∼50 Pt ∼50 films can be influenced by the deposition conditions, variability in the low-temperature ordering kinetics should be expected among Fe ∼50 Pt ∼50 films prepared under different conditions

  4. Growth of single crystals of BaFe12O19 by solid state crystal growth

    International Nuclear Information System (INIS)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-01-01

    Single crystals of BaFe 12 O 19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe 12 O 19 are buried in BaFe 12 O 19 +1 wt% BaCO 3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe 12 O 19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe 12 O 19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth. - Highlights: • Single crystals of BaFe 12 O 19 are grown by solid state crystal growth. • A single crystal up to ∼130 μm thick (c-axis direction) grows on the seed crystal. • The single crystal and surrounding ceramic matrix have similar composition. • Micro-Raman scattering shows the single crystal has the BaFe 12 O 19 structure.

  5. Long-range chemical order effects upon the magnetic anisotropy of FePt alloys from an ab initio electronic structure theory

    Science.gov (United States)

    Staunton, J. B.; Ostanin, S.; Razee, S. S. A.; Gyorffy, B.; Szunyogh, L.; Ginatempo, B.; Bruno, Ezio

    2004-12-01

    The magnetocrystalline anisotropy (MCA) of bulk and thick films of FePt is calculated from a 'first-principles' theory. The starting point is a description from electronic density functional theory for systems of interacting electrons moving in lattices of ions. Relativistic effects such as spin-orbit coupling are included. FePt readily transforms into a CuAu-type (L 10) ordered phase and this coincides with the material's high anisotropy. Here we describe how to calculate the MCA of a partially ordered alloy and to extract its dependence on the long range chemical order parameter η. We present calculations of the MCA of FePt as a function of η and find excellent agreement with the experimental data of Okamoto et al (2002 Phys. Rev. B 66 024413) and others with respect to the magnetic easy axis, the magnitude of the MCA and its trend with decreasing η. We also study the paramagnetic phase of the ordered alloy using the 'disordered local moment' picture of metallic magnetism at finite temperatures. We calculate a Curie temperature of 935 K in reasonable agreement with experiment (710 K) and find the easy axis for the onset of ferromagnetic order to coincide with the magnetic easy axis found at low temperatures.

  6. Angled-focused 45 MHz PMN-PT single element transducer for intravascular ultrasound imaging.

    Science.gov (United States)

    Yoon, Sangpil; Williams, Jay; Kang, Bong Jin; Yoon, Changhan; Cabrera-Munoz, Nestor; Jeong, Jong Seob; Lee, Sang Goo; Shung, K Kirk; Kim, Hyung Ham

    2015-06-01

    A transducer with an angled and focused aperture for intravascular ultrasound imaging has been developed. The acoustic stack for the angled-focused transducer was made of PMN-PT single crystal with one matching layer, one protective coating layer, and a highly damped backing layer. It was then press-focused to a desired focal length and inserted into a thin needle housing with an angled tip. A transducer with an angled and unfocused aperture was also made, following the same fabrication procedure, to compare the performance of the two transducers. The focused and unfocused transducers were tested to measure their center frequencies, bandwidths, and spatial resolutions. Lateral resolution of the angled-focused transducer (AFT) improved more than two times compared to that of the angled-unfocused transducer (AUT). A tissue-mimicking phantom in water and a rabbit aorta tissue sample in rabbit blood were scanned using AFT and AUT. Imaging with AFT offered improved contrast, over imaging with AUT, of the tissue-mimicking phantom and the rabbit aorta tissue sample by 23 dB and 8 dB, respectively. The results show that AFT has strong potential to provide morphological and pathological information of coronary arteries with high resolution and high contrast.

  7. Pt/Cu single-atom alloys as coke-resistant catalysts for efficient C-H activation

    Science.gov (United States)

    Marcinkowski, Matthew D.; Darby, Matthew T.; Liu, Jilei; Wimble, Joshua M.; Lucci, Felicia R.; Lee, Sungsik; Michaelides, Angelos; Flytzani-Stephanopoulos, Maria; Stamatakis, Michail; Sykes, E. Charles H.

    2018-03-01

    The recent availability of shale gas has led to a renewed interest in C-H bond activation as the first step towards the synthesis of fuels and fine chemicals. Heterogeneous catalysts based on Ni and Pt can perform this chemistry, but deactivate easily due to coke formation. Cu-based catalysts are not practical due to high C-H activation barriers, but their weaker binding to adsorbates offers resilience to coking. Using Pt/Cu single-atom alloys (SAAs), we examine C-H activation in a number of systems including methyl groups, methane and butane using a combination of simulations, surface science and catalysis studies. We find that Pt/Cu SAAs activate C-H bonds more efficiently than Cu, are stable for days under realistic operating conditions, and avoid the problem of coking typically encountered with Pt. Pt/Cu SAAs therefore offer a new approach to coke-resistant C-H activation chemistry, with the added economic benefit that the precious metal is diluted at the atomic limit.

  8. Pt/Cu single-atom alloys as coke-resistant catalysts for efficient C–H activation

    Energy Technology Data Exchange (ETDEWEB)

    Marcinkowski, Matthew D.; Darby, Matthew T.; Liu, Jilei; Wimble, Joshua M.; Lucci, Felicia R.; Lee, Sungsik; Michaelides, Angelos; Flytzani-Stephanopoulos, Maria; Stamatakis, Michail; Sykes, E. Charles H.

    2018-01-08

    The recent availability of shale gas has led to a renewed interest in C-H bond activation as the first step towards synthesis of fuels and fine chemicals. Heterogeneous catalysts based on Ni and Pt can perform this chemistry, but deactivate easily due to coke formation. Cu- based catalysts are not practical for this chemistry due to high C-H activation barriers, but their weaker binding to adsorbates offers resilience to coking. Utilizing Pt/Cu single atom alloys (SAAs) we examine C-H activation in a number of systems including methyl groups, methane, and butane using a combination of simulations, surface science, and catalysis studies. We find that Pt/Cu SAAs activate C-H bonds more efficiently than Cu, are stable for days under realistic operating conditions, and avoid the problem of coking typically encountered with Pt. Pt/Cu SAAs therefore offer a new approach to coke resistant C-H activation chemistry with the added economic benefit that the precious metal is diluted at the atomic limit.

  9. FePO4based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

    Science.gov (United States)

    Zeng, Libin; Li, Xinyong; Shi, Yueran; Qi, Yefei; Huang, Daqiong; Tadé, Moses; Wang, Shaobin; Liu, Shaomin

    2017-05-15

    A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO 4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO 4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO 4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT). Copyright © 2016. Published by Elsevier B.V.

  10. Single crystal Fe elements patterned by one-step selective chemical wet etching

    NARCIS (Netherlands)

    Sun, Li; Wong, P.K.J.; Niu, Daxin; Zou, Xiao; Zhai, Ya; Wu, Jing; Xu, Yongbing; Zhai, Hongru

    2010-01-01

    A technique has been developed to pattern single crystal ultrathin Fe films by selective chemical wet etching of the Au capping layer and then simultaneous oxidization of the ferromagnetic Fe layer underneath. The focused magneto-optical Kerr effect and ferromagnetic resonance measurements

  11. Icosahedral Pt-centered Pt13 and Pt19 carbonyl clusters decorated by [Cd5(μ-Br)5Br(5-x)(solvent)x]x+ rings reminiscent of the decoration of Au-Fe-CO and Au-thiolate nanoclusters: a unifying approach to their electron counts.

    Science.gov (United States)

    Femoni, Cristina; Iapalucci, Maria Carmela; Longoni, Giuliano; Zacchini, Stefano; Zarra, Salvatore

    2011-03-02

    The new [Pt(13)(CO)(12){Cd(5)(μ-Br)(5)Br(2)(dmf)(3)}(2)](2-) and [Pt(19)(CO)(17){Cd(5)(μ-Br)(5)Br(3)(Me(2)CO)(2)}{Cd(5)(μ-Br)(5)Br(Me(2)CO)(4)}](2-) clusters have been obtained in good yields by reaction of [Pt(12)(CO)(24)](2-) with CdBr(2)·H(2)O in dmf at 90 °C and structurally characterized by X-ray diffraction. Their structures consist of a Pt-centered Pt(13)(CO)(12) icosahedron and a Pt(19)(CO)(17) interpenetrated double icosahedron, respectively, decorated by two Cd(5)(μ-Br)(5)Br(5-x)(solvent)(x) rings. Their surface decoration may be related to that of Au-Fe-CO clusters as well as to the staple motifs stabilizing gold-thiolates nanoclusters. An oversimplified and unifying approach to interpret their electron count is suggested.

  12. Dynamic properties of Ca{sub 10}(Pt{sub 3}As{sub 8})(Fe{sub 1-x}Pt{sub x}As){sub 10} in the superconducting state explored by NMR in high fields

    Energy Technology Data Exchange (ETDEWEB)

    Brueckner, Felix; Sarkar, Rajib; Surmach, Maksym; Inosov, Dmytro; Klauss, Hans-Henning [Institut fuer Festkoerperphysik, TU Dresden (Germany); Reyes, Arneil P.; Kuhns, Philip L. [National High Magnetic Field Laboratory, Tallahassee, FL (United States)

    2016-07-01

    The triclinic iron-based superconductor Ca{sub 10}(Pt{sub 3}As{sub 8})(Fe{sub 1-x}Pt{sub x}As){sub 10} with a T{sub c} of 13 K exhibits a unique pseudogap phase below T* = 45 K, recently probed with inelastic neutron scattering. This phase has been attributed to a possible preformation of Cooper pairs. We present detailed NMR results, including {sup 75}As and {sup 195}Pt spectra as well as T{sub 1} measurements. These experiments reveal a drop of spin fluctuations just below T* with a hysteresis in temperature, associated with the emergence of the pseudogap phase. Interestingly, no anomaly at T{sub c} is found. At 3 K, a peak in the T{sub 1} relaxation rate appears, until 1/T{sub 1} eventually vanishes at lower temperatures. This behavior is persistent in large magnetic fields up to 17 T. To interpret these results, scenarios including magnetic order below T* are quite unprobable, since Korringa law is well complied at higher temperatures and no magnetic order is found in μSR. However, the origin of the unique behavior remains unclear for now.

  13. Correlação entre a estrutura atômica superficial e o processo de adsorção-dessorção reversível de hidrogênio em eletrodos monocristalinos Pt(111, Pt(100 e Pt(110 The correlation between the atomic surface structure and the reversible adsorption-desorption of hydrogen on single crystal Pt (111, Pt (100 and Pt (110 electrodes

    Directory of Open Access Journals (Sweden)

    Valderi Pacheco dos Santos

    2001-12-01

    Full Text Available Platinum is widely used as electrode in electrocatalytic processes, however the use of polycrystalline electrodes introduces a series of variables in the electrochemical system due to the aleatory contribution of all the crystallographic orientations with different surface packing of atoms. Single crystal platinum electrodes of low Miller index present surface structure of high regularity and serve as model to establish a correlation among the macroscopic and microscopic properties of the electrochemical interface. Therefore, the main aim of this work is the study of the voltammetric profiles of the reversible adsorption-desorption of hydrogen on Pt(100, Pt(110 and Pt(111, in order to correlate the electrochemical properties of each different orientation with the surface atomic structure.

  14. Pt nanoparticle modified single walled carbon nanotube network electrodes for electrocatalysis: control of the specific surface area over three orders of magnitude

    NARCIS (Netherlands)

    Miller, T.S.; Sansuk, S.; Lai, Stanley; Macpherson, J.V.; Unwin, P.R.

    2015-01-01

    The electrodeposition of Pt nanoparticles (NPs) on two-dimensional single walled carbon nanotube (SWNT) network electrodes is investigated as a means of tailoring electrode surfaces with a well-defined amount of electrocatalytic material. Both Pt NP deposition and electrocatalytic studies are

  15. The A1 to L10 transformation in FePt films with ternary alloying additions of Mg, V, Mn, and B

    International Nuclear Information System (INIS)

    Wang, B.; Barmak, K.; Klemmer, T. J.

    2011-01-01

    The impact of ternary additions of Mg, V, Mn, and B on the A1 [face centered cubic (fcc)] to L1 0 phase transformation has been studied. The films were cosputter deposited from elemental targets at room temperature and annealed after deposition. The films had Mg additions in the range ∼0-2.6 at.%, V additions in the range 0.7-12.2 at.%, Mn additions in the range 2.2-16.3 at.%, and B additions in the range 1.2-12.9 at.%. For all four ternary alloy systems, annealing resulted in the formation of no other phases than the L1 0 phase. Ternary additions of C than the binary FePt films with the same Pt content.

  16. Growth and characterizations of Ba2Ti2Fe2As4O single crystals

    Directory of Open Access Journals (Sweden)

    Yun-Lei Sun, Abduweli Ablimit, Jin-Ke Bao, Hao Jiang, Jie Zhou and Guang-Han Cao

    2013-01-01

    Full Text Available Single crystals of a new iron-based superconductor Ba2Ti2Fe2As4O have been grown successfully via a Ba2As3-flux method in a sealed evacuated quartz tube. Bulk superconductivity with Tc ~ 21.5 K was demonstrated in resistivity and magnetic susceptibility measurements after the as-grown crystals were annealed at 500 °C in vacuum for a week. X-ray diffraction patterns confirm that the annealed and the as-grown crystals possess the identical crystallographic structure of Ba2Ti2Fe2As4O. Energy-dispersive x-ray spectra indicate that partial Ti/Fe substitution exists in the [Fe2As2] layers and the annealing process redistributes the Ti within the Fe-plane. The ordered Fe-plane stabilized by annealing exhibits superconductivity with magnetic vortex pinned by Ti.

  17. Formic acid decomposition on Pt1/Cu (111) single platinum atom catalyst: Insights from DFT calculations and energetic span model analysis

    Science.gov (United States)

    Wang, Ying-Fan; Li, Kun; Wang, Gui-Chang

    2018-04-01

    Inspired by the recent surface experimental results that the monatomic Pt catalysts has more excellent hydrogen production that Cu(111) surface, the mechanism of decomposition of formic acid on Cu(111) and single atom Pt1/Cu(111) surface was studied by periodic density functional theory calculations in the present work. The results show that the formic acid tends to undergo dehydrogenation on both surfaces to obtain the hydrogen product of the target product, and the selectivity and catalytic activity of Pt1/Cu (111) surface for formic acid dehydrogenation are better. The reason is that the single atom Pt1/Cu(111) catalyst reduces the reaction energy barrier (i.e., HCOO → CO2 + H) of the critical step of the dehydrogenation reaction due to the fact that the single atom Pt1/Cu(111) catalyst binds formate weakly compared to that of Cu (111) one. Moreover, it was found that the Pt1/Cu (111) binds CO more strongly than that of Cu (111) one and thus leading to the difficult for the formation of CO. These two factors would make the single Pt atom catalyst had the high selectivity for the H2 production. It is hoped that the present work may help people to design the efficient H2 production from HCOOH decomposition by reduce the surface binding strength of HCOO species, for example, using the low coordination number active site like single atom or other related catalytic system.

  18. Examining the rudimentary steps of the oxygen reduction reaction on single-atomic Pt using Ti-based non-oxide supports

    DEFF Research Database (Denmark)

    Tak, Young Joo; Yang, Sungeun; Lee, Hyunjoo

    2018-01-01

    In the attempt to reduce the high-cost and improve the overall durability of Pt-based electrocatalysts for the oxygen reduction reaction (ORR), density-functional theory (DFT) calculations have been performed to study the energetics of the elementary steps that occur during ORR on TiN(100)- and T...... of the single-atom Pt catalyst, and directly influences the rudimentary ORR steps on these single-atom platinized supports....

  19. Activation of surface lattice oxygen in single-atom Pt/CeO 2 for low-temperature CO oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Nie, Lei; Mei, Donghai; Xiong, Haifeng; Peng, Bo; Ren, Zhibo; Pereira Hernandez, Xavier I.; DelaRiva, Andrew; Wang, Meng; Engelhard, Mark H.; Kovarik, Libor; Datye, Abhaya K.; Wang, Yong

    2017-12-14

    While single-atom catalysts can provide high catalytic activity and selectivity, application in industrial catalysts demands long term performance and the ability to regenerate the catalysts. We have investigated the factors that lead to improved catalytic activity of a Pt/CeO2 catalyst for low temperature CO oxidation. Single-atom Pt/CeO2 becomes active for CO oxidation under lean condition only at elevated temperatures, because CO is strongly bound to ionic Pt sites. Reducing the catalyst, even under mild conditions, leads to onset of CO oxidation activity even at room temperature. This high activity state involves the transformation of mononuclear Pt species to sub-nanometer sized Pt particles. Under oxidizing conditions, the Pt can be restored to its stable, single-atom state. The key to facile regeneration is the ability to create mobile Pt species and suitable trapping sites on the support, making this a prototypical catalyst system for industrial application of single-atom catalysis.

  20. Structure and magnetism of single-phase epitaxial gamma '-Fe4N

    NARCIS (Netherlands)

    Costa-Kramer, JL; Borsa, DM; Garcia-Martin, JM; Martin-Gonzalez, MS; Boerma, DO; Briones, F

    Single phase epitaxial pure gamma(')-Fe4N films are grown on MgO (001) by molecular beam epitaxy of iron in the presence of nitrogen obtained from a radio frequency atomic source. The epitaxial, single phase nature of the films is revealed by x-ray diffraction and by the local magnetic environment

  1. Radiation- and phonon-bottleneck--induced tunneling in the Fe8 single-molecule magnet

    Science.gov (United States)

    Bal, M.; Friedman, Jonathan R.; Chen, W.; Tuominen, M. T.; Beedle, C. C.; Rumberger, E. M.; Hendrickson, D. N.

    2008-04-01

    We measure magnetization changes in a single crystal of the single-molecule magnet Fe8 when exposed to intense, short (spin dynamics, allowing observation of thermally assisted resonant tunneling between spin states at the 100 ns time scale. Detailed numerical simulations quantitatively reproduce the data and yield a spin-phonon relaxation time T1~40 ns.

  2. Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges

    Science.gov (United States)

    Zhao, Jiong; Deng, Qingming; Avdoshenko, Stanislav M.; Fu, Lei; Eckert, Jürgen; Rümmeli, Mark H.

    2014-01-01

    Single-atom catalysts are of great interest because of their high efficiency. In the case of chemically deposited sp2 carbon, the implementation of a single transition metal atom for growth can provide crucial insight into the formation mechanisms of graphene and carbon nanotubes. This knowledge is particularly important if we are to overcome fabrication difficulties in these materials and fully take advantage of their distinct band structures and physical properties. In this work, we present atomically resolved transmission EM in situ investigations of single Fe atoms at graphene edges. Our in situ observations show individual iron atoms diffusing along an edge either removing or adding carbon atoms (viz., catalytic action). The experimental observations of the catalytic behavior of a single Fe atom are in excellent agreement with supporting theoretical studies. In addition, the kinetics of Fe atoms at graphene edges are shown to exhibit anomalous diffusion, which again, is in agreement with our theoretical investigations. PMID:25331874

  3. CO oxidation mechanism on the γ-Al{sub 2}O{sub 3} supported single Pt atom: First principle study

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Hongwei, E-mail: gaohongw369@ms.xjb.ac.cn

    2016-08-30

    Highlights: • DFT studied on CO oxidation mechanism on Pt/γ-Al{sub 2}O{sub 3} catalyst. • DFT studied on the adsorption properties of single Pt on Pt/γ-Al{sub 2}O{sub 3} catalyst. • Pt adsorptions on the Al-terminated surface are more favorable than the ones on the O-terminated surface. • The reactive O*−O−C*=O intermediate mechanism is the dominant reaction pathway for CO oxidation on Pt/γ-Al{sub 2}O{sub 3}. - Abstract: Understanding the role of metal-support interaction for the supported single-atom catalysts is very important in heterogeneous catalysis. Here, Three different CO oxidation mechanisms on Pt/γ-Al{sub 2}O{sub 3} catalyst were probed by periodic density functional theory (DFT) calculations in detail, namely the reactive O*−O−C*=O intermediate mechanism, the reactive CO{sub 3} intermediate mechanism and the Pt-Al{sup 3+} double sites mechanism. According to the calculated results analysis, we concluded that the dominant reaction pathway at the low temperatures is the reactive O*−O−C*=O intermediate mechanism. Our results are in very good agreement with the experimental evidence for O*−O−C*=O coverage on Pt/γ-Al{sub 2}O{sub 3} at room temperature by an in situ diffuse reflectance infrared detector.

  4. Possible Implication of a Single Nonextensive p(T) Distribution for Hadron Production in High-Energy pp Collisions

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Cheuk-Yin [ORNL; Wilk, Grzegorz [National Centre for Nuclear Research, Warsaw, Poland; Cirto, Leonardo J. L. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Brazil; Tsallis, Constantino [Centro Brasileiro de Pesquisas Fisicas (CBPF), Brazil

    2015-01-01

    Multiparticle production processes in pp collisions at the central rapidity region are usually considered to be divided into independent "soft" and "hard" components. The first is described by exponential (thermal-like) transverse momentum spectra in the low-p(T) region with a scale parameter T associated with the temperature of the hadronizing system. The second is governed by a power-like distributions of transverse momenta with power index n at high-p(T) associated with the hard scattering between partons. We show that the hard-scattering integral can be approximated as a nonextensive distribution of a quasi-power-law containing a scale parameter T and a power index n =1/(q-1), where q is the nonextensivity parameter. We demonstrate that the whole region of transverse momenta presently measurable at LHC experiments at central rapidity (in which the observed cross sections varies by 14 orders of magnitude down to the low p(T) region) can be adequately described by a single nonextensive distribution. These results suggest the dominance of the hard-scattering hadron-production process and the approximate validity of a "no-hair" statistical-mechanical description of the p(T) spectra for the whole p(T) region at central rapidity for pp collisions at high-energies.

  5. Influence of piezoelectric strain on the Raman spectra of BiFeO{sub 3} films deposited on PMN-PT substrates

    Energy Technology Data Exchange (ETDEWEB)

    Himcinschi, Cameliu, E-mail: himcinsc@physik.tu-freiberg.de; Talkenberger, Andreas; Kortus, Jens [TU Bergakademie Freiberg, Institute of Theoretical Physics, 09596 Freiberg (Germany); Guo, Er-Jia [Institute of Physics, Martin-Luther-University Halle-Wittenberg, 06099 Halle (Germany); Institute for Metallic Materials, IFW Dresden, 01069 Dresden (Germany); Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States); Dörr, Kathrin [Institute of Physics, Martin-Luther-University Halle-Wittenberg, 06099 Halle (Germany); Institute for Metallic Materials, IFW Dresden, 01069 Dresden (Germany)

    2016-01-25

    BiFeO{sub 3} epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.28PbTiO{sub 3} (PMN-PT) substrates with a conductive buffer layer (La{sub 0.7}Sr{sub 0.3}MnO{sub 3} or SrRuO{sub 3}) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows one to directly obtain a quantitative correlation between the strain and the shift of the Raman-active phonons. This is a prerequisite for making Raman scattering a strong tool to probe the strain coupling in multiferroic nanostructures. Using the Poisson's number for BiFeO{sub 3}, one can determine the volume change induced by strain, and therefore the Grüneisen parameters for specific phonon modes.

  6. Formation of SmFe5(0001) ordered alloy thin films on Cu(111) single-crystal underlayers

    International Nuclear Information System (INIS)

    Yabuhara, Osamu; Ohtake, Mitsuru; Nukaga, Yuri; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-01-01

    SmFe 5 (0001) single-crystal thin films are prepared by molecular beam epitaxy employing Cu(111) single-crystal underlayers on MgO(111) substrates. The Cu atoms diffuse into the Sm-Fe layer and substitute the Fe sites in SmFe 5 structure forming an alloy compound of Sm(Fe,Cu) 5 . The Sm(Fe,Cu) 5 film is more Cu enriched with increasing the substrate temperature. The Cu underlayer plays an important role in assisting the formation of the ordered phase.

  7. A GREENER SYNTHESIS OF CORE (FE, CU)-SHELL (AU, PT, PD AND AG) NANOCRYSTALS USING AQUEOUS VITAMIN C

    Science.gov (United States)

    A greener method to fabricate the novel core (Fe and Cu)-shell (noble metals) metal nanocrystals using aqueous ascorbic acid (vitamin C) is described. Transition metal salts such as Cu and Fe were reduced using ascorbic acid, a benign naturally available antioxidant, and then add...

  8. Magnetic properties of a TbFe3.5Al8.5 single crystal

    NARCIS (Netherlands)

    Brommer, P.E.; de Boer, F.R.; Duong, N.P.; Buschow, K.H.J.; Brück, E.H.

    2004-01-01

    We have studied the magnetic behaviour of a (tetragonal) TbFe3.5Al8.5 single crystal extending earlier work on a TbFe4.4Al7.6 one. At 5K, the magnetisation curve measured along the [0 0 1] direction points to easy-plane behaviour, whereas that along the [1 0 0] direction shows a strong hysteresis,

  9. Heat capacity anomalies in Fe8 single crystal

    Science.gov (United States)

    Fominaya, F.; Gandit, P.; Gaudin, G.; Chaussy, J.; Sessoli, R.; Sangregorio, C.

    1999-05-01

    A preliminary heat capacity study of Fe8 molecules as a function of applied magnetic field, temperature and measuring frequency is presented. The heat capacity versus temperature curve shows in zero field several peaks between 2 and 3 K. The anomalies shift to a lower temperature when a magnetic field is applied. With increasing field the peaks are smeared. No frequency dependence could be established in the measured range of ω =217-4440 Hz. We have also performed heat capacity measurements as a function of magnetic field at fixed temperature. Between 2 and 3 K a pattern of well developed peaks at discrete magnetic field values is observed. The pattern strongly changes in the small temperature range between 2.3 and 2.5 K.

  10. Bulk Superconductivity and Disorder in Single Crystals of LaFePO

    Energy Technology Data Exchange (ETDEWEB)

    Analytis, James G.; Chu, Jiun-Haw; Erickson, Ann S.; Kucharczyk, Chris; /Stanford U., Appl. Phys. Dept.; Serafin, Alessandro; Carrington, Antony; /Bristol U.; Cox, Catherine; Kauzlarich, Susan M.; Hope, Hakon; /UC, Davis. Dept. Chem.

    2010-02-15

    We have studied the intrinsic normal and superconducting properties of the oxypnictide LaFePO. These samples exhibit bulk superconductivity and the evidence suggests that stoichiometric LaFePO is indeed superconducting, in contrast to other reports. We find that superconductivity is independent of the interplane residual resistivity {rho}{sub 0} and discuss the implications of this on the nature of the superconducting order parameter. Finally we find that, unlike T{sub c}, other properties in single-crystal LaFePO including the resistivity and magnetoresistance, can be very sensitive to disorder.

  11. PENJADWALAN JOBS PADA SINGLE MACHINE DENGAN MEMINIMUMKAN VARIANS WAKTU PENYELESAIAN JOBS Studi Kasus di P.T. XYZ

    Directory of Open Access Journals (Sweden)

    I Nyoman Sutapa

    2001-01-01

    Full Text Available This paper discusses a jobs scheduling on a single machine to minimize variance of job completion time. The objective is especially important in situations where it is desirable to provide customers or jobs with approximately the same treatment. In this case, data are collected from P.T. 'XYZ'. The focus of discussion is LB/KB Departement (Leather Board/Carton Board with carton board's production line, which produces carton board. Carton board's size is 150 x 110 cm and its thickness from 0,6 mm to 2,5 mm. In this paper a comparison analysis, the deviation of the objective value given by a heuristic (Vh method from the objective value given by P.T. 'XYZ' (Vp, is made. The percentage of deviation Vh from Vp is 50,36 %, which shows that the performance of heuristic is better, that is variance of job completion time by heuristic method smaller than by P.T. 'XYZ'. Besides the above discussion, the weakness dan superiority of heuristic are analyzed too. Abstract in Bahasa Indonesia : Makalah ini membahas penjadwalan jobs pada single machine dengan tujuan meminimumkan varians waktu penyelesaian job, yaitu untuk memberikan konsumen atau jobs kurang lebih perlakuan yang sama. Data yang diambil dalam pembahasan ini berasal dari perusahaan P.T. 'XYZ', di mana departemen yang menjadi fokus pembahasan adalah Departemen LB/KB (Leather Board/Karton Board dengan lintasan produksi karton board yang menghasilkan produk carton board ukuran 150 x 110 cm, dengan ketebalan 0,6 mm sampai dengan 2,5 mm. Dalam makalah ini dilakukan analisis perbandingan jadwal jobs pada proses produksi di perusahaan yang telah ada dengan jadwal jobs menggunakan metode heuristic, yaitu menggunakan persentase penyimpangan Vh (varians waktu penyelesaian jobs metode heuristic dari Vp (varians waktu penyelesaian jobs perusahaan. Dari hasil analisis didapatkan bahwa persentase penyimpangan Vh dari Vp sebesar 50,36%, hal ini menunjukkan bahwa performance metode heuristic lebih baik, yaitu

  12. Performance of direct-driven flapping-wing actuator with piezoelectric single-crystal PIN-PMN-PT

    Science.gov (United States)

    Ozaki, Takashi; Hamaguchi, Kanae

    2018-02-01

    We present a prototype flapping-wing actuator with a direct-driven mechanism to generate lift in micro- and nano-aerial vehicles. This mechanism has an advantage of simplicity because it has no transmission system between the actuator and wing. We fabricated the piezoelectric unimorph actuator from single-crystal PIN-PMN-PT, which achieved a lift force up to 1.45 mN, a value about 1.9 times larger than the mass of the actuator itself. This is the first reported demonstration of an insect-scale actuator with a direct-driven mechanism that can generate a lift force greater than its own weight.

  13. Temperature evolution of magnetic structure of HoFeO3 by single crystal neutron diffraction

    Directory of Open Access Journals (Sweden)

    T. Chatterji

    2017-04-01

    Full Text Available We have investigated the temperature evolution of the magnetic structures of HoFeO3 by single crystal neutron diffraction. The three different magnetic structures werevfound as a function of temperature for HoFeO3. In all three phases the fundamental coupling between the Fe sub-lattices remains the same and only their orientation and the degree of canting away from the ideal axial direction varies. The magnetic polarisation of the Ho sub-lattices in these two higher temperature regions, in which the major components of the Fe moment lie along x and y, is very small. The canting of the moments from the axial directions is attributed to the antisymmetric interactions allowed by the crystal symmetry. In the low temperature phase two further structural transitions are apparent in which the spontaneous magnetisation changes sign with respect to the underlying antiferromagnetic configuration. In this temperature range the antisymmetric exchange energy varies rapidly as the the Ho sub-lattices begin to order. So long as the ordered Ho moments are small the antisymmetric exchange is due only to Fe-Fe interactions, but as the degree of Ho order increases the Fe-Ho interactions take over whilst at the lowest temperatures, when the Ho moments approach saturation the Ho-Ho interactions dominate. The reversals of the spontaneous magnetisation found in this study suggest that in HoFeO3 the sums of the Fe-Fe and Ho-Ho antisymmetric interactions have the same sign as one another, but that of the Ho-Fe terms is opposite.

  14. ZIF-8 with Ferrocene Encapsulated: A Promising Precursor to Single-Atom Fe Embedded Nitrogen-Doped Carbon as Highly Efficient Catalyst for Oxygen Electroreduction.

    Science.gov (United States)

    Wang, Jinpeng; Han, Guokang; Wang, Liguang; Du, Lei; Chen, Guangyu; Gao, Yunzhi; Ma, Yulin; Du, Chunyu; Cheng, Xinqun; Zuo, Pengjian; Yin, Geping

    2018-03-05

    The oxygen reduction reaction (ORR) plays an important role in the fields of energy storage and conversion technologies, including metal-air batteries and fuel cells. The development of nonprecious metal electrocatalysts with both high ORR activity and durability to replace the currently used costly Pt-based catalyst is critical and still a major challenge. Herein, a facile and scalable method is reported to prepare ZIF-8 with single ferrocene molecules trapped within its cavities (Fc@ZIF-8), which is utilized as precursor to porous single-atom Fe embedded nitrogen-doped carbon (Fe-N-C) during high temperature pyrolysis. The catalyst shows a half-wave potential (E 1/2 ) of 0.904 V, 67 mV higher than commercial Pt/C catalyst (0.837 V), which is among the best compared with reported results for ORR. Significant electrochemical properties are attributed to the special configuration of Fc@ZIF-8 transforming into a highly dispersed iron-nitrogen coordination moieties embedded carbon matrix. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Molecular [(Fe3)–(Fe3)] and [(Fe4)–(Fe4)] coordination cluster pairs as single or composite arrays.

    Science.gov (United States)

    Sañudo, E Carolina; Uber, Jorge Salinas; Pons Balagué, Alba; Roubeau, Olivier; Aromí, Guillem

    2012-08-06

    The synthesis of molecular cluster pairs is a challenge for coordination chemists due to the potential applications of these species in molecular spintronics or quantum computing. The ligand H(4)L, 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-methoxybenzene, has been successfully used to obtain a series of such complexes using the basic Fe(III) trinuclear carboxylates as starting materials. Synthetic control has allowed the isolation of the two molecular cluster pairs that form the composite [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2)[Fe(3)O(PhCO(2))(5)(py)(H(2)L)](2) (1). The dimers of trinuclear units, [Fe(3)O(PhCO(2))(5)(H(2)O)(H(2)L)](2) (2) and [Fe(3)O(o-MePhCO(2))(5)(H(2)L)(py)](2) (3), and the dimers of tetranuclear units, [Fe(4)O(2)(PhCO(2))(6)(H(2)L)(pz)](2) (4) and [Fe(4)O(2)(o-MePhCO(2))(6)(H(2)L)(pz)](2) (5), are presented here. The magnetic properties of the reported aggregates show that they are pairs of semi-independent clusters weakly interacting magnetically as required for two-qubit quantum gates.

  16. Size-dependent effects in supported highly dispersed Fe{sub 2}O{sub 3} catalysts, doped with Pt and Pd

    Energy Technology Data Exchange (ETDEWEB)

    Cherkezova-Zheleva, Zara; Shopska, Maya, E-mail: shopska@ic.bas.bg; Mitov, Ivan; Kadinov, Georgi [Bulgarian Academy of Sciences, Institute of Catalysis (Bulgaria)

    2010-06-15

    Series of Fe and Fe-Me (Me = Pt or Pd) catalyst supported on {gamma}-Al{sub 2}O{sub 3}, TiO{sub 2} (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

  17. The combination of directional outputs and single-mode operation in circular microdisk with broken PT symmetry.

    Science.gov (United States)

    Song, Qinghai; Li, Jiankai; Sun, Wenzhao; Zhang, Nan; Liu, Shuai; Li, Meng; Xiao, Shumin

    2015-09-21

    Monochromaticity and directionality are two key characteristics of lasers. However, the combination of directional emission and single-mode operation is quite challenging, especially for the on-chip devices. Here we propose a microdisk laser with single-mode operation and directional emissions by exploiting the recent developments associated with parity-time (PT) symmetry. This is accomplished by introducing one-dimensional periodic gain and loss into a circular microdisk, which induces a coupling between whispering gallery modes with different radial numbers. The lowest threshold mode is selected at the positions with least initial wavelength difference. And the directional emissions are formed by the introduction of additional grating vectors by the periodic distribution of gain and loss regions. We believe this research will impact the practical applications of on-chip microdisk lasers.

  18. Designed synthesis of MOx(M = Zn, Fe, Sn, Ni, Mn, Co, Ce, Mg, Ag), Pt, and Au nanoparticles supported on hierarchical CuO hollow structures.

    Science.gov (United States)

    Zhang, Zailei; Jung, Ji Chul; Yan, Ning

    2016-12-01

    Despite intensive research into support substrates for the dispersal of nanoparticles and their applications, there has been a lack of general methods to produce metal oxide hollow substrates supporting a wide range of metal and metal oxides. Herein, a synthetic protocol for the preparation of CuO hollow structure-supported MO x (M = Zn, Fe, Ni, Sn, Mn, Co, Ce, Mg, and Ag) and noble metals (Pt and Au) with the desired properties and shell structure, such as CuO/Fe 2 O 3 , CuO/ZnO, CuO/SnO 2 , CuO/MgO, CuO/NiO, CuO/Mn 2 O 3 , CuO/CoO, CuO/CeO 2 , CuO/Ag 2 O, CuO/Pt, CuO/Au hollow cubes, CuO/ZnO double-shell hollow cubes, CuO/SnO 2 double-shell hollow octahedra, CuO/SnO 2 /Fe 2 O 3 and CuO/Mn 2 O 3 /NiO double-shell hollow cubes, was developed based on controlled calcination and etching. These hybrid hollow structures were employed not only as support substrates but also as active constituents for catalytic reactions. As an example, we demonstrated that CuO/ZnO hollow cubes are remarkably efficient in converting solid chitin biomass to liquid chemicals in methanol. In addition, CuO/ZnO double-shell hollow cubes were highly effective in the oxidation of benzyl alcohol in the presence of H 2 O 2 , whereas CuO/Pt and CuO/Au hollow cubes promoted the oxidation of benzyl alcohol in pure O 2 . The strategy developed in this work extends the controllable fabrication of high-quality CuO hollow structure-supported nanoparticles using various compositions and shell structures, paving the way to the exploration and systematic comparison of these materials in a wider range of applications.

