Defect mediated magnetic interaction and high Tc ferromagnetism in Co doped ZnO nanoparticles.

Science.gov (United States)

Pal, Bappaditya; Giri, P K

2011-10-01

Structural, optical and magnetic studies have been carried out for the Co-doped ZnO nanoparticles (NPs). ZnO NPs are doped with 3% and 5% Co using ball milling and ferromagnetism (FM) is studied at room temperature and above. A high Curie temperature (Tc) has been observed from the Co doped ZnO NPs. X-ray diffraction and high resolution transmission electron microscopy analysis confirm the absence of metallic Co clusters or any other phase different from würtzite-type ZnO. UV-visible absorption and photoluminescence studies on the doped samples show change in band structure and oxygen vacancy defects, respectively. Micro-Raman studies of doped samples shows defect related additional strong bands at 547 and 574 cm(-1) confirming the presence of oxygen vacancy defects in ZnO lattice. The field dependence of magnetization (M-H curve) measured at room temperature exhibits the clear M-H loop with saturation magnetization and coercive field of the order of 4-6 emu/g and 260 G, respectively. Temperature dependence of magnetization measurement shows sharp ferromagnetic to paramagnetic transition with a high Tc = 791 K for 3% Co doped ZnO NPs. Ferromagnetic ordering is interpreted in terms of overlapping of polarons mediated through oxygen vacancy defects based on the bound magnetic polaron (BMP) model. We show that the observed FM data fits well with the BMP model involving localised carriers and magnetic cations.

Ferromagnetic nanoparticles for magnetic hyperthermia and thermoablation therapy

Energy Technology Data Exchange (ETDEWEB)

Kita, Eiji; Kayano, Takeru; Sato, Suguru; Minagawa, Makoto; Yanagihara, Hideto; Kishimoto, Mikio [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan); Oda, Tatsuya; Hashimoto, Shinji; Yamada, Keiichi; Ohkohchi, Nobuhiro [Department of Surgery, Advanced Biomedical Applications, Graduate School of Comprehensive Human Science, University of Tsukuba, Tsukuba 305-8575 (Japan); Mitsumata, Chiharu, E-mail: kita@bk.tsukuba.ac.j [Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan)

2010-12-01

The use of ferromagnetic nanoparticles for hyperthermia and thermoablation therapies has shown great promise in the field of nanobiomedicine. Even local hyperthermia offers numerous advantages as a novel cancer therapy; however, it requires a remarkably high heating power of more than 1 kW g{sup -1} for heat agents. As a candidate for high heat generation, we focus on ferromagnetic nanoparticles and compare their physical properties with those of superparamagnetic substances. Numerical simulations for ideal single-domain ferromagnetic nanoparticles with cubic and uniaxial magnetic symmetries were carried out and MH curves together with minor loops were obtained. From the simulation, the efficient use of an alternating magnetic field (AMF) having a limited amplitude was discussed. Co-ferrite nanoparticles with various magnitudes of coercive force were produced by co-precipitation and a hydrothermal process. A maximum specific loss power of 420 W g{sup -1} was obtained using an AMF at 117 kHz with H{sub 0} = 51.4 kA m{sup -1} (640 Oe). The relaxation behaviour in the ferromagnetic state below the superparamagnetic blocking temperature was examined by Moessbauer spectroscopy.

Room temperature ferromagnetism in ZnO prepared by microemulsion

Directory of Open Access Journals (Sweden)

Qingyu Xu

2011-09-01

Full Text Available Clear room temperature ferromagnetism has been observed in ZnO powders prepared by microemulsion. The O vacancy (VO clusters mediated by the VO with one electron (F center contributed to the ferromagnetism, while the isolated F centers contributed to the low temperature paramagnetism. Annealing in H2 incorporated interstitial H (Hi in ZnO, and removed the isolated F centers, leading to the suppression of the paramagnetism. The ferromagnetism has been considered to originate from the VO clusters mediated by the Hi, leading to the enhancement of the coercivity. The ferromagnetism disappeared after annealing in air due to the reduction of Hi.

High-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

International Nuclear Information System (INIS)

Tu, Nguyen Thanh; Hai, Pham Nam; Anh, Le Duc; Tanaka, Masaaki

2016-01-01

We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga_1_−_x,Fe_x)Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy. Magnetic circular dichroism spectroscopy and anomalous Hall effect measurements indicate intrinsic ferromagnetism of these samples. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III-V ferromagnetic semiconductors.

Evidence of weak ferromagnetism in chromium(III) oxide particles

International Nuclear Information System (INIS)

Vazquez-Vazquez, Carlos; Banobre-Lopez, Manuel; Lopez-Quintela, M.A.; Hueso, L.E.; Rivas, J.

2004-01-01

The low temperature (4< T(K)<350) magnetic properties of chromium(III) oxide particles have been studied. A clear evidence of the presence of weak ferromagnetism is observed below 250 K. The magnetisation curves as a function of the applied field show coercive fields due to the canted antiferromagnetism of the particles. Around 55 K a maximum is observed in the zero-field-cooled curves; this maximum can be assumed as a blocking temperature, similarly to ultrafine ferromagnetic particles

High-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

Energy Technology Data Exchange (ETDEWEB)

Tu, Nguyen Thanh [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physics, Ho Chi Minh City University of Pedagogy, 280, An Duong Vuong Street, District 5, Ho Chi Minh City 748242 (Viet Nam); Hai, Pham Nam [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-0033 (Japan); Center for Spintronics Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Anh, Le Duc [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Tanaka, Masaaki [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Center for Spintronics Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2016-05-09

We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga{sub 1−x},Fe{sub x})Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy. Magnetic circular dichroism spectroscopy and anomalous Hall effect measurements indicate intrinsic ferromagnetism of these samples. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III-V ferromagnetic semiconductors.

Study of high-coercivity sintered NdFeB magnets

International Nuclear Information System (INIS)

Bai, G.; Gao, R.W.; Sun, Y.; Han, G.B.; Wang, B.

2007-01-01

Magnetic powders for sintered NdFeB magnets have been prepared by using an advanced processing method including strip casting, hydrogen decrepitation, jet milling and rubber isotropic press. The effects of Dy, Ga and Co addition on the microstructure and magnetic properties of sintered magnets have been investigated. By adopting a suitable component ratio and adjusting proper technological parameters, we have prepared high-coercivity sintered NdFeB magnets with hard magnetic properties of j H c =25.6 kOe, B r =13.2 kG and (BH) max =39.9 MGOe. The temperature coefficient of coercivity of the magnets (between 20 and 150 deg. C) is -0.53% deg. C. The magnetic properties at high temperature satisfy the needs of permanent magnet motors

High-coercivity ultrafine-grained anisotropic Nd–Fe–B magnets processed by hot deformation and the Nd–Cu grain boundary diffusion process

International Nuclear Information System (INIS)

Sepehri-Amin, H.; Ohkubo, T.; Nagashima, S.; Yano, M.; Shoji, T.; Kato, A.; Schrefl, T.; Hono, K.

2013-01-01

The grain boundary diffusion process using an Nd 70 Cu 30 eutectic alloy has been applied to hot-deformed anisotropic Nd–Fe–B magnets, resulting in a substantial enhancement of coercivity, from 1.5 T to 2.3 T, at the expense of remanence. Scanning electron microscopy showed that the areal fraction of an Nd-rich intergranular phase increased from 10% to 37%. The intergranular phase of the hot-deformed magnet initially contained ∼55 at.% ferromagnetic element, while it diminished to an undetectable level after the process. Microscale eutectic solidification of Nd/NdCu as well as a fine lamellae structure of Nd 70 (Co,Cu) 30 /Nd were observed in the intergranular phase. Micromagnetic simulations indicated that the reduction of the magnetization in the intergranular phases leads to the enhancement of coercivity in agreement with the experimental observation

Study of high-coercivity sintered NdFeB magnets

Energy Technology Data Exchange (ETDEWEB)

Bai, G. [School of Physics and Microelectronics, Shandong University, Jinan, 250100 (China); Department of Mathematics and Physics, Xi' an Institute of Technology, Xi' an, 710032 (China); Gao, R.W. [School of Physics and Microelectronics, Shandong University, Jinan, 250100 (China)]. E-mail: gaorwbox@sdu.edu.cn; Sun, Y. [School of Physics and Microelectronics, Shandong University, Jinan, 250100 (China); Han, G.B. [School of Physics and Microelectronics, Shandong University, Jinan, 250100 (China); Wang, B. [School of Physics and Microelectronics, Shandong University, Jinan, 250100 (China); Baotou Rare Earth Research Institute, Batou 014030 (China)

2007-01-15

Magnetic powders for sintered NdFeB magnets have been prepared by using an advanced processing method including strip casting, hydrogen decrepitation, jet milling and rubber isotropic press. The effects of Dy, Ga and Co addition on the microstructure and magnetic properties of sintered magnets have been investigated. By adopting a suitable component ratio and adjusting proper technological parameters, we have prepared high-coercivity sintered NdFeB magnets with hard magnetic properties of {sub j} H {sub c}=25.6 kOe, B {sub r}=13.2 kG and (BH){sub max}=39.9 MGOe. The temperature coefficient of coercivity of the magnets (between 20 and 150 deg. C) is -0.53% deg. C. The magnetic properties at high temperature satisfy the needs of permanent magnet motors.

UH.sub.3./sub.-based ferromagnets: new look at an old material

Czech Academy of Sciences Publication Activity Database

Havela, L.; Paukov, M.; Tkach, I.; Matěj, Z.; Kriegner, D.; Mašková, S.; Vondráčková, B.; Prachařová, M.; Turek, I.; Diviš, M.; Cieslar, M.; Drozdenko, D.; Kim-Ngan, N.-T.H.; Andreev, Alexander V.