  19. Adsorption of Ni, Pd, Pt, Cu, Ag and Au on the Fe3O4(111) surface

    Science.gov (United States)

    Yu, Xiaohu; Tian, Xinxin; Wang, Shengguang

    2014-10-01

    The interaction of Group 10 and 11 transition metals with the magnetite (111) surface has been investigated using the GGA + U density functional theory and periodic slab surface models. It was found that these transition metals adsorb stronger on an oxygen-terminated magnetite (111) surface than on an iron-terminated surface. On an oxygen-terminated surface, the adsorption strength is in the order of Ni > Pt Cu > Pd > Ag Au. In contrast, the order on an iron-terminated surface is Ni > Pt Cu > Au > Pd Ag. The adsorption strength was found to correlate well with the average lengths of metal-oxygen bonds. The magnetite (111) surfaces largely modify the electronic structures of the transition metals. Compared to their density of states in bulk structures, the atomically adsorbed transition metals have narrower d bands, and their d-band centers are closer to the Fermi levels. This implies the higher activities of the atomically adsorbed transition metals.

  20. Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction

    OpenAIRE

    Goto, Sho; Kura, Hiroaki; Watanabe, Eiji; Hayashi, Yasushi; Yanagihara, Hideto; Shimada, Yusuke; Mizuguchi, Masaki; Takanashi, Koki; Kita, Eiji

    2017-01-01

    Tetrataenite (L10-FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L10-FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L10-FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to ...

  1. Effect of Fe Content on Olivine Viscosity at the P-T Conditions of Terrestrial-Planet Interiors

    Science.gov (United States)

    Raterron, P.; Holyoke, C. W., III; Tokle, L.; Hilairet, N.; Merkel, S.; Hirth, G.; Weidner, D. J.

    2016-12-01

    The top parts of the mantle of terrestrial planets are olivine-rich, with Fe/(Mg+Fe) ratio lower than 2% for Mercury, up to 25-30% for Mars, and intermediate compositions for the Earth, the Moon and Venus. Results of experiments at low pressure (Zhao et al., 2009, EPSL, 287, 229-240) indicate that increasing Fe content dramatically decreases olivine viscosity. Thus, the Martian upper mantle may be 10 times less viscous than the Earth's at the same conditions. However, there is no data available on the effect of iron on olivine plasticity at pressures relevant to planetary interiors. We deformed polycrystalline olivine specimens with various Fe contents ranging from 0% (pure forsterite) to 100% (pure fayalite), at temperatures (T) in excess of 1000°C and pressures (P) in the range of 2 - 6 GPa, in the Deformation-DIA apparatus (D-DIA) coupled with X-ray synchrotron radiation. Pressure, differential stress and strain rate were measured in situ by X-ray diffraction and radiography. Stacked cylindrical specimens with different iron contents were deformed in series to compare their viscosities at identical T, P and differential stress. We observed that increasing pressure dramatically decreases the viscosity contrast between Fe-poor olivine and Fe-rich olivine, while increasing differential stress has the opposite effect. Hence, the range of viscosities expected in planetary mantles - in the low-P and high-stress regime of the uppermost mantle and in the high-P and low-stress regime of the deep mantle - may be radically different, depending on their iron contents. We will present these new data which may have significant implications for the convection mode and thermal history of terrestrial-planet mantles.

  2. Agglomeration and sintering in annealed FePt nanoparticle assemblies studied by small angle neutron scattering and x-ray diffraction

    International Nuclear Information System (INIS)

    Thomson, T.; Lee, S.L.; Oates, C.J.; Toney, M.F.; Dewhurst, C.D.; Ogrin, F.Y.; Sun, S.

    2005-01-01

    In this work we give a detailed account of complementary small angle neutron scattering and x-ray diffraction studies of polymer mediated, self-assembled FePt nanoparticle arrays as a function of annealing temperature. The combination of these two techniques provides significantly greater physical insight than is available using either individually. Since both methods integrate over a large number of particles statistically meaningful data can be obtained in contrast to imaging techniques where typically only small areas are analyzed. The data show that the median particle size increases with annealing at temperatures of 580 deg. C and above. The data also demonstrate that the distribution of particle diameters is significant and increases with annealing temperature. These results allow a comprehensive structural model of the annealed assemblies to be developed in terms of particle sintering and agglomeration. This enhanced understanding will allow new strategies to be pursued in realizing the potential of nanoparticle assemblies as a monodispersed data storage medium

  3. Magnetoelastic interactions in a Cr+1.9 at% Fe alloy single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Derrett, H.A.; Prinsloo, A.R.E.; Alberts, H.L. E-mail: hla@na.rau.ac.za; Venter, A.M

    2004-05-01

    Measurements of the elastic constants and nonlinear acoustic properties of a Cr+1.9 at% Fe alloy single crystal are reported. The results indicate anomalous magnetoelastic coupling of the spin-density-wave with the acoustic phonons below and around the Neel temperature.

  4. Passive Fe2+ : ZnSe single-crystal Q switch for 3-mu m lasers

    NARCIS (Netherlands)

    Voronov, AA; Kozlovskii, [No Value; Korostelin, YV; Podmar'kov, YP; Polushkin, VG; Frolov, MP

    Passive Q-switching of 3-mu m lasers with the help of a Fe2+ : ZnSe single crystal is demonstrated. The 6-mJ, 50-ns giant pulses are obtained from a 2.9364-mu m Er : YAG laser by using this passive Q switch.

  5. Magnetocrystalline anisotropy and compositional order in Fe0.5Pt0.5: Calculations from an ab initio electronic model

    Science.gov (United States)

    Ostanin, S.; Razee, S. S. A.; Staunton, J. B.; Ginatempo, B.; Bruno, Ezio

    2003-01-01

    The magnetic properties of FePt samples, potential materials for high density recording media, depend sharply on the degree of chemical ordering produced during their preparation. This has prompted our investigation of the chemical order in both paramagnetic (P) and ferromagnetic (F) phases of a Fe0.5Pt0.5 solid solution and its effect upon the magnetocrystalline anisotropy (MAE) of the latter phase. Our "first-principles" theory uses density functional electronic structure calculations and a mean field treatment of both compositional and magnetic "local moment" fluctuations. We find both phases to be unstable to L10 (CuAu)-type order below temperatures of 1975 K (P) and 1565 K (F) which compares well with that found experimentally (≈1600 K) and our estimate of the Curie temperature as 575 K is also in fair agreement (710 K). For L10 order the calculated MAE is uniaxial with a simple form, υL10c(0,0,1)2 sin2 θ, where the coefficient υL10=9.7×108 erg/cm3, c(0,0,1) is the degree of order (between 0 and 0.5) and θ is the angle between the magnetization direction and the magnetic easy axis, which lies perpendicular to the layering of the L10 structure, also consistent with experimental data. Tetragonal distortions of the underlying face-centered-cubic lattice that occur as chemical order sets in are found to have a much smaller effect on the MAE.

  6. Surface acoustic load sensing using a face-shear PIN-PMN-PT single-crystal resonator.

    Science.gov (United States)

    Kim, Kyungrim; Zhang, Shujun; Jiang, Xiaoning

    2012-11-01

    Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) resonators for surface acoustic load sensing are presented in this paper. Different acoustic loads are applied to thickness mode, thickness-shear mode, and face-shear mode resonators, and the electrical impedances at resonance and anti-resonance frequencies are recorded. More than one order of magnitude higher sensitivity (ratio of electrical impedance change to surface acoustic impedance change) at the resonance is achieved for the face-shear-mode resonator compared with other resonators with the same dimensions. The Krimholtz, Leedom, and Matthaei (KLM) model is used to verify the surface acoustic loading effect on the electrical impedance spectrum of face-shear PIN-PMN-PT single-crystal resonators. The demonstrated high sensitivity of face-shear mode resonators to surface loads is promising for a broad range of applications, including artificial skin, biological and chemical sensors, touch screens, and other touch-based sensors.

  7. Characteristic length scale of the magnon accumulation in Fe{sub 3}O{sub 4}/Pt bilayer structures by incoherent thermal excitation

    Energy Technology Data Exchange (ETDEWEB)

    Anadón, A., E-mail: anadonb@unizar.es; Lucas, I.; Morellón, L. [Instituto de Nanociencia de Aragón, Universidad de Zaragoza, E-50018 Zaragoza (Spain); Departamento de Física de la Materia Condensada, Universidad de Zaragoza, E-50009 Zaragoza (Spain); Ramos, R. [WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Spin Quantum Rectification Project, ERATO, Japan Science and Technology Agency, Sendai 980-8577 (Japan); Algarabel, P. A. [Departamento de Física de la Materia Condensada, Universidad de Zaragoza, E-50009 Zaragoza (Spain); Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza and Consejo Superior de Investigaciones Científicas, 50009 Zaragoza (Spain); Ibarra, M. R.; Aguirre, M. H. [Instituto de Nanociencia de Aragón, Universidad de Zaragoza, E-50018 Zaragoza (Spain); Departamento de Física de la Materia Condensada, Universidad de Zaragoza, E-50009 Zaragoza (Spain); Laboratorio de Microscopías avanzadas, Universidad de Zaragoza, 50018 Zaragoza (Spain)

    2016-07-04

    The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe{sub 3}O{sub 4}/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K.

  8. X-ray photoelectron spectroscopy studies on single crystalline β-FeSi{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Wei, E-mail: mao@nuclear.jp [The Micro Analysis Laboratory, Tandem Accelerator, The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan); Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Udono, Haruhiko [Department of Electrical and Electronic Engineering, Ibaraki University, Hitachi, Ibaraki 316-8511 (Japan); Yamaguchi, Kenji [Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); Terai, Takayuki [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Matsuzaki, Hiroyuki [The Micro Analysis Laboratory, Tandem Accelerator, The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan); Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2016-05-01

    In order to realize the photoluminescence of semiconducting β-FeSi{sub 2} homoepitaxial films, surface preparation of single crystalline β-FeSi{sub 2} is of critical importance. An atomically flat and clean substrate surface of β-FeSi{sub 2} was prepared by sputtering with 2 keV Ar{sup +} ions or by heating at 850 °C. The structure of the native surface oxide and the removal of this layer were investigated though X-ray photoelectron spectroscopy measurements. No significant deviation of the stoichiometry was detected in the surface region. Our results suggest that a surface prepared in this way is an eligible substrate for homoepitaxy of β-FeSi{sub 2}. - Highlights: • A clean surface of single crystalline (beta)-FeSi{sub 2} was prepared by Ar{sup +} sputtering or by heating. • The removal of surface oxide during the surface treatment is elucidated. • The native surface oxides are identified as SiO{sub 2} on top and SiO{sub x} as the inner layer. • There is no significant deviation of surface stoichiometry on the clean surface.

  9. Tuning the band structure and superconductivity in single-layer FeSe by interface engineering.

    Science.gov (United States)

    Peng, R; Xu, H C; Tan, S Y; Cao, H Y; Xia, M; Shen, X P; Huang, Z C; Wen, C H P; Song, Q; Zhang, T; Xie, B P; Gong, X G; Feng, D L

    2014-09-26

    The interface between transition metal compounds provides a rich playground for emergent phenomena. Recently, significantly enhanced superconductivity has been reported for single-layer FeSe on Nb-doped SrTiO3 substrate. Yet it remains mysterious how the interface affects the superconductivity. Here we use in situ angle-resolved photoemission spectroscopy to investigate various FeSe-based heterostructures grown by molecular beam epitaxy, and uncover that electronic correlations and superconducting gap-closing temperature (Tg) are tuned by interfacial effects. Tg up to 75 K is observed in extremely tensile-strained single-layer FeSe on Nb-doped BaTiO3, which sets a record high pairing temperature for both Fe-based superconductor and monolayer-thick films, providing a promising prospect on realizing more cost-effective superconducting device. Moreover, our results exclude the direct correlation between superconductivity and tensile strain or the energy of an interfacial phonon mode, and highlight the critical and non-trivial role of FeSe/oxide interface on the high Tg, which provides new clues for understanding its origin.

  10. $A_{LL}(p_T)$ for single hadron photoproduction at high $p_T$

    CERN Document Server

    Levillain, Maxime

    2015-01-01

    In order to understand the gluon contribution to the nucleon spin, some experiments can study the production of hadrons at high transverse momemtum from lepton-nucleon or nucleon-nucleon scattering. RHIC has recently measured such double spin asymmetries $A_{LL}(p_T)$ for pion production at high center of mass energies, and inclusion of its data to global fits based on NLO collinear pQCD calculations gives some constraints on the gluon polarization in the range $0.051$ GeV/c and center of mass energy $\\sqrt{s}\\approx 18$ GeV. All COMPASS data taken from 2002 to 2011 by scattering 160 GeV polarized muons on longitudinally polarized $^6$LiD and NH$_3$ targets have been used, and the number of hadrons collected with $p_T>1$ GeV/c for this analysis amounts to about 10 millions. The obtained asymmetries will be compared to theoretical predictions of at NLO without gluon resummation calculation.

  11. Reactive Stresses in Ni49Fe18Ga27Co6 Shape-Memory-Alloy Single Crystals

    Science.gov (United States)

    Averkin, A. I.; Krymov, V. M.; Guzilova, L. I.; Timashov, R. B.; Soldatov, A. V.; Nikolaev, V. I.

    2018-03-01

    The reactive stresses induced in Ni49Fe18Ga27Co6-alloy single crystals during martensitic transformations with a limited possibility of shape-memory-strain recovery have been experimentally studied. The data on these crystals are compared with the results obtained previously for Cu-Al-Ni, Ni-Ti, and Ni‒Fe-Ga crystals. The potential of application of the Ni49Fe18Ga27Co6 single crystals in designing drives and power motors is demonstrated.

  12. Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac

    OpenAIRE

    Hill, S.; Maccagnano, S.; Park, K.; Achey, R. M.; North, J. M.; Dalal, N. S.

    2001-01-01

    It is shown that our multi-high-frequency (40-200 GHz) resonant cavity technique yields distortion-free high field EPR spectra for single crystal samples of the uniaxial and biaxial spin S = 10 single molecule magnets (SMMs) [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O and [Fe8O2(OH)12(tacn)6]Br8.9H2O. The observed lineshapes exhibit a pronounced dependence on temperature, magnetic field, and the spin quantum numbers (Ms values) associated with the levels involved in the transitions. Measurements ...

  13. Structural and physical properties of new uranium and transition element ternary stannides (Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt); Proprietes structurales et physiques de nouveaux stannures ternaires a base d'uranium et d'element de transition (Fe, Co, Ni, Rh, Pd, Ir, Pt)

    Energy Technology Data Exchange (ETDEWEB)

    Mirambet, F

    1993-12-15

    This work is dedicated to the study of ternary stannides based on uranium. The author reviews the structural, magnetic and electric properties of different families of stannides. The study of the U{sub 2}M{sub 2}Sn family where M stands for Fe, Co, Ni, Ru, Rh, Pd, Ir and Pt shows that the magnetic behaviour of uranium in these compounds is strongly influenced by the transition element M, which is explained by the hybridization force 5f(U) - nd(M) that depends on the number of electrons on the d shell of the M element. For instance, for the elements whose d shell is low filled (Fe, Ru), the U{sub 2}M{sub 2}Sn stannides show no magnetic order. On the other hand, when the number of d-electrons increases, a magnetic order appears progressively.

  14. Direct Production of High $p_T$ Single Photons at the CERN Intersecting Storage Rings

    CERN Document Server

    Diakonou, M; Resvanis, L.K.; Filippas, T.A.; Fokitis, E.; Trakkas, C.; Cnops, A.M.; Cobb, J.H.; Fowler, E.C.; Hood, D.M.; Iwata, S.; Palmer, R.B.; Rahm, D.C.; Rehak, P.; Stumer, I.; Fabjan, C.W.; Fields, T.; Lissauer, D.; Mannelli, I.; Molzon, W.; Mouzourakis, P.; Nakamura, K.; Nappi, A.; Willis, W.J.

    1979-01-01

    Single photon production in pp collisions at 30 < √ s < 62 GeV has been measured with liquid-argon-lead calorimeters at the CERN ISR. This process remains approximately constant with increasing √ s . For fixed √ s , the single photon to π 0 ratio increases strongly with increase in p T . The γ π 0 ratio is about 0.2 for p T above 4.5 GeV/c.

  15. Neutron scattering investigation of the magnetic order in single crystalline BaFe2As2

    OpenAIRE

    Kofu, M.; Qiu, Y.; Bao, Wei; Lee, S. -H.; Chang, S.; Wu, T.; Wu, G.; Chen, X. H.

    2009-01-01

    The magnetic structure of BaFe2As2 was completely determined from polycrystalline neutron diffraction measurements soon after the ThCr2Si2-type FeAs-based superconductors were discovered. Both the moment direction and the in-plane antiferromagnetic wavevector are along the longer a-axis of the orthorhombic unit cell. There is only one combined magnetostructural transition at about 140 K. However, a later single-crystal neutron diffraction work reported contradicting results. Here we show neut...

  16. Effect of the compressive stress on both polarization rotation and phase transitions in PMN-30%PT single crystal

    Directory of Open Access Journals (Sweden)

    Hui Zhang

    2014-05-01

    Full Text Available In this paper, we have investigated the dependence of both the electromechanical effect and the electrostriction on the compressive stress in PMN-30%PT single crystal on the basis of single domain polarization rotation model. In the model, the electroelastic energy induced by the compressive stress is taken into account. The results have demonstrated that the compressive stress can lead to a significant change in the initial polarization state in the crystal. The reason lies in the stress induced anisotropy which is the coupling between the compressive stress and the electrostrictive coefficients. Thus, the initial polarization state in single crystal is determined by the combination of both electrocrystalline anisotropy and the stress induced anisotropy. The compressive stress along the [100] axis can make the polarization in the crystal be perpendicular to the stress direction, and make it difficult to be polarized to the saturation. This model is useful for better understanding both the polarization rotation and electromechanical effect in ferroelectric crystals with the compressive stress present.

  17. First-order phase transitions in CaFe2As2 single crystal: a local probe study

    International Nuclear Information System (INIS)

    Alzamora, M; Munevar, J; Baggio-Saitovitch, E; Bud'ko, S L; Ni Ni; Canfield, P C; Sanchez, D R

    2011-01-01

    57 Fe Moessbauer spectroscopy has been used to investigate the structural and magnetic phase transitions of CaFe 2 As 2 (T N = 173 K) single crystals. For this compound we found that V ZZ is positive and parallel to the c-axis of the tetragonal structure. For CaFe 2 As 2 a magnetic hyperfine field B hf was observed at the 57 Fe nucleus below T N ∼ 173 K. Analysis of the temperature dependence of B hf data using the Bean-Rodbell model shows that the Fe spins undergo a first-order magnetic transition at ∼ 173 K. A collinear antiferromagnetic structure is established below this temperature with the Fe spin lying in the (a, b) plane. Below T N the paramagnetic fraction of Fe decreases down to 150 K and for lower temperatures all the Fe spins are magnetically ordered.

  18. A binuclear Fe(III)Dy(III) single molecule magnet. Quantum effects and models.

    Science.gov (United States)

    Ferbinteanu, Marilena; Kajiwara, Takashi; Choi, Kwang-Yong; Nojiri, Hiroyuki; Nakamoto, Akio; Kojima, Norimichi; Cimpoesu, Fanica; Fujimura, Yuichi; Takaishi, Shinya; Yamashita, Masahiro

    2006-07-19

    The binuclear [FeIII(bpca)(mu-bpca)Dy(NO3)4], having Single Molecule Magnet (SMM) properties, belonging to a series of isostructural FeIIILnIII complexes (Ln = Eu, Gd, Tb, Dy, Ho) and closely related FeIILnIII chain structures, was characterized in concise experimental and theoretical respects. The low temperature magnetization data showed hysteresis and tunneling. The anomalous temperature dependence of Mössbauer spectra is related to the onset of magnetic order, consistent with the magnetization relaxation time scale resulting from AC susceptibility measurements. The advanced ab initio calculations (CASSCF and spin-orbit) revealed the interplay of ligand field, spin-orbit, and exchange effects and probed the effective Ising nature of the lowest states, involved in the SMM and tunneling effects.

  19. Magnetocrystalline two-fold symmetry in CaFe2O4 single crystal

    International Nuclear Information System (INIS)

    Gandhi, Ashish Chhaganlal; Das, Rajasree; Chou, Fang-Cheng; Lin, Jauyn Grace

    2017-01-01

    Understanding of magnetocrystalline anisotropy in CaFe 2 O 4 is a matter of importance for its future applications. A high quality single crystal CaFe 2 O 4 sample is studied by using synchrotron x-ray diffraction, a magnetometer and the electron spin resonance (ESR) technique. A broad feature of the susceptibility curve around room temperature is observed, indicating the development of 1D spin interactions above the on-set of antiferromagnetic transition. The angular dependency of ESR reveals an in-plane two-fold symmetry, suggesting a strong correlation between the room temperature spin structure and magnetocrystalline anisotropy. This finding opens an opportunity for the device utilizing the anisotropy field of CaFe 2 O 4 . (paper)

  20. Growth, structure and magnetic properties of single crystalline Fe/CoO/Ag(001) bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Abrudan, R.M.

    2007-07-16

    The structural and magnetic properties of epitaxially deposited single-crystalline CoO layers and Fe/CoO bilayers on Ag(001) were investigated. CoO films on Ag(001) exhibit (1 x 1) Low Energy Electron Diffraction (LEED) patterns similar to the clean Ag(001) substrate. The vertical interlayer spacing of the CoO films, deduced from a kinematic analysis of LEED I(E) curves, is a {sub perpendicular} {sub to} /2=2.17 Aa, slightly expanded along the film normal. Scanning Tunneling Microscopy (STM) show a big improvement in the surface roughness after annealing the CoO films at 750 K in oxygen atmosphere. Magnetic measurements using the magneto-optical Kerr effect (MOKE) show a characteristic increase of the coercive field when the Fe/CoO bilayer system is cooled down from room temperature to 150 K. The ordering temperature for the antiferromagnetic layer is in the same range as the Neel temperature for bulk CoO (T{sub N}=290 K). X-ray absorption spectroscopy was employed to probe magnetic and electronic properties with elemental selectivity. Absorption spectra taken from bilayers with different amounts of deposited Fe show only a weak indication for the formation of Fe oxide at the Fe/CoO interface (0.3 ML Fe). From the spectral shape it is concluded that an FeO type of oxide is formed. X-ray Magnetic Circular Dichroism (XMCD) measurements exhibit a sizeable induced ferromagnetic signal at the Co L{sub 2,3} absorption edge, corresponding to an interface layer of 1.1 ML in which the magnetic spins couple with the Fe layer. The angular dependence of the X-ray Magnetic Linear Dichroism (XMLD) and X-ray Magnetic Circular Dichroism XMCD at both the Co and Fe L{sub 2,3} edges shows the orientation of the Co and Fe moments in the bilayers with respect to the crystallographic direction. PhotoElectron Emission Microscope (PEEM) is used to image each ferromagnetic and antiferromagnetic layer separately. Magnetic contrast due to the induced magnetic spins at the interface is also

  1. Hydrogenation of the alpha,beta-Unsaturated Aldehydes Acrolein, Crotonaldehyde, and Prenal over Pt Single Crystals: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    Energy Technology Data Exchange (ETDEWEB)

    Kliewer, C.J.; Somorjai, G.A.

    2008-11-26

    Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three {alpha},{beta}-unsaturated aldehydes, acrolein, crotonaldehyde, and prenal, over Pt(111) at Torr pressures (1 Torr aldehyde, 100 Torr hydrogen) in the temperature range of 295K to 415K. SFG-VS data showed that acrolein has mixed adsorption species of {eta}{sub 2}-di-{sigma}(CC)-trans, {eta}{sub 2}-di-{sigma}(CC)-cis as well as highly coordinated {eta}{sub 3} or {eta}{sub 4} species. Crotonaldehyde adsorbed to Pt(111) as {eta}{sub 2} surface intermediates. SFG-VS during prenal hydrogenation also suggested the presence of the {eta}{sub 2} adsorption species, and became more highly coordinated as the temperature was raised to 415K, in agreement with its enhanced C=O hydrogenation. The effect of catalyst surface structure was clarified by carrying out the hydrogenation of crotonaldehyde over both Pt(111) and Pt(100) single crystals while acquiring the SFG-VS spectra in situ. Both the kinetics and SFG-VS showed little structure sensitivity. Pt(100) generated more decarbonylation 'cracking' product while Pt(111) had a higher selectivity for the formation of the desired unsaturated alcohol, crotylalcohol.

  2. Inclusive photoproduction of single charged particles at high pT

    International Nuclear Information System (INIS)

    Apsimon, R.J.; Flower, P.S.; Hallewell, G.; Morris, J.A.G.; Morris, J.V.; Paterson, C.N.; Sharp, P.H.; Atkinson, M.; Brook, N.; Coyle, P.; Dickinson, B.; Donnachie, A.; Doyle, A.T.; Ellison, R.J.; Foster, J.M.; Hughes-Jones, R.E.; Ibbotson, M.; Kolya, S.D.; Lafferty, G.D.; McCann, H.; McManus, C.; Mercer, D.; Ottewell, P.J.; Reid, D.; Thompson, R.J.; Waterhouse, J.; Barberis, D.; Davenport, M.; Eades, J.; McClatchey, R.; Brodbeck, T.J.; Charity, T.; Clegg, A.B.; Henderson, R.C.W.; Hickman, M.T.; Keemer, N.R.; Newton, D.; O'Connor, A.; Wilson, G.W.; Danaher, S.; Galbraith, W.; Thacker, N.A.; Thompson, L.

    1989-01-01

    Single charged-particle inclusive cross sections for photon, pion and kaon beams on hydrogen at the CERN-SPS are presented as functions of p T and x F . Data cover the range 0.0 T F T < 1.6 GeV/c for the photon-induced data. Using the hadron-induced data to estimate the hadronic behaviour of the photon, the difference distributions and ratios of cross sections are a measure of the contribution of the point-like photon interactions. The data are compared with QCD calculations and show broadly similar features. (orig.)

  3. Photon-assisted tunneling in a Fe-8 single-molecule magnet

    OpenAIRE

    Sorace, L.; Wernsdorfer, W.; Thirion, C.; Barra, A. L.; Pacchioni, M.; Mailly, D.; Barbara, B.

    2003-01-01

    The low temperature spin dynamics of a Fe8 Single-Molecule Magnet was studied under circularly polarized electromagnetic radiation allowing us to establish clearly photon-assisted tunneling. This effect, while linear at low power, becomes highly non-linear above a relatively low power threshold. This non-linearity is attributed to the nature of the coupling of the sample to the thermostat.These results are of great importance if such systems are to be used as quantum computers.

  4. Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

    OpenAIRE

    Y Yousefi; H Fakhari; K Muminov; M R Benam

    2018-01-01

    Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3) generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons). For this SMM, it is established that the use of quadrupole excitation (g dependence) changes not only the location of the quenching points, but also the n...

  5. The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet.

    Science.gov (United States)

    Saalfrank, Rolf W; Scheurer, Andreas; Bernt, Ingo; Heinemann, Frank W; Postnikov, Andrei V; Schünemann, Volker; Trautwein, Alfred X; Alam, Mohammad S; Rupp, Holger; Müller, Paul

    2006-06-21

    Star-shaped complex [Fe(III)[Fe(III)(L1)2]3] (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by Mössbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane. The unit cell of 3.4CHCl3 contains the enantiomers (delta)-[(S,S)(R,R)(R,R)] and (lambda)-[(R,R)(S,S)(S,S)], whereas in case of 3.3CH2Cl2 four independent molecules, forming pairs of the enantiomers [lambda-(R,R)(R,R)(R,R)]-3 and [lambda-(S,S)(S,S)(S,S)]-3, were observed in the unit cell. According to SQUID measurements, the antiferromagnetic intramolecular coupling of the iron(III) ions in 3 results in a S = 10/2 ground state multiplet. The anisotropy is of the easy-axis type. EPR measurements enabled an accurate determination of the ligand-field splitting parameters. The ferric star 3 is a single-molecule magnet (SMM) and shows hysteretic magnetization characteristics below a blocking temperature of about 1.2 K. However, weak intermolecular couplings, mediated in a chainlike fashion via solvent molecules, have a strong influence on the magnetic properties. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were used to determine the structural and electronic properties of star-type tetranuclear iron(III) complex 3. The molecules were deposited onto highly ordered pyrolytic graphite (HOPG). Small, regular molecule clusters, two-dimensional monolayers as well as separated single molecules were observed. In our STS measurements we found a rather large contrast at the expected locations of the metal centers of the molecules. This direct addressing of the metal centers was confirmed by DFT calculations.

  6. London penetration depth measurements in Ba (Fe1-xTx)2As2(T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Gordon, Ryan T. [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    The London penetration depth has been measured in various doping levels of single crystals of Ba(Fe1-xTx)2As2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors by utilizing a tunnel diode resonator (TDR) apparatus. All in-plane penetration depth measurements exhibit a power law temperature dependence of the form Δλab(T) = CTn, indicating the existence of low-temperature, normal state quasiparticles all the way down to the lowest measured temperature, which was typically 500 mK. Several different doping concentrations from the Ba(Fe1-xTx)2As2 (T=Co,Ni) systems have been measured and the doping dependence of the power law exponent, n, is compared to results from measurements of thermal conductivity and specific heat. In addition, a novel method has been developed to allow for the measurement of the zero temperature value of the in-plane penetration depth, λab(0), by using TDR frequency shifts. By using this technique, the doping dependence of λab(0) has been measured in the Ba(Fe1-xCox)2As2 series, which has allowed also for the construction of the doping-dependent superfluid phase stiffness, ρs(T) = [λ(0)/λ(T)]2. By studying the effects of disorder on these superconductors using heavy ion irradiation, it has been determined that the observed power law temperature dependence likely arises from pair-breaking impurity scattering contributions, which is consistent with the proposed s±-wave symmetry of the superconducting gap in the dirty scattering limit. This hypothesis is supported by the measurement of an exponential temperature dependence of the penetration depth in the intrinsically clean LiFeAs, indicative of a nodeless superconducting gap.

  7. High-pressure single-crystal neutron scattering study of magnetic and Fe vacancy orders in (Tl,Rb)2Fe4Se5 superconductor

    OpenAIRE

    Ye, Feng; Bao, Wei; Chi, Songxue; Santos, Antonio M. dos; Molaison, Jamie J.; Fang, Minghu; Wang, Hangdong; Wang, Qianhui Mao Jinchen; Liu, Juanjuan; Sheng, Jieming

    2014-01-01

    The magnetic and iron vacancy orders in superconducting (Tl,Rb)2Fe4Se5 single-crystals are investigated by using a high-pressure neutron diffraction technique. Similar to the temperature effect, the block antiferromagnetic order gradually decreases upon increasing pressure while the Fe vacancy superstructural order remains intact before its precipitous disappearance at the critical pressure Pc = 8.3 GPa. Combined with previously determined Pc for superconductivity, our phase diagram under pre...

  8. Synchrotron Based Structural Investigations of Mass-Selected PtxGd Nanoparticles and a Gd/Pt(111) Single Crystal for Electrochemical Oxygen Reduction

    DEFF Research Database (Denmark)

    Pedersen, Anders Filsøe; Velazquez-Palenzuela, Amado Andres; Masini, Federico

    2015-01-01

    The sluggish kinetics of the oxygen reduction reaction (ORR) hinders the commercialization of proton exchange membrane fuel cells (PEMFC). The ORR activity is enhanced by alloying Pt with late transition 3d metals (i.e. Fe, Co, Ni, and Cu)1. However, these compounds tend to degrade in a fuel cell....... In this work, we present the experimental results of mass-selected PtxGd nanoparticles synthesized by gas aggregation after sputtering of an alloy target in an ultrahigh vacuum (UHV)3. PtxGd nanoparticles with nominal sizes of 3, 5, 7, and 9 nm were selected using time-of-flight mass filtering and deposited...... is separated from the Pt5Gd alloy, and the analysis of both diffraction patterns are presented. By investigating such well-defined structures, we gain valuable scientific insight into the relationship between their structure and functionality. On the basis of this insight, we can develop even better catalysts...

  9. Mechanistic insight into the enhanced photocatalytic activity of single-atom Pt, Pd or Au-embedded g-C3N4

    Science.gov (United States)

    Tong, Tong; Zhu, Bicheng; Jiang, Chuanjia; Cheng, Bei; Yu, Jiaguo

    2018-03-01

    Single atoms of platinum (Pt), palladium (Pd) or gold (Au) trapped by two-dimensional graphitic carbon nitride (g-C3N4) exhibit superior photocatalytic performance. However, the underlying mechanism of single-atom noble metal/g-C3N4 photocatalytic system is still unclear. Herein, the structural, electronic and optical properties of single-atom Pt, Pd and Au loaded on bilayer g-C3N4 (BL-g-C3N4) substrate were investigated by density functional theory (DFT) simulations. The results indicate that single-atom Pt/Pd/Au loading can significantly narrow the band gap of g-C3N4 and thus increase its light absorption in the visible-light region. Rather than being adsorbed on the surface, Pt and Pd atoms tend to be embedded into g-C3N4 interlayer and act as bridges to facilitate the interlayer charge carrier transfer due to the effects of conduction band offset. In particular, an internal electric field is generated in Pt/BL-g-C3N4, which is further beneficial for separating charge carrier of photoexcited g-C3N4. By contrast, Au can only be adsorbed on the g-C3N4 surface (in the six-fold cavity) and deliver a limited amount of charge carrier excited in the N-conjugated aromatic pore of g-C3N4 surface. Our finding is conducive to understanding the interactive relationship between single-atom noble metal co-catalysts and g-C3N4 and to the design of high-efficiency photocatalyst.

  10. Microstructure and magnetic properties of FeCo epitaxial thin films grown on MgO single-crystal substrates

    International Nuclear Information System (INIS)

    Shikada, Kouhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-01-01

    FeCo epitaxial films were prepared on MgO(100), MgO(110), and MgO(111) substrates by ultrahigh vacuum molecular beam epitaxy. FeCo thin films with (100), (211), and (110) planes parallel to the substrate surface grow on respective MgO substrates. FeCo/MgO interface structures are studied by high-resolution cross-sectional transmission electron microscopy and the epitaxial growth mechanism is discussed. Atomically sharp boundaries are recognized between the FeCo thin films and the MgO substrates where misfit dislocations are introduced in the FeCo thin films presumably to decrease the lattice misfits. Misfit dislocations are observed approximately every 9 and 1.4 nm in FeCo thin film at the FeCo/MgO(100) and the FeCo/MgO(110) interfaces, respectively. X-ray diffraction analysis indicates that the lattice spacing measured parallel to the single-crystal substrate surfaces are in agreement within 0.1% with those of the respective bulk values of Fe 50 Co 50 alloy crystal, showing that the FeCo film strain is very small. The magnetic anisotropies of these epitaxial films basically reflect the magnetocrystalline anisotropy of bulk FeCo alloy crystal

  11. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

    Science.gov (United States)

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2016-02-08

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

  12. Device for Controlled Distribution of FePt Nanoparticles Formations in a Stream of Liquid Medium under Influence of Magnetic Field

    Directory of Open Access Journals (Sweden)

    Karolis ŠILEIKA

    2014-04-01

    Full Text Available In this research paper a design of magnetic device comprising Halbach arrays which maximizes the magnetic forces acting on magnetic nanoparticles and which can be used for successful steering of said particles to a zone of interest and captured thereat while exhibiting a certain flow and accumulation pattern after injection into a stream of a liquid medium is presented. The aim was to investigate efficiency of such design of a magnetic device for application in magnetic targeting techniques. The presented construction was assembled from 10 magnetic elements having the same dimensions and residual magnetic field, and casing of Plexiglas material. Aggregating of clusters of FePt nanoparticles was evidently successful at preferable region located between two opposing parts of a magnetic device, which was tested for flow rates of (1 – 10 mL/min of main stream medium. To simulate the viscosity of blood a 1.5 % PVP 90 solution was used as the flowing medium. The shallow depth of targeting was chosen for practical reason: to ensure a maximum visibility of particle "steering" pattern obtainable by the magnetic device consisting of two adjacent parts comprising Halbach arrays. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.3371

  13. Binary and tertiary reaction cross-sections of V, Cr, Mn, Fe, Ni, Cu, Zr, Nb, Mo, Ta, W, Pt and their isotopes

    International Nuclear Information System (INIS)

    Garg, S.B.