2016-01-01

Roč. 400, Feb (2016), 130-136 ISSN 0304-8853 Institutional support: RVO:68378271 Keywords : uranium * hydride * ferromagnetism * coercivity * magnetostriction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.630, year: 2016

Ferromagnetic behavior of nanocrystalline Cu–Mn alloy prepared by ball milling

Energy Technology Data Exchange (ETDEWEB)

Mondal, B.N., E-mail: bholanath_mondal@yahoo.co.in [Department of Central Scientific Services, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India); Sardar, G. [Department of Zoology, Baruipur College, South 24 parganas 743 610 (India); Nath, D.N. [Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India); Chattopadhyay, P.P. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711 103 (India)

2014-12-15

50Cu–50Mn (wt%) alloy was produced by ball milling. The milling was continued up to 30 h followed by isothermal annealing over a four interval of temperature from 350 to 650 °C held for 1 h. Crystallite size, lattice strain, lattice parameter were determined by Rietveld refinement structure analysis of X-ray diffraction data. The amount of dissolved/precipitated Mn (wt%) after ball milling/milling followed by annealing was calculated by quantative phase analysis (QPA). The increase of coercivity could be attributed to the introduction of lattice strain and reduction of crystallite size as a function of milling time. Electron paramagnetic resonance and superconducting quantum interface device analysis indicate that soft ferromagnetic behavior has been achieved by ball milled and annealed Cu–Mn alloy. The maximum coercivity value of Cu–Mn alloy obtained after annealing at 350 °C for 1 h is 277 Oe. - Highlights: • A small amount of Mn has dissolved in Cu after ball milling for 30 h. • Coercivity of the Cu–Mn alloy has increased with an increase in milling time. • Substantial MnO has formed after annealing at 650 °C for 1 h. • The ball milled and annealed alloy have revealed soft ferromagnetic behavior. • The alloy annealed at 350 °C shows the maximum value of coercivity.

'Blocking' effects in magnetic resonance? The ferromagnetic nanowires case

International Nuclear Information System (INIS)

Ramos, C.A.; De Biasi, E.; Zysler, R.D.; Vassallo Brigneti, E.; Vazquez, M.

2007-01-01

We present magnetic resonance results obtained at L, X, and Q bands (1.2, 9.4 and 34GHz, respectively) on ferromagnetic nanowires with a hysteresis cycle characterized by a remanent magnetization M r /M s ∼0.92 and a coercive field H c =1.0kOe. The hysteretic response of the ferromagnetic resonance spectra is discussed in terms of independent contributions of the nanowires aligned along and opposite to the applied field. We will discuss the implications of this study on the magnetic resonance in nanoparticles and other systems with large anisotropy

The preparation of sintered NdFeB magnet with high-coercivity and high temperature-stability

Energy Technology Data Exchange (ETDEWEB)

Yan, G H; Chen, R J; Ding, Y; Guo, S; Lee, Don; Yan, A R, E-mail: yangh@nimte.ac.cn [Zhejiang province Key Laboratory of Magnetic Materials and Application Technology, Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201 (China)

2011-01-01

The NdFeB magnets with high intrinsic coercivity have been produced by using the conventional powder metallurgy method (including SC, HD and JM) of sintered NdFeB magnets. The effects of grain boundary phases on the microstructure and magnetic properties of as-sintered and annealed magnets have been tried to investigate. Also the Curie temperature of the magnets was studied. By adopting suitable component ratio of some heavy rare-earth atoms and some micro-quantity additives, we have prepared high-coercivity sintered NdFeB magnets with magnetic properties of {sub j}H{sub c}=36.3kOe, B{sub r}=11.7kGs and (BH){sub max}=34.0MGOe. The temperature coefficient of residual magnetic flux of the magnets (between 20 and 200 deg. C) is -0.113%/deg. C, while the temperature coefficient of intrinsic coercivity -0.355%/deg. C. The Curie temperature of the magnets is about 342 deg. C.

The preparation of sintered NdFeB magnet with high-coercivity and high temperature-stability

International Nuclear Information System (INIS)

Yan, G H; Chen, R J; Ding, Y; Guo, S; Lee, Don; Yan, A R

2011-01-01

The NdFeB magnets with high intrinsic coercivity have been produced by using the conventional powder metallurgy method (including SC, HD and JM) of sintered NdFeB magnets. The effects of grain boundary phases on the microstructure and magnetic properties of as-sintered and annealed magnets have been tried to investigate. Also the Curie temperature of the magnets was studied. By adopting suitable component ratio of some heavy rare-earth atoms and some micro-quantity additives, we have prepared high-coercivity sintered NdFeB magnets with magnetic properties of j H c =36.3kOe, B r =11.7kGs and (BH) max =34.0MGOe. The temperature coefficient of residual magnetic flux of the magnets (between 20 and 200 deg. C) is -0.113%/deg. C, while the temperature coefficient of intrinsic coercivity -0.355%/deg. C. The Curie temperature of the magnets is about 342 deg. C.

Micromagnetic simulation of the orientation dependence of grain boundary properties on the coercivity of Nd-Fe-B sintered magnets

Directory of Open Access Journals (Sweden)

Jun Fujisaki

2016-05-01

Full Text Available This paper is focused on the micromagnetic simulation study about the orientation dependence of grain boundary properties on the coercivity of polycrystalline Nd-Fe-B sintered magnets. A multigrain object with a large number of meshes is introduced to analyze such anisotropic grain boundaries and the simulation is performed by combining the finite element method and the parallel computing. When the grain boundary phase parallel to the c-plane is less ferromagnetic the process of the magnetization reversal changes and the coercivity of the multigrain object increases. The simulations with various magnetic properties of the grain boundary phases are executed to search for the way to enhance the coercivity of polycrystalline Nd-Fe-B sintered magnets.

Low-energy mechanically milled τ-phase MnAl alloys with high coercivity and magnetization

International Nuclear Information System (INIS)

Lu, Wei; Niu, Junchao; Wang, Taolei; Xia, Kada; Xiang, Zhen; Song, Yiming; Zhang, Hong; Yoshimura, Satoru; Saito, Hitoshi

2016-01-01

The high cost of rare earth elements makes the use of high-performance permanent magnets commercially very expensive. MnAl magnetic material is one of the most promising Rare-Earth-free permanent magnets due to its obvious characteristics. However, the coercivity of MnAl alloys produced by melt spinning followed by appropriate treatment is relatively low. In this investigation, a high coercivity up to 5.3 kOe and saturation magnetization of ∼62 emu/g (with an applied magnetic field of 19.5 kOe) were obtained in the mechanically milled τ-phase Mn_5_7Al_4_3 alloy. As milling time goes on, the coercivity firstly increases and then decreases, leading to the formation of knee-point coercivity, while the saturation magnetization decreases simultaneously. The structural imperfections such as disordering and defects play the most important role in the changes of magnetic properties of τ-phase MnAl alloys processed by low-energy mechanical milling. The present results will be helpful for the development of processing protocols for the optimization of τ-phase MnAl alloys as high performance Rare-Earth-free permanent magnets. - Highlights: • Successful fabrication of pure τ-phase Mn_5_7Al_4_3 alloy by melt spinning and low-energy ball milling processes. • High coercivity (~5.3 kOe) and magnetization (~62 emu/g) were obtained in τ-phase Mn_5_7Al_4_3 alloy. • Disordering and defects play the most important role in the changes of magnetic properties.

Low-energy mechanically milled τ-phase MnAl alloys with high coercivity and magnetization

Energy Technology Data Exchange (ETDEWEB)

Lu, Wei, E-mail: weilu@tongji.edu.cn [School of Materials Science and Engineering, Shanghai Key Lab. of D& A for Metal-Functional Materials, Tongji University, Shanghai 200092 (China); Research Center for Engineering Science, Akita University, Akita 010-8502 Japan (Japan); Niu, Junchao; Wang, Taolei; Xia, Kada; Xiang, Zhen; Song, Yiming [School of Materials Science and Engineering, Shanghai Key Lab. of D& A for Metal-Functional Materials, Tongji University, Shanghai 200092 (China); Zhang, Hong; Yoshimura, Satoru; Saito, Hitoshi [Research Center for Engineering Science, Akita University, Akita 010-8502 Japan (Japan)

2016-08-05

The high cost of rare earth elements makes the use of high-performance permanent magnets commercially very expensive. MnAl magnetic material is one of the most promising Rare-Earth-free permanent magnets due to its obvious characteristics. However, the coercivity of MnAl alloys produced by melt spinning followed by appropriate treatment is relatively low. In this investigation, a high coercivity up to 5.3 kOe and saturation magnetization of ∼62 emu/g (with an applied magnetic field of 19.5 kOe) were obtained in the mechanically milled τ-phase Mn{sub 57}Al{sub 43} alloy. As milling time goes on, the coercivity firstly increases and then decreases, leading to the formation of knee-point coercivity, while the saturation magnetization decreases simultaneously. The structural imperfections such as disordering and defects play the most important role in the changes of magnetic properties of τ-phase MnAl alloys processed by low-energy mechanical milling. The present results will be helpful for the development of processing protocols for the optimization of τ-phase MnAl alloys as high performance Rare-Earth-free permanent magnets. - Highlights: • Successful fabrication of pure τ-phase Mn{sub 57}Al{sub 43} alloy by melt spinning and low-energy ball milling processes. • High coercivity (~5.3 kOe) and magnetization (~62 emu/g) were obtained in τ-phase Mn{sub 57}Al{sub 43} alloy. • Disordering and defects play the most important role in the changes of magnetic properties.

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.

High-coercivity FePt sputtered films

International Nuclear Information System (INIS)

Luong, N.H.; Hiep, V.V.; Hong, D.M.; Chau, N.; Linh, N.D.; Kurisu, M.; Anh, D.T.K.; Nakamoto, G.

2005-01-01

Fe 56 Pt 44 thin films have been prepared by RF magnetron sputtering on Si substrates. The substrate temperature was kept at 350 deg C. The X-ray diffraction patterns of as-deposited FePt films exhibited a disordered structure. Annealing of the films at 650-685 deg C for 1 h yielded an ordered L1 0 phase with FCT structure. The high value for coercivity H C of 17 kOe was obtained at room temperature for the 68 nm thick film annealed at 685 deg C. The hard magnetic properties as well as grain structure of the films strongly depend on the annealing conditions

High-coercive garnet films for thermo-magnetic recording

International Nuclear Information System (INIS)

Berzhansky, V N; Danishevskaya, Y V; Nedviga, A S; Milyukova, H T

2016-01-01

The possibility of using high-coercive of garnet films for thermo-magnetic recording is related with the presence of the metastable domain structure, which arises due to a significant mismatch of the lattice parameters of the film and the substrate. In the work the connection between facet crystal structure of elastically strained ferrite garnets films and the domain structure in them is established by methods of phase contrast and polarization microscopy. (paper)

Thin Co films with tunable ferromagnetic resonance frequency

International Nuclear Information System (INIS)

Maklakov, Sergey S.; Maklakov, Sergey A.; Ryzhikov, Ilya A.; Rozanov, Konstantin N.; Osipov, Alexey V.

2012-01-01

The tailored production of thin Co films of 50 nm thick with ferromagnetic resonance frequency in a range from 2.9 to 7.3 GHz using the DC magnetron sputtering is reported. The ferromagnetic resonance frequency, coercivity, effective magnetic field and nanocrystalline structure parameters are shown to be governed by the Co deposition rate. For this investigation, FMR, VSM and TEM techniques were used. - Highlights: ► Thin Co films with FMR frequency in a range from 2.9 to 7.3 GHz are obtained. ► The films' properties are governed by the deposition rate during DC magnetron sputtering. ► FMR, VSM and TEM techniques were used during the study.

Hysteresis in conducting ferromagnets

International Nuclear Information System (INIS)

Schneider, Carl S.; Winchell, Stephen D.

2006-01-01

Maxwell's magnetic diffusion equation is solved for conducting ferromagnetic cylinders to predict a magnetic wave velocity, a time delay for flux penetration and an eddy current field, one of five fields in the linear unified field model of hysteresis. Measured Faraday voltages for a thin steel toroid are shown to be proportional to magnetic field step amplitude and decrease exponentially in time due to maximum rather than average permeability. Dynamic permeabilities are a field convolution of quasistatic permeability and the delay function from which we derive and observe square root dependence of coercivity on rate of field change

Angular dependence of the coercivity in arrays of ferromagnetic nanowires

International Nuclear Information System (INIS)

Holanda, J.; Silva, D.B.O.; Padrón-Hernández, E.

2015-01-01

We present a new magnetic model for polycrystalline nanowires arrays in porous anodic aluminum oxide. The principal consideration here is the crystalline structure and the morphology of the wires and them the dipolar interactions between the crystals into the wire. Other aspect here is the direct calculation of the dipolar energy for the interaction of one wire with the others in the array. The free energy density was formulated for polycrystalline nanowires arrays in order to determinate the anisotropy effective field. It was using the microstructure study by scanning and transmission electron microscopy for the estimation of the real structure of the wires. After the structural analysis we used the angular dependences for the coercivity field and for the remnant magnetization to determine the properties of the wires. All analysis were made by the theory treatment proposed by Stoner and Wohlfarth

Angular dependence of the coercivity in arrays of ferromagnetic nanowires

Energy Technology Data Exchange (ETDEWEB)

Holanda, J. [Departamento de Física, Universidade Federal de Pernambuco, Recife 50670-901, PE (Brazil); Silva, D.B.O. [Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, Recife 50670-901, PE (Brazil); Padrón-Hernández, E., E-mail: padron@df.ufpe.br [Departamento de Física, Universidade Federal de Pernambuco, Recife 50670-901, PE (Brazil); Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, Recife 50670-901, PE (Brazil)

2015-03-15

We present a new magnetic model for polycrystalline nanowires arrays in porous anodic aluminum oxide. The principal consideration here is the crystalline structure and the morphology of the wires and them the dipolar interactions between the crystals into the wire. Other aspect here is the direct calculation of the dipolar energy for the interaction of one wire with the others in the array. The free energy density was formulated for polycrystalline nanowires arrays in order to determinate the anisotropy effective field. It was using the microstructure study by scanning and transmission electron microscopy for the estimation of the real structure of the wires. After the structural analysis we used the angular dependences for the coercivity field and for the remnant magnetization to determine the properties of the wires. All analysis were made by the theory treatment proposed by Stoner and Wohlfarth.

Scaling of coercivity in a 3d random anisotropy model

Energy Technology Data Exchange (ETDEWEB)

Proctor, T.C., E-mail: proctortc@gmail.com; Chudnovsky, E.M., E-mail: EUGENE.CHUDNOVSKY@lehman.cuny.edu; Garanin, D.A.

2015-06-15

The random-anisotropy Heisenberg model is numerically studied on lattices containing over ten million spins. The study is focused on hysteresis and metastability due to topological defects, and is relevant to magnetic properties of amorphous and sintered magnets. We are interested in the limit when ferromagnetic correlations extend beyond the size of the grain inside which the magnetic anisotropy axes are correlated. In that limit the coercive field computed numerically roughly scales as the fourth power of the random anisotropy strength and as the sixth power of the grain size. Theoretical arguments are presented that provide an explanation of numerical results. Our findings should be helpful for designing amorphous and nanosintered materials with desired magnetic properties. - Highlights: • We study the random-anisotropy model on lattices containing up to ten million spins. • Irreversible behavior due to topological defects (hedgehogs) is elucidated. • Hysteresis loop area scales as the fourth power of the random anisotropy strength. • In nanosintered magnets the coercivity scales as the six power of the grain size.

High coercivity in rare-earth lean nanocomposite magnets by grain boundary infiltration

Energy Technology Data Exchange (ETDEWEB)

Madugundo, Rajasekhar, E-mail: mraja@udel.edu [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Salazar-Jaramillo, Daniel [BCMaterials, Bizkaia Science and Technology Park, E-48160 Derio (Spain); Manuel Barandiaran, Jose [BCMaterials, Bizkaia Science and Technology Park, E-48160 Derio (Spain); Department of Electricity & Electronics, University of the Basque Country (UPV/EHU), E-48080 Bilbao (Spain); Hadjipanayis, George C., E-mail: hadji@udel.edu [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

2016-02-15

A significant enhancement in coercivity was achieved by grain boundary modification through low temperature infiltration of Pr{sub 75}(Cu{sub 0.25}Co{sub 0.75}){sub 25} eutectic alloy in rare-earth lean (Pr/Nd)–Fe–B/α-Fe nanocomposite magnets. The infiltration procedure was carried out on ribbons and hot-deformed magnets at 600–650 °C for different time durations. In Nd{sub 2}Fe{sub 14}B/α-Fe ribbons, the coercivity increased from 5.3 to 23.8 kOe on infiltration for 4 h. The Pr{sub 2}Fe{sub 14}B/α-Fe hot-deformed magnet shows an increase in coercivity from 5.4 to 22 kOe on infiltration for 6 h. The increase in the coercivity comes at the expense of remnant magnetization. X-ray diffraction studies confirm the presence of both the hard Nd{sub 2}Fe{sub 14}B and soft α-Fe phases. A decrease in the soft α-Fe phase content was observed after infiltration. - Highlights: • Enhancement in coercivity was achieved by grain boundary modification. • Coercivity increased from 5.3 to 23.8 kOe in Nd{sub 2}Fe{sub 14}B/α-Fe on infiltration. • Pr{sub 2}Fe{sub 14}B/α-Fe deformed magnet shows an increase in coercivity from 5.4 to 22 kOe. • The increase in the coercivity comes at the expense of remnant magnetization. • A decrease in the soft α-Fe phase content was observed after infiltration.

Control of room-temperature defect-mediated ferromagnetism in VO{sub 2} films

Energy Technology Data Exchange (ETDEWEB)

Yang, Tsung-Han, E-mail: tyang3@ncsu.edu [NSF Center for Advanced Materials and Smart Structures, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907 (United States); Nori, Sudhakar; Mal, Siddhartha; Narayan, Jagdish [NSF Center for Advanced Materials and Smart Structures, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907 (United States)

2011-09-15

We report interesting ferromagnetic properties and their control in a vanadium-based oxide system driven by stoichiometric defects. Vanadium oxide (VO{sub 2}) thin films were grown on c-plane sapphire substrates by a pulsed laser deposition technique under different ambient conditions. The ferromagnetism of the epitaxial VO{sub 2} films can be switched on and off by altering the cooling ambient parameters. In addition, the saturated magnetic moments and coercivity of the VO{sub 2} films were found to be a function of the oxygen partial pressure during the growth process. The room-temperature ferromagnetic properties of VO{sub 2} films were correlated with the nature of the microstructure and the growth parameters. The origin of the induced magnetic properties are qualitatively understood to stem from intrinsic structural and stoichiometric defects.

Room-temperature ferromagnetic Cr-doped Ge/GeOx core–shell nanowires

Science.gov (United States)

Katkar, Amar S.; Gupta, Shobhnath P.; Motin Seikh, Md; Chen, Lih-Juann; Walke, Pravin S.

2018-06-01

The Cr-doped tunable thickness core–shell Ge/GeOx nanowires (NWs) were synthesized and characterized using x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and magnetization studies. The shell thickness increases with the increase in synthesis temperature. The presence of metallic Cr and Cr3+ in core–shell structure was confirmed from XPS study. The magnetic property is highly sensitive to the core–shell thickness and intriguing room temperature ferromagnetism is realized only in core–shell NWs. The magnetization decreases with an increase in shell thickness and practically ceases to exist when there is no core. These NWs show remarkably high Curie temperature (TC > 300 K) with the dominating values of its magnetic remanence (MR) and coercivity (HC) compared to germanium dilute magnetic semiconductor nanomaterials. We believe that our finding on these Cr-doped Ge/GeOX core–shell NWs has the potential to be used as a hard magnet for future spintronic devices, owing to their higher characteristic values of ferromagnetic ordering.

Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese—gallium nanoparticles

International Nuclear Information System (INIS)

Feng Jun-Ning; Liu Wei; Geng Dian-Yu; Ma Song; Yu Tao; Zhao Xiao-Tian; Dai Zhi-Ming; Zhao Xin-Guo; Zhang Zhi-Dong

2014-01-01

The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic (AFM) manganese-oxide shell and a ferromagnetic-like core of manganese—gallium (MnGa) compounds, are studied. The core-shell structure is confirmed by transmission electron microscope (TEM). The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic (FI) D0 22 -type Mn 3 Ga, ferromagnetic (FM) Mn 8 Ga 5 , and AFM D0 19 -type Mn 3 Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at low temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias (EB) effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe (1 Oe = 79.5775 A·m −1 ) and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively. (special topic — international conference on nanoscience and technology, china 2013)

Magnetic properties and microstructure study of high coercivity Au/FePt/Au trilayer thin films

International Nuclear Information System (INIS)

Chen, S.K.; Yuan, F.T.; Liao, W.M.; Hsu, C.W.; Horng, Lance

2006-01-01

High-coercivity Au(60 nm)/FePt(δ nm)/Au(60 nm) trilayer samples were prepared by sputtering at room temperature, followed by post annealing at different temperatures. For the sample with δ=60 nm, L1 ordering transformation occurs at 500 deg. C. Coercivity (H c ) is increased with the annealing temperature in the studied range 400-800 deg. C. The H c value of the trilayer films is also varied with thickness of FePt intermediate layer (δ), from 27 kOe for δ=60 nm to a maximum value of 33.5 kOe for δ=20 nm. X-ray diffraction data indicate that the diffusion of Au atoms into the FePt L1 lattice is negligible even after a high-temperature (800 deg. C) annealing process. Furthermore, ordering parameter is almost unchanged as δ is reduced from 60 to 15 nm. Transmission electron microscope (TEM) photos indicate that small FePt Ll particles are dispersed amid the large-grained Au. We believe that the high coercivity of the trilayer sample is attributed to the small and uniform grain sizes of the highly ordered FePt particles which have perfect phase separation with Au matrix

High coercivity Gd-substituted Ba hexaferrites, prepared by chemical coprecipitation

Science.gov (United States)

Litsardakis, G.; Manolakis, I.; Serletis, C.; Efthimiadis, K. G.

2008-04-01

A series of Gd-substituted Ba hexaferrites with nominal formula (Ba1-xGdx)Oṡ5.25 Fe2O3 (x=0-0.30) were prepared by the chemical coprecipitation method from nitrate precursors and heating at T =800-1200°C for 2h. The samples have been examined by x-ray diffraction, vibrating-sample magnetometer, and scanning electron microscopy methods. Gd substituted samples form single phase materials with the M-type hexaferrite structure at all heating temperatures, in the range of x ⩽0.10-0.20. The saturation magnetization (at 1.8T) varies slightly with x in most cases and, for x =0.05-0.10, it increases up to 66.7Am2/kg, exceeding the value of the unsubstituted hexaferrite. A strong enhancement of the coercivity is observed for all substituted samples, with maximum values Hc=457kA/m for the single-phase x =0.10 sample annealed at 1000°C and Hc=477kA/m for the x =0.25 sample annealed at 1100°C which contains Fe2O3 and GdFeO3 impurities. As the variation of coercivity with either substitution rate (x ) or annealing temperature is not monotonic, three different factors may account for the high coercivities that are obtained: (a) an inhibition of grain growth due to the presence of Gd, (b) a possible inherent effect on magnetocrystalline anisotropy, especially for single phase samples, and (c) a microstructural effect of secondary phases.

Room temperature p-type conductivity and coexistence of ferroelectric order in ferromagnetic Li doped ZnO nanoparticles

KAUST Repository

Awan, Saif Ullah; Hasanain, S. K.; Anjum, Dalaver H.; Awan, M. S.; Shah, Saqlain A.

2014-01-01

for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5kV/cm (0.11 μC/cm2) and 2.8k

Analysis of electrical-field-dependent Dzyaloshinskii-Moriya interaction and magnetocrystalline anisotropy in a two-dimensional ferromagnetic monolayer

Science.gov (United States)

Liu, Jie; Shi, Mengchao; Lu, Jiwu; Anantram, M. P.

2018-02-01

We analyze the impacts of the electric field on the Dzyaloshinskii-Moriya interaction, magnetocrystalline anisotropy, and intrinsic ferromagnetism of the recently discovered two-dimensional ferromagnetic chromium tri-iodide (Cr I3 ) monolayer, by combining density functional theory and Monte Carlo simulations. By taking advantage of the counterbalancing effects of anisotropic symmetric exchange energy and antisymmetric exchange energy, it is shown that the intrinsic ferromagnetism can be manipulated by externally applied off-plane electric fields. The results quantitatively reveal the impacts of off-plane electric field on the lattice structure, magnetic anisotropy energy, symmetric and antisymmetric exchange energies, Curie temperature, magnetic hysteresis, and coercive field. The physical mechanism of all-electrical control of magnetism proposed here is useful for creating next-generation magnetic device technologies based on the recently discovered two-dimensional ferromagnetic crystals.

Defect-tuning exchange bias of ferromagnet/antiferromagnet core/shell nanoparticles by numerical study

International Nuclear Information System (INIS)

Mao Zhongquan; Chen Xi; Zhan Xiaozhi

2012-01-01

The influence of non-magnetic defects on the exchange bias (EB) of ferromagnet (FM)/antiferromagnet (AFM) core/shell nanoparticles is studied by Monte Carlo simulations. It is found that the EB can be tuned by defects in different positions. Defects at both the AFM and FM interfaces reduce the EB field while they enhance the coercive field by decreasing the effective interface coupling. However, the EB field and the coercive field show respectively a non-monotonic and a monotonic dependence on the defect concentration when the defects are located inside the AFM shell, indicating a similar microscopic mechanism to that proposed in the domain state model. These results suggest a way to optimize the EB effect for applications. (paper)

Very high coercivities of top-layer diffusion Au/FePt thin films

International Nuclear Information System (INIS)

Yuan, F.T.; Chen, S.K.; Liao, W.M.; Hsu, C.W.; Hsiao, S.N.; Chang, W.C.

2006-01-01

The Au/FePt samples were prepared by depositing a gold cap layer at room temperature onto a fully ordered FePt layer, followed by an annealing at 800 deg. C for the purpose of interlayer diffusion. After the deposition of the gold layer and the high-temperature annealing, the gold atoms do not dissolve into the FePt Ll 0 lattice. Compared with the continuous FePt film, the TEM photos of the bilayer Au(60 nm)/FePt(60 nm) show a granular structure with FePt particles embedded in Au matrix. The coercivity of Au(60 nm)/FePt(60 nm) sample is 23.5 kOe, which is 85% larger than that of the FePt film without Au top layer. The enhancement in coercivity can be attributed to the formation of isolated structure of FePt ordered phase

Identifying the sources of ferromagnetism in sol-gel synthesized Zn{sub 1−x}Co{sub x}O (0≤x≤0.10) nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Beltrán, J.J., E-mail: jjbj08@gmail.com [Grupo de Energías Alternativas y Biomasa (GEAB-CIDTEC), Universidad Popular del Cesar, UPC, Balneario Hurtado Via Patillal, Valledupar (Colombia); Grupo de Estado Sólido, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, UdeA, Calle 70 No 52-21, Medellín (Colombia); Barrero, C.A. [Grupo de Estado Sólido, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia, UdeA, Calle 70 No 52-21, Medellín (Colombia); Punnoose, A. [Department of Physics, Boise State University, Boise, ID 83725-1570 (United States)

2016-08-15

We have carefully investigated the structural, optical and electronic properties and related them with changes in the magnetism of sol-gel synthesized Zn{sub 1−x}Co{sub x}O (0≤x≤0.10) nanoparticles. Samples with x≤0.05 were free of spurious phases. Samples with x≤0.03 were found to be with only high spin Co{sup 2+} ions into ZnO structure, whereas sample with x=0.05, exhibited the presence of high spin Co{sup 2+} and low spin Co{sup 3+}. We found that the intensity of the main EPR peak associated with Co{sup 2+} varies with the nominal Co content in a similar manner as the saturation magnetization and coercive field do. These results point out that the ferromagnetism in these samples should directly be correlated with the presence of divalent cobalt ions. Bound magnetic polaron (BMP) model and the charge transfer model are insufficient to explain the ferromagnetic properties of Zn{sub 1−x}Co{sub x}O nanoparticles. The room temperature ferromagnetism (RTFM) may be originated from a combination of several factors such as the interaction of high spin Co{sup 2+} ions, perturbation/alteration and/or changes in the electronic structure of ZnO close to the valence band edge and grain boundary effects. - Graphical abstract: The intensity of the main EPR peak associated with Co{sup 2+} varies with the nominal Co content in a similar manner as the saturation magnetization and coercive field do. These results point out that the ferromagnetism in these samples should directly be correlated with the presence of Co{sup 2+} ions. Display Omitted - Highlights: • Systematic and carefully study of physical-chemical properties of Zn{sub 1−x}Co{sub x}O nanoparticles. • Samples with x=0.01 and 0.03 were found to be with only high spin Co{sup 2+}. • Sample with x=0.05, exhibited the presence of high spin Co{sup 2+} and low spin Co{sup 3+}. • The BMP and charge transfer models seem not explain the ferromagnetic properties. • RTFM: high spin Co{sup 2+} ions

Soft magnetic properties of hybrid ferromagnetic films with CoFe, NiFe, and NiFeCuMo layers

Energy Technology Data Exchange (ETDEWEB)

Choi, Jong-Gu [Eastern-western Biomedical Engineering, Sangji University, Wonju 220-702 (Korea, Republic of); Hwang, Do-Guwn [Dept. of Oriental Biomedical Engineering, Sangji University, Wonju 220-702 (Korea, Republic of); Rhee, Jang-Roh [Dept. of Physics, Sookmyung Women' s University, Seoul 140-742 (Korea, Republic of); Lee, Sang-Suk, E-mail: sslee@sangji.ac.kr [Dept. of Oriental Biomedical Engineering, Sangji University, Wonju 220-702 (Korea, Republic of)

2011-09-30

Two-layered ferromagnetic alloy films (NiFe and CoFe) with intermediate NiFeCuMo soft magnetic layers of different thicknesses were investigated to understand the relationship between coercivity and magnetization process by taking into account the strength of hard-axis saturation field. The thickness dependence of H{sub EC} (easy-axis coercivity), H{sub HS} (hard-axis saturation field), and {chi} (susceptibility) of the NiFeCuMo thin films in glass/Ta(5 nm)/[CoFe or NiFe(5 nm-t/2)]/NiFeCuMo(t = 0, 4, 6, 8, 10 nm)/[CoFe or NiFe(5 nm-t/2)]/Ta(5 nm) films prepared using the ion beam deposition method was determined. The magnetic properties (H{sub EC}, H{sub HS}, and {chi}) of the ferromagnetic CoFe, NiFe three-layers with an intermediate NiFeCuMo super-soft magnetic layer were strongly dependent on the thickness of the NiFeCuMo layer.

Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

International Nuclear Information System (INIS)

Loeffler, J.; Wagner, W.; Svygenhoven, H. van; Meier, J.; Doudin, B.; Ansermet, J.P.

1997-01-01

The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs

Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

Energy Technology Data Exchange (ETDEWEB)

Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)

1997-09-01

The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.

Coercivity in SmCo hard magnetic films for MEMS applications

Energy Technology Data Exchange (ETDEWEB)

Pina, E. [Instituto de Magnetismo Aplicado, RENFE-UCM, Universidad Complutense de Madrid, P.O. Box 155, 28230 Las Rozas, Madrid (Spain)]. E-mail: epina@renfe.es; Palomares, F.J. [Instituto de Ciencia de Materiales de Madrid-CSIC, c/ Sor Juana Ines de la Cruz s/n, 28049 Madrid (Spain); Garcia, M.A. [Instituto de Magnetismo Aplicado, RENFE-UCM, Universidad Complutense de Madrid, P.O. Box 155, 28230 Las Rozas, Madrid (Spain); Cebollada, F. [Departamento de Fisica Aplicada a las Telecomunicaciones, EUITT-UPM, Crtra. De Valencia km 7, 28031 Madrid (Spain); Hoyos, A. de [Instituto de Magnetismo Aplicado, RENFE-UCM, Universidad Complutense de Madrid, P.O. Box 155, 28230 Las Rozas, Madrid (Spain); Romero, J.J. [Instituto de Magnetismo Aplicado, RENFE-UCM, Universidad Complutense de Madrid, P.O. Box 155, 28230 Las Rozas, Madrid (Spain); Hernando, A. [Instituto de Magnetismo Aplicado, RENFE-UCM, Universidad Complutense de Madrid, P.O. Box 155, 28230 Las Rozas, Madrid (Spain); Unidad asociada ICMM-IMA. P.O. Box 155, 28230 Las Rozas Madrid (Spain); Gonzalez, J.M. [Unidad asociada ICMM-IMA. P.O. Box 155, 28230 Las Rozas Madrid (Spain)

2005-04-15

In this work we have investigated the thermal dependence of coercivity in 1.5 {mu}m thick SmCo{sub 5} films fabricated by sputtering technique. Samples were deposited onto Si substrates kept at different temperatures. Samples grown below 450 deg. C are amorphous, present low coercivity and require further crystallization processes in order to obtain the 1:5 SmCo hard phase. Samples grown at 450 deg. C are nanocrystalline in the as-deposited state and exhibit high room temperature in-plane coercivity. Correlation between the thermal dependence of coercivity and the nanostructure has been analyzed in the frame of the so-called micromagnetic model.

Coercivity in SmCo hard magnetic films for MEMS applications

International Nuclear Information System (INIS)

Pina, E.; Palomares, F.J.; Garcia, M.A.; Cebollada, F.; Hoyos, A. de; Romero, J.J.; Hernando, A.; Gonzalez, J.M.

2005-01-01

In this work we have investigated the thermal dependence of coercivity in 1.5 μm thick SmCo 5 films fabricated by sputtering technique. Samples were deposited onto Si substrates kept at different temperatures. Samples grown below 450 deg. C are amorphous, present low coercivity and require further crystallization processes in order to obtain the 1:5 SmCo hard phase. Samples grown at 450 deg. C are nanocrystalline in the as-deposited state and exhibit high room temperature in-plane coercivity. Correlation between the thermal dependence of coercivity and the nanostructure has been analyzed in the frame of the so-called micromagnetic model

Thermal effect on magnetic parameters of high-coercivity cobalt ferrite

Energy Technology Data Exchange (ETDEWEB)

Chagas, E. F., E-mail: efchagas@fisica.ufmt.br; Ponce, A. S.; Prado, R. J.; Silva, G. M. [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá-MT (Brazil); Bettini, J. [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, 13083-970 Campinas (Brazil); Baggio-Saitovitch, E. [Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150 Urca. Rio de Janeiro (Brazil)

2014-07-21

We prepared very high-coercivity cobalt ferrite nanoparticles synthesized by a combustion method and using short-time high-energy mechanical milling to increase strain and the structural defects density. The coercivity (H{sub C}) of the milled sample reached 3.75 kOe—a value almost five times higher than that obtained for the non-milled material (0.76 kOe). To investigate the effect of the temperature on the magnetic behavior of the milled sample, we performed a thermal treatment on the milled sample at 300, 400, and 600 °C for 30 and 180 min. We analyzed the changes in the magnetic behavior of the nanoparticles due to the thermal treatment using the hysteresis curves, Williamson-Hall analysis, and transmission electron microscopy. The thermal treatment at 600 °C causes decreases in the microstructural strain and density of structural defects resulting in a significant decrease in H{sub C}. Furthermore, this thermal treatment increases the size of the nanoparticles and, as a consequence, there is a substantial increase in the saturation magnetization (M{sub S}). The H{sub C} of the samples treated at 600 °C for 30 and 180 min were 2.24 and 1.93 kOe, respectively, and the M{sub S} of these same samples increased from 57 emu/g to 66 and 70 emu/g, respectively. The H{sub C} and the M{sub S} are less affected by the thermal treatment at 300 and 400 °C.

Nickel/carbon core/shell nanotubes: Lanthanum nickel alloy catalyzed synthesis, characterization and studies on their ferromagnetic and lithium-ion storage properties

International Nuclear Information System (INIS)

Anthuvan Rajesh, John; Pandurangan, Arumugam; Senthil, Chenrayan; Sasidharan, Manickam

2014-01-01

Highlights: • Ni/CNTs core/shell structure was synthesized using LaNi 5 alloy catalyst by CVD. • The magnetic and lithium-ion storage properties of Ni/CNTs structure were studied. • The specific Ni/CNTs structure shows strong ferromagnetic property with large coercivity value of 446.42 Oe. • Ni/CNTs structure shows enhanced electrochemical performance in terms of stable capacity and better rate capability. - Abstract: A method was developed to synthesize ferromagnetic nickel core/carbon shell nanotubes (Ni/CNTs) by chemical vapor deposition using Pauli paramagnetic lanthanum nickel (LaNi 5 ) alloy both as a catalyst and as a source for the Ni-core. The Ni-core was obtained through oxidative dissociation followed by hydrogen reduction during the catalytic growth of the CNTs. Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD) analyses reveal that the Ni-core exists as a face centered cubic single crystal. The magnetic hysteresis loop of Ni/CNTs particle shows increased coercivity (446.42 Oe) than bulk Ni at room temperature. Furthermore, the Ni/CNTs core/shell particles were investigated as anode materials in lithium-ion batteries. The Ni/CNTs electrode delivered a high discharge capacity of 309 mA h g −1 at 0.2 C, and a stable cycle-life, which is attributed to high structural stability of Ni/CNTs electrode during electrochemical lithium-ion insertion and de-insertion redox reactions

Study of high coercive force films made by vacuum deposition of cobalt onto chromium

International Nuclear Information System (INIS)

Randet, Denis

1969-01-01

A new method to make high coercive force films, by successive evaporations of chromium and cobalt, was demonstrated in 1966 at the 'Laboratoire d'Electronique et de Technologie de l'Informatique'. This work first contains a description of the magnetic properties of these films according to the conditions of preparation. These properties, which are isotropic in the plane of the film, are then related to the crystallographic structure of chromium and cobalt, in particular through electron microscopy. It is concluded that the coercive force is essentially due to the high magneto-crystalline anisotropy of cobalt in its hexagonal phase and depends, altogether with the shape of the hysteresis loop, on the magnetostatic coupling between the grains, which varies according to their dimensions. The chromium underlayer, if its surface is free enough of oxygen contamination, induces the growth of the hexagonal phase and influences the grain size of cobalt by a sort of epitaxy. At last, the behaviour of the Co/Cr films as a magnetic recording material is briefly examined and discussed. (author) [fr

Magnetic measurements of suspended functionalised ferromagnetic beads under DC applied fields

International Nuclear Information System (INIS)

De Los Santos V, Luis; Llandro, Justin; Lee, Dongwook; Mitrelias, Thanos; Palfreyman, Justin J.; Hayward, Thomas J.; Cooper, Jos; Bland, J.A.C.; Barnes, Crispin H.W.; Arroyo C, Juan L.; Lees, Martin

2009-01-01

In this work, a simple technique to obtain the hysteresis loops of magnetic beads (Spherotech Inc.) in liquid suspension is presented. The magnetic measurements were taken in a DC Magnetic Property Measurement System (MPMS-SQUID sensor). Samples were based on ferromagnetic beads (surface-functionalized NH 2 , mean diameter 4.32 μm) prepared in three conditions: dry, suspended in sucrose solution and in suspension after functionalization with fluorophore. Special small containers (1.3 cm long) made of non magnetic plastic were designed to hold the beads in liquid. The results indicate that the bead's remnant magnetization is half of the value at maximum applied field in all cases. However, due to the additional degrees of rotational freedom, beads suspended in a liquid do not present coercivity. The use of ferromagnetic beads and magnetic elements of different architectures for applications in bioassays is also discussed.