    1982-01-01

    Neutron induced binary and tertiary reaction cross-sections have been evaluated for V, Cr, Mn, Fe, Ni, Cu, Zr, Nb, Mo, Ta, W, Pt and their isotopes in the 'energy range 0.5 MeV to 20 MeV using the nuclear statistical empirical model. The reactions considered are (n,n'), (n,2n), (n,3n), (n,p), (n,d), (n,t), (n, 3 He), (n,α), (n,np), (n,nd), (n,nt), (n,n 3 He), (n,nα), (n,pn), (n,2p), (n,ν), (n,αp), (n,dn) and (n,pα). Most of the above mentioned elements are used as structural materials in nuclear reactors and the measured cross-section data for the above listed reactions are seldom available for the radiation damage and safety analysis. With a view to providing these data, this nuclear model based evaluation has been undertaken. The associated uncertainties in the cross-sections and their fission averages have also been evaluated. (author)

  14. Cell characteristics of FePt nano-dot memories with a high-k Al2O3 blocking oxide

    International Nuclear Information System (INIS)

    Lee, Gae Hun; Lee, Jung Min; Yang, Hyung Jun; Song, Yun Heub; Bea, Ji Cheol; Tanaka, Testsu

    2012-01-01

    The cell characteristics of an alloy FePt nano-dot (ND) charge trapping memory with a high-k dielectric as a blocking oxide was investigated. Adoption of a high-k Al 2 O 3 material as a blocking oxide for the metal nano-dot memory provided a superior scaling of the operation voltage compared to silicon oxide under a similar gate leakage level. For the 40-nm-thick high-k (Al 2 O 3 ) blocking oxide, we confirmed an operation voltage reduction of ∼7 V under the same memory window on for silicon dioxide. Also, this device showed a large memory window of 7.8 V and a low leakage current under 10 -10 A in an area of Φ 0.25 mm. From these results, the use of a dielectric (Al 2 O 3 ) as a blocking oxide for a metal nano-dot device is essential, and a metal nano-dot memory with a high-k dielectric will be one of the candidates for a high-density non-volatile memory device.

  15. Encapsulation of Ni0.8Zn0.2Fe2O4 single crystals in multiwall carbon nanotubes.

    Science.gov (United States)

    Yahya, Noorhana; Akhtar, Majid Niaz; Koziol, Krzysztof

    2012-10-01

    Magnetic nanoparticles in the hollow region of carbon nanotubes have attraction due to their changing physical electrical and magnetic properties. Nickel zinc ferrite plays an important role in many applications due to its superior magnetic properties. Ni0.8Zn0.2Fe2O4 single crystals were encapsulated in multiwall carbon nanotubes (MWCNTs). The magnetic nano crystals were prepared using a sol-gel self combustion method at the sintering temperature of 750 degrees C and were characterized by XRD, FESEM, TEM and VSM. Initial permeability, Q-factor and relative loss factor were measured by impedance vector network analyzer. XRD patterns were used for the phase identification. FESEM images show morphology and dimensions of the grains of Ni0.8Zn0.2Fe2O4 single crystals and Ni0.8Zn0.2Fe2O4 single crystals in MWCNTs. TEM images were used to investigate single crystal and encapsulation of Ni0.8Zn0.2Fe2O4 single crystals in the MWCNTs. VSM results confirmed super paramagnetic behaviour of encapsulated Ni0.8Zn0.2Fe2O4 single crystals. It was also attributed that encapsulated Ni0.8Zn0.2Fe2O4 single crystals in MWCNTs showed a higher initial permeability (51.608), Q-factor (67.069), and low loss factor (0.0002) as compared to Ni0.8Zn0.2Fe2O4 single crystals. The new encapsulated Ni0.8Zn0.2Fe2O4 single crystals in the MWCNTs may have potential applications in electronic and medical industries.

  16. Study on the effect of the metal-support (Fe-MgO and Pt-MgO) interaction in alcohol-CVD synthesis of carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Steplewska, Anna, E-mail: asteplewska@zut.edu.pl; Borowiak-Palen, Ewa [West Pomeranian University of Technology, Centre of Knowledge Based Nanomaterials and Technologies, Institute of Chemical and Environment Engineering (Poland)

    2011-05-15

    This study presents the effect of the metal-support interaction in two systems: (1) iron particle, and (2) platinum particles, being supported on magnesium oxide (MgO) nanopowder in alcohol-CVD process for carbon nanotubes (CNTs) growth. The employment of the different metals but the same substrate (with equal molar ratio) resulted in the synthesis of single-walled CNTs (SWCNTs) or double-walled CNTs (DWCNTs), using iron and platinum, respectively. Furthermore, along with the prolongation of the process time, the decrease of the mean nanotubes diameter in case of iron-catalyzed materials was detected. Interestingly, the extention of the growth time in the synthesis using Pt/MgO resulted in the synthesis of the thicker mean nanotubes diameter. However, for both applied catalytic systems the reduction of the diameter distribution of the tubes and the increase of relative purity of the samples upon the growth time increase were detected.

  17. Synthesis of R/sub 2/Fe/sub 14/B single crystals

    International Nuclear Information System (INIS)

    Das, B.N.; Koon, N.C.

    1987-01-01

    Single crystals of R/sub 2/Fe/sub 14/B weighing 5 to 15 g were grown from a liquid melt by tri-arc and levitation Czochralski methods. The arc method was used for the growth of smaller size crystals from 5 to 7 g, and the levitation method was used for the growth of larger sizes, from 10 to 15 g. Crystals of (R/sub 1/)/sub 2-x/(R/sub 2/)/sub x/Fe/sub 14/B could also be grown with isomorphous replacement of rare earth atoms. The starting alloy composition for the crystal growth process was chosen based on solidification microstructure. In this paper the authors discuss the solidification microstructure, isomorphous replacement, seeding and their interactions with the crystal growth processes and crystal quality

  18. Direct versus ligand-exchange synthesis of [PtAg28(BDT)12(TPP)4]4-nanoclusters: effect of a single-atom dopant on the optoelectronic and chemical properties.

    Science.gov (United States)

    Bootharaju, Megalamane S; Kozlov, Sergey M; Cao, Zhen; Harb, Moussab; Parida, Manas R; Hedhili, Mohamed N; Mohammed, Omar F; Bakr, Osman M; Cavallo, Luigi; Basset, Jean-Marie

    2017-07-13

    Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg 28 NCs produces a mixture of [Ag 29 (BDT) 12 (TPP) 4 ] 3- and [PtAg 28 (BDT) 12 (TPP) 4 ] 4- NCs (TPP: triphenylphosphine; BDT: 1,3-benzenedithiolate). Here, we designed a ligand-exchange (LE) strategy to synthesize single-sized, Pt-doped, superatomic Ag NCs [PtAg 28 (BDT) 12 (TPP) 4 ] 4- by LE of [Pt 2 Ag 23 Cl 7 (TPP) 10 ] NCs with BDTH 2 (1,3-benzenedithiol). The doped NCs were thoroughly characterized by optical and photoelectron spectroscopy, mass spectrometry, total electron count, and time-dependent density functional theory (TDDFT). We show that the Pt dopant occupies the center of the PtAg 28 cluster, modulates its electronic structure and enhances its photoluminescence intensity and excited-state lifetime, and also enables solvent interactions with the NC surface. Furthermore, doped NCs showed unique reactivity with metal ions - the central Pt atom of PtAg 28 could not be replaced by Au, unlike the central Ag of Ag 29 NCs. The achieved synthesis of single-sized PtAg 28 clusters will facilitate further applications of the LE strategy for the exploration of novel multimetallic NCs.

  19. Direct versus ligand-exchange synthesis of [PtAg28(BDT)12(TPP)4]4− nanoclusters: effect of a single-atom dopant on the optoelectronic and chemical properties

    KAUST Repository

    Bootharaju, Megalamane Siddaramappa

    2017-06-07

    Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg28 NCs produces a mixture of [Ag29(BDT)12(TPP)4]3- and [PtAg28(BDT)12(TPP)4]4- NCs (TPP: triphenylphosphine; BDT: 1,3-benzenedithiolate). Here, we designed a ligand-exchange (LE) strategy to synthesize single-sized, Pt-doped, superatomic Ag NCs [PtAg28(BDT)12(TPP)4]4- by LE of [Pt2Ag23Cl7(TPP)10] NCs with BDTH2 (1,3-benzenedithiol). The doped NCs were thoroughly characterized by optical and photoelectron spectroscopy, mass spectrometry, total electron count, and time-dependent density functional theory (TDDFT). We show that the Pt dopant occupies the center of the PtAg28 cluster, modulates its electronic structure and enhances its photoluminescence intensity and excited-state lifetime, and also enables solvent interactions with the NC surface. Furthermore, doped NCs showed unique reactivity with metal ions - the central Pt atom of PtAg28 could not be replaced by Au, unlike the central Ag of Ag29 NCs. The achieved synthesis of single-sized PtAg28 clusters will facilitate further applications of the LE strategy for the exploration of novel multimetallic NCs.

  20. Pt, Co–Pt and Fe–Pt alloy nanoclusters encapsulated in virus capsids

    International Nuclear Information System (INIS)

    Okuda, M; Eloi, J-C; Jones, S E Ward; Schwarzacher, W; Verwegen, M; Cornelissen, J J L M

    2016-01-01

    Nanostructured Pt-based alloys show great promise, not only for catalysis but also in medical and magnetic applications. To extend the properties of this class of materials, we have developed a means of synthesizing Pt and Pt-based alloy nanoclusters in the capsid of a virus. Pure Pt and Pt-alloy nanoclusters are formed through the chemical reduction of [PtCl 4 ] − by NaBH 4 with/without additional metal ions (Co or Fe). The opening and closing of the ion channels in the virus capsid were controlled by changing the pH and ionic strength of the solution. The size of the nanoclusters is limited to 18 nm by the internal diameter of the capsid. Their magnetic properties suggest potential applications in hyperthermia for the Co–Pt and Fe–Pt magnetic alloy nanoclusters. This study introduces a new way to fabricate size-restricted nanoclusters using virus capsid. (paper)

  1. Single-crystalline M-type Sr Hexaferrites studied by {sup 57}Fe Mössbauer spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Nagasawa, Nobumoto, E-mail: rk15v002@stkt.u-hyogo.ac.jp; Ikeda, Shugo [University of Hyogo, Graduate School of Material Science and Center for Novel Material Science under Multi-extreme Conditions (Japan); Shimoda, Aiko; Waki, Takeshi; Tabata, Yoshikazu; Nakamura, Hiroyuki [Kyoto University, Department of Material Science and Engineering (Japan); Kobayashi, Hisao [University of Hyogo, Graduate School of Material Science and Center for Novel Material Science under Multi-extreme Conditions (Japan)

    2016-12-15

    The {sup 57}Fe Mössbauer spectra of the single crystalline and the finely ground Sr{sub 1−x}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe{sup 2+} ions in the Fe{sup 3+} ions were not observed in our Sr{sub 1−x}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} samples. In SrFe{sub 12}O{sub 19}, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr{sub 0.544}La{sub 0.456}Fe{sub 11.775}Co{sub 0.225}O{sub 19}. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co{sup 2+} ion for the Fe{sup 3+} ion changes the center shifts of the Fe{sup 3+} ions near the Co{sup 2+} ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co{sup 2+} ions occupy the 4f{sub 1} and the 4f{sub 2} sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe{sup 3+} ions.

  2. Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction.

    Science.gov (United States)

    Goto, Sho; Kura, Hiroaki; Watanabe, Eiji; Hayashi, Yasushi; Yanagihara, Hideto; Shimada, Yusuke; Mizuguchi, Masaki; Takanashi, Koki; Kita, Eiji

    2017-10-16

    Tetrataenite (L1 0 -FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L1 0 -FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L1 0 -FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to derive single-phase L1 0 -FeNi with an order parameter of 0.71. The transformation of disordered-phase FeNi into the L1 0 phase increased the coercive force from 14.5 kA/m to 142 kA/m. The proposed method not only significantly accelerates the development of magnets using L1 0 -FeNi but also offers a new synthesis route to obtain ordered alloys in non-equilibrium states.

  3. Solid state single crystal growth of three-dimensional faceted LaFeAsO crystals

    Science.gov (United States)

    Kappenberger, Rhea; Aswartham, Saicharan; Scaravaggi, Francesco; Blum, Christian G. F.; Sturza, Mihai I.; Wolter, Anja U. B.; Wurmehl, Sabine; Büchner, Bernd

    2018-02-01

    Solid state single crystal growth (SSCG) is a crystal growth technique where crystals are grown from a polycrystalline matrix. Here, we present single crystals of the iron pnictide LaFeAsO grown via SSCG using NaAs as a liquid phase to aid crystallization. The size of the as-grown crystals are up to 2 × 3 × 0.4 mm3. Typical for this method, but very uncommon for crystals of the pnictide superconductors and especially for the oxypnictides, the crystals show pronounced facets caused by considerable growth in c direction. The crystals were characterized regarding their composition, structure, magnetic, and thermodynamic properties. This sets the stage for further measurements for which single crystals are crucial such as any c axis and reciprocal space dependent measurements.

  4. An internal magnetic field strategy to reuse pulverized active materials for high performance: a magnetic three-dimensional ordered macroporous TiO2/CoPt/α-Fe2O3 nanocomposite anode.

    Science.gov (United States)

    Tang, Yiping; Hong, Liang; Li, Jiquan; Hou, Guangya; Cao, Huazhen; Wu, Liankui; Zheng, Guoqu; Wu, Qingliu

    2017-05-09

    A ferromagnetic three-dimensional ordered macroporous TiO 2 /CoPt/α-Fe 2 O 3 (3DOMTCF) nanocomposite was synthesized via a sol-gel approach templated by poly(methyl methacrylate) (PMMA) microspheres. After magnetization, it exhibited an extremely high reversible capacity and a long cycle life, which were ascribed to the internal magnetic field for reusing pulverized active materials and its unique structure.

  5. Alliages magnétiques FePd et FePt en couches minces sous contrainte épitaxiale : mise en ordre en température et propriétés magnétiques

    Science.gov (United States)

    Arenal de La Concha, R.; Schuster, I.; Halley, D.; Marty, A.; Bayle-Guillemaud, P.

    2002-07-01

    In order to increase the storage capacities of the media of magnetic recording one seeks to decrease the size of the magnetic fields which carry information. The growth of thin layers of magnetic alloys in ordered phases makes it possible to plan structures with very strong perpendicular magnetic anisotropy, necessary to obtain stable fields in spite of their reduced size. We studied, thanks to an original device of in temperature X-rays diffraction, the ordering of FePd layers or FePt deposited by MBE in different states of initial order and constraint, then submitted to heat treatment. The ordering occured along the growth axis. The structure of the layers is very inhomogeneous: not ordered and ordered domains coexist, with or without defect in the stacking of the L10 phase, even domains of other phases. The small zones, which have been ordered during the growth, do not seem to take part in the development of the long range order during the treatment. The evolution of the ordered fraction is identical whatever the imposed state of epitaxial stress. Modifications of the experimental conditions make it possible from now to plan more systematic measurements with a temperature history more rigorous in order to confirm these observations. Afin d'augmenter les capacités de stockage des media d'enregistre ment magnétique, on cherche à diminuer la taille des domaines magnétiques qui portent l'information. L'élaboration de couches minces d'alliages magnétiques dans des phases ordonnées permet d'envisager des structures à très forte anisotropie magnétique perpendiculaire, nécessaire pour obtenir des domaines stables malgré leur taille réduite. Nous avons étudié, grâce à un dispositif original de diffraction X en température, la mise en ordre de couches FePd ou FePt déposées par MBE dans des états différents d'ordre initial et de contrainte. La mise en ordre se fait selon l'axe de croissance. La structure des couches est très inhomogène : coexistent

  6. Cyclic Deformation Behavior of Aged FeNiCoAlTa Single Crystals

    Science.gov (United States)

    Krooß, P.; Niendorf, T.; Karaman, I.; Chumlyakov, Y.; Maier, H. J.

    2012-11-01

    The cyclic deformation behavior of [001] oriented Fe-28Ni-17Co-11.5Al-2.5Ta (at.%) shape memory single crystals was investigated under tension. Dog-bone shaped specimens were tested up to 100 cycles after different aging heat treatments in order to characterize the cyclic stress-strain response and functional degradation. The smaller particles formed as a consequence of short aging for 1 h at 700°C, as compared to longer aging for 7 h, resulted in significantly enhanced resistance to cyclic degradation.

  7. Photon-assisted tunneling in a Fe8 single-molecule magnet

    Science.gov (United States)

    Sorace, L.; Wernsdorfer, W.; Thirion, C.; Barra, A.-L.; Pacchioni, M.; Mailly, D.; Barbara, B.

    2003-12-01

    The low-temperature spin dynamics of a Fe8 single-molecule magnet was studied under circularly polarized electromagnetic radiation allowing us to establish clearly photon-assisted tunneling. This effect, while linear at low power, becomes highly nonlinear above a relatively low-power threshold. Heating due to phonon emission, spin-spin interactions, and coherent emission/absorption of photons might lead to the observed nonlinearity. These results are of importance if such systems are to be used as quantum computers.

  8. Effects of a single high dose of 55Fe in mice

    International Nuclear Information System (INIS)

    Laissue, J.A.; Burlington, H.; Cronkite, E.P.; Heldman, B.; Reincke, U.

    1979-01-01

    High doses of 55 Fe induced cytocide in maturing erythroid cells, due to the short-range deposition of decay energy. Organ damage at the time of death was evaluated in a group of 45 female mice of the C 57 BL/6 J strain given a single i.v. injection of 2,800 μCi, 1,400 μCi or 700 μCi of 55 FeCl 3 when 10 to 14 weeks old. A corresponding amount of cold iron was given to control animals by the same route. Radioiron-treated mice died spontaneously, or were killed when moribund. Mice given 2,800 μCi died after a median survival time of 27 days with severe depletion of hemopoietic cells in bone marrow and spleen, marked atrophy of lymphoid tissues and mild liver damage. After 1,400 μCi or 700 μCi, the median survival time was 117 and 439, respectively. In contrast, median survival was 847 days in control animals allowed to survive. In the two lower 55 Fe-dose groups, there was a dose-dependent pancytopenia. Atrophy of lymphoid tissues was moderate, and signs of liver damage slight. The degree of organ hemosiderosis in experimental and control animals was slight to moderate. Organ damage associated with deposition of cold iron was not apparent in tissue sections. Morphological signs of damage to non-hemopoietic organs such as the liver were not conspicuous. Direct radiation damage, primarily to the erythroid series, and competition for stem cells between the heavily depleted erythroid and the other hemopoietic cell lines must be considered among the possible factors leading to pancytopenia. Out of 14 55 Fe-treated mice who survived longer than 300 days developed tumors of hemopoietic and lymphoid tissues, or osteosarcomas. (orig./MG) [de

  9. Single-Atom Au/NiFe Layered Double Hydroxide Electrocatalyst: Probing the Origin of Activity for Oxygen Evolution Reaction.

    Science.gov (United States)

    Zhang, Jingfang; Liu, Jieyu; Xi, Lifei; Yu, Yifu; Chen, Ning; Sun, Shuhui; Wang, Weichao; Lange, Kathrin M; Zhang, Bin

    2018-03-21

    A fundamental understanding of the origin of oxygen evolution reaction (OER) activity of transition-metal-based electrocatalysts, especially for single precious metal atoms supported on layered double hydroxides (LDHs), is highly required for the design of efficient electrocatalysts toward further energy conversion technologies. Here, we aim toward single-atom Au supported on NiFe LDH ( s Au/NiFe LDH) to clarify the activity origin of LDHs system and a 6-fold OER activity enhancement by 0.4 wt % s Au decoration. Combining with theoretical calculations, the active behavior of NiFe LDH results from the in situ generated NiFe oxyhydroxide from LDH during the OER process. With the presence of s Au, s Au/NiFe LDH possesses an overpotential of 0.21 V in contrast to the calculated result (0.18 V). We ascribe the excellent OER activity of s Au/NiFe LDH to the charge redistribution of active Fe as well as its surrounding atoms causing by the neighboring s Au on NiFe oxyhydroxide stabilized by interfacial CO 3 2- and H 2 O interfacing with LDH.

  10. Preparation and structural characterization of FeCo epitaxial thin films on insulating single-crystal substrates

    International Nuclear Information System (INIS)

    Nishiyama, Tsutomu; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2010-01-01

    FeCo epitaxial films were prepared on MgO(111), SrTiO 3 (111), and Al 2 O 3 (0001) single-crystal substrates by ultrahigh vacuum molecular beam epitaxy. The effects of insulating substrate material on the film growth process and the structures were investigated. FeCo(110) bcc films grow on MgO substrates with two type domains, Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS) relationships. On the contrary, FeCo films grown on SrTiO 3 and Al 2 O 3 substrates include FeCo(111) bcc crystal in addition to the FeCo(110) bcc crystals with NW and KS relationships. The FeCo(111) bcc crystal consists of two type domains whose orientations are rotated around the film normal by 180 deg. each other. The out-of-plane and the in-plane lattice spacings of FeCo(110) bcc and FeCo(111) bcc crystals formed on the insulating substrates are in agreement with those of the bulk Fe 50 Co 50 (at. %) crystal with small errors ranging between +0.2% and +0.4%, showing that the strains in the epitaxial films are very small.

  11. Electronic origin of high-temperature superconductivity in single-layer FeSe superconductor.

    Science.gov (United States)

    Liu, Defa; Zhang, Wenhao; Mou, Daixiang; He, Junfeng; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Zhao, Lin; He, Shaolong; Peng, Yingying; Liu, Xu; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Hu, Jiangping; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2012-07-03

    The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (T(c)) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-T(c) superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature T(c)~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-T(c) superconductivity in iron-based superconductors.

  12. Temperature induced Spin Switching in SmFeO3 Single Crystal

    Science.gov (United States)

    Cao, Shixun; Zhao, Huazhi; Kang, Baojuan; Zhang, Jincang; Ren, Wei

    2014-08-01

    The prospect of controlling the magnetization (M) of a material is of great importance from the viewpoints of fundamental physics and future applications of emerging spintronics. A class of rare-earth orthoferrites RFeO3 (R is rare-earth element) materials exhibit striking physical properties of spin switching and magnetization reversal induced by temperature and/or applied magnetic field. Furthermore, due to the novel magnetic, magneto-optic and multiferroic properties etc., RFeO3 materials are attracting more and more interests in recent years. We have prepared and investigated a prototype of RFeO3 materials, namely SmFeO3 single-crystal. And we report magnetic measurements upon both field cooling (FC) and zero-field cooling (ZFC) of the sample, as a function of temperature and applied magnetic field. The central findings of this study include that the magnetization of single-crystal SmFeO3 can be switched by temperature, and tuning the magnitude of applied magnetic field allows us to realize such spin switching even at room temperature.

  13. Weak superconducting pairing and a single isotropic energy gap in stoichiometric LiFeAs.

    Science.gov (United States)

    Inosov, D S; White, J S; Evtushinsky, D V; Morozov, I V; Cameron, A; Stockert, U; Zabolotnyy, V B; Kim, T K; Kordyuk, A A; Borisenko, S V; Forgan, E M; Klingeler, R; Park, J T; Wurmehl, S; Vasiliev, A N; Behr, G; Dewhurst, C D; Hinkov, V

    2010-05-07

    We report superconducting (SC) properties of stoichiometric LiFeAs (T(c)=17 K) studied by small-angle neutron scattering (SANS) and angle-resolved photoemission (ARPES). Although the vortex lattice exhibits no long-range order, well-defined SANS rocking curves indicate better ordering than in chemically doped 122 compounds. The London penetration depth lambda(ab)(0)=210+/-20 nm, determined from the magnetic field dependence of the form factor, is compared to that calculated from the ARPES band structure with no adjustable parameters. The temperature dependence of lambda(ab) is best described by a single isotropic SC gap Delta(0)=3.0+/-0.2 meV, which agrees with the ARPES value of Delta(0)(ARPES)=3.1+/-0.3 meV and corresponds to the ratio 2Delta/k(B)T(c)=4.1+/-0.3, approaching the weak-coupling limit predicted by the BCS theory. This classifies LiFeAs as a weakly coupled single-gap superconductor.

  14. Scattering of atomic and molecular ions from single crystal surfaces of Cu, Ag and Fe

    International Nuclear Information System (INIS)

    Zoest, J.M. van.

    1986-01-01

    This thesis deals with analysis of crystal surfaces of Cu, Ag and Fe with Low Energy Ion scattering Spectroscopy (LEIS). Different atomic and molecular ions with fixed energies below 7 keV are scattered by a metal single crystal (with adsorbates). The energy and direction of the scattered particles are analysed for different selected charge states. In that way information can be obtained concerning the composition and atomic and electronic structure of the single crystal surface. Energy spectra contain information on the composition of the surface, while structural atomic information is obtained by direction measurements (photograms). In Ch.1 a description is given of the experimental equipment, in Ch.2 a characterization of the LEIS method. Ch.3 deals with the neutralization of keV-ions in surface scattering. Two different ways of data interpretation are presented. First a model is treated in which the observed directional dependence of neutralization action of the first atom layer of the surface is presented by a laterally varying thickness of the neutralizing layer. Secondly it is shown that the data can be reproduced by a more realistic, physical model based on atomic transition matrix elements. In Ch.4 the low energy hydrogen scattering is described. The study of the dissociation of H 2 + at an Ag surface r0230ted in a model based on electronic dissociation, initialized by electron capture into a repulsive (molecular) state. In Ch.5 finally the method is applied to the investigation of the surface structure of oxidized Fe. (Auth.)

  15. Synaptic Plasticity and Learning Behaviors Mimicked in Single Inorganic Synapses of Pt/HfOx/ZnOx/TiN Memristive System

    Science.gov (United States)

    Wang, Lai-Guo; Zhang, Wei; Chen, Yan; Cao, Yan-Qiang; Li, Ai-Dong; Wu, Di

    2017-01-01

    In this work, a kind of new memristor with the simple structure of Pt/HfOx/ZnOx/TiN was fabricated completely via combination of thermal-atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). The synaptic plasticity and learning behaviors of Pt/HfOx/ZnOx/TiN memristive system have been investigated deeply. Multilevel resistance states are obtained by varying the programming voltage amplitudes during the pulse cycling. The device conductance can be continuously increased or decreased from cycle to cycle with better endurance characteristics up to about 3 × 103 cycles. Several essential synaptic functions are simultaneously achieved in such a single double-layer of HfOx/ZnOx device, including nonlinear transmission properties, such as long-term plasticity (LTP), short-term plasticity (STP), and spike-timing-dependent plasticity. The transformation from STP to LTP induced by repetitive pulse stimulation is confirmed in Pt/HfOx/ZnOx/TiN memristive device. Above all, simple structure of Pt/HfOx/ZnOx/TiN by ALD technique is a kind of promising memristor device for applications in artificial neural network.

  16. A sensitive sandwich-type immunosensor for the detection of galectin-3 based on N-GNRs-Fe-MOFs@AuNPs nanocomposites and a novel AuPt-methylene blue nanorod.

    Science.gov (United States)

    Tang, Zhiyong; He, Junlin; Chen, Jun; Niu, Yazhen; Zhao, Yilin; Zhang, Yuchan; Yu, Chao

    2018-03-15

    We are presenting an electrochemical immunosensor for the determination of Galectin-3 (Gal-3), a biomarker of heart failure. A glassy carbon electrode (GCE) was modified with a film of a composite made from the N-doped graphene nanoribbons immobilized Fe-based-Metal-organic frameworks deposited with Au nanoparticles (N-GNRs-Fe-MOFs@AuNPs). Primary antibody against Gal-3 (Gal-3-Ab 1 ) was immobilized on the Au nanoparticles on the surface of the modified GCE which then was blocked with bovine serum albumin. Signal amplification is crucial for obtaining low detection limits in biosensors. Here, a relatively simple and ultrasensitive sandwich-type electrochemical immunosensor based on novel signal generation and amplification was developed for the determination of Gal-3. A kind of novel redox-active species, AuPt-Methylene blue (MB) (AuPt-MB) nanocomposites, was synthesized by a one-pot method for the first time. Wherein, MB as a kind of the electron transfer mediators in an amperometric biosensor is responsible for electron production and signal amplification. The rod-like AuPt-MB nanohybrids displayed uniform morphology and good electrochemical activity and can combine with the second antibodies against Gal-3 (Gal-3-Ab 2 ). And the AuPt-MB-Ab 2 coupled with the N-GNRs-Fe-MOFs@AuNPs-Ab 1 to form the sandwich type format that can greatly enhance the biosensor's sensitivity. Under optimal conditions, the designed immunosensor exhibited a linear concentration range from 100fgmL -1 to 50ngmL -1 , with a low detection limit of 33.33fgmL -1 (S/N = 3) for Gal-3 in spiked serum. Additionally, the designed immunosensor showed acceptable selectivity, reproducibility and stability. The satisfactory results in analyzing human serum samples indicated potential application promising in monitoring biomarkers. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Population Pharmacokinetic Modelling of FE 999049, a Recombinant Human Follicle-Stimulating Hormone, in Healthy Women After Single Ascending Doses

    OpenAIRE

    Rose, Trine H?yer; R?shammar, Daniel; Erichsen, Lars; Grundemar, Lars; Ottesen, Johnny T.

    2016-01-01

    Objective The purpose of this analysis was to develop a population pharmacokinetic model for a novel recombinant human follicle-stimulating hormone (FSH) (FE 999049) expressed from a human cell line of foetal retinal origin (PER.C6?) developed for controlled ovarian stimulation prior to assisted reproductive technologies. Methods Serum FSH levels were measured following a single subcutaneous FE 999049 injection of 37.5, 75, 150, 225 or 450?IU in 27 pituitary-suppressed healthy female subjects...

  18. Dependency of tunneling magnetoresistance ratio on Pt seed-layer thickness for double MgO perpendicular magnetic tunneling junction spin-valves with a top Co2Fe6B2 free layer ex-situ annealed at 400 °C.

    Science.gov (United States)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-02

    For the double MgO based perpendicular magnetic tunneling junction (p-MTJ) spin-valves with a top Co 2 Fe 6 B 2 free layer ex situ annealed at 400 °C, the tunneling-magnetoresistance ratio (TMR) strongly depended on the platinum (Pt) seed layer thickness (t Pt ): it peaked (∼134%) at a specific t Pt (3.3 nm). The TMR ratio was initially and slightly increased from 113%-134% by the enhancement of the magnetic moment of the Co 2 Fe 6 B 2 pinned layer when t Pt increased from 2.0-3.3 nm, and then rapidly decreased from 134%-38.6% by the degrading face-centered-cubic crystallinity of the MgO tunneling barrier when t Pt increased from 3.3-14.3 nm.

  19. Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

    Directory of Open Access Journals (Sweden)

    Y Yousefi

    2018-02-01

    Full Text Available Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3 generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons. For this SMM, it is established that the use of quadrupole excitation (g dependence changes not only the location of the quenching points, but also the number of these points. Also, these quenching points are the steps in hysteresis loops of this SMM. If dipole and quadrupole excitations in classical energy considered, the number of these steps equals to the number that obtained from experimental data.

  20. Biodistribution and dosimetry of 195mPt-cisplatin in normal volunteers. Imaging agent for single photon emission computed tomography.

    Science.gov (United States)

    Sathekge, M; Wagener, J; Smith, S V; Soni, N; Marjanovic-Painter, B; Zinn, C; Van de Wiele, C; D'Asseler, Y; Perkins, G; Zeevaart, J R

    2013-12-13

    195mPt-cisplatin is regarded as a promising imaging agent for optimizing dosage in patients receiving cisplatin chemotherapy. We investigated the whole-body distribution and radiation dosimetry of 195mPt-cisplatin in humans. Whole-body scans were obtained up to 144 h after intravenous injection of 112.4 MBq 195mPt-cisplatin in each of five subjects. Blood samples were taken at various times up to 144 h after injection. Urine was collected up to 114 h after injection for calculation of renal clearance and whole-body clearance. Time/activity curves were generated by fitting the organ-specific geometric mean counts, obtained from regions of interest, on the respective images as a function of the time after injection. OLINDA software package was applied to calculate the absorbed radiation dose for various organs. Most of the activity (32 ± 4%) was excreted in the urine during the first 5 h. The effective clearance half-life derived from extrapolation of the whole-body curve was 40 hours (1.7 days). On average, the highest dose was received by the kidneys (mean dose received 2.68 ± 1.5 mGy/MBq), followed by the spleen (mean dose received 1.6 ± 0.8 mGy/MBq) followed by the liver (mean dose received 1.45 ± 0.38 mGy/MBq). The estimated mean effective dose for the adult subject was 0.185 ± 0.034 mSv/MBq. 195mPt-cisplatin proved a safe radiopharmaceutical with a favourable biodistribution for early and delayed imaging of pathology above the diaphragm. The ED obtained was 0.185 ± 0.034 mSv/MBq. The highest organ dose was received by the kidneys (2.68 ± 1.5 mGy/MBq).

  1. Thermal expansion and magnetostriction of UPd 3 and U(Pd 1- xPt x) 3 single crystals

    Science.gov (United States)

    Zochowski, S. W.; McEwen, K. A.

    1994-04-01

    The localised-moment system UPd 3 exhibits quadrupolar and magnetic phase transitions, at T1 ≈ 7 K and T2 ≈ 4.5 K, respectively. We have followed the magnetic field dependence of the transitions in thermal expansion and magnetostriction measurements. The thermal expansion is large and highly anisotropic, as is the magnetostriction below T2. The transitions are extremely sensitive to Pt doping.

  2. Spatiotemporal dynamics of the spin transition in [Fe (HB(tz)3) 2] single crystals

    Science.gov (United States)

    Ridier, Karl; Rat, Sylvain; Shepherd, Helena J.; Salmon, Lionel; Nicolazzi, William; Molnár, Gábor; Bousseksou, Azzedine

    2017-10-01

    The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe (HB (tz )3)2] (tz = 1 ,2 ,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of ˜1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 µm/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin → high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø = 2 μ m ) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.

  3. Dielectric properties of layered FeGaInS{sub 4} single crystals in an alternating electric field

    Energy Technology Data Exchange (ETDEWEB)

    Mammadov, F. M. [Azerbaijan National Academy of Sciences, Nagiyev Institute of Catalysis and Inorganic Chemistry (Azerbaijan); Niftiyev, N. N., E-mail: namiq7@bk.ru [Azerbaijan State Pedagogical University (Azerbaijan)

    2016-09-15

    The results of investigations of the frequency and temperature dependences of dielectric losses and the imaginary part of the dielectric permittivity in FeGaInS{sub 4} single crystals are presented. Their experimental values are determined. It is established that the loss tangent and the imaginary part of the permittivity of FeGaInS{sub 4} single crystals in a field with frequencies of 10{sup 4}–10{sup 6} Hz decrease inversely proportional to the frequency (tanδ ~ 1/ω), and the conductivity is characterized by the band–hopping mechanism. For FeGaInS{sub 4}, the relaxation time is calculated, and it is established that there is a mechanism of electron polarization caused by thermal motion in this crystal.

  4. Experimental and theoretical studies of vibrational density of states in Fe3O4 single-crystalline thin films

    NARCIS (Netherlands)

    Handke, B; Kozlowski, A; Parlinski, K; Przewoznik, J; Slezak, T; Chumakov, AI; Niesen, L; Kakol, Z; Korecki, J

    This paper presents experimental and theoretical studies of lattice vibrations in a single-crystalline Fe3O4(001) thin film. The investigations were carried out in order to see how the lattice dynamics changes at the Verwey transition. Vibrational densities of states (DOS) were obtained from nuclear

  5. Preparation of Nd{sub 2}Fe{sub 14}B nanoparticles under femtosecond laser ablation in liquid

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, T; Shimotsuma, Y; Sakakura, M; Nishi, M; Miura, K; Hirao, K [Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, 615-8510 (Japan); Sagawa, M, E-mail: yamamoto@curl1.kuic.kyoto-u.ac.jp [Intermetallics CO., LTD., Kyoto, 615-8245 (Japan)

    2011-10-29

    Nd{sub 2}Fe{sub 14}B and FePt nanoparticles with a diameter below the diffraction limit of laser light were successfully prepared by an ultrashort pulse laser ablation in cyclohexane. The self-passivating amorphous carbon layer resulting from the fragmentation of the surrounding solvent prevents the nanoparticle from aggregation and oxidation. The coercivity of the Nd{sub 2}Fe{sub 14}B nanoparticles smaller than the critical single domain size was about 2.2 times as high as that of the initial Nd{sub 2}Fe{sub 14}B particles in spite of the decrease in crystallinity. Furthermore, the coercivity of the FePt nanoparticles after heat treatment dramatically increased, which was about 20 times higher than that of the initial FePt sample.

  6. Electron transport in a Pt-CO-Pt nanocontact: Density functional theory calculations

    DEFF Research Database (Denmark)

    Strange, Mikkel; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2006-01-01

    We have performed first-principles calculations for the mechanic and electric properties of pure Pt nanocontacts and a Pt contact with a single CO molecule adsorbed. For the pure Pt contacts we see a clear difference between point contacts and short chains in good agreement with experiments. We i...... of the transmission function for the Pt-CO-Pt contact, and show that the conductance is largely determined by the local d band at the Pt apex atoms....

  7. Investigation of the correlation between stoichiometry and thermoelectric properties in a PtSb2 single crystal

    DEFF Research Database (Denmark)

    Søndergaard, Martin; Christensen, Mogens; Bjerg, Lasse

    2012-01-01

    -Ray Fluorescence and Inductively Coupled Plasma revealed Sb deficiency in the crystal, which explains the observed high charge carrier concentration and metallic properties. The transport properties were measured in the temperature range T = 20-300 K on a polycrystalline sample. Furthermore, ab initio theoretical...... utilizing X-Ray Diffraction and Energy Dispersive X-Ray Spectroscopy. The correlation between Pt/Sb ratio and physical property parameters - Seebeck coefficient, mobility, resistivity and charge carrier concentration - was studied. Elemental analysis by Energy Dispersive X-Ray Spectroscopy, X...

  8. Site selective Cu2+ substitution in single crystal Fe3O4 biocompatible nanospheres by solvothermal reflux method

    Science.gov (United States)

    Manohar, A.; Krishnamoorthi, C.

    2017-09-01

    Transition metal cations distribution among tetrahedral and octahedral sites in Fe3O4 has profound influence on it properties. The cations distribution among these sites were influenced by crystal field stabilization energy (CFSE) of a substituent ion. It was reported that Cu2+ substitutes both Fe3+ in tetrahedral and Fe2+ in octahedral sites of magnetite though it has high CFSE for octahedral sites. Thus it promotes mixed (normal & inverse) spinel structure and hence the properties deviate from the prediction. Here we show that selective octahedral site substitution of Fe2+ by Cu2+ in single crystal Fe3O4 nanoparticles was possible by solvothermal reflux method at moderate temperatures (≈300 °C). It was attributed to reduced energy barrier for crystallization and high diffusion coefficient of the metal cations at moderate temperature in low viscous organic solvents mixture, at ambient pressure, compared to coprecipitation and solid state reaction protocols. In addition, effective removal of exothermic crystal lattice energy, released during nucleation and growth process, by natural gas bubbles formed in the reflux organic solvent mixture. This promotes effective diffusion of cations during the growth process and easy octahedral occupation by Cu2+ in Fe1-xCuxFe2O4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 & 0.6) single crystal nanospheres. The octahedral substitution was confirmed by reduction of crystal lattice parameter as well as ferromagnetic strength of octahedral sublattice with enhanced Cu2+ concentration. In addition, morphology, lattice vibrational frequency and electron excitation spectra of the nanospheres were studied. The Langevin function fit analysis reveals that superparamagnetic domain diameter were slightly less than the particle diameter obtained from TEM micrograph.

  9. Thickness-dependent multiferroic behavior of BiFe0.75Cr0.25O3 films over Pt(111)/Ti/SiO2/Si substrate

    Science.gov (United States)

    William, R. V.; Sivaprakash, P.; Marikani, A.; Reddy, V. Raghavendra; Arumugam, S.

    2018-02-01

    We present here the experimental results of BiFe0.75Cr0.25O3 (BFCO) thin film deposited by sol-gel spin coating technique directly on Pt(111)/Ti/SiO2/Si substrate at different thicknesses. The crystal structure of BFCO has been investigated using X-ray diffraction which acts as a double perovskite structure with high crystallinity obtained at 400 °C. Further microscopic studies such as scanning electron microscope (SEM) with EDAX, transmission electron microscope (TEM) were also used in identifying the grain size and particle distribution over Pt (111) substrate. Atomic force microscopy (AFM) on the films at a different thickness (- 80 to - 250 nm) reveals that the surface roughness and other amplitude parameters increases with the increase in thickness signifying an increase of grain size with thickness. Increase in grain size and substrate clamping effect between the BFCO film and the substrate induces change in ferroelectric polarization and dielectric properties in relation to thickness effect. Similarly, decrease in magnetization from 9.241 emu/cm3 (- 80 nm) to 5.7791 emu/cm3 (- 250 nm) is attributed to the formation of anti-sites and anti-phase boundaries in the films. In addition, temperature dependence of magnetization reveals ferromagnetic super-exchange interaction of BFCO which is unlike the spin structure of antiferromagnetic BiFeO3.

  10. Peculiarities of superconductivity in the single-layer FeSe /SrTi O3 interface

    Science.gov (United States)

    Gor'kov, Lev P.

    2016-02-01

    Observation of replica bands in the angle-resolved photoemission spectroscopy (ARPES) spectra of single-layer FeSe on a strontium titanate substrate revealed a phonon component contribution to mechanisms behind its high-Tc superconductivity. We study the interaction of the in-layer FeSe electrons with the electric potential of the longitudinal (LO) modes at the surface of bulk SrTi O3 . A two-dimensional system of charges at the FeSe /SrTi O3 interface includes both the itinerant and the immobile electrons. The latter significantly change the interface characteristics, increasing screening at the substrate surface and thereby reducing the strength of the electron-LO-phonon interaction. In what follows, the dielectric constant serves as a free parameter and is determined using the ARPES measurements of the replicas. Two-dimensional Coulomb screening is accounted for in the random-phase approximation. It is shown that the model is applicable over the entire range of the parameters typical for current experiments. The estimates from this model make possible the conclusion that the LO-phonon-mediated pairing alone cannot account for the temperatures of the superconducting transitions Tc in the single-layer FeSe /SrTi O3 reported in these experiments. This does not exclude that the LO-phonon mechanisms can become more significant in differently and better prepared single-layer FeSe films. Available experiments are briefly discussed. Thus far no measurements exist on the dependence of Tc on the concentration of electrons doped into the in-layer FeSe band.

  11. Magnetization, shape memory and hysteresis behavior of single and polycrystalline FeNiCoTi

    International Nuclear Information System (INIS)

    Sehitoglu, H.; Efstathiou, C.; Maier, H.J.; Chumlyakov, Y.

    2005-01-01

    We report on the shape memory characteristics and magnetic behavior of polycrystalline and single crystalline FeNiCoTi. Predeforming the samples in the martensitic state and biasing of the martensite variants produced anisotropy in the magnetization behavior allowing the 'easy axis' to be identified as the 'a-axis' in the martensitic state. Based on these results, we provide an estimate of the magnetic anisotropy energy as 8.34x10 5 ergs/cm 3 . The results confirm the different magnetization behavior in the martensitic and austenitic states, and the shift in transformation temperatures upon application of a magnetic field. Shape memory strains near 2.5% are demonstrated under constant stress temperature cycling and upon heating at zero stress after deformation. We present a thermodynamics based theory that explains the origin of the hysteresis in this class of alloys emanating from the dissipation of energy due to plastic deformation. We predict the thermal hysteresis (135 K), and the shift in transformation temperature (14 K) with applied magnetic fields in agreement with the experimental results. The possibility of utilizing these classes of alloys as magnetic shape memory alloys is discussed

  12. Analysis of morphology and residual porosity in selective laser melting of Fe powders using single track experiments

    Science.gov (United States)

    Shutov, I. V.; Gordeev, G. A.; Kharanzhevskiy, E. V.; Krivilyov, M. D.

    2017-04-01

    Morphology and residual porosity of single tracks obtained by pulse selective laser melting (SLM) of Fe powder have been studied by metallography. Multiple cross sections of the stainless substrate with the single tracks deposited by SLM are examined and classified depending on processing parameters. A sustainable scanning strategy to reduce residual porosity is suggested for pulse laser annealing. The developed method is suitable both for improvement of processing regimes in commercial SLM machines and validation of numerical models in additive manufacturing of metal parts. The effect of the beam radius, pulse energy, its frequency and duration on a shape of the single track and its adhesion to the substrate is revealed.

  13. Rich magnetoelectric phase diagrams of multiferroic single-crystal α -NaFeO2

    Science.gov (United States)

    Terada, Noriki; Ikedo, Yuta; Sato, Hirohiko; Khalyavin, Dmitry D.; Manuel, Pascal; Miyake, Atsushi; Matsuo, Akira; Tokunaga, Masashi; Kindo, Koichi

    2017-07-01

    The magnetic and dielectric properties of the multiferroic triangular lattice magnet compound α -NaFeO2 were studied by magnetization, specific heat, dielectric permittivity, and pyroelectric current measurements and by neutron diffraction experiments using single crystals grown by a hydrothermal synthesis method. This work produced magnetic field (in the monoclinic a b -plane, Ba b, and along the c*-axis, Bc) versus temperature magnetic phase diagrams, including five and six magnetically ordered phases in Ba b and along Bc, respectively. In zero magnetic field, two spin-density-wave orderings with different k vectors—(0 ,q ,1/2 ) in phase I and (qa,qb,qc ) in phase II—appeared at T =9.5 and 8.25 K, respectively. Below T =5 K, a commensurate order with k =(0.5 ,0 ,0.5 ) was stabilized as the ground state in phase III. Both Ba b≥3 T and Bc≥5 T were found to induce ferroelectric phases at the lowest temperature (2 K), with an electric polarization that was not confined to any highly symmetric directions in phases IVa b (3.3 ≤Ba b≤8.5 T), Va b (8.5 ≤Ba b≤13.6 T), IVc (5.0 ≤Bc≤8.5 T), and Vc (8.5 ≤Bc≤13.5 T). In phase VIc, within a narrow temperature region in Bc, the polarization was confined to the a b plane. For each of the ferroelectric phases, the k vector was (qa,qb,qc ), and noncollinear structures were identified, including a general spiral in IVa b an a b cycloid in IVc and Vc, and a proper screw in VIc, along with a triclinic 11' magnetic point group allowing polarization in the general direction. Comparing the polarization direction to the magnetic structures in the ferroelectric phases, we conclude that the extended inverse Dzyaloshinskii-Moriya mechanism expressed by the orthogonal components p1∝ri j×(Si×Sj) and p2∝Si×Sj can explain the polarization directions. Based on calculations incorporating exchange interactions up to fourth-nearest-neighbor (NN) couplings, we infer that competition among antiferromagnetic second NN

  14. Chemically ordered face-centred tetragonal Fe–Pt nanoparticles ...

    Indian Academy of Sciences (India)

    2012-02-21

    Feb 21, 2012 ... Chemically ordered face-centred tetragonal (fct) Fe–Pt alloy nanoparticles (NPs) embedded SiO2 films were synthesized on ... Heat treatment of Fe/Pt co-doped films in air caused generation of Pt NPs first. At this stage, Fe ..... NPs (a small Fe metal peak is observed in figure 3a, curve 2) and most of the iron ...

  15. Single-Amino Acid Modifications Reveal Additional Controls on the Proton Pathway of [FeFe]-Hydrogenase

    Energy Technology Data Exchange (ETDEWEB)

    Cornish, Adam J.; Ginovska, Bojana; Thelen, Adam; da Silva, Julio C. S.; Soares, Thereza A.; Raugei, Simone; Dupuis, Michel; Shaw, Wendy J.; Hegg, Eric L.

    2016-06-07

    The proton pathway of [FeFe]-hydrogenase is essential for enzymatic H2 production and oxidation and is composed of four residues and a modeled water molecule. Recently, a computational analysis of this pathway revealed that the solvent-exposed residue of the pathway (Glu282) could form hydrogen bonds to two residues outside of the pathway (Arg286 and Ser320), implicating that these residues could function in regulating proton transfer. Substituting Arg286 with leucine eliminates hydrogen bonding with Glu282 and results in a 2.5-fold enhancement in H2 production activity, suggesting that Arg286 serves an important role in controlling the rate of proton delivery. In contrast, substitution of Ser320 with alanine reduces the rate approximately 5-fold, implying that it either acts as a member of the pathway or influences Glu282 to enable proton transfer. Interestingly, QM/MM and molecular dynamics calculations indicate that Ser320 does not play an electronic or structural role. QM calculations also estimate that including Ser320 in the pathway does not significantly change the barrier to proton movement, providing further support for its role as a member of the proton pathway. While further studies are needed to quantify the role of Ser320, collectively, these data provide evidence that the enzyme scaffold plays a significant role in modulating the activity of the enzyme, demonstrating that the rate of intraprotein proton transfer can be accelerated, particularly in a non-biological context. This work was supported by the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science, DE-FC02-07ER64494). In addition, support from the DOE Office of Science Early Career Research Program through the Office of Basic Energy Sciences (WJS, BGP, SR) is gratefully acknowledged. Computational resources were provided at W. R. Wiley Environmental Molecular Science Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of

  16. Local Weak Ferromagnetism in Single-Crystalline Ferroelectric BiFeO3

    DEFF Research Database (Denmark)

    Ramazanoglu, M.; Laver, Mark; Ratcliff, W.

    2011-01-01

    regions of dimension 0.03 microns along [11̅ 0], to several microns along [111], confirming a long-standing theoretical prediction. The average local magnetization is 0.06  μB/Fe. Our results provide an indication of the intrinsic macroscopic magnetization to be expected in ferroelectric BiFeO3 thin films...

  17. Structure, morphology, and magnetic properties of Fe nanoparticles deposited onto single-crystalline surfaces

    Directory of Open Access Journals (Sweden)

    Armin Kleibert

    2011-01-01

    Full Text Available Background: Magnetic nanostructures and nanoparticles often show novel magnetic phenomena not known from the respective bulk materials. In the past, several methods to prepare such structures have been developed – ranging from wet chemistry-based to physical-based methods such as self-organization or cluster growth. The preparation method has a significant influence on the resulting properties of the generated nanostructures. Taking chemical approaches, this influence may arise from the chemical environment, reaction kinetics and the preparation route. Taking physical approaches, the thermodynamics and the kinetics of the growth mode or – when depositing preformed clusters/nanoparticles on a surface – the landing kinetics and subsequent relaxation processes have a strong impact and thus need to be considered when attempting to control magnetic and structural properties of supported clusters or nanoparticles.Results: In this contribution we focus on mass-filtered Fe nanoparticles in a size range from 4 nm to 10 nm that are generated in a cluster source and subsequently deposited onto two single crystalline substrates: fcc Ni(111/W(110 and bcc W(110. We use a combined approach of X-ray magnetic circular dichroism (XMCD, reflection high energy electron diffraction (RHEED and scanning tunneling microscopy (STM to shed light on the complex and size-dependent relation between magnetic properties, crystallographic structure, orientation and morphology. In particular XMCD reveals that Fe particles on Ni(111/W(110 have a significantly lower (higher magnetic spin (orbital moment compared to bulk iron. The reduced spin moments are attributed to the random particle orientation being confirmed by RHEED together with a competition of magnetic exchange energy at the interface and magnetic anisotropy energy in the particles. The RHEED data also show that the Fe particles on W(110 – despite of the large lattice mismatch between iron and tungsten – are

  18. Pressure-dependence of the zero-field splittings for the Fe8 single-molecule magnet

    Science.gov (United States)

    Takahashi, S.; Thompson, E.; Hill, S.; Tozer, S. W.; Harter, A. G.; Dalal, N. S.

    2006-03-01

    We present a study of the pressure-dependent electron paramagnetic resonance (EPR) spectrum for the Fe8 single-molecule magnet (SMM). The biaxial [Fe8O2(OH)12(tacn)6]Br8.9H2O (Fe8) SMM has recently been studied extensively because its low-temperature magnetization dynamics are dominated by quantum tunneling of its spin S = 10 magnetic moment through a sizeable anisotropy barrier. To date, chemical methods have usually been employed in order to control the magnetic quantum tunneling (MQT) behavior of a SMM, e.g. by varying the magnetic ions in the molecular core, or the ligand/solvent environment. The advantage of this approach is that many different SMMs can be realized in this way, with widely varying MQT behavior. However, controllable variation of MQT is difficult. As an alternative approach for manipulation of the MQT, we have recently studied the effect of physical pressure on the Fe8 SMM. In this presentation, we show the pressure dependence of the zero-field splittings of Fe8, as studied by an angle and pressure-dependent high-frequency EPR technique.

  19. The remanence ratio in CoFe2O4nanoparticles with approximate single-domain sizes.

    Science.gov (United States)

    Xu, Shitao; Ma, Yongqing; Geng, Bingqian; Sun, Xiao; Wang, Min

    2016-12-01

    Approximately single-domain-sized 9-, 13-, and 16-nm CoFe 2 O 4 nanoparticles are synthesized using the thermal decomposition of a metal-organic salt. By means of dilution and reduction, the concentration, moment, and anisotropy of nanoparticles are changed and their influence on the magnetic properties is investigated. The relation of M r /M s  ∝ 1/lgH dip is observed, where M r /M s is the remanence ratio and H dip is the maximum dipolar field. Especially, such relation is more accurate for the nanoparticle systems with higher concentration and higher moment, i.e., larger H dip . The deviation from M r /M s  ∝ 1/lgH dip appearing at low temperatures can be attributed to the effects of surface spins for the single-phase CoFe 2 O 4 nanoparticles and to the pinning effect of CoFe 2 O 4 on CoFe 2 for the slightly reduced nanoparticles. Graphical Abstract Approximately single-domain-sized 9-, 13-, and 16-nm CoFe 2 O 4 nanoparticles were synthesized and then the concentration, moment, and anisotropy of these NPs were changed. The correlation of M r /M s  ∝ 1/lgH dip was observed, independent of the size, concentration, moment, and anisotropy, and especially, such correlation is more accurate for the nanoparticle systems with higher concentration or moment, i.e., stronger dipolar interaction, which has not been reported before as far as we know.

  20. DFT + U investigation on the adsorption and initial decomposition of methylamine by a Pt single-atom catalyst supported on rutile (110) TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Lv, Cun-Qin [College of Chemistry and Environmental Engineering, Shanxi Datong University, Datong 037009, Shanxi Province (China); Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071 (China); Liu, Jian-Hong, E-mail: ljh173@126.com [College of Chemistry and Environmental Engineering, Shanxi Datong University, Datong 037009, Shanxi Province (China); Guo, Yong; Li, Xue-Mei [College of Chemistry and Environmental Engineering, Shanxi Datong University, Datong 037009, Shanxi Province (China); Wang, Gui-Chang, E-mail: wangguichang@nankai.edu.cn [Department of Chemistry, Tianjin Key Lab. of Metal and Molecule-Based Material Chemistry, Nankai University, Tianjin 300071 (China)

    2016-12-15

    Highlights: • DFT + U is used to investigate the initial decomposition of methylamine. • The adsorption characteristics of possible intermediates involved in methylamine initial decomposition are discussed. • The energy barriers of the possible elementary reactions involved are obtained. • C−H bond scission is the most favored among the C−H, N−H and C−N bond breakings in methylamine. - Abstract: The adsorption and initial decomposition for methylamine catalyzed by a single Pt atom supported on rutile (110) titania (namely, Pt{sub 1}/TiO{sub 2}–R(110)) surface have been investigated by the density functional theory slab calculations with Hubbard corrections (DFT + U). The main purpose of the work is to better understand the role of dispersed platinum metal on the surface of rutile (110) titania in the initial decomposition of methylamine. Our calculated results show that the barriers increased with the order of C−H < N−H < C−N, which indicates that the C−H bond is the easiest to decompose and the C−N bond is the most difficult to break.

  1. Enhancement of the oxygen reduction on nitride stabilized pt-M (M=Fe, Co, and Ni) core–shell nanoparticle electrocatalysts

    KAUST Repository

    Kuttiyiel, Kurian A.

    2015-04-01

    Given the harsh operating conditions in hydrogen/oxygen fuel cells, the stability of catalysts is one of the critical questions affecting their commercialization. We describe a distinct class of oxygen reduction (ORR) core–shell electrocatalysts comprised of nitride metal cores enclosed by thin Pt shells that is easily synthesized. The synthesis is reproducible and amenable to scale up. Our theoretical analysis and the experimental data indicate that metal nitride nanoparticle cores could significantly enhance the ORR activity as well as the durability of the core–shell catalysts as a consequence of combined geometrical, electronic and segregation effects on the Pt shells. In addition to its fuel cells application, this class of catalysts holds promise to significantly contribute in resolving the problem of platinum scarcity and furthermore indicates the guidelines for future research and development.

  2. Electric field mediated non-volatile tuning magnetism at the single-crystalline Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 interface.

    Science.gov (United States)

    Zhang, Chao; Wang, Fenglong; Dong, Chunhui; Gao, Cunxu; Jia, Chenglong; Jiang, Changjun; Xue, Desheng

    2015-03-07

    We report non-volatile electric-field control of magnetism modulation in Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) heterostructure by fabricating an epitaxial Fe layer on a PMN-PT substrate using a molecular beam epitaxy technique. The remnant magnetization with a different electric field shows a non-symmetric loop-like shape, which demonstrates a change of interfacial chemistry and a large magnetoelectric coupling in Fe/PMN-PT at room temperature to realize low loss multistate memory under an electric field. Fitting with the angular-dependence of the in-plane magnetization reveals that the magnetoelectric effect is dominated by the direct electric-field effect rather than the strain effect at the interface. The magnetoelectric effect and the induced surface anisotropy are found to be dependent on the Fe film thickness and are linear with respect to the applied electric field.

  3. Steam reforming of methane over Pt/Rh based wire mesh catalyst in single channel reformer for small scale syngas production

    DEFF Research Database (Denmark)

    Sigurdsson, Haftor Örn; Kær, Søren Knudsen

    2012-01-01

    of a catalytic parallel plate type heat exchanger (CPHE) reformer stack, where coated Pt/Rh based wire mesh is used as a catalyst. Heat is supplied to the endothermic reaction with infrared electric heaters. All the experiments were performed under atmospheric pressure and at stable operating conditions......The purpose of this study is to investigate a small scale steam methane reformer for syngas production for a micro combined heat and power (mCPH) unit under different operational conditions. The study presents an experimental analysis of the performance of a specially built single channel...... to evaluate the effect of flow maldistribution in a CPHE reformer stack on the CH4 conversion and H2 yield....

  4. Effects of single metal atom (Pt, Pd, Rh and Ru) adsorption on the photocatalytic properties of anatase TiO2

    Science.gov (United States)

    Jin, Cui; Dai, Ying; Wei, Wei; Ma, Xiangchao; Li, Mengmeng; Huang, Baibiao

    2017-12-01

    The effects of single metal atom (Pt, Pd, Rh and Ru) adsorption on the photocatalytic properties of anatase TiO2 are investigated by means of the first-principles calculations based on density functional theory (DFT). Our results show that the most stable adsorption site for single metal atom on anatase TiO2 (101) surface is the bridge site formed by two twofold coordinated oxygen (O2c) atoms at the step edge. Due to the charge transfer from metal atoms to anatase TiO2 (101) surface, the work function of adsorbed surface is significantly smaller than the clean one, indicating enhanced surface activity. Fukui functions are highly localized around the isolated metal atoms, indicating that single metal atoms on anatase TiO2 (101) surface serve as the active reduction and oxidation sites in the photocatalytic process. Photo-induced electrons in the electronically excited TiO2 photocatalyst can be transferred to target species through the deposited single atoms. The band structures of host TiO2 are almost unchanged upon the adsorption, and the metal induced states are located in the band gap of the host. Remarkably, due to the metal atoms adsorption, the upward shift of conduction band edge will improve the reducing capacity of anatase TiO2. Moreover, when single metal atoms are adsorbed, potential energy of topmost surface Ti atoms turns to get close to the vacuum level, which significantly facilitates the electron transfer for hydrogen evolution. Results in this work provide new insights into improving the photocatalytic performance by single metal atoms adsorption.

  5. Impulse voltage control of continuously tunable bipolar resistive switching in Pt/Bi{sub 0.9}Eu{sub 0.1}FeO{sub 3}/Nb-doped SrTiO{sub 3} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Maocai; Liu, Meifeng; Wang, Xiuzhang [Hubei Normal University, Institute for Advanced Materials, and School of Physics and Electronic Science, Huangshi (China); Li, Meiya; Zhu, Yongdan; Zhao, Meng; Zhang, Feng; Xie, Shuai [Wuhan University, School of Physics and Technology, and Key Laboratory of Artificial Micro/Nano Structures of the Ministry of Education, Wuhan (China); Hu, Zhongqiang [Northeastern University, Department of Electrical and Computer Engineering, Boston, MA (United States); Liu, Jun-Ming [Nanjing University, Laboratory of Solid State Microstructures, Nanjing (China)

    2017-03-15

    Epitaxial Bi{sub 0.9}Eu{sub 0.1}FeO{sub 3} (BEFO) thin films are deposited on Nb-doped SrTiO{sub 3} (NSTO) substrates by pulsed laser deposition to fabricate the Pt/BEFO/NSTO (001) heterostructures. These heterostructures possess bipolar resistive switching, where the resistances versus writing voltage exhibits a distinct hysteresis loop and a memristive behavior with good retention and anti-fatigue characteristics. The local resistive switching is confirmed by the conductive atomic force microscopy (C-AFM), suggesting the possibility to scale down the memory cell size. The observed memristive behavior could be attributed to the ferroelectric polarization effect, which modulates the height of potential barrier and width of depletion region at the BEFO/NSTO interface. The continuously tunable resistive switching behavior could be useful to achieve non-volatile, high-density, multilevel random access memory with low energy consumption. (orig.)

  6. A high sensitive biosensor based on FePt/CNTs nanocomposite/N-(4-hydroxyphenyl)-3,5-dinitrobenzamide modified carbon paste electrode for simultaneous determination of glutathione and piroxicam.

    Science.gov (United States)

    Karimi-Maleh, Hassan; Tahernejad-Javazmi, Fahimeh; Ensafi, Ali A; Moradi, Reza; Mallakpour, Shadpour; Beitollahi, Hadi

    2014-10-15

    This study describes the development, electrochemical characterization and utilization of novel modified N-(4-hydroxyphenyl)-3,5-dinitrobenzamide-FePt/CNTs carbon paste electrode for the electrocatalytic determination of glutathione (GSH) in the presence of piroxicam (PXM) for the first time. The synthesized nanocomposite was characterized with different methods such as TEM and XRD. The modified electrode exhibited a potent and persistent electron mediating behavior followed by well-separated oxidation peaks of GSH and PXM. The peak currents were linearly dependent on GSH and PXM concentrations in the range of 0.004-340 and 0.5-550 µmol L(-1), with detection limits of 1.0 nmol L(-1) and 0.1 µmolL(-1), respectively. The modified electrode was successfully used for the determination of the analytes in real samples with satisfactory results. Copyright © 2014 Elsevier B.V. All rights reserved.

  7. Detailed single-crystal EPR line shape measurements for the single-molecule magnets Fe8Br and Mn12-acetate

    Science.gov (United States)

    Hill, S.; Maccagnano, S.; Park, Kyungwha; Achey, R. M.; North, J. M.; Dalal, N. S.

    2002-06-01

    It is shown that our multi-high-frequency (40-200 GHz) resonant cavity technique yields distortion-free high-field electron paramagnetic resonance (EPR) spectra for single-crystal samples of the uniaxial and biaxial spin S=10 single-molecule magnets (SMM's) [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O and [Fe8O2(OH)12(tacn)6]Br8.9H2O. The observed line shapes exhibit a pronounced dependence on temperature, magnetic field, and the spin quantum numbers (MS values) associated with the levels involved in the transitions. Measurements at many frequencies allow us to separate various contributions to the EPR linewidths, including significant D strain, g strain, and broadening due to the random dipolar fields of neighboring molecules. We also identify asymmetry in some of the EPR line shapes for Fe8 and a previously unobserved fine structure to some of the EPR lines for both the Fe8 and Mn12 systems. These findings prove relevant to the mechanism of quantum tunneling of magnetization in these SMM's.

  8. Evaluation of the prognostic factors in patients with pT3N0 or pT1N2-3 gastric cancer: a single institutional retrospective cohort study.

    Science.gov (United States)

    Terada, Mitsumi; Kinoshita, Takahiro; Kaito, Akio; Sugita, Shizuki; Watanabe, Masahiro; Hayashi, Ryuichi

    2018-03-01

    The impact of adjuvant chemotherapy on the survival of patients with the pT3N0/pT1N2-3 subset of Stage II gastric cancer is unclear. The aim of this study was to evaluate the survival rate of pT3N0/pT1N2-3 patients who were treated by surgery alone and to identify a high-risk group within this cohort. A total of 258 patients with pT3N0/pT1N2-3 gastric cancer who underwent gastrectomy alone in our hospital between January 1992 and December 2012 were enrolled in the present study. Their medical records were retrospectively reviewed to evaluate the survival rates and investigate prognostic factors. The 3- and 5-year recurrence-free survival rates of this cohort were 84 and 80%, respectively. The 3- and 5-year overall survival rates were 89 and 83%, respectively. A multivariate analysis revealed that pathological venous infiltration was an independent prognostic factor. The survival of patients with pathological venous infiltration was significantly worse than that of those without (5-year recurrence-free survival, 75 vs. 90%, p = 0.0005; 5-year overall survival, 78 vs. 91%, p = 0.0062). The prognosis of pT3N0/pT1N2-3 gastric cancer patients treated by surgery alone was relatively good; however, patients with pathological vessel infiltration may be at high risk of recurrence and could be candidates for adjuvant chemotherapy.

  9. A Mononuclear Fe(III) Single Molecule Magnet with a 3/2↔5/2 Spin Crossover

    DEFF Research Database (Denmark)

    Mossin, Susanne L.; Tran, Ba L.; Adhikari, Debashis

    2012-01-01

    The air stable complex [(PNP)FeCl2] (1) (PNP = N[2-P(CHMe2)2-4-methylphenyl]2–), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh3, displays an unexpected S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetiza......The air stable complex [(PNP)FeCl2] (1) (PNP = N[2-P(CHMe2)2-4-methylphenyl]2–), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh3, displays an unexpected S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID...... magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveal complex 1 to have frequency dependence on the out-of-phase signal and thus being a single molecular magnet with a thermally activated barrier of Ueff = 32–36 cm–1 (47–52 K). Variable-temperature Mössbauer data also...

  10. Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ′-Fe4N thin films

    Directory of Open Access Journals (Sweden)

    Kazuki Kabara

    2016-05-01

    Full Text Available Transverse anisotropic magnetoresistance (AMR effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component ( C 2 tr exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C 2 tr shows a positive small value (0.12% from 300 K to 50 K. However, the C 2 t r increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C 2 tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C 2 t r above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002.

  11. Magnetic order and lattice distortion in Rh- and Cu-doped BaFe2As2 single crystals

    Science.gov (United States)

    Kreyssig, A.; Kim, M. G.; Nandi, S.; Tian, W.; Zarestky, J.; Thaler, A.; Ni, N.; Bud'Ko, S. L.; Canfield, P. C.; McQueeney, R. J.; Goldman, A. I.

    2010-03-01

    Recent investigations of superconducting Co-doped BaFe2As2 have highlighted the interplay between superconductivity, magnetism and structure. Here we report on the antiferromagnetic order, lattice distortion and their response to superconductivity in Rh-doped BaFe2As2 and compare the behavior with non-superconducting Cu-doped BaFe2As2 single crystals. Results of the neutron scattering experiment performed at HB1A, HFIR, Oak Ridge, are correlated with high-resolution x-ray diffraction, resistance and magnetization measurements. The magnetic and structural phase transitions are similarly suppressed by the different dopings and the temperature dependencies of the order parameters are comparable, whereas only the Rh-doped sample shows a reduction of the antiferromagnetically ordered Fe moment in the superconducting state as reported for the Co-doped series. -- The work at the Ames Laboratory was supported by the US DOE, office of science, under contract No. DE-AC02-07CH11358.

  12. Application of synchrotron radiation to analyze the precipitation in ODS materials before irradiation in Fe-9%Cr single grain of powder and consolidated Fe-18%Cr

    Energy Technology Data Exchange (ETDEWEB)

    Bechade, J.-L., E-mail: jean-luc.bechade@cea.fr [CEA, DEN, Service de Recherches Metallurgiques Appliquees, 91191 Gif-sur-Yvette (France); Menut, D., E-mail: denis.menut@cea.fr [CEA, DEN, Service de Recherches Metallurgiques Appliquees, 91191 Gif-sur-Yvette (France); Lescoat, M.-L., E-mail: marie-laure.lescoat@cea.fr [CEA, DEN, Service de Recherches Metallurgiques Appliquees, 91191 Gif-sur-Yvette (France); Sitaud, B., E-mail: bruno.sitaud@synchrotron-soleil.fr [Synchrotron SOLEIL, Division Experiences, Ligne de MARS, L' Orme des Merisiers, Saint Aubin BP48, 91 192 Gif-sur-Yvette Cedex (France); Schlutig, S., E-mail: sandrine.schlutig@synchrotron-soleil.fr [Synchrotron SOLEIL, Division Experiences, Ligne de MARS, L' Orme des Merisiers, Saint Aubin BP48, 91 192 Gif-sur-Yvette Cedex (France); Solari, P.L., E-mail: pier-lorenzo.solari@synchrotron-soleil.fr [Synchrotron SOLEIL, Division Experiences, Ligne de MARS, L' Orme des Merisiers, Saint Aubin BP48, 91 192 Gif-sur-Yvette Cedex (France); Llorens, I., E-mail: isabelle.llorens@synchrotron-soleil.fr [Synchrotron SOLEIL, Division Experiences, Ligne de MARS, L' Orme des Merisiers, Saint Aubin BP48, 91 192 Gif-sur-Yvette Cedex (France); Hermange, H., E-mail: herve.hermange@synchrotron-soleil.fr [Synchrotron SOLEIL, Division Experiences, Ligne de MARS, L' Orme des Merisiers, Saint Aubin BP48, 91 192 Gif-sur-Yvette Cedex (France); and others

    2012-09-15

    Oxide Dispersion Strengthened (ODS) materials are candidates for structural components of GEN IV and fusion reactors. These materials are reinforced by nano-oxides (size of the smallest <3 nm) and the excellent mechanical properties obtained with such materials have to be kept in service. The aim of this paper is to present the capabilities of the synchrotron radiation to finely characterize the dispersion of second phases in ODS steels (Fe-9%Cr single grain of powder and consolidated Fe-18%Cr) and to study the precipitation mechanisms. This paper illustrates the results from first analyses performed on various unirradiated ODS steels elaborated at CEA using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) at the Multi-Analysis on Radioactive Sample (MARS) beamline of the SOLEIL synchrotron facility. The complementarities of both techniques, XRD and XAS, especially well appropriated to structural and local environment analyses for nano particles are presented. Results obtained with synchrotron radiation are also enriched by comparison with Transmission Electron Microscopy (TEM) observations performed on similar samples.

  13. [Fe(III)(dmbpy)(CN)4]-: a new building block for designing single-chain magnets.

    Science.gov (United States)

    Toma, Luminita Marilena; Pasán, Jorge; Ruiz-Pérez, Catalina; Lloret, Francesc; Julve, Miguel

    2012-11-28

    We herein present the synthesis and magneto-structural study of a new family of heterobimetallic chains of general formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n)·pnH(2)O [dmbpy = 4,4'-dimethyl-2,2'-bipyridine; M = Mn (2), Cu (3), Ni (4) and Co (5) with p = 4 (2), 3 (3), 9 (4) and 3.5 (5)] which were prepared by using the mononuclear PPh(4)[Fe(III)(dmbpy)(CN)(4)]·3H(2)O (1) building block (PPh(4)(+) = tetraphenylphosphonium) as a ligand toward fully solvated M(II) ions. The structure of 1 consists of discrete [Fe(III)(dmbpy)(CN)(4)](-) anions, tetraphenylphosphonium cations and noncoordinated water molecules. Complexes 2-5 are isostructural compounds whose structure consists of neutral 4,2-wave like heterobimetallic chains of formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n) where the [Fe(III)(dmbpy)(CN)(4)](-) entity adopts a bis-monodentate coordination mode toward trans-[M(II)(H(2)O)(2)] units through two of its four cyanide groups in cis positions. 1 exhibits the magnetic behaviour of magnetically isolated six-coordinate low-spin Fe(III) complexes with an important orbital contribution. 2 behaves as ferrimagnetic Fe(III)(2)Mn(II) chains, whereas 3-5 exhibit intrachain ferromagnetic couplings between the low-spin Fe(III) and either Cu(II) (3), Ni (4) or Co(II) (5) as well as frequency-dependence of the out-of-phase ac susceptibility signals below 3.0 (3), 5.5 (4) and 5.0 K (5). The relaxation time and the energy to reverse the magnetization of 3-5 are related to the anisotropy of the M(II) center and to the intra- and interchain magnetic interactions. Unprecedentedly in the world of cyanide-bearing complexes, 5 exhibits a double slow relaxation of the magnetization.