Monte Carlo simulations of core/shell nanoparticles containing interfacial defects: Role of disordered ferromagnetic spins

International Nuclear Information System (INIS)

Ho, Le Bin; Lan, Tran Nguyen; Hai, Tran Hoang

2013-01-01

In this work, we have used the Monte Carlo simulation to investigate the magnetic properties of an isolated composite magnetic nanoparticle with ferromagnetic (FM) core and antiferromagnetic (AFM) shell morphology. The defects were assumed to be randomly located at the AFM interface. The Néel anisotropy was used for the FM interface spins at where there are the lacks of crystal symmetry due to the vacancies at AFM interface. With a moderate defect concentration, the coercive field non-monotonously depends on the Néel anisotropy. We have examined the dependence of coercivity, exchange bias field, and vertical shift on defect concentration. We found that in addition to AFM shell, the disordered FM interface is another pining-source for exchange bias phenomenon. We discuss our simulated results in the relation to recent experimental findings

Thermoplastic deformation of ferromagnetic CoFe-based bulk metallic glasses

Science.gov (United States)

Wu, Chenguang; Hu, Renchao; Man, Qikui; Chang, Chuntao; Wang, Xinmin

2017-12-01

The superplastic deformation behavior of the ferromagnetic Co31Fe31Nb8B30 bulk metallic glass (BMG) in the supercooled liquid region was investigated. At a given temperature, the BMG exhibits a Newtonian behavior at low strain rates but a non-Newtonian behavior at high strain rates. The high thermal stability of this glassy alloy system offers an enough processing window to thermoplastic forming (TPF), and the strong processing ability was examined by simple micro-replication experiments. It is demonstrated that the TPF formability on length scales ranging down to nanometers can be achieved in the selected experimental condition. Based on the analysis of deformation behavior, the nearly full density sample (i.e. nearly 100%), was produced from water-atomized glassy powders and consolidated by the hot-pressing technique. The sample exhibits good soft-magnetic and mechanical properties, i.e., low coercive force of 0.43 Oe, high initial permeability of 4100 and high Vickers hardness 1398. These results suggest that the hot-pressing process opens up possibilities for the commercial exploitation of BMGs in engineering applications.

Nonthermal Photocoercivity Effect in a Low-Doped (Ga,Mn)As Ferromagnetic Semiconductor

Science.gov (United States)

Astakhov, G. V.; Hoffmann, H.; Korenev, V. L.; Kiessling, T.; Schwittek, J.; Schott, G. M.; Gould, C.; Ossau, W.; Brunner, K.; Molenkamp, L. W.

2009-05-01

We report a photoinduced change of the coercive field, i.e., a photocoercivity effect (PCE), under very low intensity illumination of a low-doped (Ga,Mn)As ferromagnetic semiconductor. We find a strong correlation between the PCE and the sample resistivity. Spatially resolved dynamics of the magnetization reversal rule out any role of thermal heating in the origin of this PCE, and we propose a mechanism based on the light-induced lowering of the domain wall pinning energy. The PCE is local and reversible, allowing writing and erasing of magnetic images using light.

Nanostructures based on superconducting Nb and ferromagnetic CuNi alloy for elaboration of spin-valve core

International Nuclear Information System (INIS)

Morari, Roman

2013-01-01

The main goal of our research group is the elaboration of superconducting spin-switch (valve) based on Ferromagnetic/Superconductor/Ferromagnetic core. We could realize all building blocks necessary for the fabrication of the core structure of the superconducting spin valve, consisting of two mirror symmetric bilayers. In other words, the spin valve consists of a F/S * /F trilayer, which can be regarded as a package of a F/S and S/F bilayer so that S * =2S in the trilayer. For such a trilayer, the theory predicts that the critical temperature depends on the relative orientation of the magnetization of the ferromagnetic layers. To enable a reversal of one of the magnetizations of the layers with respect to the other by an external magnetic field, the coercive forces of the F layers have to be different due to either intrinsic properties or to an antiferromagnetic pinning layer delivering an exchange bias. The main points of our study are presented here. (author)

High coercivity microcrystalline Nd-rich Nd–Fe–Co–Al–B bulk magnets prepared by direct copper mold casting

Energy Technology Data Exchange (ETDEWEB)

Zhao, L.Z.; Hong, Y. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Fang, X.G. [Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510640 (China); Qiu, Z.G.; Zhong, X.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Gao, X.S. [Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510640 (China); Liu, Z.W., E-mail: zwliu@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China)

2016-06-15

High coercivity Nd{sub 25}Fe{sub 40}Co{sub 20}Al{sub 15−x}B{sub x} (x=7–15) hard magnets were prepared by a simple process of injection casting. Different from many previous investigations on nanocomposite compositions, the magnets in this work contain hard magnetic Nd{sub 2}(FeCoAl){sub 14}B, Nd-rich, and Nd{sub 1+ε}(FeCo){sub 4}B{sub 4} phases. The magnetic properties, phase evolution, and microstructure of the as-cast and annealed magnets were investigated. As the boron content increased from 7 to 11 at%, the intrinsic coercivity H{sub cj} of the as-cast magnet increased from 816 to 1140 kA/m. The magnets annealed at 750 °C have shown more regular and smaller grains than the as-cast alloys, especially for the x=11 alloy. The high intrinsic coercivities for the annealed alloys with x=8~11 result from the presence of small-sized grains in the microstructure. The highest H{sub cj} of 1427 kA/m was obtained for the heat treated alloy with x=10. This work provides an alternative approach for preparing fully dense Nd-rich bulk hard magnets with relatively good properties. - Highlights: • 2 mm hard magnetic Nd{sub 25}Fe{sub 40}Co{sub 20}Al{sub 15−x}B{sub x} rods were prepared by direct casting. • High coercivity of 1.78 T was achieved in x=11 sample after heat treatment. • Small grains are responsible for the significant increase in H{sub C} after annealing. • Nd{sub 2}Fe{sub 14}B grains with two different sizes lead to two-step demagnetization process.

Defects related room temperature ferromagnetism in Cu-implanted ZnO nanorod arrays

International Nuclear Information System (INIS)

Li, D.; Li, D.K.; Wu, H.Z.; Liang, F.; Xie, W.; Zou, C.W.; Shao, L.X.

2014-01-01

Highlights: • Room temperature ferromagnetism was observed in Cu-implanted ZnO nanorod arrays. • Cu-implanted ZnO nanorods show a saturation magnetization value of 1.82 μ B /Cu. • The origin of ferromagnetism can be explained by the defects related bound magnetic polarons. -- Abstract: Room temperature ferromagnetism (FM) was observed in Cu-implanted ZnO nanorod arrays. The implantation dose for Cu ions was 1 × 10 16 cm −2 and the implantation energy was 100 keV. The ion implantation induced defects and disorder has been observed by the XRD, PL and TEM experiments. The PL spectrum revealed a dominant luminescence peaks at 390 nm and a broad and strong green emission at 500–700 nm, which is considered to be related to the ionized oxygen vacancy. Cu-implanted ZnO nanorods annealed at 500 °C show a saturation magnetization value of 1.82 μ B /Cu and a positive coercive field of 68 Oe. The carrier concentration is not much improved after annealing and in the order of 10 16 cm −3 , which suggests that FM does not depend upon the presence of a significant carrier concentration. The origin of ferromagnetism behavior can be explained on the basis of electrons and defects that form bound magnetic polarons, which overlap to create a spin-split impurity band

Phase-field-crystal model for magnetocrystalline interactions in isotropic ferromagnetic solids

Science.gov (United States)

Faghihi, Niloufar; Provatas, Nikolas; Elder, K. R.; Grant, Martin; Karttunen, Mikko

2013-09-01

An isotropic magnetoelastic phase-field-crystal model to study the relation between morphological structure and magnetic properties of pure ferromagnetic solids is introduced. Analytic calculations in two dimensions were used to determine the phase diagram and obtain the relationship between elastic strains and magnetization. Time-dependent numerical simulations in two dimensions were used to demonstrate the effect of grain boundaries on the formation of magnetic domains. It was shown that the grain boundaries act as nucleating sites for domains of reverse magnetization. Finally, we derive a relation for coercivity versus grain misorientation in the isotropic limit.

High coercivity Sm-Co thin films from elemental Sm/Co multilayer deposition and their microstructural aspects

Energy Technology Data Exchange (ETDEWEB)

Krishnan, M. [Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560 017 (India); Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Predeep, P. [Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Sridhara Rao, D.V. [Defence Metallurgical Research Laboratories, Hyderabad 500058 (India); Prajapat, C.L.; Singh, M.R. [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Barshilia, Harish C. [Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560 017 (India); Chowdhury, P., E-mail: pchowdhury@nal.res.in [Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore 560 017 (India)

2017-05-15

Hard magnetic thin films with high coercivity were fabricated by magnetron sputtering on MgO(100) and quartz substrates. The films were grown by depositing sequentially Sm and Co layers at an elevated substrate temperature of 500 °C. Subsequent post-annealing was carried out at various temperatures in range of 500–700 °C to form Sm-Co hard magnetic thin films. X-ray diffraction studies revealed the formation of randomly oriented SmCo{sub 5} crystallites on quartz substrate, whereas, a textured growth of Sm{sub 2}Co{sub 7} with strong (110) crystalline phases was observed on MgO substrate. Microstructural analyses were carried out using Transmission Electron Microscopy (TEM) for samples grown on MgO substrate at 650 °C and inferred the presence of high density planar defects along with large grain boundaries. Further microdiffraction studies confirmed the presence of SmCo{sub 3} as an impurity phase in the films. Magnetic hysteresis measurements indicate the square hysteresis behaviors with high coercivity value of 3.1 T and 2.7 T for 650 °C annealed samples on both MgO and quartz substrates, respectively. The origin of such high coercivity value was then correlated with pinning type of spin reversal mechanism as confirmed through the analyses of demagnetization curves. The magnetic force microscopy images for films on MgO substrate, annealed at 650 °C, revealed the presence of magnetic domains with size higher than 1 µm. The formed magnetic domains lacked well defined boundaries indicating an enhanced exchange coupling between the grain clusters. - Highlights: • Ewald technique in micromagnetic simulations with periodic boundary conditions. • Effect of micromagnetic parameters on hysteresis in exchange spring magnets. • Importance of the interface exchange coupling for hard-soft nanocomposites. • Geometry dependence of the optimal soft phase size in exchange spring magnets.

Coercive diplomacy

DEFF Research Database (Denmark)

Jakobsen, Peter Viggo

2016-01-01

separate strategic eras with distinct challenges and theoretical developments are identified since the field’s emergence in the 1960s: the Cold War, the humanitarian 1990s, the war on terror and the hybrid future. The record clearly shows that skilful use of coercive diplomacy can resolve crises...