  14. Remarkable Electromechanical Coupling in the 2–2 Composite Based on Single-domain PMN–0.33PT Crystal

    Directory of Open Access Journals (Sweden)

    Vitaly Yu. TOPOLOV

    2009-10-01

    Full Text Available A novel parallel-connected 2–2 single-domain 0.67Pb(Mg1/3Nb2/3O3 – 0.33PbTiO3 crystal / polymer composite with various orientations of polarization vectors of the components is proposed to analyze behavior of electromechanical coupling factors k*3j and k*k where j = 1, 2 and 3. It is shown that the combination of the highly piezo-active relaxor-ferroelectric single-domain component and the piezoelectric polymer provides considerable values of k*k (min k*k » –0.8 and max k*k» 0.7 and |k*33| (about 0.9. The active role of the polarization orientation effect and the composite structure in attaining the high performance is emphasized in this work. A strong correlation between k*k and the hydrostatic piezoelectric coefficient is first revealed near min k*k and max k*k of the 2–2 composite. Some advantages concerned with the presence of the single-domain component in the 2–2 composite are discussed in connection with the large values of k*3j and k*k as well as with the considerable anisotropy of k*3j.

  15. First-principle study of single TM atoms X (X=Fe, Ru or Os) doped monolayer WS2 systems

    Science.gov (United States)

    Zhu, Yuan-Yan; Zhang, Jian-Min

    2018-05-01

    We report the structural, magnetic and electronic properties of the pristine and single TM atoms X (X = Fe, Ru or Os) doped monolayer WS2 systems based on first-principle calculations. The results show that the W-S bond shows a stronger covalent bond, but the covalency is obviously weakened after the substitution of W atom with single X atoms, especially for Ru (4d75s1) with the easily lost electronic configuration. The smaller total energies of the doped systems reveal that the spin-polarized states are energetically favorable than the non-spin-polarized states, and the smallest total energy of -373.918 eV shows the spin-polarized state of the Os doped monolayer WS2 system is most stable among three doped systems. In addition, although the pristine monolayer WS2 system is a nonmagnetic-semiconductor with a direct band gap of 1.813 eV, single TM atoms Fe and Ru doped monolayer WS2 systems transfer to magnetic-HM with the total moments Mtot of 1.993 and 1.962 μB , while single TM atom Os doped monolayer WS2 systems changes to magnetic-metal with the total moments Mtot of 1.569 μB . Moreover, the impurity states with a positive spin splitting energies of 0.543, 0.276 and 0.1999 eV near the Fermi level EF are mainly contributed by X-dxy and X-dx2-y2 states hybridized with its nearest-neighbor atom W-dz2 states for Fe, Ru and Os doped monolayer WS2 system, respectively. Finally, we hope that the present study on monolayer WS2 will provide a useful theoretical guideline for exploring low-dimensional spintronic materials in future experiments.

  16. Three wave coupling and explosive instability of magneto-elastic excitations in FeBO3 single crystal

    International Nuclear Information System (INIS)

    Yevstafyev, O.; Preobrazhensky, V.; Pernod, P.; Berzhansky, V.

    2011-01-01

    Parametric generation of coupled triads of magneto-elastic waves is studied experimentally in FeBO 3 single crystal under transversal electromagnetic pumping at the temperature range 77-293 K. The explosive supercritical dynamics of three wave coupling is observed when the pumping phase is modulated according to the nonlinear frequency shift of an excited magnetoelastic mode. The experimental results are in agreement with strongly nonlinear model of magneto-elastic excitations in antiferromagnets with 'easy plane' magnetic anisotropy. - Research highlights: → Parametric excitation of coupled magneto-elastic triads in FeBO 3 under EM pumping. → Quasi-singular pumping phase modulation to compensate nonlinear frequency shift. → Observation of explosive instability at the temperature range 77-293 K. → Supercritical triads excitation strongly nonlinear model of magneto-elastic dynamics.

  17. Compact Ag@Fe3O4 Core-shell Nanoparticles by Means of Single-step Thermal Decomposition Reaction

    Science.gov (United States)

    Brollo, Maria Eugênia F.; López-Ruiz, Román; Muraca, Diego; Figueroa, Santiago J. A.; Pirota, Kleber R.; Knobel, Marcelo

    2014-10-01

    A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

  18. In-Plane Electronic Anisotropy of Underdoped ___122___ Fe-Arsenide Superconductors Revealed by Measurements of Detwinned Single Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, Ian Randal

    2012-05-08

    The parent phases of the Fe-arsenide superconductors harbor an antiferromagnetic ground state. Significantly, the Neel transition is either preceded or accompanied by a structural transition that breaks the four fold symmetry of the high-temperature lattice. Borrowing language from the field of soft condensed matter physics, this broken discrete rotational symmetry is widely referred to as an Ising nematic phase transition. Understanding the origin of this effect is a key component of a complete theoretical description of the occurrence of superconductivity in this family of compounds, motivating both theoretical and experimental investigation of the nematic transition and the associated in-plane anisotropy. Here we review recent experimental progress in determining the intrinsic in-plane electronic anisotropy as revealed by resistivity, reflectivity and ARPES measurements of detwinned single crystals of underdoped Fe arsenide superconductors in the '122' family of compounds.

  19. Population Pharmacokinetic Modelling of FE 999049, a Recombinant Human Follicle-Stimulating Hormone, in Healthy Women After Single Ascending Doses

    DEFF Research Database (Denmark)

    Rose, Trine Høyer; Röshammar, Daniel; Erichsen, Lars

    2016-01-01

    Objective: The purpose of this analysis was to develop a population pharmacokinetic model for a novel recombinant human follicle-stimulating hormone (FSH) (FE 999049) expressed from a human cell line of foetal retinal origin (PER.C6) developed for controlled ovarian stimulation prior to assisted...... effects population pharmacokinetic modelling in NONMEM 7.2.0. Results: A one-compartment model with first-order absorption and elimination rates was found to best describe the data. A transit model was introduced to describe a delay in the absorption process. The apparent clearance (CL/F) and apparent...... volume of distribution (V/F) estimates were found to increase with body weight. Body weight was included as an allometrically scaled covariate with a power exponent of 0.75 for CL/F and 1 for V/F. Conclusions: The single-dose pharmacokinetics of FE 999049 were adequately described by a population...

  20. Thermally activated flux flow in FeSe0.5Te0.5 superconducting single crystal

    Science.gov (United States)

    Hamad, R. M.; Kayed, T. S.; Kunwar, S.; Ziq, Kh A.

    2017-07-01

    The current-voltage (J-E) isotherms of single crystal FeSe0.5Te0.5 sample have been measured at several temperatures near the transition temperature (Tc) and under applied magnetic fields (H). A power law (E ˜ Jβ ) has been used to fit the data and evaluate the activation energy Uo (T) using β = Uo/kBT. At low current density (J > Jc vortex flux flow (FF) behavior is expected. The effects of applied magnetic field on FF and TAFF also been investigated. We found that Uo(FF) was reduced with by about an order of magnitude in magnetic fields as low as ˜1.5 Tesla-the reduction in Uo(TAFF) is even faster than in Uo(FF)-hence reflecting the low pinning nature (defects, vacancies etc.) of FeSe0.5Te0.5 superconductor.

  1. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    International Nuclear Information System (INIS)

    Lowe, M.; McGrath, R.; Sharma, H. R.; Yadav, T. P.; Fournée, V.; Ledieu, J.

    2015-01-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe 3 O 4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol

  2. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    Science.gov (United States)

    Lowe, M.; Yadav, T. P.; Fournée, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.

    2015-03-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  3. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    Energy Technology Data Exchange (ETDEWEB)

    Lowe, M.; McGrath, R.; Sharma, H. R. [Surface Science Research Centre and The Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom); Yadav, T. P. [Hydrogen Energy Centre, Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Fournée, V.; Ledieu, J. [Institut Jean Lamour (UMR7198 CNRS-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex (France)

    2015-03-07

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe{sub 3}O{sub 4} rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  4. Growth, mechanical, and magnetic study of SmFeO{sub 3} single crystal grown by optical floating zone technique

    Energy Technology Data Exchange (ETDEWEB)

    Babu, P. Ramesh [Centre for Crystal Growth, VIT University, Vellore, Tamil Nadu (India); Bhaumik, Indranil [Crystal Growth Laboratory, Laser Materials Development and Devices Division, RRCAT, Indore (India); Ganesamoorthy, S. [Material Science Group, IGCAR, Kalpakkam, Tamil Nadu (India); Kalainathan, S., E-mail: kalainathan@yahoo.com [Centre for Crystal Growth, VIT University, Vellore, Tamil Nadu (India); Bhatt, R.; Karnal, A.K.; Gupta, P.K. [Crystal Growth Laboratory, Laser Materials Development and Devices Division, RRCAT, Indore (India)

    2016-08-15

    Single crystals of Samarium orthoferrite (SmFeO{sub 3}) have been grown by the optical floating zone technique. The growth parameters to yield good quality crystals are 5 mm/h for pulling and 30–40 rpm for rotation. The mechanical behavior of the grown crystal has been investigated. Rosette pattern has been observed around the indentation and the microhardness has been found to decreases non-linearly with the applied load. For load higher than 1.96 N there is a transition from palmqvist to median crack due to plastic deformation of the crystal. The hardness parameters like fracture toughness, brittleness index, and yield strength have also been calculated for palmqvist and median cracks occurring on the crystal surface. The magnetic investigations revealed that a magnetic transition in the range of 300–180 K. Above 180 K, the magnetization decreases as Sm and Fe sublattices have opposite spins. At high temperature, two anomalies are observed, one due to near spin reorientation (T{sub SR} = 480 K) and the other is AFM to paramagnetic transitions (T{sub N} = 670 K). The M–H curves exhibit a shape change with temperature due to the emergence and enlargement of multi-domain state of the SmFeO{sub 3} crystals. Bloch parameter (3.28 × 10{sup −5} K{sup −3/2}) has also been evaluated. - Highlights: • SmFeO{sub 3} single crystals have been grown by OFZ technique in air. • The microhardness has been found to decreases non-linearly with the applied load. • At 472 K, spin reorientation occurs in Fe sublattice. • The M–H curves exhibit a shape change with temperature due to the emergence and enlargement of multi-domain state. • Bloch 3/2-law holds good for SmFeO{sub 3} (B-parameter as 3.28 × 10{sup −5} K{sup −3/2}).

  5. Single step preparation of NdFeB alloy by magnesiothermic reduction-diffusion process

    International Nuclear Information System (INIS)

    Singha, Vinay Kant; Surendranathana, A.O.; John Berchmans, L.

    2014-01-01

    Magnesiothermic reduction is a new approach to produce the NdFeB alloy on a commercial scale. Similar studies were conducted for the preparation of LaNi 5 and SmCo 5 using magnesium as the reductant. In the present investigation NdFeB Hard magnetic bulk materials were synthesized by metallothermic 'Reduction – Diffusion (R-D) Process' using Magnesium as a reductant. For this process oxide precursors of Nd, Fe and B were blended with flux (LiCl/CaCl 2 ) and Mg chips were sandwiched in alternate layers. Thermal analysis (TGA/DTA) was carried out to find the dissociation and decomposition temperature of the reactants. The phase analysis, structure, and elemental composition were assessed by X-ray diffraction (XRD) and electron dispersive spectrometry (EDS). The infrared (IR) spectra were recorded by Fourier transform infrared spectrometer (FTIR). The morphological features and particle size was assessed by scanning electron microscope (SEM). The magnetic behaviour of the alloy was assessed using electron paramagnetic resonance (EPR) and vibratory sample magnetometer (VSM). From these studies it has been concluded that the NdFeB magnetic particles can be prepared using magnesium as the reductant. The process is faster and consumes very less amount of energy for the completion as compared to conventional calciothermic reduction process. Traces of MgO were detected in the alloy which increases the perpendicular anisotropy, thus increasing the coercivity of the material

  6. Synthesis and magnetic properties of single-crystalline BaFe12O19 nanoparticles

    International Nuclear Information System (INIS)

    Yu Jiangying; Tang Shaolong; Zhai Lin; Shi Yangguang; Du Youwei

    2009-01-01

    Rod-like and platelet-like nanoparticles of simple-crystalline barium hexaferrite (BaFe 12 O 19 ) have been synthesized by the molten salt method. Both particle size and morphology change with the reaction temperature and time. The easy magnetization direction (0 0 l) of the BaFe 12 O 19 nanoparticles has been observed directly by performing X-ray diffraction on powders aligned at 0.5 T magnetic field. The magnetic properties of the BaFe 12 O 19 magnet were investigated with various sintering temperatures. The maximum values of saturation magnetization (σ s =65.8 emu/g), remanent magnetization (σ r =56 emu/g) and coercivity field (H ic =5251 Oe) of the aligned samples occurred at the sintering temperatures of 1100 deg. C. These results indicate that BaFe 12 O 19 nanoparticles synthesized by the molten salt method should enable detailed investigation of the size-dependent evolution of magnetism, microwave absorption, and realization of a nanodevice of magnetic media.

  7. One-step synthesis of single phase micro-sized BaFe12O19 hexaplates via a modified hydrothermal approach

    International Nuclear Information System (INIS)

    Cao, Liangliang; Zeng, Yanwei; Ding, Chuan; Li, Rongjie; Li, Chuanming; Zhang, Chengzhe

    2016-01-01

    Single phase BaFe 12 O 19 ferrite identified by X-ray diffraction and Raman spectroscopy has been successfully synthesized using Fe(NO 3 ) 3 ·9H 2 O and Ba(NO 3 ) 2 as starting materials and NaOH as a precipitant via a modified one-step hydrothermal approach which involves the elimination of carbonate radicals from reaction system based on the stoichiometric ratio of [Ba 2+ ]/[Fe 3+ ]. Hydrothermal products under various synthetic conditions were studied, including different addition amounts of Ba(NO 3 ) 2 in the modified operation, reaction temperatures and times, and hydroxyl concentrations. The BaFe 12 O 19 particles featuring an excellent hexagonal plates shape can be hydrothermally synthesized with the aid of polyethylene glycol. It has been found that the presence of α-Fe 2 O 3 in a traditional hydrothermal process is motivated by the deviation from the desired [Ba 2+ ]/[Fe 3+ ] ratio caused by the negligent precipitation of Ba 2+ ions to BaCO 3 . An investigation on the preferred hydrothermal product through thermodynamic calculation shows that the reduction in Gibbs free energy for the exclusive formation of BaFe 12 O 19 with 1 mol of Fe 3+ ions at 220 °C is approximately 32 kJ higher than that for the complete transformation to α-Fe 2 O 3 with an equal consumption quantity of Fe 3+ ions. - Highlights: • Pure BaFe 12 O 19 was hydrothermally synthesized based on the stoichiometric ratio. • A modified operation was employed to eliminate self-invited carbonate ions. • BaFe 12 O 19 particles feature an excellent micro-sized hexaplates shape. • BaFe 12 O 19 was thermodynamically confirmed to be preferred result instead of α-Fe 2 O 3 .

  8. Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. 1 and 2

    International Nuclear Information System (INIS)

    Brieger, M.

    2004-01-01

    The established statistical interpretation of quantum mechanics never envisioned our today's ability to handle and investigate single particles in trap devices. After scrutinizing the development of quantum mechanics, we point out that Schroedinger's equation establishes an energy representation, which obtains the energy eigenvalues as extrema of the energy curve or on the energy hypersurface, respectively. We also strongly emphasize its never exhausted capability of accounting in classical terms and full detail for the dynamics of single particles in closed systems. This is demonstrated for several familiar examples. They show that the eigensolutions to Schroedinger's equation must not blindly be identified with physically stationary states. The gained insight into the true dynamics allows to describe, without involving QED, the time evolution of a complete spontaneous transition as being driven by unbalanced internal dynamics. This mechanism relies on the fact that perfect balances are only possible in the exact extrema of the total energy and that any deviation, which is characterized by nonstationary states, makes multipole moments oscillate and emit electromagnetic radiation. (orig.)

  9. Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. 1 and 2

    Energy Technology Data Exchange (ETDEWEB)

    Brieger, M. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany). Inst. fuer Technische Physik

    2004-07-01

    The established statistical interpretation of quantum mechanics never envisioned our today's ability to handle and investigate single particles in trap devices. After scrutinizing the development of quantum mechanics, we point out that Schroedinger's equation establishes an energy representation, which obtains the energy eigenvalues as extrema of the energy curve or on the energy hypersurface, respectively. We also strongly emphasize its never exhausted capability of accounting in classical terms and full detail for the dynamics of single particles in closed systems. This is demonstrated for several familiar examples. They show that the eigensolutions to Schroedinger's equation must not blindly be identified with physically stationary states. The gained insight into the true dynamics allows to describe, without involving QED, the time evolution of a complete spontaneous transition as being driven by unbalanced internal dynamics. This mechanism relies on the fact that perfect balances are only possible in the exact extrema of the total energy and that any deviation, which is characterized by nonstationary states, makes multipole moments oscillate and emit electromagnetic radiation. (orig.)

  10. Common crystalline and magnetic structure of superconducting A2Fe4Se5 (A=K,Rb,Cs,Tl) single crystals measured using neutron diffraction.

    Science.gov (United States)

    Ye, F; Chi, S; Bao, Wei; Wang, X F; Ying, J J; Chen, X H; Wang, H D; Dong, C H; Fang, Minghu

    2011-09-23

    Single-crystal neutron diffraction studies on superconductors A(2)Fe(4)Se(5), where A=Rb, Cs, (Tl, Rb), and (Tl, K) (T(c) ∼ 30 K), uncover the same Fe vacancy ordered crystal structure and the same block antiferromagnetic order as in K(2)Fe(4)Se(5). The Fe order-disorder transition occurs at T(S)=500-578 K, and the antiferromagnetic transition at T(N) = 471-559 K with an ordered magnetic moment ∼3.3μ(B)/Fe at 10 K. Thus, all recently discovered A intercalated iron selenide superconductors share the common crystalline and magnetic structure, which are very different from previous families of Fe-based superconductors, and constitute a distinct new 245 family.

  11. Single-phase {beta}-FeSi{sub 2} thin films prepared on Si wafer by femtosecond laser ablation and its photoluminescence at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Lu Peixiang [State Key Laboratory of Laser Technology and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)]. E-mail: lupeixiang@mail.hust.edu.cn; Zhou Youhua [State Key Laboratory of Laser Technology and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China) and Physics and Information School, Jianghan University, Wuhan 430056 (China)]. E-mail: yhzhou@jhun.edu.cn; Zheng Qiguang [State Key Laboratory of Laser Technology and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Yang Guang [State Key Laboratory of Laser Technology and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2006-02-06

    Single-phase {beta}-FeSi{sub 2} thin films were prepared on Si(100) and Si(111) wafers by using femtosecond laser deposition with a FeSi{sub 2} alloy target for the first time. X-ray diffraction (XRD), field scanning electron microscopy (FSEM), scanning probe microscopy (SPM), electron backscattered diffraction pattern (EBSD), and Fourier-transform Raman infrared spectroscopy (FTRIS) were used to characterize the structure, composition, and properties of the {beta}-FeSi{sub 2}/Si films. The orientation of {beta}-FeSi{sub 2} grains was found to depend on the orientation of the Si substrates, and photoluminescence at wavelength of 1.53 {mu}m was observed from the single-phase {beta}-FeSi{sub 2}/Si thin film at room temperature (20 {sup o}C)

  12. Chemical insights into the synthesis and properties of polycrystalline and single crystal iron scandium sulfide (FeSc2S4)

    Science.gov (United States)

    Morey, Jennifer R.; Plumb, Kemp W.; Koohpayeh, Seyed M.; Broholm, Collin L.; McQueen, Tyrel M.

    Iron scandium sulfide, FeSc2S4, has recently attracted significant theoretical and experimental interest as a candidate spin-orbital liquid. An AB2X4 spinel, FeSc2S4 (space group Fd-3m, No. 227) features a high degree of frustration associated with the Fe2+, which occupies the A-site diamond sublattice and is tetrahedrally coordinated by sulfur. The Fe2+ ion is in a high spin (S =2) state, resulting in orbital degeneracy due to a single hole on the e orbitals. We report the strides we have made to produce material in powder and single crystal form, and the relationship between the chemistry and the structural, magnetic, and thermodynamic properties of FeSc2S4. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Grant No. DEFG02-08ER46544.

  13. Effect of Spin-Crossover-Induced Pore Contraction on CO2–Host Interactions in the Porous Coordination Polymers [Fe(pyrazine)M(CN)4] (M = Ni, Pt)

    Energy Technology Data Exchange (ETDEWEB)

    Culp, Jeffrey T; Chen, De-Li; Liu, Jinchen; Chirdon, Danielle; Kauffman, Kristi; Goodman, Angela; Johnson, J Karl

    2013-02-01

    Variable-temperature in situ ATR-FTIR spectra are presented for the porous spin-crossover compounds [Fe(pyrazine)Ni(CN)4] and [Fe(pyrazine)Pt(CN)4] under CO2 pressures of up to 8 bar. Significant shifts in the ν3 and ν2 IR absorption bands of adsorbed CO2 are observed as the host materials undergo transition between low- and high-spin states. Computational models used to determine the packing arrangement of CO2 within the pore structures show a preferred orientation of one of the adsorbed CO2 molecules with close O=C=O···H contacts with the pyrazine pillar ligands. The interaction is a consequence of the commensurate distance of the inter-pyrazine separations and the length of the CO2 molecule, which allows the adsorbed CO2 to effectively bridge the pyrazine pillars in the structure. The models were used to assign the distinct shifts in the IR absorption bands of the adsorbed CO2 that arise from changes in the O=C=O···H contacts that strengthen and weaken in correlation with changes in the Fe–N bond lengths as the spin state of Fe changes. The results indicate that spin-crossover compounds can function as a unique type of flexible sorbent in which the pore contractions associated with spin transition can affect the strength of CO2–host interactions.

  14. Enhancement in electro-oxidation of methanol over PtRu black catalyst through strong interaction with iron oxide nanocluster.

    Science.gov (United States)

    Jeon, Min Ku; Lee, Ki Rak; Woo, Seong Ihl

    2010-11-02

    One of the major issues in direct methanol fuel cell research is to develop a new catalyst for methanol electro-oxidation reaction (MOR) with high activity and low cost. In this study, a new, simple, and economic way was introduced to improve the catalytic activity of commercial PtRu black catalyst for the MOR. A nanocomposite electrode was fabricated by mixing the PtRu catalyst with Fe(2)O(3) nanoclusters. When 10 wt % of the PtRu catalyst was replaced by the Fe(2)O(3) nanoclusters, mass activity (A/g(Pt)) increased by 80% compared to that of the pure PtRu catalyst. Specific activity of the mixed catalyst was 100% higher than that of the pure PtRu catalyst. The nanocomposite catalysts were also applied to single cells. Although the amount of the PtRu catalyst was reduced by 10 wt %, 10% higher potential was observed in the nanocomposite catalysts at a current density of 100 mA/cm(2).

  15. Temperature dependent tunneling study of CaFe1.96Ni0.04As2 single crystals

    International Nuclear Information System (INIS)

    Dutta, Anirban; Gupta, Anjan K.; Thamizhavel, A.

    2014-01-01

    We report on temperature dependent scanning tunneling microscopy and spectroscopy studies on CaFe 1.96 Ni 0.04 As 2 single crystals in 5.4 – 19.7 K temperature range across the normal metal - superconductor transition temperature, T C = 14K. The in-situ cleaved crystals show reasonably flat surface with signatures of atomic resolution. The tunnel spectra show significant spatial inhomogeneity below T C , which reduces significantly as the temperature goes above the T C . We discuss these results in terms of an inhomogeneous electronic phase that may exist due to the vicinity of this composition to the quantum critical point

  16. Magnetic field-driven 3D-Heisenberg-like phase transition in single crystalline helimagnet FeGe

    Science.gov (United States)

    Xu, Lisha; Fan, Jiyu; Sun, Weifeng; Zhu, Yan; Hu, Dazhi; Liu, Jindong; Ji, Yanda; Shi, Daning; Yang, Hao

    2017-07-01

    Significant microscopic information about fundamental magnetic interactions of magnetic materials is probed via the critical behavior of paramagnetic-ferromagnetic phase transition. In this work, we demonstrate that the critical behavior of cubic single crystalline FeGe belongs to the isotropic 3D-Heisenberg universality class by measuring the field dependence of magnetic entropy change. The above transition is one of the magnetic field-driven phase transitions but has a feature of the crossover from first- to second-order phase transition. A phenomenological model based on the evolution of magnetic skyrmions was proposed to qualitatively understand the phase transition.

  17. Electrical properties of InP:Fe single crystals implanted by phosphorus ions

    International Nuclear Information System (INIS)

    Radautsan, S.I.; Tiginyanu, I.M.; Pyshnaya, N.B.

    1988-01-01

    Investigations of phosphorus ion implantation in InP:Fe monocrystals and of the post-implantation annealing process upon the electrical properties of InP:Fe were carried out. The electrical parameters of the samples have been determined by Hall effect measurements. The curves of electron surface concentration n s and mobility μ s as functions of annealing temperature in the range of 200 to 600 0 C are shown and discussed. In order to estimate the depth of donor levels in annealed samples the temperature dependence of the surface Hall coefficient has been studied in the range 100 to 400 K. The thermal electron activation energy has been determined to be 0.09 eV

  18. AFM observation of Fe-Al single crystals under in situ deformation

    Czech Academy of Sciences Publication Activity Database

    Veselý, J.; Cieslar, M.; Kopeček, Jaromír

    2012-01-01

    Roč. 122, č. 3 (2012), s. 618-621 ISSN 0587-4246. [International Symposium on Physics of Materials, ISPMA /12./. Praha, 04.09.2011-08.09.2011] R&D Projects: GA ČR(CZ) GAP107/10/0438 Institutional research plan: CEZ:AV0Z10100520 Keywords : atomic force microscopy * Fe 3 Al * TEM Subject RIV: JG - Metallurgy Impact factor: 0.531, year: 2012

  19. Paramagnetic Spin Correlations in CaFe2As2 Single Crystals

    International Nuclear Information System (INIS)

    Omar Diallo, Souleymane; Pratt, Daniel; Fernandes, Rafael; Tian, Wei; Zarestky, J.L.; Lumsden, Mark D.; Perring, T.G.; Broholm, C.; Ni, Ni; Budko, S.L.; Canfield, Paul; Li, Haifeng; Vaknin, D.; Kreyssig, A.; Goldman, A.I.; Mcqueeney, R.J.

    2010-01-01

    Magnetic correlations in the paramagnetic phase of CaFe2As2(TN=172 K) have been examined by means of inelastic neutron scattering from 180 K ( 1.05TN) up to 300 K (1.8TN). Despite the first-order nature of the magnetic ordering, strong but short-ranged antiferromagnetic (AFM) correlations are clearly observed. These correlations, which consist of quasielastic scattering centered at the wave vector QAFM of the low-temperature AFM structure, are observed up to the highest measured temperature of 300 K and at high energy transfer ( >60 meV). The L dependence of the scattering implies rather weak interlayer coupling in the tetragonal c direction corresponding to nearly two-dimensional fluctuations in the (ab) plane. The spin correlation lengths within the Fe layer are found to be anisotropic, consistent with underlying fluctuations of the AFM stripe structure. Similar to the cobalt-doped superconducting BaFe2As2 compounds, these experimental features can be adequately reproduced by a scattering model that describes short-ranged and anisotropic spin correlations with overdamped dynamics.

  20. Synthesis and magnetotransport studies of single nickel-rich NiFe nanowire

    International Nuclear Information System (INIS)

    Rheem, Y; Yoo, B-Y; Koo, B K; Beyermann, W P; Myung, N V

    2007-01-01

    One of the main concerns in the preparation of alloy nanowires is the ability to synthesize compositionally uniform nanowires along the axis. Since most of the conventional mild acidic permalloy (Ni 80 Fe 20 ) electroplating baths consist of an extremely low concentration of Fe ions compared with Ni ions, the electrodeposition of iron is controlled by mass transfer, which leads to a significant change in the composition along the axis of the nanowire. To overcome this obstacle, we developed a new acidic chloride electrolyte with a high concentration of Fe and Ni ions to electrodeposit homogeneous nanowires. After synthesizing nanowires, the temperature dependent magneto- and electro-transport properties of individual nanowires were investigated. The temperature coefficient of resistance of a nanowire is much lower than the bulk counterpart, which might be attributed to a higher residual resistivity. The magnetoresistance shows a typical anisotropic magnetoresistance behaviour where the maximum anisotropic magnetoresistance ratio decreased with increasing temperature. The angular dependence of the magnetization switching field indicated that curling is the magnetization reversal mode at all temperatures

  1. Chemical doping in pnictides superconductors: The case of Ca(Fe1-xXx) 2As2 , X = Co, Ni, Pt

    Science.gov (United States)

    Continenza, Alessandra; Profeta, Gianni

    2018-04-01

    We present a comparative and detailed study of transition metal doping in CaFe2As2. Comparing with several experimental results and carefully analyzing how the states at the Fermi level are affected by doping we show that: i) simulation of real doping and considering induces structural relaxations are crucial to correctly address the physical mechanisms induced by transition metal substitutions; ii) different dopant concentration induces changes on the band structure that can not be described within a simple rigid-band picture; iii) careful comparison with the available ARPES results shows that the main effects on band filling and symmetry can be caught within DFT.

  2. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    Directory of Open Access Journals (Sweden)

    Tae Ho Yeom

    2016-04-01

    Full Text Available In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  3. Preparation of Pt-Re/Vulcan carbon nanocomposites using a single-source molecular precursor and relative performance as a direct methanol fuel cell electrooxidation catalyst.

    Science.gov (United States)

    Anderson, Angela D; Deluga, Gregg A; Moore, Joshua T; Vergne, Matthew J; Hercules, David M; Kenik, Edward A; Lukehart, C M

    2004-09-01

    Pt-Re/Vulcan carbon powder nanocomposites have been prepared with total metal loadings of 18 wt.% and 40 wt.% using a new non-cluster (1:1)-PtRe bimetallic precursor as the source of metal. Pt-Re nanoparticles having an average diameter of ca. 6 nm and atomic stoichiometry near 1:1 are formed. TEM, on-particle HR-EDS, and powder XRD data are consistent with the formation of Pt-Re alloy nanoparticles having a hexagonal unit cell with cell constants of a = 2.77 A and c = 4.47 A. A nanocomposite prepared at higher total metal loading under more rigorous thermal treatment also contains Pt-Re alloy nanoparticles having a fcc unit cell structure (a = 3.95 A). The precise dependence of Pt-Re nanocrystal structure on the thermal history of the nanocomposite specimen has not been investigated in detail. While these Pt-Re/carbon nanocomposites are active as anode catalysts in operating direct methanol fuel cells, the measured performance is less than that of commercial Pt-Ru/carbon catalysts and has marginal practical importance.

  4. Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. III and IV

    Energy Technology Data Exchange (ETDEWEB)

    Brieger, M. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany). Inst. fuer Technische Physik

    2005-07-01

    The rigorous solution to Schroedinger's nonrelativistic time-dependent equation of a single electron's spin-orbit or magnetic hyperfine interaction reveals the full dynamics of angular momentum coupling especially in the presence of an external, arbitrarily oriented magnetic field. Besides of making a description of major dynamical properties possible in simple classical terms, it also sheds new light on the seeming quantization of states: They turn out to be exceptional states of dynamical balance, which in the field-free case are only made possible by the respective pairs of Clebsch-Gordan coefficients. Moreover, the results not only show that integer and half-integer quantum numbers of the total angular momentum only apply to this special case but that in the general case they are also able to obtain the well-known splitting pattern of the stationary energy levels in the field as produced by separately identifiable, field-dependent contributions from the spin-orbit or the magnetic hyperfine interactions on the one hand, and the magnetic dipole interaction with external magnetic fields on the other in a way not accessible to the Breit-Rabi formula. The results further demonstrate that the total magnetic moment responds quite sensitively to even weak field strengths, i.e., with substantial changes although the linear Zeeman effect suggests their seeming constancy in low fields also for levels with vertical stroke M{sub J} vertical stroke < l+1/2. Although Schroedinger's equation is equivalent to an energy representation this detailed description of the behavior of the total magnetic moment is made possible by the fortunate fact that the coupling magnetic moments enter the Hamiltonian linearly. This circumstance can be exploited to describe in full detail how the total magnetic moment behaves in an arbitrarily oriented magnetic field. It is found that its motion in this environment consists of a basic Larmor precession about the field direction

  5. A Common Single-Site Pt(II)–O(OH) x – Species Stabilized by Sodium on “Active” and “Inert” Supports Catalyzes the Water-Gas Shift Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ming [Department; Liu, Jilei [Department; Lee, Sungsik [X-ray; Zugic, Branko [Department; Huang, Jun [School; Allard, Lawrence F. [Materials; Flytzani-Stephanopoulos, Maria [Department

    2015-03-05

    While it is long known that different types of support oxides have different capabilities to anchor metals and thus tailor the catalytic behavior, it is not always clear whether the support is a mere carrier of the active metal site, itself not participating directly in the reaction pathway. We report that catalytically similar single-atom centric Pt sites are formed by binding to sodium ions through ?O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41. Loading of 0.5 wt.% Pt on all these supports, preserves the Pt in atomic dispersion as Pt(II), the Pt-O(OH)x- species catalyzing the water-gas shift reaction (WGS) from ~120 to 400 oC. Since the effect of support is ?indirect,? these findings pave the way for the use of a variety of earth-abundant supports as carriers of atomically dispersed platinum for application to catalytic fuel-gas processing.

  6. Giant volume magnetostriction in the Y{sub 2}Fe{sub 17} single crystal at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Nikitin, S. A., E-mail: nikitin@phys.msu.ru; Pankratov, N. Yu.; Smarzhevskaya, A. I.; Politova, G. A. [Physics Faculty, Lomonosov Moscow State University, Moscow 119992 (Russian Federation); Pastushenkov, Yu. G., E-mail: yupast@mail.ru; Skokov, K. P. [Physics Faculty, Tver State University, 170100 Tver (Russian Federation); Moral, A. del [Laboratorio de Magnetismo de Slidos, Departamento de Fisica de Materia Condensada and Instituto de Ciencia de Materiales de Aragn, Facultad de Ciencias, Universidad de Zaragoza-C.S.I.C, E-50009 Zaragoza (Spain)

    2015-05-21

    An investigation of the Y{sub 2}Fe{sub 17} compound belonging to the class of intermetallic alloys of rare-earth and 3d-transition metals is presented. The magnetization, magnetostriction, and thermal expansion of the Y{sub 2}Fe{sub 17} single crystal were studied. The forced magnetostriction and magnetostriction constants were investigated in the temperature range of the magnetic ordering close to the room temperature. The giant field induced volume magnetostriction was discovered in the room temperature region in the magnetic field up to 1.2 T. The contributions of both anisotropic single-ion and isotropic pair exchange interactions to the volume magnetostriction and magnetostriction constants were determined. The experimental results were interpreted within the framework of the Standard Theory of Magnetostriction and the Landau thermodynamic theory. It was found out that the giant values of the volume magnetostriction were caused by the strong dependence of the 3d-electron Coulomb charge repulsion on the deformations and width of the 3d-electron energy band.

  7. Theoretical analysis and numerical simulation of electromagnetic parameters of Fe-C coaxial single fiber

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Wei, E-mail: cslggncl@163.com [Key Laboratory of Safety Design and Reliability Technology for Engineering Vehicle, Hunan Province, Changsha University of Science and Technology, Changsha 410114 (China); Hunan Province Higher Education Key Laboratory of Modeling and Monitoring on the Near-Earth Electromagnetic Environments, Changsha University of Science & Technology, Changsha 410114 (China); College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Chemical and Biomolecular Engineering Department, University of Tennessee, Knoxville, TN 37996 (United States); Zhu, Xukun; Kuang, Jiacai [Key Laboratory of Safety Design and Reliability Technology for Engineering Vehicle, Hunan Province, Changsha University of Science and Technology, Changsha 410114 (China); Hunan Province Higher Education Key Laboratory of Modeling and Monitoring on the Near-Earth Electromagnetic Environments, Changsha University of Science & Technology, Changsha 410114 (China); Yi, Shihe; Cheng, Haifeng [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073 (China); Guo, Zhanhu; He, Qingliang [Chemical and Biomolecular Engineering Department, University of Tennessee, Knoxville, TN 37996 (United States)

    2017-06-15

    Highlights: • Theoretical formula and calculation results of effective permeability and effective permittivity of the Fe-C coaxial fiber are obtained based on the Maxwell equation. • The coaxial fiber has stronger anisotropy and better electromagnetic dissipation performance than the hollow carbon fiber and solid iron fiber with the same volume content. • Greater conductivity, larger aspect ratio, thin iron shell play important roles to improve the electromagnetic matching ability and microwave attenuation for the Fe-C coaxial fibers. - Abstract: Based on the Maxwell equation, the electromagnetic model in the coaxial fiber was described. The interaction with electromagnetic wave was analysed and the theoretical formula of axial permeability (μ{sub ∥}), axial permittivity (ε{sub ∥}), radial permeability (μ{sub ⊥}) and radial permittivity (ε{sub ⊥}) of Fe-C coaxial fiber were derived, and the demagnetization factor (N) of fibrous material was revised. Calculation results indicate that the composite fiber has stronger anisotropy and better EM dissipation performance than the hollow carbon fiber and solid iron fiber with the same volume content. These properties can be enhanced through increasing aspect ratio and carbon content. The μ{sub ‖} is 5.18-4.46i, μ{sub ⊥} is 2.58-0.50i, ε{sub ∥} is 7.63-6.97i, and ε{sub ⊥} is 1.98-0.15i when the electromagnetic wave frequency is 5 GHz with the outer diameter of 0.866 μm, inner diameter of 0.500 μm, and length of 20 μm. The maximum of the imaginary part of μ{sub ∥} and ε{sub ∥} are much larger than that of μ{sub ⊥} and ε{sub ⊥} when the structural parameters change, and the maximum of μ{sub ∥} and ε{sub ∥} can reach 6.429 and 23.59. Simulation results show that greater conductivity, larger aspect ratio, thin iron shell play important roles to improve the electromagnetic matching ability and microwave attenuation for the Fe-C coaxial fibers.

  8. Facile single-step ammonia heat-treatment and quenching process for the synthesis of improved Pt/N-graphene catalysts

    Science.gov (United States)

    Xiong, Bin; Zhou, Yingke; O'Hayre, Ryan; Shao, Zongping

    2013-02-01

    In this work, we present a facile route to prepare electrocatalysts for methanol oxidation. The catalyst synthesis route involves the simultaneous reduction and nitrogen doping of graphene oxide (GO) along with the reduction of H2PtCl6 to Pt by a facile ammonia gas heat-treatment and quenching process. The resulting catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy while their electrocatalytic activity toward the oxidation of methanol is evaluated by cyclic voltammetry. The obtained Pt/graphene composites consist of crystalline Pt nanoparticles in the range of 1-4 nm which are well-dispersed on the N-doped graphene sheets. The best Pt/N-graphene catalyst composite is obtained after a 5 min ammonia treatment at 800 °C followed by rapid ammonia gas quenching at room temperature. This catalyst demonstrates superior catalytic activity for methanol electro-oxidation, with a peak current density of 0.218 A mgPt-1, which is about five times higher than an undoped (hydrogen treated and quenched) Pt/graphene control catalyst. The excellent electrocatalytic performance of the ammonia quenched catalyst is attributed to the nitrogenous functional groups and dopants in the graphene sheets that are formed during the facile quenching process in ammonia.

  9. Photorefractive features of non-stoichiometry codoped Hf:Fe:LiNbO3 single crystals

    International Nuclear Information System (INIS)

    Liu, Bo; Li, Chunliang; Bi, Jiancong; Sun, Liang; Xu, Yuheng

    2008-01-01

    Hf(2mol%):Fe(0.05wt%):LiNbO 3 crystals with various [Li]/[Nb] ratios of 0.94, 1.05, 1.2 and 1.38 have been grown. The photorefractive resistant ability increases with the accretion of [Li]/[Nb] ratio. When the ratio of [Li]/[Nb] is 1.20 or 1.38, the OH - absorption band shifts to about 3477cm -1 . The mechanisms of the photorefractive resistant ability increase and the absorption band shift have been discussed. The exponential gain coefficient (Γ) of the crystals was measured with two-beam coupling method and the effective charge carrier concentration (N eff ) was calculated. The results show that Γ and N eff increase with the accretion of [Li]/[Nb] ratio. The temperature effect of codoped Hf:Fe:LiNbO 3 crystals was also studied, it was found that the exponential gain coefficient increase dramatically at about 55 C, 70 C and 110 C, this is due to the inner electric field which is resulted from structure phase change. (copyright 2007 WILEY -VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Ferroelectric and electrical characterization of multiferroic BiFeO3 at the single nanoparticle level

    Science.gov (United States)

    Vasudevan, R. K.; Bogle, K. A.; Kumar, A.; Jesse, S.; Magaraggia, R.; Stamps, R.; Ogale, S. B.; Potdar, H. S.; Nagarajan, V.

    2011-12-01

    Ferroelectric BiFeO3 (BFO) nanoparticles deposited on epitaxial substrates of SrRuO3 (SRO) and La1-xSrxMnO3 (LSMO) were studied using band excitation piezoresponse spectroscopy (BEPS), piezoresponse force microscopy (PFM), and ferromagnetic resonance (FMR). BEPS confirms that the nanoparticles are ferroelectric in nature. Switching behavior of nanoparticle clusters were studied and showed evidence for inhomogeneous switching. The dimensionality of domains within nanoparticles was found to be fractal in nature, with a dimensionality constant of ˜1.4, on par with ferroelectric BFO thin-films under 100 nm in thickness. Ferromagnetic resonance studies indicate BFO nanoparticles only weakly affect the magnetic response of LSMO.

  11. Ferroelectric and electrical characterization of multiferroic BiFeO3 at the single nanoparticle level

    Energy Technology Data Exchange (ETDEWEB)

    Vasudevan, Rama K [ORNL; Bogle, K A [University of New South Wales, Sydney, Australia; Kumar, Amit [ORNL; Jesse, Stephen [ORNL; Magaraggia, R [University of Glasgow; Stamps, R [University of Glasgow; Ogale, S [National Chemical Laboratory, India; Potdar, H S [National Chemical Laboratory, India

    2011-01-01

    Ferroelectric BiFeO3 (BFO) nanoparticles deposited on epitaxial substrates of SrRuO3 (SRO) and La1xSrxMnO3 (LSMO) were studied using band excitation piezoresponse spectroscopy (BEPS), piezoresponse force microscopy (PFM), and ferromagnetic resonance (FMR). BEPS confirms that the nanoparticles are ferroelectric in nature. Switching behavior of nanoparticle clusters were studied and showed evidence for inhomogeneous switching. The dimensionality of domains within nanoparticles was found to be fractal in nature, with a dimensionality constant of 1.4, on par with ferroelectric BFO thin-films under 100 nm in thickness. Ferromagnetic resonance studies indicate BFO nanoparticles only weakly affect the magnetic response of LSMO.

  12. Structural and magnetic transitions in spinel FeM n2O4 single crystals

    Science.gov (United States)

    Nepal, Roshan; Zhang, Qiang; Dai, Samuel; Tian, Wei; Nagler, S. E.; Jin, Rongying

    2018-01-01

    Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that FeM n2O4 undergoes one structural and two magnetic transitions. The structural transition occurs at Ts˜595 K from cubic at high temperatures to tetragonal at low temperatures. Two magnetic transitions are ferrimagnetic at TFI -1˜373 K and TFI -2˜50 K , respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to the low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.

  13. First-order phase transitions in CaFe{sub 2}As{sub 2} single crystal: a local probe study

    Energy Technology Data Exchange (ETDEWEB)

    Alzamora, M; Munevar, J; Baggio-Saitovitch, E [Centro Brasileiro de Pesquisas Fisicas, Rua Xavier Sigaud 150, Urca 22290-180, Rio de Janeiro, RJ (Brazil); Bud' ko, S L; Ni Ni; Canfield, P C [Ames Laboratory, US DOE and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Sanchez, D R [Universidade Federal Fluminense, Instituto de Fisica, Avenida Milton Tavares de Souza, s/n-Campus da Praia Vermelha, 24210-346 Niteroi, RJ (Brazil)

    2011-04-13

    {sup 57}Fe Moessbauer spectroscopy has been used to investigate the structural and magnetic phase transitions of CaFe{sub 2}As{sub 2} (T{sub N} = 173 K) single crystals. For this compound we found that V{sub ZZ} is positive and parallel to the c-axis of the tetragonal structure. For CaFe{sub 2}As{sub 2} a magnetic hyperfine field B{sub hf} was observed at the {sup 57}Fe nucleus below T{sub N} {approx} 173 K. Analysis of the temperature dependence of B{sub hf} data using the Bean-Rodbell model shows that the Fe spins undergo a first-order magnetic transition at {approx} 173 K. A collinear antiferromagnetic structure is established below this temperature with the Fe spin lying in the (a, b) plane. Below T{sub N} the paramagnetic fraction of Fe decreases down to 150 K and for lower temperatures all the Fe spins are magnetically ordered.

  14. Structure and superconductivity of (Li1-x Fe x )OHFeSe single crystals grown using A x Fe2-y Se2 (A  =  K, Rb, and Cs) as precursors.

    Science.gov (United States)

    Yu, G; Zhang, G Y; Ryu, G H; Lin, C T

    2016-01-13

    We present results on the hydrothermal growth of ([Formula: see text])OHFeSe single crystals using floating-zone-grown [Formula: see text] (A  =  K, Rb, and Cs) as precursors. The growth proceeds by the hydrothermal ion exchange of Li/Fe-O-H for K, Rb, and Cs, resulting in a stacking layer of ([Formula: see text])OH sandwiched between the FeSe layers. Optimal growth parameters are achieved using high quality A 0.80Fe1.81Se2 single crystals added to the mixtures of LiOH, H2O, Fe and C(NH2)2Se in an autoclave and subsequently heated to 120 °C for 2 d, to obtain highest quality single crystals. The obtained crystals have lateral dimensions up to centimeters, with the final size related to that of the precursor crystal used. All ([Formula: see text])OHFeSe single crystals show a superconducting transition temperature T c  >  42 K, regardless of the phase of the precursor such as superconducting K0.80Fe1.81Se2 (T c  =  29.31 K) or non-superconducting Rb0.80Fe1.81Se2 or poor-superconducting Cs0.80Fe1.81Se2 (T c  =  28.67 K). The T c and transition width ΔT vary in the obtained single crystals, due to the inhomogeneity of the ionic exchange. X-ray diffraction analysis demonstrates that the 245 insulating phase is absent in the ion-exchanged single crystals, while it is observed in the [Formula: see text] precursors. Comparative studies of the structure, magnetization, and superconductivity on the parent A 0.80Fe1.81Se2 and the ion-exchanged ([Formula: see text])OHFeSe crystals are discussed. A phase diagram including antiferromagnetic spin density wave and superconducting phases is also proposed.

  15. Ethylene hydrogenation catalysis on Pt(111) single-crystal surfaces studied by using mass spectrometry and in situ infrared absorption spectroscopy

    Science.gov (United States)

    Tillekaratne, Aashani; Simonovis, Juan Pablo; Zaera, Francisco

    2016-10-01

    The catalytic hydrogenation of ethylene promoted by a Pt(111) single crystal was studied by using a ultrahigh-vacuum surface-science instrument equipped with a so-called high-pressure cell. Kinetic data were acquired continuously during the catalytic conversion of atmospheric-pressure mixtures of ethylene and hydrogen by using mass spectrometry while simultaneously characterizing the surface species in operando mode by reflection-absorption infrared spectroscopy (RAIRS). Many observations reported in previous studies of this system were corroborated, including the presence of adsorbed alkylidyne intermediates during the reaction and the zero-order dependence of the rate of hydrogenation on the pressure of ethylene. In addition, the high quality of the kinetic data, which could be recorded continuously versus time and processed to calculate time-dependent turnover frequencies (TOFs), afforded a more detailed analysis of the mechanism. Specifically, deuterium labeling could be used to estimate the extent of isotope scrambling reached with mixed-isotope-substituted reactants (C2H4 + D2 and C2D4 + H2). Perhaps the most important new observation from this work is that, although extensive H-D exchange takes place on ethylene before being fully converted to ethane, the average stoichiometry of the final product retains the expected stoichiometry of the gas mixture, that is, four regular hydrogen atoms and two deuteriums per ethane molecule in the case of the experiments with C2H4 + D2. This means that no hydrogen atoms are removed from the surface via their inter-recombination to produce X2 (X = H or D). It is concluded that, under catalytic conditions, hydrogen surface recombination is much slower than ethylene hydrogenation and H-D exchange.

  16. Electronic evidence of an insulator-superconductor crossover in single-layer FeSe/SrTiO3 films.

    Science.gov (United States)

    He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2014-12-30

    In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.

  17. Electronic evidence of an insulator–superconductor crossover in single-layer FeSe/SrTiO3 films

    Science.gov (United States)

    He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X. J.

    2014-01-01

    In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator–superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator–superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator–superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator–superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature. PMID:25502774

  18. Thermal annealing and pressure effects on BaFe2-xCoxAs2 single crystals.

    Science.gov (United States)

    Shin, Dongwon; Jung, Soon-Gil; Prathiba, G; Seo, Soonbeom; Choi, Ki-Young; Kim, Kee Hoon; Park, Tuson

    2017-11-26

    We investigate the pressure and thermal annealing effects on BaFe2-xCoxAs2 (Co-Ba122) single crystals with x = 0.1 and 0.17 via electrical transport measurements. The thermal annealing treatment not only enhances the superconducting transition temperature (Tc) from 9.6 to 12.7 K for x = 0.1 and from 18.1 to 21.0 K for x = 0.17, but also increases the antiferromagnetic transition temperature (TN). Simultaneous enhancement of Tc and TN by the thermal annealing treatment indicates that thermal annealing could substantially improve the quality of the Co-doped Ba122 samples. Interestingly, Tc of the Co-Ba122 compounds shows a scaling behavior with a linear dependence on the resistivity value at 290 K, irrespective of tuning parameters, such as chemical doping, pressure, and thermal annealing. These results not only provide an effective way to access the intrinsic properties of the BaFe2As2 system, but also may shed a light on designing new materials with higher superconducting transition temperature. © 2017 IOP Publishing Ltd.

  19. Thermal annealing and pressure effects on BaFe2-xCoxAs2single crystals.

    Science.gov (United States)

    Shin, Dongwon; Jung, Soon-Gil; Prathiba, G; Seo, Soonbeom; Choi, Ki-Young; Kim, Kee Hoon; Park, Tuson

    2017-12-08

    We investigate the pressure and thermal annealing effects on BaFe 2-x Co x As 2 (Co-Ba122) single crystals with x  =  0.1 and 0.17 via electrical transport measurements. The thermal annealing treatment not only enhances the superconducting transition temperature (T c ) from 9.6 to 12.7 K for x  =  0.1 and from 18.1 to 21.0 K for x  =  0.17, but also increases the antiferromagnetic transition temperature (T N ). Simultaneous enhancement of T c and T N by the thermal annealing treatment indicates that thermal annealing could substantially improve the quality of the Co-doped Ba122 samples. Interestingly, T c of the Co-Ba122 compounds shows a scaling behavior with a linear dependence on the resistivity value at 290 K, irrespective of tuning parameters such as chemical doping, pressure, and thermal annealing. These results not only provide an effective way to access the intrinsic properties of the BaFe 2 As 2 system, but may also shed a light on designing new materials with higher superconducting transition temperature.

  20. Some positive effects of introducing Pt4+ and Fe3+ to the MnMo-oxide anode deposited on IrO2/Ti substrate for best oxygen evolution efficiency during electrolysis in 0.5M NaCl solution

    OpenAIRE

    Abou Shahba, R.M.; Attia, E.M.; Deiab, N.M.

    2013-01-01

    NaCl solution (0.5 M) of pH 2 was electrolyzed at 1000 Am−2 at room temperature. Addition of Pt4+ and Fe3+ to the prepared MnMo-oxide anode deposited on IrO2/Ti substrate, significantly improves the performance of anode for the oxygen evolution reaction (OER) during NaCl electrolysis. After 2000 h of electrolysis, the oxygen evolution efficiency (OEE) is in the order of MnMoPt-oxide > MnMoFe-oxide > MnMo-oxide anodes with 100%, 99%, and 93.2% OEE, respectively. The loss in weight of MnMo-oxid...

  1. Solid-state reactivity explored in situ by synchrotron radiation on single crystals: from SrFeO2.5 to SrFeO3 via electrochemical oxygen intercalation

    International Nuclear Information System (INIS)

    Maity, A; Dutta, R; Penkala, B; Ceretti, M; Letrouit-Lebranchu, A; Perichon, A; Paulus, W; Chernyshov, D; Piovano, A; Bossak, A; Meven, M

    2015-01-01

    In this study we demonstrate the feasibility of following up a chemical reaction by single crystal x-ray (synchrotron) diffraction under operando conditions, carried out in a specially designed electrochemical cell mounted on the BM01A at the European Synchrotron Radiation Facility (ESRF). We investigated in detail the electrochemical oxidation of SrFeO 2.5 to SrFeO 3 on a spherical single crystal of 70 µm diameter by in situ diffraction at an ambient temperature. Complete data sets were obtained by scanning the whole reciprocal space using a 2M Pilatus detector, resulting in 3600 frames with a resolution of 0.1° per data set, each obtained in 18 min. The crystal was mounted in a specially designed electrochemical cell with 1N KOH used as the electrolyte. During the electrochemical oxidation, the reaction proceeds following the phase sequence SrFeO 2.5 /SrFeO 2.75 /SrFeO 2.875 /SrFeO 3 , structurally accompanied by establishing a complex series of long-range oxygen vacancy ordering, which gets instantly organized at ambient temperature. The topotactic reaction pathway is discussed in terms of the evolution of the twin domain structure. The formation of SrFeO 2.875 is accompanied by the formation of diffuse streaks along the [1 0 0]-direction of the perovskite cell, reaching high d-spacings. The diffuse streaks are discussed and are thought to originate from a modified twin structure induced by the SrFeO 2.75 to SrFeO 2.875 transition, and the associated changes in the domain structure, developed during the oxygen intercalation. We equally analysed and discussed in detail the twin structure of all the title compounds. We confirm the ground state of SrFeO 2.5 is able to adopt the Imma space group symmetry, showing stacking faults of the tetrahedral layers along the stacking axis of the brownmillerite unit cell, indicated by the 1D diffuse rods. We showed that in situ single crystal diffraction has huge potential in the study of non-stoichiometric compounds

  2. Solid-state reactivity explored in situ by synchrotron radiation on single crystals: from SrFeO2.5 to SrFeO3 via electrochemical oxygen intercalation

    Science.gov (United States)

    Maity, A.; Dutta, R.; Penkala, B.; Ceretti, M.; Letrouit-Lebranchu, A.; Chernyshov, D.; Perichon, A.; Piovano, A.; Bossak, A.; Meven, M.; Paulus, W.

    2015-12-01

    In this study we demonstrate the feasibility of following up a chemical reaction by single crystal x-ray (synchrotron) diffraction under operando conditions, carried out in a specially designed electrochemical cell mounted on the BM01A at the European Synchrotron Radiation Facility (ESRF). We investigated in detail the electrochemical oxidation of SrFeO2.5 to SrFeO3 on a spherical single crystal of 70 µm diameter by in situ diffraction at an ambient temperature. Complete data sets were obtained by scanning the whole reciprocal space using a 2M Pilatus detector, resulting in 3600 frames with a resolution of 0.1° per data set, each obtained in 18 min. The crystal was mounted in a specially designed electrochemical cell with 1N KOH used as the electrolyte. During the electrochemical oxidation, the reaction proceeds following the phase sequence SrFeO2.5/SrFeO2.75/SrFeO2.875/SrFeO3, structurally accompanied by establishing a complex series of long-range oxygen vacancy ordering, which gets instantly organized at ambient temperature. The topotactic reaction pathway is discussed in terms of the evolution of the twin domain structure. The formation of SrFeO2.875 is accompanied by the formation of diffuse streaks along the [1 0 0]-direction of the perovskite cell, reaching high d-spacings. The diffuse streaks are discussed and are thought to originate from a modified twin structure induced by the SrFeO2.75 to SrFeO2.875 transition, and the associated changes in the domain structure, developed during the oxygen intercalation. We equally analysed and discussed in detail the twin structure of all the title compounds. We confirm the ground state of SrFeO2.5 is able to adopt the Imma space group symmetry, showing stacking faults of the tetrahedral layers along the stacking axis of the brownmillerite unit cell, indicated by the 1D diffuse rods. We showed that in situ single crystal diffraction has huge potential in the study of non-stoichiometric compounds under operando

  3. Single and double [ital K]-shell ionization and electron-transfer cross sections for Fe and Ni bombarded by S ions and Fe by Si ions at 1. 25--4. 70 MeV/amu

    Energy Technology Data Exchange (ETDEWEB)

    Tribedi, L.C.; Prasad, K.G.; Tandon, P.N. (Tata Institute of Fundamental Research, Bombay 400005 (India)); Chen, Z.; Lin, C.D. (Department of Physics, Kansas State University, Manhattan, Kansas (United States))

    1994-02-01

    Single and double [ital K]-shell vacancy production and [ital K]-[ital K] electron-transfer cross sections have been measured in the limit of zero target thickness for Fe and Ni induced by 1.25--4.70 MeV/amu [sup 28]Si and [sup 32]S ions. The fluorescence yield [omega][sub [ital k

  4. Upper critical fields and thermally-activated transport of Nd(0.7Fe0.3) FeAs single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Balakirev, Fedor F [Los Alamos National Laboratory; Jaroszynski, J [NHMFL, FSU; Hunte, F [NHMFL, FSU; Balicas, L [NHMFL, FSU; Jo, Youn - Jung [NHMFL, FSU; Raicevic, I [NHMFL, FSU; Gurevich, A [NHMFL, FSU; Larbalestier, D C [NHMFL, FSU; Fang, L [CHINA; Cheng, P [CHINA; Jia, Y [CHINA; Wen, H H [CHINA

    2008-01-01

    We present measurements of the resistivity and the upper critical field H{sub c2} of Nd(O{sub 0.7}F{sub 0.3})FeAs single crystals in strong DC and pulsed magnetic fields up to 45 T and 60 T, respectively. We found that the field scale of H{sub c2} is comparable to {approx}100 T of high T{sub c} cuprates. H{sub c2}(T) parallel to the c-axis exhibits a pronounced upward curvature similar to what was extracted from earlier measurements on polycrystalline samples. Thus this behavior is indeed an intrinsic feature of oxypnictides, rather than manifestation of vortex lattice melting or granularity. The orientational dependence of H{sub c2} shows deviations from the one-band Ginzburg-Landau scaling. The mass anisotropy decreases as T decreases, from 9.2 at 44K to 5 at 34K. Spin dependent magnetoresistance and nonlinearities in the Hall coefficient suggest contribution to the conductivity from electron-electron interactions modified by disorder reminiscent that of diluted magnetic semiconductors. The Ohmic resistivity measured below T{sub c} but above the irreversibility field exhibits a clear Arrhenius thermally activated behavior over 4--5 decades. The activation energy has very different field dependencies for H{parallel}ab and H{perpendicular}ab. We discuss to what extent different pairing scenarios can manifest themselves in the observed behavior of H{sub c2}, using the two-band model of superconductivity. The results indicate the importance of paramagnetic effects on H{sub c2}(T), which may significantly reduce H{sub c2}(0) as compared to H{sub c2}(0) {approx}200--300 T based on extrapolations of H{sub c2}(T) near T{sub c} down to low temperatures.

  5. A temperature dependent tunneling study of the spin density wave gap in EuFe2As2 single crystals.

    Science.gov (United States)

    Dutta, Anirban; Anupam; Hossain, Z; Gupta, Anjan K

    2013-09-18

    We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF). The gap becomes more pronounced upon entering the SDW state with a gap value ∼90 meV at 15 K. However, the zero bias conductance remains finite down to 15 K indicating a finite DOS at the EF in the SDW phase. Furthermore, no noticeable change is observed in the DOS at the antiferromagnetic ordering transition of Eu(2+) moments at 19 K.

  6. Morphology and magnetic flux distribution in superparamagnetic, single-crystalline Fe{sub 3}O{sub 4} nanoparticle rings

    Energy Technology Data Exchange (ETDEWEB)

    Takeno, Yumu [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Murakami, Yasukazu, E-mail: murakami@tagen.tohoku.ac.jp, E-mail: kannanmk@uw.edu; Shindo, Daisuke [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Center for Emergent Matter Science, RIKEN, Wako 351-0198 (Japan); Sato, Takeshi [Hitachi High-Technologies Corporation, 1040 Ichige, Hitachinaka-shi, Ibaraki 312-0033 (Japan); Tanigaki, Toshiaki [Center for Emergent Matter Science, RIKEN, Wako 351-0198 (Japan); Central Research Laboratory, Hitachi, Ltd., Hatoyama 350-0395 (Japan); Park, Hyun Soon [Center for Emergent Matter Science, RIKEN, Wako 351-0198 (Japan); Department of Materials Science and Engineering, Dong-A University, Busan 604-714, Republic of South Korea (Korea, Republic of); Ferguson, R. Matthew [LodeSpin Labs, P.O. Box 95632, Seattle, Washington 91845 (United States); Krishnan, Kannan M., E-mail: murakami@tagen.tohoku.ac.jp, E-mail: kannanmk@uw.edu [Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195-2120 (United States)

    2014-11-03

    This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe{sub 3}O{sub 4} nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.

  7. Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors

    NARCIS (Netherlands)

    De Boer, R.W.I.; Stassen, A.F.; Craciun, M.F.; Mulder, C.L.; Molinari, A.; Rogge, S.; Morpurgo, A.F.

    2005-01-01

    We report the observation of ambipolar transport in field-effect transistors fabricated on single crystals of copper- and iron-phthalocyanine, using gold as a high work-function metal for the fabrication of source and drain electrodes. In these devices, the room-temperature mobility of holes reaches

  8. Some positive effects of introducing Pt4+ and Fe3+ to the MnMo-oxide anode deposited on IrO2/Ti substrate for best oxygen evolution efficiency during electrolysis in 0.5 M NaCl solution

    Directory of Open Access Journals (Sweden)

    R.M. Abou Shahba

    2013-06-01

    Full Text Available NaCl solution (0.5 M of pH 2 was electrolyzed at 1000 Am−2 at room temperature. Addition of Pt4+ and Fe3+ to the prepared MnMo-oxide anode deposited on IrO2/Ti substrate, significantly improves the performance of anode for the oxygen evolution reaction (OER during NaCl electrolysis. After 2000 h of electrolysis, the oxygen evolution efficiency (OEE is in the order of MnMoPt-oxide > MnMoFe-oxide > MnMo-oxide anodes with 100%, 99%, and 93.2% OEE, respectively. The loss in weight of MnMo-oxide is reduced from about 13% to 3.2% and 0.0% by addition of iron and platinum cations, to the deposition electrolyte. The mean average grain size of MnO2, MnMo-, MnMoFe- and MnMoPt-oxide deposits prepared in electrolytes of pH 0.0 are in the range of 25.5, 16.22, 13.5 ∼ 16.5 and 13 ∼ 17.5 nm, respectively. The physicochemical properties of the deposits were characterized using X-ray diffraction spectroscopy (XRD, energy dispersive X-ray spectroscopy (EDX, scanning electron microscopy (SEM and electrochemical techniques. EDX analysis illustrates that IrO2/Ti is stable during the deposition process and behaves only as conductive substrate. SEM illustrates that, all elements constituting MnMoPt- and MnMoFe-oxide deposits are homogeneously distributed in the oxide surface.

  9. Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films.

    Science.gov (United States)

    He, Shaolong; He, Junfeng; Zhang, Wenhao; Zhao, Lin; Liu, Defa; Liu, Xu; Mou, Daixiang; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

    2013-07-01

    The recent discovery of possible high-temperature superconductivity in single-layer FeSe films has generated significant experimental and theoretical interest. In both the cuprate and the iron-based high-temperature superconductors, superconductivity is induced by doping charge carriers into the parent compound to suppress the antiferromagnetic state. It is therefore important to establish whether the superconductivity observed in the single-layer sheets of FeSe--the essential building blocks of the Fe-based superconductors--is realized by undergoing a similar transition. Here we report the phase diagram for an FeSe monolayer grown on a SrTiO3 substrate, by tuning the charge carrier concentration over a wide range through an extensive annealing procedure. We identify two distinct phases that compete during the annealing process: the electronic structure of the phase at low doping (N phase) bears a clear resemblance to the antiferromagnetic parent compound of the Fe-based superconductors, whereas the superconducting phase (S phase) emerges with the increase in doping and the suppression of the N phase. By optimizing the carrier concentration, we observe strong indications of superconductivity with a transition temperature of 65±5 K. The wide tunability of the system across different phases makes the FeSe monolayer ideal for investigating not only the physics of superconductivity, but also for studying novel quantum phenomena more generally.

  10. Facile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method

    Science.gov (United States)

    Ogi, Takashi; Dani Nandiyanto, Asep Bayu; Kisakibaru, Yutaka; Iwaki, Toru; Nakamura, Keitaro; Okuyama, Kikuo

    2013-04-01

    When nitrogen was inserted into the spherical α-Fe/Al2O3 core shell of 45 nm nanoparticles, the XRD pattern showed a clear change in the crystal modification from a body-centered cubic crystal to that of a single-phase α″-Fe16N2 structure. SEM, TEM, and energy-dispersive X-ray spectroscopy mapping analysis gave the particle size distributions, the shell thickness, and the Fe and Al elements. An examination of the total electron yield (surface sensitive) and fluorescence yield (bulk sensitive) of X-ray absorption fine structure on Fe and N atoms of these core shell nanoparticles confirmed the nitriding of the core iron and showed iron oxide formations on the core surface, indicating stability and resistivity performance. The nitriding process also changed the magnetic properties from paramagnetic to ferromagnetic with a coercivity above 3000 Oe, indicating a promising material for a "rear-earth-free" giant magnet.

  11. Reclamation of acid pickling waste: A facile route for preparation of single-phase Fe{sub 3}O{sub 4} nanoparticle

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wenxue; Lu, Bin; Tang, Huihui; Zhao, Jingxiang; Cai, Qinghai, E-mail: caiqinghai@yahoo.com

    2015-05-01

    Using an alternative method of dropwise addition of iron salt in NaOH aqueous solution, nanocrystalline Fe{sub 3}O{sub 4} materials were prepared from acid pickling waste as a starting material with ultrasonic enhancement and polyethylene glycol as a dispersant, as proved by XRD, TEM, TG–DSC and ICP-MS. The results showed that the Fe{sub 3}O{sub 4} material was a well-crystallized magnetite with an average size of about 25 nm and purity 99.15%. Magnetic measurement revealed the nanocrystals were stronger superparamagnetic with a saturation magnetization of 82.1 emu/g. - Graphical abstract: A facile method for the preparation of single-phase Fe{sub 3}O{sub 4} nanoparticle from acid pickling waste by chemical precipitation was explored. The results characterized by XRD, FT-IR, TEM, TG–DSC, ICP-MS and magnetic measurement showed that the obtained Fe{sub 3}O{sub 4} nanomaterial was well-crystallized magnetite and stronger superparamagnetic with single phase. - Highlights: • Reclamation of acid pickling waste. • An alternative route for preparation of Fe{sub 3}O{sub 4}. • Nanocrystals with single phase. • Stronger superparamagnetic nature.

  12. Fe-Ti-O based catalyst for large-chiral-angle single-walled carbon nanotube growth

    DEFF Research Database (Denmark)

    He, Maoshuai; Zhang, Lili; Jiang, Hua

    2016-01-01

    Fe nanoparticles with subsequent high-temperature air calcination, which favours the formation of a homogeneous Fe-Ti-O solid solution. Using CO as the carbon feedstock, chemical vapour deposition growth of SWNTs at 800 °C was demonstrated on the Fe-Ti-O catalyst. Nanobeam electron diffraction...

  13. Resistive random access memory utilizing ferritin protein with Pt nanoparticles

    International Nuclear Information System (INIS)

    Uenuma, Mutsunori; Kawano, Kentaro; Zheng Bin; Okamoto, Naofumi; Horita, Masahiro; Yoshii, Shigeo; Yamashita, Ichiro; Uraoka, Yukiharu

    2011-01-01

    This study reports controlled single conductive paths found in resistive random access memory (ReRAM) formed by embedding Pt nanoparticles (Pt NPs) in NiO film. Homogeneous Pt NPs produced and placed by ferritin protein produce electric field convergence which leads to controlled conductive path formation. The ReRAM with Pt NPs shows stable switching behavior. A Pt NP density decrease results in an increase of OFF state resistance and decrease of forming voltage, whereas ON resistance was independent of the Pt NP density, which indicates that a single metal NP in a memory cell will achieve low power and stable operation.

  14. Electrocatalytic properties of Pt/carbon composite nanofibers

    International Nuclear Information System (INIS)

    Lin Zhan; Ji Liwen; Zhang Xiangwu

    2009-01-01

    Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H 2 SO 4 and 5.0 mM K 4 [Fe(CN) 6 ] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm -2 has the highest activity.

  15. Pt, PtCo and PtNi electrocatalysts prepared by mechanical alloying for the oxygen reduction reaction in 0.5 M H{sub 2}SO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Contreras, M.A. [Instituto Nacional de Investigaciones Nucleares, Depto. de Quimica, Apdo. Postal 18-1027 Col. Escandon, C.P.11801 Mexico D.F. (Mexico); Instituto Politecnico Nacional, Depto. de Ing. Metalurgica, 07300 Mexico D.F. (Mexico); Fernandez-Valverde, S.M. [Instituto Nacional de Investigaciones Nucleares, Depto. de Quimica, Apdo. Postal 18-1027 Col. Escandon, C.P.11801 Mexico D.F. (Mexico); Vargas-Garcia, J.R. [Instituto Politecnico Nacional, Depto. de Ing. Metalurgica, 07300 Mexico D.F. (Mexico); Cortes-Jacome, M.A.; Toledo-Antonio, J.A.; Angeles-Chavez, C. [Instituto Mexicano del Petroleo, Programa de Ingenieria Molecular, Eje Central Lazaro Cardenas 152, Mexico, D.F.,0 7730 (Mexico)

    2008-11-15

    Electrocatalysts of Pt, PtCo and PtNi powders for the oxygen reduction reaction (ORR) were processed by Mechanical Alloying. Physical characterization was made by X-ray diffraction, scanning electron microscopy and scanning transmission electron microscopy. It was found that milled powders formed agglomerates in the range of 0.2-20 {mu}m formed by nanometric size crystallites. The synthesized powders were alloys of PtFe, PtCoFe and PtNiFe due to iron incorporation during the milling process. The binding energies of Pt in the alloys were determined by XPS. Polarization curves were obtained by Rotating Disk Electrode technique in 0.5 M H{sub 2}SO{sub 4} to determine the electrocatalytic activity of the mechanically alloyed powders. Tafel curves were plotted and kinetic parameters for the ORR were calculated. The PtFe alloy showed the highest electrocatalytic activity for the ORR. However, the lowest overpotential was found for the PtCoFe alloy and it also showed a higher current exchange density. A linear relationship was found between the Pt-binding energy in the alloys and the overpotential at the same current density independent of the Pt alloy composition. (author)

  16. Thickness dependence of the conductivity of thin films (La,Sr)FeO3 deposited on MgO single crystal

    DEFF Research Database (Denmark)

    Mosleh, Majid; Pryds, Nini; Hendriksen, Peter Vang

    2007-01-01

    Thin films of La0.6Sr0.4FeO3-delta of different thicknesses have been deposited on single crystal MgO substrate by pulsed laser deposition (PLD). The deposited films are characterized by XRD before and after annealing, by scanning electron microscopy (SEM) for morphological characterization and b...