Broadband strip-line ferromagnetic resonance spectroscopy of soft magnetic CoFeTaZr patterned thin films

Science.gov (United States)

Gupta, S.; Kumar, D.; Jin, T. L.; Nongjai, R.; Asokan, K.; Ghosh, A.; Aparnadevi, M.; Suri, P.; Piramanayagam, S. N.

2018-05-01

In this paper, magnetic and magnetization dynamic properties of compositionally patterned Co46Fe40Ta9Zr5 thin films are investigated. A combination of self-assembly and ion-implantation was employed to locally alter the composition of Co46Fe40Ta9Zr5 thin film in a periodic manner. 20 keV O+ and 60 keV N+ ions were implanted at different doses in order to modify the magnetization dynamic properties of the samples in a controlled fashion. Magnetic hysteresis loop measurements revealed significant changes in the coercivity for higher influences of 5 × 1016 ions per cm2. In particular, N+ implantation was observed to induce two phase formation with high and low coercivities. Broadband strip-line ferromagnetic resonance spectroscopy over wide range of frequency (8 - 20 GHz) was used to study the magnetization dynamics as a function of ion-beam dosage. With higher fluences, damping constant showed a continuous increase from 0.0103 to 0.0430. Such control of magnetic properties at nano-scale using this method is believed to be useful for spintronics and microwave device applications.

Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

International Nuclear Information System (INIS)

Wu, Stephen M.; Hoffman, Jason; Pearson, John E.; Bhattacharya, Anand

2014-01-01

The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe 3 O 4 with the ferromagnetic metal Co 0.2 Fe 0.6 B 0.2 (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe 3 O 4 into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.

The coercivity mechanism of Pr–Fe–B nanoflakes prepared by surfactant-assisted ball milling

Energy Technology Data Exchange (ETDEWEB)

Zuo, Wen-Liang, E-mail: wlzuo@iphy.ac.cn; Zhang, Ming; Niu, E.; Shao, Xiao-Ping; Hu, Feng-Xia; Sun, Ji-Rong; Shen, Bao-Gen, E-mail: shenbg@aphy.iphy.ac.cn

2015-09-15

The strong (00l) textured Pr{sub 12+x}Fe{sub 82−x}B{sub 6} (x=0, 1, 2, 3, 4) nanoflakes with high coercivity were prepared by surfactant-assisted ball milling (SABM). The thickness and length of the flakes are mainly in the range of 50−200 nm and 0.5−2 μm, respectively. A coercivity of 4.16 kOe for Pr{sub 15}Fe{sub 79}B{sub 6} nanoflakes was obtained, which is the maximum coercivity of R{sub 2}Fe{sub 14}B (R=Pr, Nd) nanoflakes or nanoparticles reported up to now. The results of XRD and SEM for the aligned Pr{sub 15}Fe{sub 79}B{sub 6} nanoflakes indicate that a strong (00l) texture is obtained and the easy magnetization direction is parallel to the surface of the flakes. The angular dependence of coercivity for aligned sample indicates that the coercivity mechanism of the as-milled nanoflakes is mainly dominated by domain wall pinning. Meanwhile, the field dependence of coercivity, isothermal (IRM) and dc demagnetizing (DCD) remanence curves also indicate that the coercivity is mainly determined by domain wall pinning, and nucleation also has an important effect. In addition, the mainly interaction of flakes is dipolar coupling. The research of coercivity mechanism for Pr{sub 15}Fe{sub 79}B{sub 6} nanoflakes is important for guidance the further increase its value, and is useful for the future development of the high performance nanocomposite magnets and soft/hard exchange spring magnets. - Highlights: • A coercivity of 4.16 kOe for Pr{sub 15}Fe{sub 79}B{sub 6} nanoflakes was obtained. • The strong (00l) textured is obtained for Pr{sub 15}Fe{sub 79}B{sub 6} nanoflakes. • The interaction of nanoflakes is mainly dipolar coupling. • Domain wall pinning is the mainly coercivity mechanism.

Enhanced coercivity thermal stability realized in Nd–Fe–B thin films diffusion-processed by Nd–Co alloys

Energy Technology Data Exchange (ETDEWEB)

Zhong, Hui; Fu, Yanqing [Key laboratory of electromagnetic processing of materials (EPM), Ministry of Education, Northeastern University, Shenyang 110819 (China); Department of Physics and Chemistry of Materials, School of Materials Science and Engineering, Northeastern University, Shenyang 110819 (China); Li, Guojian; Liu, Tie [Key laboratory of electromagnetic processing of materials (EPM), Ministry of Education, Northeastern University, Shenyang 110819 (China); Cui, Weibin, E-mail: cuiweibin@epm.neu.edu.cn [Key laboratory of electromagnetic processing of materials (EPM), Ministry of Education, Northeastern University, Shenyang 110819 (China); Department of Physics and Chemistry of Materials, School of Materials Science and Engineering, Northeastern University, Shenyang 110819 (China); Liu, Wei; Zhang, Zhidong [Shenyang National Laboratory for Materials Science, Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS), Shenyang 110016 (China); Wang, Qiang, E-mail: wangq@mail.neu.edu.cn [Key laboratory of electromagnetic processing of materials (EPM), Ministry of Education, Northeastern University, Shenyang 110819 (China)

2017-03-15

A proposed Nd{sub 2}Fe{sub 14}B-core/Nd{sub 2}(Fe, Co){sub 14}B-shell microstructure was realized by diffusion-processing textured Nd{sub 14}Fe{sub 77}B{sub 9} single-layer film with Nd{sub 100−x}Co{sub x} (x=10, 20 and 40) alloys to improve the coercivity thermal stability. The ambient coercivity was increased from around 1 T in single-layer film to nearly 2 T in diffusion-processed films, which was due to the Nd-rich grain boundaries as seen from transmission electron microscopy (TEM) images. The coercivity thermal stability was improved by the core/shell microstructure because Nd-rich grain boundaries provided the high ambient coercivity and Co-rich shell provided the improved coercivity stability. - Highlights: • Core–shell microstructure proposed for enhancing the coercivity thermal stability. • Coercivity enhanced to nearly 2 T by diffusion-processing with Nd–Co alloy. • Good squareness and highly textured microstructure obtained. • Nd-rich phases observed by TEM after diffusion process. • Coercivity thermal stability improved with minor Co addition in grain boundary regions.

Synthesis, morphology and microstructure of pomegranate-like hematite (α-Fe2O3) superstructure with high coercivity

International Nuclear Information System (INIS)

Tadic, Marin; Citakovic, Nada; Panjan, Matjaz; Stanojevic, Boban; Markovic, Dragana; Jovanovic, Đorđe; Spasojevic, Vojislav

2012-01-01

Highlights: ► We found superior magnetic properties of the hematite (α-Fe 2 O 3 ). ► TEM and HRTEM images show a pomegranate-like superstructure. ► Magnetic measurements display high coercivity H C = 4350 Oe at the room temperature. - Abstract: We found novel and superior magnetic properties of the hematite (α-Fe 2 O 3 ) that originate from an internal microstructure of particles and strong inter-particle interactions between nanocrystal sub-units. The hematite particles were synthesized by thermal decomposition of iron (III) nitrate without any template or surfactant. The purity, size, crystallinity, morphology, microstructure and magnetic features of the as-prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and SQUID magnetometry. An XRD study reveals a pure phase of α-Fe 2 O 3 whereas TEM shows α-Fe 2 O 3 spheres with a diameter of about 150 nm. RS also shows high quality and purity of the sample. Moreover, TEM and HRTEM images show a pomegranate-like superstructure and evidence that the spherical particles are composed of individual well-crystallized nanoparticle sub-units (self-assembled nanoparticles) with a size of about 20 nm. Magnetic measurements display hysteretic behavior at the room temperature with remanent magnetization M r = 0.731 emu/g, saturation magnetization M S = 6.83 emu/g and coercivity H C = 4350 Oe, as well as the Morin transition at T M = 261 K. These results and comparison with those in the literature reveal that the sample has extremely high coercivity. The magnetic properties of the sample are discussed in relation to morphology, internal microstructure, surface effects and exchange and dipole–dipole interactions.

Synthesis of core-shell hematite (α-Fe2O3) nanoplates: Quantitative analysis of the particle structure and shape, high coercivity and low cytotoxicity

Science.gov (United States)

Tadic, Marin; Kopanja, Lazar; Panjan, Matjaz; Kralj, Slavko; Nikodinovic-Runic, Jasmina; Stojanovic, Zoran

2017-05-01

Hematite core-shell nanoparticles with plate-like morphology were synthesized using a one-step hydrothermal synthesis. An XRPD analysis indicates that the sample consist of single-phase α-Fe2O3 nanoparticles. SEM and TEM measurements show that the hematite sample is composed of uniform core-shell nanoplates with 10-20 nm thickness, 80-100 nm landscape dimensions (aspect ratio ∼5) and 3-4 nm thickness of the surface shells. We used computational methods for the quantitative analysis of the core-shell particle structure and circularity shape descriptor for the quantitative shape analysis of the nanoparticles from TEM micrographs. The calculated results indicated that a percentage of the shell area in the nanoparticle area (share [%]) is significant. The determined values of circularity in the perpendicular and oblique perspective clearly show shape anisotropy of the nanoplates. The magnetic properties revealed the ferromagnetic-like properties at room temperature with high coercivity HC = 2340 Oe, pointing to the shape and surface effects. These results signify core-shell hematite nanoparticles' for practical applications in magnetic devices. The synthesized hematite plate-like nanoparticles exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating the safe use of these nanoparticles for biomedical applications.

Absence of field anisotropy in the intrinsic ferromagnetic signals of highly oriented pyrolytic graphite

International Nuclear Information System (INIS)

Ballestar, A.; Setzer, A.; Esquinazi, P.; Garcia, N.