  17. Synthesis of BiFeO3 thin films on single-terminated Nb : SrTiO3 (111 substrates by intermittent microwave assisted hydrothermal method

    Directory of Open Access Journals (Sweden)

    Ivan Velasco-Davalos

    2016-06-01

    Full Text Available We report on a simple and fast procedure to create arrays of atomically flat terraces on single crystal SrTiO3 (111 substrates and the deposition of ferroelectric BiFeO3 thin films on such single-terminated surfaces. A microwave-assisted hydrothermal method in deionized water and ammonia solution selectively removes either (SrO34− or Ti4+ layers to ensure the same chemical termination on all terraces. Measured step heights of 0.225 nm (d111 and uniform contrast in the phase image of the terraces confirm the single termination in pure and Nb doped SrTiO3 single crystal substrates. Multiferroic BiFeO3 thin films were then deposited by the same microwave assisted hydrothermal process on Nb : SrTiO3 (111 substrates. Bi(NO33 and Fe(NO33 along with KOH served as the precursors solution. Ferroelectric behavior of the BiFeO3 films on Nb : SrTiO3 (100 substrates was verified by piezoresponse force microscopy.

  18. PtxGd alloy formation on Pt(111): Preparation and structural characterization

    DEFF Research Database (Denmark)

    Ulrikkeholm, Elisabeth Therese; Pedersen, Anders Filsøe; Vej-Hansen, Ulrik Grønbjerg

    2016-01-01

    Pt x Gd single crystals have been prepared in ultra high vacuum (UHV). This alloy shows promising catalytic properties for the oxygen reduction reaction. The samples were prepared by using vacuum deposition of a thick layer of Gd on a sputter cleaned Pt(111) single crystal, resulting in a ∼63nm...

  19. Oriented single-crystal nuclear resonance vibrational spectroscopy of [Fe(TPP)(MI)(NO)]: quantitative assessment of the trans effect of NO.

    Science.gov (United States)

    Lehnert, Nicolai; Sage, J Timothy; Silvernail, Nathan; Scheidt, W Robert; Alp, E Ercan; Sturhahn, Wolfgang; Zhao, Jiyong

    2010-08-02

    This paper presents oriented single-crystal Nuclear Resonance Vibrational Spectroscopy (NRVS) data for the six-coordinate (6C) ferrous heme-nitrosyl model complex [(57)Fe(TPP)(MI)(NO)] (1; TPP(2-) = tetraphenylporphyrin dianion; MI = 1-methylimidazole). The availability of these data enables for the first time the detailed simulation of the complete NRVS data, including the porphyrin-based vibrations, of a 6C ferrous heme-nitrosyl, using our quantum chemistry centered normal coordinate analysis (QCC-NCA). Importantly, the Fe-NO stretch is split by interaction with a porphyrin-based vibration into two features, observed at 437 and 472 cm(-1). The 437 cm(-1) feature is strongly out-of-plane (oop) polarized and shows a (15)N(18)O isotope shift of 8 cm(-1) and is therefore assigned to nu(Fe-NO). The admixture of Fe-N-O bending character is small. Main contributions to the Fe-N-O bend are observed in the 520-580 cm(-1) region, distributed over a number of in-plane (ip) polarized porphyrin-based vibrations. The main component, assigned to delta(ip)(Fe-N-O), is identified with the feature at 563 cm(-1). The Fe-N-O bend also shows strong mixing with the Fe-NO stretching internal coordinate, as evidenced by the oop NRVS intensity in the 520-580 cm(-1) region. Very accurate normal mode descriptions of nu(Fe-NO) and delta(ip)(Fe-N-O) have been obtained in this study. These results contradict previous interpretations of the vibrational spectra of 6C ferrous heme-nitrosyls where the higher energy feature at approximately 550 cm(-1) had usually been associated with nu(Fe-NO). Furthermore, these results provide key insight into NO binding to ferrous heme active sites in globins and other heme proteins, in particular with respect to (a) the effect of hydrogen bonding to the coordinated NO and (b) changes in heme dynamics upon NO coordination. [Fe(TPP)(MI)(NO)] constitutes an excellent model system for ferrous NO adducts of myoglobin (Mb) mutants where the distal histidine (His64

  20. Cation distribution in a Fe-bearing K-feldspar from Itrongay,Madagascar. A combined neutron- and X-ray single crystal diffractionstudy

    Energy Technology Data Exchange (ETDEWEB)

    Ackermann, Sonia; Kunz, Martin; Armbruster, Thomas; Schefer,Jurg; Hanni, Henry

    2005-05-02

    We determined the cation distribution and ordering of Si, Al and Fe on the tetrahedral sites of a monoclinic low-sanidine from Itrongay, Madagascar, by combined neutron- and X-ray single-crystal diffraction. The cation distribution was determined by means of a simultaneous refinement using neutron- and X-ray data, as well as by combining scattering densities obtained from separate refinements with chemical data from a microprobe experiment. The two methods give the same results and show that Fe is fully ordered on T1, whereas Al shows a high degree of disorder. Based on this and previously published temperature-dependent X-ray data, we conclude that it is preferential ordering of Fe on T1 even at high temperature, rather than a high diffusion kinetics of Fe, which causes this asymmetry in ordering behavior between Al and Fe. The preferential ordering of Fe3+ relative to Al3+ in T1 is consistent with its 25 percent larger ionic radius.

  1. Perpendicular magnetic tunnel junctions with a synthetic storage or reference layer: A new route towards Pt- and Pd-free junctions

    Science.gov (United States)

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2016-02-01

    We report here the development of Pt and Pd-free perpendicular magnetic tunnel junctions (p-MTJ) for STT-MRAM applications. We start by studying a p-MTJ consisting of a bottom synthetic Co/Pt reference layer and a synthetic FeCoB/Ru/FeCoB storage layer covered with an MgO layer. We first investigate the evolution of RKKY coupling with Ru spacer thickness in such a storage layer. The coupling becomes antiferromagnetic above 0.5 nm and its strength decreases monotonously with increasing Ru thickness. This contrasts with the behavior of Co-based systems for which a maximum in interlayer coupling is generally observed around 0.8 nm. A thin Ta insertion below the Ru spacer considerably decreases the coupling energy, without basically changing its variation with Ru thickness. After optimization of the non-magnetic and magnetic layer thicknesses, it appears that such a FeCoB/Ru/FeCoB synthetic storage layer sandwiched between MgO barriers can be made stable enough to actually be used as hard reference layer in single or double magnetic tunnel junctions, the storage layer being now a single soft FeCoB layer. Finally, we realize Pt- or Pd-free robust perpendicular magnetic tunnel junctions, still keeping the advantage of a synthetic reference layer in terms of reduction of stray fields at small pillar sizes.

  2. Inclusions related to catalyst and medium for transmitting pressure in diamond single crystals grown at high temperature and high pressure from the Fe-C system

    International Nuclear Information System (INIS)

    Yin Longwei; Li Musen; Hao Zhaoyin; Zhang Jiongfa

    2001-01-01

    Inclusion entrapment in a crystal is one of the most important characteristics for the crystal growth technique from solution. Diamond single crystals grown from the Fe-C system at high temperature-high pressure usually contain inclusions related to the molten catalyst and the medium (pyrophyllite) for transmitting pressure. During the growth of the diamond, the inclusions are trapped by the growth front or are formed through reaction between the contaminants trapped in the diamond. In the present article, the inclusions related to the catalyst and pyrophyllite were systemically examined by transmission electron microscopy. The chemical composition and crystal structure of the inclusions were, for the first time, determined by selected area electron diffraction pattern combined with energy dispersive x-ray spectrometry. It was shown that the inclusions are mainly composed of orthorhombic Fe 3 C, orthorhombic FeSi 2 , hexagonal SiO 2 and face-centred cubic SiC. (author)

  3. Enhanced superconductivity and anisotropy of FeTe0.6Se0.4 single crystals with Li -NH3 intercalation

    Science.gov (United States)

    Li, Chenghe; Sun, Shanshan; Wang, Shaohua; Lei, Hechang

    2017-10-01

    We report a systematic study of anisotropy resistivity, magnetoresistance, and Hall effect of Li0.32(NH3)yFe2Te1.2Se0.8 single crystals. When compared to the parent compound FeTe0.6Se0.4 , the Li-NH3 intercalation not only increases the superconducting transition temperature but also enhances the electronic anisotropy in both normal and superconducting states. Moreover, in contrast to the parent compound, the Hall coefficient RH becomes negative at low temperature, indicating electron-type carriers are dominant due to Li doping. On the other hand, the sign reverse of RH at high temperature and the failure of scaling behavior of magnetoresistance imply that hole pockets may be still crossing or just below the Fermi energy level, leading to the multiband behavior in Li0.32(NH3)yFe2Te1.2Se0.8 .

  4. Pt surface segregation in bimetallic Pt 3M alloys: A density functional theory study

    Science.gov (United States)

    Ma, Yuguang; Balbuena, Perla B.

    A simplified 5-layer slab model is used to study Pt segregation at Pt 3M(1 1 1) surfaces (M = Ag, Au, Co, Cr, Cu, Fe, Ir, Mn, Mo, Ni, Pd, Re, Rh, Ru, Ti, V). The calculated segregation energies are generally in good agreement with the experimental results. However, for Pt 3Ti(1 1 1) and Pt 3Mn(1 1 1), the model is unable to give the correct prediction because the experimental subsurface compositions are very different from those of the model. Pt segregation is found to be correlated with the subsurface atomic structure, the size of metal atoms and the surface energy. Interestingly, the calculations show that the displacement of M atoms at the topmost Pt 3M layer can be used to predict the surface segregation trend. The local geometries for the segregation and non-segregation structures are carefully compared and the surface geometric effect on the oxygen reduction reaction (ORR) activity is discussed. In particular, it is determined that the enhanced ORR activity for the Pt-skin surfaces of Pt 3Ni(1 1 1) and Pt 3Co(1 1 1) alloys are not caused by geometric effects.

  5. Imaging of domains in single crystals of BiFeO3-PbTiO3 using various microscopy techniques

    Science.gov (United States)

    Burnett, T. L.; Comyn, T. P.; Bell, A. J.; Condliffe, E.; Lloyd, G.

    2006-02-01

    Single crystals of BiFeO3-PbTiO3 have been grown from a PbO:Bi2O3 flux by cooling at a rate of 2°C/hour from the melt. Faceted crystals of various morphologies were produced and the size of the crystals ranged from less than 0.5mm to 5mm. Initial measurements were made using the scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX) semi-quantifying the composition of the crystals as well as electron probe microanalysis (EPMA). Powder X-ray diffraction (XRD) of the crushed and sieved crystals established that the structure was rhombohedral perovskite for the (BiFeO3)0.75-(PbTiO3)0.25 composition and tetragonal perovskite for the (BiFeO3)0.50-(PbTiO3)0.50 composition and mixed phase for the (BiFeO3)0.65-(PbTiO3)0.35 and (BiFeO3)0.70- (PbTiO3)0.30. X-ray pole figures verified that the (BiFeO3)0.75-(PbTiO3)0.25 crystal had grown with a single orientation, the [100] direction. Structures that are believed to be domains have been observed through optical and electron microscopy in backscattered mode. This interim report of on going investigations seeks to eventually confirm the domain structure in the crystals with electron back-scattered diffraction (EBSD).

  6. Electron paramagnetic resonance investigations of Fe3+ doped layered TiInS2 and TiGaSe2 single crystals

    International Nuclear Information System (INIS)

    Faik, Mikailov; Bulat, Rameev; Sinan, Kazan; Bekir, Aktash; Faik, Mikailov; Bulat, Rameev

    2005-01-01

    Full text : TiInS 2 and TiGaSe 2 single crystals doped by paramagnetic Fe ions have been studied at room temperature by Electron Paramagnetic Resonance (EPR) technique. A fine structure of EPR spectra of paramagnetic Fe 3 + ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe 3 + centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe 3 + site and CF parameters were determined. It was established that symmetry axis of the axial component in the CF is making an angle of about 48 and 43 degree with the plane of layers of TiInS 2 and TiGaSe 2 crystals respectively. Experimental results indicate that the Fe ions substitute In (GA) at the center of InS 4 (GaSe 4 ) tetrahedrons, and the rhombic distortion of the CF is caused by the TI ions located in the trigonal cavities between the tethedral complexes

  7. Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Chengzhou [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Fu, Shaofang [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Song, Junhua [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Shi, Qiurong [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Su, Dong [Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton NY 11973 USA; Engelhard, Mark H. [Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland WA 99354 USA; Li, Xiaolin [Energy and Environmental Directory, Pacific Northwest National Laboratory, Richland WA 99354 USA; Xiao, Dongdong [Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland WA 99354 USA; Li, Dongsheng [Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland WA 99354 USA; Estevez, Luis [Energy and Environmental Directory, Pacific Northwest National Laboratory, Richland WA 99354 USA; Du, Dan [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Lin, Yuehe [School of Mechanical and Materials Engineering, Washington State University, Pullman WA 99164 USA; Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland WA 99354 USA

    2017-02-06

    Finely controlled synthesis of high active and robust non-precious metal catalysts with excellent electrocatalytic efficiency towards oxygen reduction reaction is extremely vital for successful implementation of fuel cells and metal batteries. Unprecedented oxygen reduction reaction electrocatalytic performances and the diversified synthetic procedure in term of favorable structure/morphology characteristics make transition metals-derived M–N–C (M=Fe, Co) structures the most promising nanocatalysts. Herein, using the nitrogen-containing small molecular and inorganic salt as precursors and ultrathin tellurium nanowires as templates, we successfully synthesized a series of well-defined M-N-doped hollow carbon nanowire aerogels through one step hydrothermal route and subsequent facile annealing treatment. Taking advantage of the porous nanostructures, one-dimensional building block as well as homogeneity of active sites, the resultant Fe-N-doped carbon hollow nanowire aerogels exhibited excellent ORR electrocatalytic performance even better than commercial Pt/C in alkaline solution, holding great potential in fuel cell applications.

  8. Pt/MOx/SiO2, Pt/MOx/TiO2, and Pt/MOx/Al2O3 Catalysts for CO Oxidation

    Directory of Open Access Journals (Sweden)

    Hongmei Qin

    2015-04-01

    Full Text Available Conventional supported Pt catalysts have often been prepared by loading Pt onto commercial supports, such as SiO2, TiO2, Al2O3, and carbon. These catalysts usually have simple metal-support (i.e., Pt-SiO2 interfaces. To tune the catalytic performance of supported Pt catalysts, it is desirable to modify the metal-support interfaces by incorporating an oxide additive into the catalyst formula. Here we prepared three series of metal oxide-modified Pt catalysts (i.e., Pt/MOx/SiO2, Pt/MOx/TiO2, and Pt/MOx/Al2O3, where M = Al, Fe, Co, Cu, Zn, Ba, La for CO oxidation. Among them, Pt/CoOx/SiO2, Pt/CoOx/TiO2, and Pt/CoOx/Al2O3 showed the highest catalytic activities. Relevant samples were characterized by N2 adsorption-desorption, X-ray diffraction (XRD, transmission electron microscopy (TEM, H2 temperature-programmed reduction (H2-TPR, X-ray photoelectron spectroscopy (XPS, CO temperature-programmed desorption (CO-TPD, O2 temperature-programmed desorption (O2-TPD, and CO2 temperature-programmed desorption (CO2-TPD.

  9. The Role of Anisotropic Exchange in Single Molecule Magnets: A CASSCF/NEVPT2 Study of the Fe4 SMM Building Block [Fe2(OCH32(dbm4] Dimer

    Directory of Open Access Journals (Sweden)

    Alessandro Lunghi

    2016-09-01

    Full Text Available The rationalisation of single molecule magnets’ (SMMs magnetic properties by quantum mechanical approaches represents a major task in the field of the Molecular Magnetism. The fundamental interpretative key of molecular magnetism is the phenomenological Spin Hamiltonian and the understanding of the role of its different terms by electronic structure calculations is expected to steer the rational design of new and more performing SMMs. This paper deals with the ab initio calculation of isotropic and anisotropic exchange contributions in the Fe(III dimer [Fe 2 (OCH 3 2 (dbm 4 ]. This system represents the building block of one of the most studied Single Molecule Magnets ([Fe 4 RC(CH 2 O 3 2 (dpm 6 ] where R can be an aliphatic chain or a phenyl group just to name the most common functionalization groups and its relatively reduced size allows the use of a high computational level of theory. Calculations were performed using CASSCF and NEVPT2 approaches on the X-ray geometry as assessment of the computational protocol, which has then be used to evinced the importance of the outer coordination shell nature through organic ligand modelization. Magneto-structural correlations as function of internal degrees of freedom for isotropic and anisotropic exchange contributions are also presented, outlining, for the first time, the extremely rapidly changing nature of the anisotropic exchange coupling.

  10. Temperature-Dependent Interplay of Dzyaloshinskii-Moriya Interaction and Single-Ion Anisotropy in Multiferroic BiFeO3

    Science.gov (United States)

    Jeong, Jaehong; Le, Manh Duc; Bourges, P.; Petit, S.; Furukawa, S.; Kim, Shin-Ae; Lee, Seongsu; Cheong, S.-W.; Park, Je-Geun

    2014-09-01

    Low-energy magnon excitations in multiferroic BiFeO3 were measured in detail as a function of temperature around several Brillouin zone centers by inelastic neutron scattering experiments on single crystals. Unique features around 1 meV are directly associated with the interplay of the Dzyaloshinskii-Moriya interaction and a small single-ion anisotropy. The temperature dependence of these and the exchange interactions were determined by fitting the measured magnon dispersion with spin-wave calculations. The spectra best fit an easy-axis type magnetic anisotropy and the deduced exchange and anisotropy parameters enable us to determine the anharmonicity of the magnetic cycloid. We then draw a direct connection between the changes in the parameters of spin Hamiltonian with temperature and the physical properties and structural deformations of BiFeO3.

  11. Fine structure of an exciton coupled to a single Fe2 + ion in a CdSe/ZnSe quantum dot

    Science.gov (United States)

    Smoleński, T.; Kazimierczuk, T.; Goryca, M.; Pacuski, W.; Kossacki, P.

    2017-10-01

    We present a polarization-resolved photoluminescence study of the exchange interaction effects in a prototype system consisting of an individual Fe2 + ion and a single neutral exciton confined in a CdSe/ZnSe quantum dot. A maximal possible number of eight fully linearly polarized lines in the bright exciton emission spectrum is observed, evidencing complete degeneracy lifting in the investigated system. We discuss the conditions required for such a scenario to take place: anisotropy of the electron-hole interaction and the zero-field splitting of the Fe2 + ion spin states. Neglecting either of these components is shown to restore partial degeneracy of the transitions, making the excitonic spectrum similar to those previously reported for all other systems of quantum dots with single magnetic dopants.

  12. Diffusion of Nb in Fe and in some Fe alloys

    International Nuclear Information System (INIS)

    Kurokawa, S.; Ruzzante, J.E.; Hey, A.M.; Dyment, F.

    1981-01-01

    Diffusion data of microalloying elements such as Nb, V, Ti, are required when analysing the transformation and recrystallization behaviour of HSLA steels in order to optimize grain refinement and precipitation hardening. The diffusion behaviour of Nb in pure Fe, Fe 1.5 Mn, Fe 0.6 Si and Fe 1.5 Mn 0.6 Si has been measured between 1080 and 1200 0 C. Results indicate that Si increases Nb diffusivity while Mn decreases it. The sequence of diffusion coeficients values is: D sup(Nb) sub(Fe 1.5 Mn) [pt

  13. Prothrombin time (PT)

    Science.gov (United States)

    PT; Pro-time; Anticoagulant-prothrombin time; Clotting time: protime; INR; International normalized ratio ... PT is measured in seconds. Most of the time, results are given as what is called INR ( ...

  14. PT and INR Test

    Science.gov (United States)

    ... as alcohol, can affect the PT and INR tests. Some antibiotics can increase the PT and INR. Barbiturates, oral ... Time ; Fibrinogen ; Coagulation Factors ; Platelet Count ; Platelet Function Tests ; Thrombin Time ; Warfarin Sensitivity Testing Conditions: Bleeding Disorders , Excessive Clotting Disorders , Vitamin ...

  15. Creation of domains by direct electron beam writing in magnesium-doped LiNbO{sub 3} and LiNbO{sub 3}:Fe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Palatnikov, M.N. [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation); Kokhanchik, L.S.; Emelin, E.V. [Institute of Microelectronics Technology and High Purity Materials of Russian Academy of Sciences, 6 Academician Ossipyan st, Chernogolovka, Moscow 142432 (Russian Federation); Sidorov, N.V. [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation); Manukovskaya, D.V., E-mail: deenka@yandex.ru [Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, 26a Akademgorodok, Apatity, Murmansk 184209 (Russian Federation)

    2016-03-01

    Highlights: • The periodic domains are created in crystal LiNbO{sub 3}:Mg by direct electron beam writing. • Periodic domains appear only at equilibrium between switching and screening times. • Equilibrium exists in crystal co-doped by Fe. • Shape and appearance of domains depend on the conductivity type. - Abstract: Domain structures in the Z-cut of highly doped LiNbO{sub 3}:Mg and LiNbO{sub 3}:Mg,Fe single crystals were created by direct electron beam writing (DEBW). It was found that the value and type of electron conductivity influence the shape and number of domains thus created. Controlled electron beam regular domains were created only in samples of the crystal LiNbO{sub 3}:Mg,Fe [MgO] = 5.16 mol.%, [Fe] = 0.007 mol.%. In highly doped LiNbO{sub 3}:Mg ([MgO] = 5.19 mol.%) crystal, the domains were formed chaotically and controlled creation of domains did not occur. The domain shapes were analyzed in the framework of the theory of screening of domain nuclei depolarizing electric fields and the influence of screening on the final shape of domains. It was found that screening of intrinsic electric fields is faster in the LiNbO{sub 3}:Mg,Fe crystal. This crystal has a high electronic conductivity of hopping type with a high mobility of charge carriers. Thus, a small amount of Fe provides equilibrium between the ferroelectric switching velocity and screening of the depolarizing electric field velocity. The results are discussed considering differences in the electron conductivity mechanisms, which control the screening of depolarizing electric field velocity and spatial charge area formed under an electron beam.

  16. Growth and Characterization of Ce- Substituted Nd2Fe1411B Single Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Susner, M. A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Conner, B. S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Saparov, B. I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; McGuire, M. A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Crumlin, E. J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source; Veith, G. M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source; Cao, H. B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division; Shanavas, K. V. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Parker, D. S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Chakoumakos, B. C. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division; Sales, B. C. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division

    2015-08-31

    Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux. Chemical and structural analysis of the crystals indicates that (Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a Vegard-like variation of the lattice constants with x. Refinements of single crystal neutron diffraction data indicate that Ce has a slight site preference (7:3) for the 4g rare earth site over the 4f site. Furthermore, magnetization measurements show that for x = 0.38 the saturation magnetization at 400 K, a temperature important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6 μB/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie temperature decreases from 586 to 543 K. First principles calculations carried out within density functional theory are used to explain the decrease in magnetic properties due to Ce substitution. Although the presence of the lower-cost and more abundant Ce slightly affects these important magnetic characteristics, this decrease is not large enough to affect a multitude of applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance permanent magnet material with substantially reduced Nd content.

  17. Risk of biochemical recurrence and timing of radiotherapy in pT3a N0 prostate cancer with positive surgical margin. A single center experience

    International Nuclear Information System (INIS)

    Hegemann, Nina-Sophie; Morcinek, Sebastian; Corradini, Stefanie; Li, Minglun; Belka, Claus; Ganswindt, Ute; Buchner, Alexander; Karl, Alexander; Stief, Christian; Knuechel, Ruth

    2016-01-01

    Despite improved biochemical recurrence-free survival rates by the use of immediate adjuvant radiotherapy (RT) in patients with locally advanced prostate cancer, disagreement about the need and timing of RT remains. From 2005-2009, 94 patients presenting with a stage pT3a N0 and microscopic positive resection margin were retrospectively analyzed after radical prostatectomy. Special attention was given to patients' outcome, the frequency of additive RT, and its efficacy. Median follow-up was 80 months. A total of 71 patients had a negative postoperative prostate-specific antigen (PSA) level (<0.07 ng/ml). Thirty-six of them did not experience any PSA relapse (subgroup 1). Fourteen of them received additive RT and during follow-up all 36 patients remained PSA negative. Of 71 initially PSA-negative patients, 35 had a biochemical relapse (subgroup 2); 28 patients underwent salvage RT. The median PSA value before salvage RT was 0.24 ng/ml and was subsequently negative (<0.07 ng/ml) in 23 patients after RT. Of the entire cohort, 23 patients had persisting PSA after surgery (subgroup 3). Of these, 18 patients received salvage RT at a median PSA level of 0.4 ng/ml. One patient in subgroup 1, 5 patients in subgroup 2, and 9 patients in subgroup 3 had ongoing androgen deprivation therapy. The present study of 94 pT3a N0 R1 prostate cancer patients provides insight into medical care of this patient cohort and underlines the need for additive RT for the majority of patients to achieve long-term biochemical control. Although immediate adjuvant RT was applied with restraint (20 %), during the observation period 60 of 94 patients (63.8 %) received RT - highlighting the need of postoperative treatment. (orig.) [de

  18. Interface-induced spin Hall magnetoresistance enhancement in Pt-based tri-layer structure.

    Science.gov (United States)

    Huang, Shun-Yu; Li, Hong-Lin; Chong, Cheong-Wei; Chang, Yu-Ying; Lee, Min-Kai; Huang, Jung-Chun-Andrew

    2018-01-08

    In this study, we integrated bilayer structure of covered Pt on nickel zinc ferrite (NZFO) and CoFe/Pt/NZFO tri-layer structure by pulsed laser deposition system for a spin Hall magnetoresistance (SMR) study. In the bilayer structure, the angular-dependent magnetoresistance (MR) results indicate that Pt/NZFO has a well-defined SMR behavior. Moreover, the spin Hall angle and the spin diffusion length, which were 0.0648 and 1.31 nm, respectively, can be fitted by changing the Pt thickness in the longitudinal SMR function. Particularly, the MR ratio of the bilayer structure (Pt/NZFO) has the highest changing ratio (about 0.135%), compared to the prototype structure Pt/Y 3 Fe 5 O 12 (YIG) because the NZFO has higher magnetization. Meanwhile, the tri-layer samples (CoFe/Pt/NZFO) indicate that the MR behavior is related with CoFe thickness as revealed in angular-dependent MR measurement. Additionally, comparison between the tri-layer structure with Pt/NZFO and CoFe/Pt bilayer systems suggests that the SMR ratio can be enhanced by more than 70%, indicating that additional spin current should be injected into Pt layer.

  19. High pressure growth and electron transport properties of superconducting SmFeAsO1−xHx single crystals

    Directory of Open Access Journals (Sweden)

    Soshi Iimura

    2017-09-01

    Full Text Available We report the single crystal growth and characterization of the highest Tc iron-based superconductor SmFeAsO1−xHx. Some sub-millimeter-sized crystals were grown using the mixture flux of Na3As + 3NaH + As at 3.0 GPa and 1473 K. The chemical composition analyses confirmed 10% substitution of hydrogen for the oxygen site (x = 0.10, however, the structural analyses suggested that the obtained crystal forms a multi-domain structure. By using the FIB technique we fabricated the single domain SmFeAsO0.9H0.10 crystal with the Tc of 42 K, and revealed the metallic conduction in in-plane (ρab, while semiconducting in the out-of-plane (ρc. From the in-plane Hall coefficient measurements, we confirmed that the dominant carrier of SmFeAsO0.9H0.10 crystal is an electron, and the hydride ion occupied at the site of the oxygen ion effectively supplies a carrier electron per iron following the equation: O2− → H− + e−.

  20. Re-creation of single phase, and improvement of magnetic property of CoFe2O4 nanoparticles versus heat treatment

    Science.gov (United States)

    Tran, N.; Kim, D. H.; Phan, T. L.; Dang, N. T.; Bach, T. N.; Manh, D. H.; Lee, B. W.

    2018-03-01

    Our studies on the crystal characterization and magnetic property of CoFe2O4 nanoparticles (NPs) point out their instability in a specific temperature range. While as-prepared NPs exhibit single phase in a cubic spinel structure, annealing at temperatures T=673-1273 K leads to the development of an impurity phase of Fe2O3. Interestingly, annealing at higher temperatures re-creates the single phase of NPs. This strongly influences their magnetic property. The magnetic inhomogeneity and/or multiple phase exist in as-prepared NPs and in those annealed below 1273 K, better magnetic property is found in the samples with annealing temperature (Tan) higher than 1273 K. Ferromagnetic-paramagnetic phase transition temperatures of these samples are located around 815-850 K, and are less dependent on Tan. At room temperature, their saturation magnetization is located in the range of 41-55 emu/g, while the coercivity can be changed from 600 to 3200 Oe. These results are related to microstructures, structural phases, and exchange interactions between Fe and Co ions situated in the A and B sites of the spinel structure, which are modified by heat treatment.

  1. Effects of intermediate layers on magnetic properties and read/write performance in CoCrPt perpendicular recording media with an FeHfN soft magnetic underlayer

    International Nuclear Information System (INIS)

    Hong, D.H.; Shin, J.N.; Lee, T.D.; Hong, S.Y.; Lee, H.J.

    2003-01-01

    In this study, the effects of CoCrPtTa and CoCrPtB magnetic intermediate layers (ILs) on the magnetic properties and read/write performance of CoCrPt/soft magnetic layer perpendicular recording media were investigated. Even though the perpendicular coercivity of the media with these ILs was reduced by 500 Oe, these media still showed a low exchange slope of 1.4 and a large negative nucleation field of about -1000 Oe. Additionally, the reduced grain size of the media with these IL was observed by transmission electron microscopy. From the read/write test, these media with ILs showed improved performance of 3-5 dB higher signal-to-noise ratio and overwrite ratio (OW) compared to the media without ILs. These enhancements could be attributed to the reduction of grain size of the magnetic layer and weakening of the intergranular interaction between grains by insertion of the IL

  2. Reclamation of acid pickling waste: A facile route for preparation of single-phase Fe3O4 nanoparticle

    Science.gov (United States)

    Zhang, Wenxue; Lu, Bin; Tang, Huihui; Zhao, Jingxiang; Cai, Qinghai

    2015-05-01

    Using an alternative method of dropwise addition of iron salt in NaOH aqueous solution, nanocrystalline Fe3O4 materials were prepared from acid pickling waste as a starting material with ultrasonic enhancement and polyethylene glycol as a dispersant, as proved by XRD, TEM, TG-DSC and ICP-MS. The results showed that the Fe3O4 material was a well-crystallized magnetite with an average size of about 25 nm and purity 99.15%. Magnetic measurement revealed the nanocrystals were stronger superparamagnetic with a saturation magnetization of 82.1 emu/g.

  3. Study on single step solid state synthesis of WC@C nanocomposite and electrochemical stability of synthesized WC@C & Pt/WC@C for alcohol oxidation (methanol/ethanol)

    Energy Technology Data Exchange (ETDEWEB)

    Singla, Gourav, E-mail: gsinghla@gmail.com; Singh, K., E-mail: kusingh@thapar.edu; Pandey, O.P., E-mail: oppandey@thapar.edu

    2016-04-25

    WC@C nano composite was prepared by a single step solid–state reaction through in situ reduction and carburization of WO{sub 3} in the presence of Mg and activated charcoal. The XRD results and thermodynamics analysis showed that the optimization of reaction temperature facilitates the reduction as well as carburization of tungsten oxide(s) at different reaction temperature. Thermogravimetric analysis of the product was done to assess the thermal stability in air. The Raman spectroscopy was used to find out the nature (amorphous/graphitic) of carbon in the obtained phase. The N{sub 2} adsorption–desorption measurement showed a narrow pore size distribution from 3 to 4 nm with BET surface area of up to 522.5 m{sup 2}/g. TEM/HRTEM images confirmed formation of the WC nano particles with spherical morphology. Electrochemical stability of pure and platinized carbide sample (Pt/WC) has been investigated using cyclic voltammetry in acidic media for alcohol (methanol and ethanol) oxidation. - Highlights: • Tungsten carbide nano powder was synthesized using charcoal as carbon source. • Formation of WC occurs through the formation of lower tungsten oxide. • CO{sub 2}/CO ratio effect the formation of WC. • Mesoporous tungsten carbide with surface areas 522.5 m{sup 2}/g obtained by using charcoal. • Pt modified WC powder showed higher electrochemical stability.

  4. Polarized Light Microscopy Study on the Reentrant Phase Transition in a (Ba1 – xKxFe2As2 Single Crystal with x = 0.24

    Directory of Open Access Journals (Sweden)

    Yong Liu

    2016-11-01

    Full Text Available A sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba1 − xKxFe2As2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba1 − xKxFe2As2 (x = 0.24 single crystal below a temperature of simultaneous structural/magnetic transition TN ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT to low temperature orthorhombic (LTO1 structure at TN ~ 80 K, LTO1 to low temperature tetragonal (LTT structure at Tc ~ 25 K, and LTT to low temperature orthorhombic (LTO2 structure at T ~ 15 K.

  5. Synthesis of High-quality Single- and Double-walled Carbon Nanotubes on Fe/MgO Catalysts

    Directory of Open Access Journals (Sweden)

    Mehran B. Kashi

    2016-06-01

    Full Text Available In this study, Fe/MgO catalysts with three different iron contents (5, 10, and 15 wt.% were prepared by three catalyst preparation methods: impregnation, solution combustion synthesis, and co-calcination of metal ni‐ trates. The resulting catalysts were subjected to methane at 900°C in order to grow carbon nanotubes (CNTs. The powders and products were then studied by X-ray diffraction (XRD, differential thermal analysis (DTA, scanning and transmission electron microscopy (SEM and TEM, and Raman spectroscopy. Formation of MgFe2O4 upon heating the catalysts to 900°C was confirmed by XRD. After the growth step, corresponding peaks of MgFe2O4 disappeared and metallic iron peaks appeared, indicating that MgFe2O4 is the responsible phase for production of iron nanoparticles. HRTEM images showed that the product on the 5 wt.% catalysts was mostly SWNTs and DWNTs with no evidence of carbon nanofi‐ bres or multi-walled carbon nanotubes on the co-calcina‐ tion catalyst. Furthermore, ID/IG ratios obtained from Raman spectra were all below 0.1, except for one sample, showing the good quality of the products.

  6. Investigating magnetic proximity effects at ferrite/Pt interfaces

    Science.gov (United States)

    Collet, M.; Mattana, R.; Moussy, J.-B.; Ollefs, K.; Collin, S.; Deranlot, C.; Anane, A.; Cros, V.; Petroff, F.; Wilhelm, F.; Rogalev, A.

    2017-11-01

    Spintronic devices based on pure spin currents have drawn a lot of attention during the last few years for low energy device design. One approach to generate pure spin currents is to combine a metallic or insulating ferromagnetic layer with a non-magnetic metallic layer with a large spin-orbit coupling. A recent controversy has arisen in the possible role of magnetic proximity effects at ferromagnetic/non-magnetic interfaces, which can hamper the understanding of pure spin current generation mechanisms. While magnetic proximity effects have been frequently observed at ferromagnetic metal/non-magnetic interfaces, there are only a few studies on ferromagnetic insulator/non-magnetic interfaces. Regarding the use of ferromagnetic insulators, the focus has been mainly on yttrium iron garnet (YIG). However, investigation of induced magnetic moments at YIG/Pt interfaces has engendered contradictory results. Here, we propose to study insulating ferrites for which electronic and magnetic properties can be modulated. Magnetic proximity effects have been investigated at MnFe2O4/Pt, CoFe2O4/Pt, and NiFe2O4/Pt interfaces by X-ray circular magnetic dichroism (XMCD) measurements at the Pt L3 edge. Although hybridization with Pt seems to be different among the ferrites, we do not detect any XMCD signal as the signature of an induced magnetism in Pt. We have then studied the Fe3O4 ferrite below and above the Verwey transition temperature. No XMCD signal has been measured in the insulating or conducting phase of Fe3O4. This suggests that the absence of magnetic proximity effects at ferrite/Pt interfaces is not linked to the insulating character or not of the ferrites.

  7. Effect of hydrogen on the growth and morphology of single wall carbon nanotubes synthesized on a Fe-Mo/MgO catalytic system

    Energy Technology Data Exchange (ETDEWEB)

    Biris, Alexandru R. [National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj Napoca, RO-3400 (Romania)], E-mail: biris@oc1.itim-cj.ro; Li Zhongrui; Dervishi, Enkeleda [Applied Science Department, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Nanotechnology Center, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Lupu, Dan [National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj Napoca, RO-3400 (Romania); Xu Yang; Saini, Viney [Applied Science Department, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Nanotechnology Center, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Watanabe, Fumiya [Nanotechnology Center, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Biris, Alexandru S. [Applied Science Department, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States); Nanotechnology Center, University of Arkansas at Little Rock, 2801 S. University Ave, Little Rock, AR 72204 (United States)], E-mail: asbiris@ualr.edu

    2008-04-21

    Single wall carbon nanotubes were synthesized from thermal pyrolysis of methane on a Fe-Mo/MgO catalyst by radio frequency catalytic chemical vapor deposition (RF-CVD) using argon as a carrier gas. Controlled amounts of hydrogen (H{sub 2}/CH{sub 4}=0-1 v/v) were introduced in separate experiments along with the carbon source. The properties and morphology of the synthesized single wall carbon nanotubes were monitored by transmission electron microscopy, Raman scattering, and thermogravimetric analysis. The nanotubes with the highest crystallinity were obtained with H{sub 2}/CH{sub 4}=0.6. By monitoring the Radial Breathing Modes present in the Raman spectra of the single-wall carbon nanotube samples, the variation of the structural and morphological properties of the carbon nanotubes with the flow level of hydrogen, reflect changes of the catalyst systems induced by the presence of hydrogen.

  8. Preparation of PtSn/C, PtRu/C, PtRh/C, PtRuRh/C and PtSnRh/C electrocatalysts using an alcohol-reduction process for methanol and ethanol oxidation; Preparacao e caracterizacao de eletrocatalisadores PtRu, PtSn, PtRh, PtRuRh e PtSnRh para oxidacao direta de alcoois em celulas a combustivel tipo PEM utilizando a metodologia da reducao por alcool

    Energy Technology Data Exchange (ETDEWEB)

    Dias, Ricardo Rodrigues

    2009-07-01

    In this work, Pt/C, PtRh (90:10), PtRh/C (50:50), PtSn/C (50:50), PtRu (50:50)/C, PtRuRh/C (50:40:10) and PtSnRh/C (50:40:10) were prepared by an alcohol-reduction process with metal loading of 20 wt.% using H{sub 2}PtCl{sub 6}.6H{sub 2}O (Aldrich), SnCl{sub 2}.2H{sub 2}O (Aldrich),and RhCl{sub 2}.XH{sub 2}O (Aldrich) as metals sources and Vulcan XC72 as support. The electrocatalysts were characterized by EDX, XRD and cyclic voltammetry (CV). The electro-oxidation of ethanol was studied by CV, chronoamperomety at room temperature in acid medium and tests at 100 deg C on a single cell of a direct methanol or ethanol fuel cell. The EDX analysis showed that the metal atomic ratios of the obtained electrocatalysts were similar to the nominal atomic ratios used in the preparation. The diffractograms of electrocatalysts prepared showed four peaks at approximately 2{theta} =40 deg, 47 deg, 67 deg and 82 deg, which are associated with the (111), (200), (220) and (311) planes, respectively, of a face cubic-centered (fcc) structure characteristic of platinum and platinum alloys. The average crystallite sizes using the Scherrer equation and the calculated values were in the range of 2-3 nm. For Pt Sn/C and PtSnRh/C two additional peaks were observed at 2 = 34 deg and 52 deg that were identified as a SnO{sub 2} phase. Pt Sn/C (50:50) and PtSnRh/C (50:40:10) electro catalyst showed the best performance for ethanol oxidation at room temperature. For methanol oxidation at room temperature Pt Ru/C, Pt Sn/C and PtRuRh/C electrocatalysts showed the best performance. Tests at 100 deg C on a single cell of a direct ethanol fuel cell PtSnRh/C showed the best performance, for methanol oxidation PtRuRh/C showed the best performance. (author)

  9. Electrocatalysis of fuel cells reaction on Pt and Pt-bimetallic anode catalysts: A selective review

    Directory of Open Access Journals (Sweden)

    Stamenković Vojislav

    2002-01-01

    Full Text Available In this review we selectively summarize recent progress, primarily from our laboratory, in the development of interrelationships between the kinetics of the fuel cells reactions and the structure/composition of anode catalysts. The focus is placed on two types of metallic surfaces: platinum single crystals and bimetallic surfaces based on Pt. In the first part it was illustrated that the hydcogen reaction is structure sensitive process, with Pt(110 being an order of magnitude more active than either of the atomically "flatter" (100 and (111 surfaces. The hydrogen reaction on Pt(hkl modified by pseudomorphic Pd (submonolayers shows the "volcano-like" behavior, having the maximum rate on Pt(111 modified by 1 ML of Pd. The Pt(111-Pd system is used to demonstrate how the energetics of intermediates formed in the hydrogen reaction is affected by interfacial bonding and energetic constraints produced between pseudomorphic Pd films and the Pt(111 substrate. In the second part it was shown that the oxidation of Ha in the presence of CO occurs concurrently with CO oxidation on Pt and Pt bimetallic surfaces. The Pt-Ru system is used to demonstrate that both the bifunctional effect and the ligand effect contribute to the influence of Ru on the CO oxidation rate and for Hz oxidation process in the presence of CO. The knowledge is then used to create the real-life catalyst with the catalytic activities which are, to the greatest extend possible similar to the tailor-made surface.

  10. Application of electrochemical method to microfabricated region in single-crystal device of FeSe1‑ x Te x superconductors

    Science.gov (United States)

    Okada, Kazuhiro; Takagi, Tomohiro; Kobayashi, Masahiro; Ohnuma, Haruka; Noji, Takashi; Koike, Yoji; Ayukawa, Shin-ya; Kitano, Haruhisa

    2018-04-01

    The application of an electrochemical method to the iron-based chalcogenide superconductors has great potentials in enhancing their properties such as the superconducting transition temperature. Unfortunately, this method has been limited to polycrystalline powders or thin film samples with a large surface area. Here, we demonstrate that the electrochemical method can be usefully applied to single-crystal devices of FeSe1‑ x Te x superconductors by combining it with the focused ion beam (FIB) microfabrication techniques. Our results open a new route to developing the high-quality superconducting devices fabricated using layered iron-based chalcogenides, whose properties are electrochemically controlled.

  11. New insights on the magnetic properties of ferromagnetic FePd3 single-crystals encapsulated inside carbon nanomaterials

    Science.gov (United States)

    Boi, Filippo S.; Du, Yuxuan; Ivaturi, Sameera; He, Yi; Wang, Shanling

    2017-03-01

    FePd3-type alloys have attracted strong interest due to their unusual pressure-induced Invar behaviour characterized by anomalously low thermal expansion properties. However, little is known about the factors controlling their magnetization properties. Here we present a chemical vapour deposition approach which allows the encapsulation of FePd3 alloys into a spherical type of carbon nanomaterial consisting of concentrically arranged distorted-carbon-layers. A dependence of the magnetic properties of this soft ferromagnetic phase on the crystal-grain-size is found by comparing the results in the present study with those reported in literature. The fabricated samples are characterized in detail by electron microscopy, x-ray and electron diffraction and magnetometry.

  12. Structure refinement of the δ1p phase in the Fe-Zn system by single-crystal X-ray diffraction combined with scanning transmission electron microscopy.

    Science.gov (United States)

    Okamoto, Norihiko L; Tanaka, Katsushi; Yasuhara, Akira; Inui, Haruyuki

    2014-04-01

    The structure of the δ1p phase in the iron-zinc system has been refined by single-crystal synchrotron X-ray diffraction combined with scanning transmission electron microscopy. The large hexagonal unit cell of the δ1p phase with the space group of P63/mmc comprises more or less regular (normal) Zn12 icosahedra, disordered Zn12 icosahedra, Zn16 icosioctahedra and dangling Zn atoms that do not constitute any polyhedra. The unit cell contains 52 Fe and 504 Zn atoms so that the compound is expressed with the chemical formula of Fe13Zn126. All Fe atoms exclusively occupy the centre of normal and disordered icosahedra. Iron-centred normal icosahedra are linked to one another by face- and vertex-sharing forming two types of basal slabs, which are bridged with each other by face-sharing with icosioctahedra, whereas disordered icosahedra with positional disorder at their vertex sites are isolated from other polyhedra. The bonding features in the δ1p phase are discussed in comparison with those in the Γ and ζ phases in the iron-zinc system.

  13. Synthesis and magneto-transport properties of single PEDOT/Ni and PEDOT/Ni30Fe70 core/shell nanowires

    International Nuclear Information System (INIS)

    Hangarter, Carlos M.; Rheem, Youngwoo; Stahovich, Thomas; Myung, Nosang V.

    2011-01-01

    Single polyethylenedioxythiophene (PEDOT) nanowires bridging pairs of electrodes were utilized as positive templates to create PEDOT/Ni and PEDOT/Ni 30 Fe 70 core/shell nanowires by electrodepositing ferromagnetic material (i.e., Ni and Ni 30 Fe 70 ) on the entire assembly, including both the electrodes and nanowire. The temperature dependence of the electrical resistance indicated that electrons are transported predominately through the ferromagnetic shell. The magnetoresistive (MR) behavior of the core/shell nanowires was investigated as a function of temperature, magnetic field orientation, shell thickness, and composition. The MR behavior of the PEDOT/Ni core/shell nanowires was anomalous for low applied magnetic fields, deviating from expected anisotropic magnetoresistance, with positive ΔR/R O values for all field orientations. PEDOT/Ni 30 Fe 70 core/shell nanowires displayed the opposite behavior, with negative ΔR/R O for both longitudinal and transverse field orientations. The origin of this magnetoresistive behavior is postulated to be a geometry induced domain wall effect.

  14. Single crystal growth of 67%BiFeO 3 -33%BaTiO 3 solution by the floating zone method

    Energy Technology Data Exchange (ETDEWEB)

    Rong, Y.; Zheng, H.; Krogstad, M. J.; Mitchell, J. F.; Phelan, D.

    2018-01-01

    The growth conditions and the resultant grain morphologies and phase purities from floating-zone growth of 67%BiFeO3-33%BaTiO3 (BF-33BT) single crystals are reported. We find two formidable challenges for the growth. First, a low-melting point constituent leads to a pre-melt zone in the feed-rod that adversely affects growth stability. Second, constitutional super-cooling (CSC), which was found to lead to dendritic and columnar features in the grain morphology, necessitates slow traveling rates during growth. Both challenges were addressed by modifications to the floating-zone furnace that steepened the temperature gradient at the melt-solid interfaces. Slow growth was also required to counter the effects of CSC. Single crystals with typical dimensions of hundreds of microns have been obtained which possess high quality and are suitable for detailed structural studies.

  15. Analysis of the effect of gallium content on the magnetomechanical behavior of single-crystal FeGa alloys using an energy-based model

    International Nuclear Information System (INIS)

    Atulasimha, Jayasimha; Flatau, Alison B; Cullen, James R

    2008-01-01

    The magnetomechanical behavior of single-crystal iron–gallium alloys with varying gallium content was found to be strongly dependent on the Ga content (Atulasimha 2006 PhD Thesis). An energy-based model (Atulasimha 2006 PhD Thesis, Armstrong and William 1997 J. Appl. Phys. 81 2321) is employed to simulate the strikingly different actuation behavior (λ–H and B–H curves under different compressive stresses) and validated against experimental data for 19, 24.7 and 29 at.% Ga, [100] oriented, slow-cooled single-crystal FeGa alloys. The effect of gallium content on the model parameters, specifically the cubic magnetocrystalline anisotropy constants and the Armstrong-smoothing factor Ω, their physical significance and ultimately their effect on the magnetomechanical behavior are analyzed and explained

  16. A Theoretical Investigation on CO Oxidation by Single-Atom Catalysts M1/γ-Al2O3(M=Pd, Fe, Co, and Ni).

    Science.gov (United States)

    Yang, Tao; Fukuda, Ryoichi; Hosokawa, Saburo; Tanaka, Tsunehiro; Sakaki, Shigeyoshi; Ehara, Masahiro

    2017-04-07

    Single-atom catalysts have attracted much interest recently because of their excellent stability, high catalytic activity, and remarkable atom efficiency. Inspired by the recent experimental discovery of a highly efficient single-atom catalyst Pd 1 /γ-Al 2 O 3 , we conducted a comprehensive DFT study on geometries, stabilities and CO oxidation catalytic activities of M 1 /γ-Al 2 O 3 (M=Pd, Fe, Co, and Ni) by using slab-model. One of the most important results here is that Ni 1 /Al 2 O 3 catalyst exhibits higher activity in CO oxidation than Pd 1 /Al 2 O 3 . The CO oxidation occurs through the Mars van Krevelen mechanism, the rate-determining step of which is the generation of CO 2 from CO through abstraction of surface oxygen. The projected density of states (PDOS) of 2 p orbitals of the surface O, the structure of CO-adsorbed surface, charge polarization of CO and charge transfer from CO to surface are important factors for these catalysts. Although the binding energies of Fe and Co with Al 2 O 3 are very large, those of Pd and Ni are small, indicating that the neighboring O atom is not strongly bound to Pd and Ni, which leads to an enhancement of the reactivity of the O atom toward CO. The metal oxidation state is suggested to be one of the crucial factors for the observed catalytic activity.

  17. The structural and magnetic properties of CsxFe2-ySe2 as determined by x ray and neutron scattering of powder and single crystal samples

    Science.gov (United States)

    Taddei, Keith; Chmaissem, Omar; Sturza, Mihai; Avci, Sevda; Claus, Helmut; Kanatzids, Mercouri; Rosenkranz, Stephan; Osborn, Ray

    2014-03-01

    The AxFe2-ySe2 family of iron selenides (A = K, Rb and Cs) has proven an intricate system for the study of unconventional superconductivity, exhibiting high temperature superconductivity (~ 30 K) and a complex structural phase transition into a biphasic state coupled with a high temperature magnetic transition (~ 500 K). While isostructural to the 122 arsenides, significant structural differences are identified. In the selenides, iron vacancies in the tetrahedral FeSe layers become ordered below a high temperature structural transition defining a main phase √ 5 × √ 5 superstructure. Coexistent with the main phase, a secondary phase of a previously contested structure is observed and it is in this biphasic state that superconductivity arises at ~ 30 K. Both powder and single crystal samples show similar phase separation and coexistence. In this talk, I will discuss structural results and lattice parameter evolution obtained from neutron powder diffraction as well as single crystal x-ray diffraction with an emphasis on a novel magnetic structural model, the identification of the secondary phase, and the nature of coincidence of the magnetic, structural and secondary phase transitions.

  18. Muon spin rotation study of magnetism and superconductivity in Ba(Fe1-xCox)2As2 single crystals

    DEFF Research Database (Denmark)

    Bernhard, C.; Wang, C. N.; Nuccio, L.

    2012-01-01

    Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1−xCox)2As2 single crystals with 0 ≤x ≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the nonsu......Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1−xCox)2As2 single crystals with 0 ≤x ≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity...... caused by the randomly distributed Co atoms. A different kind of magnetic order that was also previously identified [C. Bernhard et al., New J. Phys. 11, 055050 (2009)] occurs at 0.055 magnetic order develops here only in parts of the sample volume...... and it seems to cooperate with superconductivity since its onset temperature coincides with Tc. Even in the strongly overdoped regime at x = 0.11, where the static magnetic order has disappeared, we find that the low-energy spin fluctuations are anomalously enhanced below Tc. These findings point toward...

  19. Sorption separation of Eu and As from single-component systems by Fe-modified biochar. Kinetic and equilibrium study

    International Nuclear Information System (INIS)

    Fristak, Vladimir; Soja, Gerhard; Michalekova-Richveisova, Barbora; Pipiska, Martin; Viglasova, Eva; Galambos, Michal; Duriska, Libor; Moreno-Jimenez, Eduardo

    2017-01-01

    The utilization of carbonaceous materials in separation processes of radionuclides, heavy metals and metalloids represents a burning issue in environmental and waste management. The main objective of this study was to characterize the effect of chemical modification of corncob-derived biochar by Fe-impregnations on sorption efficiency of Eu and As as a model compounds of cationic lanthanides and anionic metalloids. The biochar sample produced in slow pyrolysis process at 500 C before (BC) and after (IBC) impregnation process was characterized by elemental, FTIR, SEM-EDX analysis to confirm the effectiveness of Fe-impregnation process. The basic physico-chemical properties showed differences in surface area and pH values of BC- and IBC-derived sorbents. Sorption processes of Eu and As by BC and IBC were characterized as a time- and initial concentration of sorbate-dependent processes. The sorption equilibrium was reached for both sorbates in 24 h of contact time. Batch equilibrium experiments revealed the increased maximum sorption capacities (Q max ) of IBC for As about more than 20 times (Q max BC 0.11 and Q max IBC 2.26 mg g -1 ). Our study confirmed negligible effect of Fe-impregnation on sorption capacity of biochar for Eu (Q max BC 0.89 and Q max IBC 0.98 mg g -1 ). The iron-impregnation of biochar-derived sorbents can be utilized as a valuable treatment method to produce stable and more effective sorption materials for various xenobiotics separation from liquid wastes and aqueous solutions.

  20. Sorption separation of Eu and As from single-component systems by Fe-modified biochar. Kinetic and equilibrium study

    Energy Technology Data Exchange (ETDEWEB)

    Fristak, Vladimir; Soja, Gerhard [Austrian Institute of Technology GmbH, Tulln (Austria). Energy Dept. Environmental Resources and Technologies; Michalekova-Richveisova, Barbora; Pipiska, Martin [Trnava Univ. (Slovakia). Dept. of Chemistry; Viglasova, Eva; Galambos, Michal [Comenius Univ., Bratislava (Slovakia). Dept. of Inorganic Chemistry; Duriska, Libor [Slovak Univ. of Technology in Bratislava, Trnava (Slovakia). Faculty of Materials Science and Technology; Moreno-Jimenez, Eduardo [Univ. Autonoma de Madrid (Spain). Dept. de Quimica Agricola y Bromatologia

    2017-03-15

    The utilization of carbonaceous materials in separation processes of radionuclides, heavy metals and metalloids represents a burning issue in environmental and waste management. The main objective of this study was to characterize the effect of chemical modification of corncob-derived biochar by Fe-impregnations on sorption efficiency of Eu and As as a model compounds of cationic lanthanides and anionic metalloids. The biochar sample produced in slow pyrolysis process at 500 C before (BC) and after (IBC) impregnation process was characterized by elemental, FTIR, SEM-EDX analysis to confirm the effectiveness of Fe-impregnation process. The basic physico-chemical properties showed differences in surface area and pH values of BC- and IBC-derived sorbents. Sorption processes of Eu and As by BC and IBC were characterized as a time- and initial concentration of sorbate-dependent processes. The sorption equilibrium was reached for both sorbates in 24 h of contact time. Batch equilibrium experiments revealed the increased maximum sorption capacities (Q{sub max}) of IBC for As about more than 20 times (Q{sub max} BC 0.11 and Q{sub max} IBC 2.26 mg g{sup -1}). Our study confirmed negligible effect of Fe-impregnation on sorption capacity of biochar for Eu (Q{sub max} BC 0.89 and Q{sub max} IBC 0.98 mg g{sup -1}). The iron-impregnation of biochar-derived sorbents can be utilized as a valuable treatment method to produce stable and more effective sorption materials for various xenobiotics separation from liquid wastes and aqueous solutions.

  1. High magnetic field susceptibility and neutron scattering measurements for ZnFe2O4 single crystal

    International Nuclear Information System (INIS)

    Kamazawa, Kazuya; Nakajima, Kenji; Kohn, Key; Tsunoda, Yorihiko

    2004-01-01

    We studied field dependences of magnetic susceptibility and neutron scattering measurements for frustrated normal spinel ZnFe 2 O 4 . Although a peak which is similar to the antiferromagnetic transition is observed at 13 K in the magnetic susceptibility, there is no magnetic long-range order in our neutron scattering measurements. When we measure the magnetic susceptibility under the high magnetic field, the peak position moves toward the high temperature. In the neutron scattering measurements, magnetic diffuse scattering around the nuclear Bragg peaks disappear under the magnetic field of 3 T

  2. Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst.

    Science.gov (United States)

    Chung, Dong Young; Jun, Samuel Woojoo; Yoon, Gabin; Kim, Hyunjoong; Yoo, Ji Mun; Lee, Kug-Seung; Kim, Taehyun; Shin, Heejong; Sinha, Arun Kumar; Kwon, Soon Gu; Kang, Kisuk; Hyeon, Taeghwan; Sung, Yung-Eun

    2017-05-17

    A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm -2 , which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extended X-ray absorption fine structure analysis combined with electrochemical test shows that carbon shell coating prevents FeP nanoparticles from oxidation, making them highly stable under hydrogen evolution reaction operation conditions. Furthermore, we demonstrate that our synthetic method is suitable for mass production, which is highly desirable for large-scale hydrogen production.

  3. Heterojunction nanowires having high activity and stability for the reduction of oxygen: Formation by self-assembly of iron phthalocyanine with single walled carbon nanotubes (FePc/SWNTs)

    KAUST Repository

    Zhu, Jia

    2014-04-01

    A self-assembly approach to preparing iron phthalocyanine/single-walled carbon nanotube (FePc/SWNT) heterojunction nanowires as a new oxygen reduction reaction (ORR) electrocatalyst has been developed by virtue of water-adjusted dispersing in 1-cyclohexyl-pyrrolidone (CHP) of the two components. The FePc/SWNT nanowires have a higher Fermi level compared to pure FePc (d-band center, DFT. =. -0.69. eV versus -0.87. eV, respectively). Consequently, an efficient channel for transferring electron to the FePc surface is readily created, facilitating the interaction between FePc and oxygen, so enhancing the ORR kinetics. This heterojunction-determined activity in ORR illustrates a new stratagem to preparing non-noble ORR electrocatalysts of significant importance in constructing real-world fuel cells. © 2013 Elsevier Inc.

  4. Evaluation of natural organic matter adsorption on Fe-Al binary oxide: Comparison with single metal oxides.

    Science.gov (United States)

    Kim, Kyung-Jo; Jang, Am

    2017-10-01

    The adsorption characteristics of three types of standard natural organic matter (NOM) on iron-aluminum (Fe-Al) binary oxide (FAO) and heated aluminum oxide (HAO) under natural surface water condition were investigated using various adsorption isotherms and kinetic models. FAO was synthesized by Fe oxide and Al oxide, mixed using the sol-gel hydrothermal method, and aluminum sulfate was used to make HAO. The amount of adsorbed NOM was increased to 79.6 mg g -1 for humic acid (HA), 101.1 mg g -1 for sodium alginate (SA) in the FAO, but the maximum adsorption capacity of bovine serum albumin (BSA) (461.3 mg g -1 ) was identified on the HAO. The adsorption of HA, BSA, and SA dramatically increased (>70%) on FAO in 5 min and HA was significantly removed (90%) among the three NOM. Mutual interaction among the adsorbed NOM (BSA) occurred on the HAO surface during adsorption due to formation of monolayer by protein molecules at neutral pH. The pseudo second order clearly represented the adsorption kinetics for both adsorbents. The equilibrium isotherm data of FAO was better exhibited by the Langmuir isotherm model than by the Freundlich isotherm, but HAO was a slightly non-linear Langmuir type. Also, the free energy, enthalpy, and entropy of adsorption were determined from the thermodynamic experiments. Adsorption on FAO was spontaneous and an exothermic process. Fluorescence excitation-emission matrix (FEEM) spectra were used to elucidate the variation in organic components. The results obtained suggests that the significant changes in the surface property of the adsorbent (large surface area, increased crystalline intensity, and fine particle size) were effectively determined by the Fe-synthesized Al oxide mixed using the sol-gel hydrothermal method. The results also suggest that the changes enhanced the adsorption capacity, whereby three NOM were notably removed on FAO regardless of NOM characteristics (hydrophobic and hydrophilic). Copyright © 2017 Elsevier

  5. Single-Crystal to Single-Crystal Transformation of a Nonporous Fe(II) Metal-Organic Framework into a Porous Metal-Organic Framework via a Solid-State Reaction.

    Science.gov (United States)

    Spirkl, Sebastian; Grzywa, Maciej; Reschke, Stephan; Fischer, Jonas K H; Sippel, Pit; Demeshko, Serhiy; Krug von Nidda, Hans-Albrecht; Volkmer, Dirk

    2017-10-16

    We report the synthesis of an air-stable nonporous coordination compound based on iron(II) centers, formate anions, and a 4,4'-bipyrazole (H 2 BPZ) ligand. Upon thermal treatment, a porous metal-organic framework (MOF) formed due to decomposition of the incorporated formate anions. This decomposition step and the following structural changes constituted a single-crystal to single-crystal transformation. The resulting [Fe(BPZ)] framework contained tetrahedrally coordinated iron(II) metal centers. The framework was sensitive toward oxidation by molecular oxygen even at temperatures of 183 K, as followed by oxygen sorption measurements and a color change from colorless to metallic black. The semiconductor properties of the oxidized material were studied by diffuse reflectance UV/vis/NIR spectroscopy and dielectric spectroscopy.

  6. Thermoelectronic transport through spin-crossover single molecule Fe[(H2Bpz2)2bipy

    Science.gov (United States)

    Liu, N.; Zhu, L.; Yao, K. L.

    2018-04-01

    By means of density functional theory combined with the method of Keldysh nonequilibrium Green’s function, the thermal transport properties of high- and low-spin states of mononuclear FeII molecules with spin-crossover characteristics are studied. It is found that the high-spin molecular junction has a larger current than the low-spin one, producing thermally-induced switching effect. Furthermore, for high spin state molecule, the spin-up thermo-current is strongly blocked, thus achieving a pure thermo spin current. The enhanced Seebeck coefficient and the figure of merit value of high-spin state indicate that it is an ideal candidate for thermoelectric applications.

  7. Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate

    Science.gov (United States)

    Wang, Zhiguang; Yang, Yaodong; Viswan, Ravindranath; Li, Jiefang; Viehland, D.

    2011-07-01

    We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain.

  8. The Moessbauer effect in Fe(III) HEDTA, Fe(III) EDTA, and Fe(III) CDTA compounds

    International Nuclear Information System (INIS)

    Prado, F.R.

    1989-01-01

    The dependence of Moessbauer spectra with pH value of Fe(III)HEDTA and Fe(III)CDTA compounds is studied. Informations on formation processes of LFe-O-FeL (L=ligand) type dimers by the relation of titration curves of Fe(III)EDTA, Fe(III)HEDTA and Fe(III)CDTA compounds with the series of Moessbauer spectra, are obtained. Some informations on Fe-O-Fe bond structure are also obtained. Comparing the titration curves with the series of Moessbauer spectra, it is concluded that the dimerization process begins when a specie of the form FeXOH α (X = EDTA, HEDTA, CDTA; α = -1, -2) arises. (M.C.K.) [pt

  9. Enhanced density of states in Li(Fe1-xCox)As single crystals near x = 0.06 as implied by transport properties

    Science.gov (United States)

    Lee, Bumsung; Khim, Seunghyun; Jeon, Byung-Jo; Park, Ju-Young; Lee, Suk Ho; Choi, Ki-Young; Stewart, G. R.; Kim, Kee Hoon

    2013-12-01

    Single crystals of Li(Fe1-xCox)As (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.1) were grown by the Sn-flux method and their resistivity behaviors were investigated. As the Co concentration x increased, the superconducting transition temperature Tc as well as the residual resistivity ratio systematically decreased, indicating a monotonic doping of electron carriers. Upon the analysis of the Fermi-liquid behavior of the resistivity and by using the Kadowaki-Woods relation, the T2 coefficient of the resistivity A and the Sommerfeld coefficient γN were found to increase abruptly near x = 0.06. This is the point in the phase diagram at which the density of states at the Fermi energy (proportional to γN) is expected to be enhanced due to the collapse of the small hole-pockets. This result suggests that the Li(Fe1-xCox)As series at least up to x = 0.08 remain as compensated metals and their transport properties are determined by multi-band effects.

  10. PT-symmetric strings

    International Nuclear Information System (INIS)

    Amore, Paolo; Fernández, Francisco M.; Garcia, Javier; Gutierrez, German

    2014-01-01

    We study both analytically and numerically the spectrum of inhomogeneous strings with PT-symmetric density. We discuss an exactly solvable model of PT-symmetric string which is isospectral to the uniform string; for more general strings, we calculate exactly the sum rules Z(p)≡∑ n=1 ∞ 1/E n p , with p=1,2,… and find explicit expressions which can be used to obtain bounds on the lowest eigenvalue. A detailed numerical calculation is carried out for two non-solvable models depending on a parameter, obtaining precise estimates of the critical values where pair of real eigenvalues become complex. -- Highlights: •PT-symmetric Hamiltonians exhibit real eigenvalues when PT symmetry is unbroken. •We study PT-symmetric strings with complex density. •They exhibit regions of unbroken PT symmetry. •We calculate the critical parameters at the boundaries of those regions. •There are exact real sum rules for some particular complex densities

  11. Experimental and ab initio study of the nuclear quadrupole interaction of 181Ta-probes in an α-Fe2O3 single crystal

    International Nuclear Information System (INIS)

    Darriba, G. N.; Muñoz, E. L.; Eversheim, P. D.; Rentería, M.

    2010-01-01

    We report perturbed-angular-correlation (PAC) experiments on 181 Hf (→ 181 Ta)-implanted corundum α-Fe 2 O 3 single crystal in order to determine the magnitude, symmetry and orientation of the electric-field-gradient (EFG) tensor at Ta donor impurity sites of this semiconductor. These results are analyzed in the framework of ab initio full-potential augmented-plane wave plus local orbital (FP-APW+lo) calculations. This combined analysis enables us to quantify the magnitude of the lattice relaxations induced by the presence of the impurity and to determine the charge state of the impurity donor level introduced by Ta in the band gap of the semiconductor.

  12. Genotoxicity, cytotoxicity, and reactive oxygen species induced by single-walled carbon nanotubes and C(60) fullerenes in the FE1-Mutatrade markMouse lung epithelial cells

    DEFF Research Database (Denmark)

    Jacobsen, Nicklas Raun; Pojana, Giulio; White, Paul

    2008-01-01

    Viability, cell cycle effects, genotoxicity, reactive oxygen species production, and mutagenicity of C(60) fullerenes (C(60)) and single-walled carbon nanotubes (SWCNT) were assessed in the FE1-Mutatrade markMouse lung epithelial cell line. None of these particles induced cell death within 24 hr...... at doses between 0 and 200 microg/ml or during long-term subculture exposure (576 hr) at 100 microg/ml, as determined by two different assays. However, cell proliferation was slower with SWCNT exposure and a larger fraction of the cells were in the G1 phase. Exposure to carbon black resulted...... by the comet assay. The mutant frequency in the cII gene was unaffected by 576 hr of exposure to either 100 microg/ml C(60) or SWCNT when compared with control incubations, whereas we have previously reported that carbon black and diesel exhaust particles induce mutations using an identical exposure scenario...

  13. Domain wall motion and magnetization reversal processes in a FeSi picture frame single crystal studied by the time-dependent neutron depolarization technique

    International Nuclear Information System (INIS)

    Schaik, F.J. van.

    1979-01-01

    The three dimensional neutron depolarization technique, which gives detailed information about the static properties of ferromagnetic materials, has been extended to a method by means of which the time dependence of magnetic phenomena can be studied. The measurement of the neutron depolarization against time is made possible by applying a periodical magnetic field on the investigated specimen and by continuous sampling of the transmitted neutron intensity in time channels, which are started synchronously with the applied field. The technique has been used in the study of the magnetic domain structure at room temperature of a (010) [001] picture frame FeSi single crystal (3.5 wt.% Si) with outer dimensions of (15 x 10 x 0.26) mm and a frame width of 2.78 mm. (Auth.)

  14. Thickness dependence of the conductivity of thin films (La,Sr)FeO3 deposited on MgO single crystal

    International Nuclear Information System (INIS)

    Mosleh, Majid; Pryds, Nini; Hendriksen, Peter Vang

    2007-01-01

    Thin films of La 0.6 Sr 0.4 FeO 3-δ of different thicknesses have been deposited on single crystal MgO substrate by pulsed laser deposition (PLD). The deposited films are characterized by XRD before and after annealing, by scanning electron microscopy (SEM) for morphological characterization and by the Van der Pauw (VDP) technique for determination of the conductivity. The temperature dependence of the conductivity in air for samples of different thickness has been investigated. The electrical conductivity of the films increases with increasing film thickness but the conductivity of all films is less than the value of the bulk material. The apparent conductivity versus temperature shows a maximum at a certain temperature (T max ). This characteristic temperature (T max ) decreases as the film thickness increases and reaches the value for bulk for thicker films. All of the samples show the same activation energy of the conductivity in the low temperature limit

  15. Measurement and Calculation of Absolute Single- and Multiple-Charge-Exchange Cross Sections for Feq+ Ions Impacting CO and CO2

    Energy Technology Data Exchange (ETDEWEB)

    Simcic, J. [Jet Propulsion Laboratory/Caltech; Schultz, David Robert [ORNL; Mawhorter, R. J. [Pomona College; Cadez, I. [Jozef Stefan Institute, Slovenia; Greenwood, J. B. [Queen' s University, Belfast; Chutjian, A. [Jet Propulsion Laboratory/Caltech; Lisse, Carey M. [Johns Hopkins University; Smith, S. J. [Indiana Wesleyan University, Marion

    2010-01-01

    Absolute cross sections are reported for single, double, and triple charge exchange of Feq+ (q=5- 13) ions with CO and CO2. The highly-charged Fe ions are generated in an electron cyclotron resonance ion source. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental results are compared with new calculations of these cross sections in the n-electron classical trajectory Monte-Carlo approximation, in which the ensuing radiative and non-radiative cascades are approximated with scaled hydrogenic transition probabilities and scaled Auger rates. The present data are needed in astrophysical applications of solar- and stellar-wind charge-exchange with comets, planetary atmospheres, and circumstellar clouds.

  16. Controlled phase evolution and the occurrence of single domain CoFe2O4 nanoparticles synthesized by PVA assisted sol-gel method

    Science.gov (United States)

    Srinivasa Rao, K.; Ranga Nayakulu, S. V.; Chaitanya Varma, M.; Choudary, G. S. V. R. K.; Rao, K. H.

    2018-04-01

    The present investigation describes the development of cobalt ferrite nanoparticles having size less than 10 nm, by a sol-gel method using polyvinyl alcohol as chelating agent. X-ray results show all the samples, annealed above 700 °C have spinel structure. The information about phase evolution with reaction temperatures was obtained by subjecting the as-prepared powder for DSC/TGA study. High saturation magnetization of 84.63 emu/g has been observed for a particle size of 8.1 nm, a rare event reported till date. The dM/dH versus H curves suggest that the transition from single domain state to multi-domain state occurs with increasing annealing temperature and the critical size for the single domain nature of CoFe2O4 is around 6.5 nm. The estimated critical diameter for single domain particle (6.7 nm) is in good agreement with that (6.5 nm) obtained from Transmission Electron Micrographs. The highest coercivity (1645 Oe) has been found for a particle of size 6.5 nm.

  17. Magnetostriction of a U.sub.2./sub.Fe.sub.13./sub.Si.sub.4./sub. single crystal

    Czech Academy of Sciences Publication Activity Database

    Andreev, Alexander V.; Tereshina, Evgeniya; Prokleška, J.

    2010-01-01

    Roč. 491, 1-2 (2010), s. 4-7 ISSN 0925-8388 R&D Projects: GA ČR GA202/09/0339 Institutional research plan: CEZ:AV0Z10100520 Keywords : uranium intermetallics * single crystals * ferromagnetism * magnetostriction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.138, year: 2010

  18. Transport properties of Lu.sub.2./sub.Fe.sub.17./sub. single crystals under extreme conditions

    Czech Academy of Sciences Publication Activity Database

    Skorokhod, Yuriy; Arnold, Zdeněk; Kamarád, Jiří; Andreev, Alexander V.

    2004-01-01

    Roč. 11, č. 3 (2004), s. 471-475 ISSN 1027-5495 R&D Projects: GA ČR(CZ) GA106/02/0943 Institutional research plan: CEZ:AV0Z1010914 Keywords : transport properties * magnetotransport properties * pressure effect * single crystals * intermetallic compounds Subject RIV: BM - Solid Matter Physics ; Magnetism

  19. Magnetic characteristics of synthetic pseudo-single-domain and multi-domain greigite (Fe3S4)

    Czech Academy of Sciences Publication Activity Database

    Chang, L.; Roberts, A. P.; Muxworthy, A. R.; Tang, Y.; Chen, Q.; Rowan, Ch. J.; Liu, Q.; Pruner, Petr

    2007-01-01

    Roč. 34, č. 24 (2007), L24304-L24304 ISSN 0094-8276 R&D Projects: GA AV ČR IAA3013406 Institutional research plan: CEZ:AV0Z30130516 Keywords : greigite * magnetic properties * grain size * pseudo-single-domain * multi-domain Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 2.744, year: 2007

  20. Controlling the Activity and Stabilit