2011-01-01

We have measured the magnetization of bulk samples of highly oriented pyrolytic graphite (HOPG) at magnetic fields applied parallel and perpendicular to the graphene layers. Within experimental error the intrinsic ferromagnetic signals of the samples show similar magnetic moments at saturation for the two magnetic field directions, in contrast to recently published data (J. Cervenka et al., Nat. Phys. 5 (2009) 840). To check that the SQUID device provides correctly the small ferromagnetic signals obtained after subtracting the 100 times larger diamagnetic background, we have prepared a sample with a superconducting Pb-film deposited on one of the HOPG surfaces. We show that the field dependence of the measured magnetic moment and after the background subtraction is highly reliable even in the sub-μ emu range providing the real magnetic properties of the embedded small ferromagnetic and superconducting signals. - Research Highlights: → We have measured the magnetization of bulk samples of highly oriented pyrolytic graphite (HOPG) at magnetic fields applied parallel and perpendicular to the graphene layers.→ Within experimental error the intrinsic ferromagnetic signals of the samples show similar magnetic moments at saturation for the two magnetic field directions.→ The absence of magnetic anisotropy of the intrinsic ferromagnetic order found in HOPG samples contrasts recently published data by Cervenka et al., Nat Phys 5, 840 (2009).

Unexpected ferromagnetic ordering enhancement with crystallite size growth observed in La{sub 0.5}Ca{sub 0.5}MnO₃ nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Iniama, G.; Ita, B. I. [Department of Pure and Applied Chemistry, University of Calabar, Calabar (Nigeria); Presa, P. de la, E-mail: pmpresa@ucm.es; Hernando, A. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Fac. CC Físicas, Dpto. Física de Materiales, Univ. Complutense de Madrid, 28040 Madrid (Spain); Alonso, J. M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Instituto de Ciencia de Materiales, CSIC, 28049-Madrid (Spain); Multigner, M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Cortés-Gil, R.; Ruiz-González, M. L. [Fac. CC Químicas, Dpto. Química Inorgánica, Univ. Complutense de Madrid, 28040 Madrid (Spain); Gonzalez-Calbet, J. M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Fac. CC Químicas, Dpto. Química Inorgánica, Univ. Complutense de Madrid, 28040 Madrid (Spain)

2014-09-21

In this paper, the physical properties of half-doped manganite La{sub 0.5}Ca{sub 0.5}MnO₃ with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering.

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Ravikumar, Patta; Kisan, Bhagaban; Perumal, A., E-mail: perumal@iitg.ernet.in [Department of Physics, Indian institute of Technology Guwahati, Guwahati 781 039 (India)

2015-08-15

We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Directory of Open Access Journals (Sweden)

Patta Ravikumar

2015-08-01

Full Text Available We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (TC around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high TC and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

Defect states and room temperature ferromagnetism in cerium oxide nanopowders prepared by decomposition of Ce-propionate

DEFF Research Database (Denmark)

Mihalache, V.; Grivel, J. C.; Secu, M.

2018-01-01

. An improvement of ferromagnetism and intensity of defect-related PL emission was observed when annealing the products in which nanocrystalline cerium oxide coexists with Ce - oxicarbonate traces, Ce2O2CO3. The experimental results were explained based on the following considerations: room temperature......Four batches of cerium oxide powders (with nanocrystallite size of 6.9 nm–572 nm) were prepared from four precursor nanopowders by thermal decomposition of Ce-propionate and annealing in air between 250 °C–1200 °C for 10 min–240 min. Ceria formation reactions, structure, vibrational, luminescence...... and magnetic properties were investigated by differential scanning calorimetry, x-ray diffraction, electron microscopy, infrared spectroscopy, photoluminescence and SQUID. All the samples exhibit room temperature ferromagnetism, RTFM, (with coercivity, Hc, of 8 Oe - 121 Oe and saturation magnetization, Ms...

Local coercive force of domain boundaries

International Nuclear Information System (INIS)

Kandaurova, G.S.; Vas'kovskij, V.O.

1980-01-01

The aim of the present paper is to show the variety of effects resulting from local coercivity using RFeO 3 orthoferrites crystals-plates, to separate factors which are not directly connected with the nature of every single defect but influence significantly Hsub(cw) local coercivity and, at last, to attract attention of physisists-theorists to new tasks of the magnetic hysteresis theory. Measurements have been carried out on a great number of defect of YFeO 3 and PyFeO 3 crystals. Such peculiarities of local coercivity as Hsub(cw) anisotropy and asymmetry, Hsub(cw) nonstability and its dependence on the sample magnetic prehistory. Qualitative explanation of these effects in based on the presumable interaction of the domain wall with magnetic heterogeneities existing in a region of structural defects

Unexpected ferromagnetic ordering enhancement with crystallite size growth observed in La0.5Ca0.5MnO3 nanoparticles

International Nuclear Information System (INIS)

Iniama, G.; Ita, B. I.; Presa, P. de la; Hernando, A.; Alonso, J. M.; Multigner, M.; Cortés-Gil, R.; Ruiz-González, M. L.; Gonzalez-Calbet, J. M.

2014-01-01

In this paper, the physical properties of half-doped manganite La 0.5 Ca 0.5 MnO 3 with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering.

Observation of ferromagnetic ordering in a stable α -Co (OH) 2 phase grown on a Mo S2 surface

Science.gov (United States)

Debnath, Anup; Bhattacharya, Shatabda; Saha, Shyamal K.

2017-12-01

Because of the potential application of Co (OH) 2 in a magnetic cooling system as a result of its superior magnetocaloric effect many people have investigated magnetic properties of Co (OH) 2 . Unfortunately, most of the works have been carried out on the β -Co (OH) 2 phase due to the fact that the α -Co (OH) 2 phase is very unstable and continuously transformed into the stable β -Co (OH) 2 phase. However, in the present work, using a Mo S2 sheet as a two-dimensional template, we have been able to synthesize a stable α -Co (OH) 2 phase in addition to a β -Co (OH) 2 phase by varying the layer thickness. It is seen that for thinner samples the β phase, while for thicker samples α phase, is grown on the Mo S2 surface. Magnetic measurements are carried out for the samples over the temperature range from 2 to 300 K and it is seen that for the β phase, ferromagnetic ordering with fairly large coercivity (1271 Oe) at 2 K is obtained instead of the usual antiferromagnetism. The most interesting result is the observation of ferromagnetic ordering with a transition temperature (Curie temperature) more than 100 K in the α -Co (OH) 2 phase. Complete saturation in the hysteresis curve under application of very low field having coercivity of ˜162 Oe at 2 K and 60 Oe at 50 K is obtained. A thin stable α -Co (OH) 2 phase grown on Mo S2 surface with very soft ferromagnetic ordering will be very useful as the core material in electromagnets.

Coercive treatment and autonomy in psychiatry.

Science.gov (United States)

Sjöstrand, Manne; Helgesson, Gert

2008-02-01

There are three lines of argument in defence of coercive treatment of patients with mental disorders: arguments regarding (1) societal interests to protect others, (2) the patients' own health interests, and (3) patient autonomy. In this paper, we analyse these arguments in relation to an idealized case, where a person with a mental disorder claims not to want medical treatment for religious reasons. We also discuss who should decide what in situations where patients with mental disorders deny treatment on seemingly rational grounds. We conclude that, in principle, coercive treatment cannot be defended for the sake of protecting others. While coercive actions can be acceptable in order to protect close family and others, medical treatment is not justified for such reasons but should be given only in the interest of patients. Coercive treatment may be required in order to promote the patient's health interests, but health interests have to waive if they go against the autonomous interests of the patient. We argue that non-autonomous patients can have reasons, rooted in their deeply-set values, to renounce compulsory institutional treatment, and that such reasons should be respected unless it can be assumed that their new predicaments have caused them to change their views.

Local coercive force of domain boundaries

Energy Technology Data Exchange (ETDEWEB)

Kandaurova, G S; Vas' kovskii, V O [Ural' skij Gosudarstvennyj Univ., Sverdlovsk (USSR)

1980-04-01

The aim of the present paper is to show the variety of effects resulting from local coercivity using RFeO/sub 3/ orthoferrites crystals-plates, to separate factors which are not directly connected with the nature of every single defect but influence significantly H/sub cw/ local coercivity and, at last, to attract attention of physisists-theorists to new tasks of the magnetic hysteresis theory. Measurements have been carried out on a great number of defect of YFeO/sub 3/ and PyFeO/sub 3/ crystals. Such peculiarities of local coercivity as H/sub cw/ anisotropy and asymmetry, H/sub cw/ nonstability and its dependence on the sample magnetic prehistory. Qualitative explanation of these effects in based on the presumable interaction of the domain wall with magnetic heterogeneities existing in a region of structural defects.

Superconducting Ferromagnetic Nanodiamond.

Science.gov (United States)

Zhang, Gufei; Samuely, Tomas; Xu, Zheng; Jochum, Johanna K; Volodin, Alexander; Zhou, Shengqiang; May, Paul W; Onufriienko, Oleksandr; Kačmarčík, Jozef; Steele, Julian A; Li, Jun; Vanacken, Johan; Vacík, Jiri; Szabó, Pavol; Yuan, Haifeng; Roeffaers, Maarten B J; Cerbu, Dorin; Samuely, Peter; Hofkens, Johan; Moshchalkov, Victor V

2017-06-27

Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature T c ∼ 3 K and a Curie temperature T Curie > 400 K. In spite of the high T Curie , our nanodiamond films demonstrate a decrease in the temperature dependence of magnetization below 100 K, in correspondence to an increase in the temperature dependence of resistivity. These anomalous magnetic and electrical transport properties reveal the presence of an intriguing precursor phase, in which spin fluctuations intervene as a result of the interplay between the two antagonistic states. Furthermore, the observations of high-temperature ferromagnetism, giant positive magnetoresistance, and anomalous Hall effect bring attention to the potential applications of our superconducting ferromagnetic nanodiamond films in magnetoelectronics, spintronics, and magnetic field sensing.

Influence of measuring temperature in size dependence of coercivity in nanostructured alloys

International Nuclear Information System (INIS)

Lopez, M.; Marin, P.; Kulik, T.; Hernando, A.

2005-01-01

An increase of coercive field with decreasing particle size has been observed in ball milled nanocomposite of Fe-rich nanocrystals embedded in an amorphous matrix. Previous works (J. Appl. Phys. 64 (1998) 6044) have concluded that for high lattice strain, , the increase of coercivity is due to the magnetoelastic anisotropy generated by . Even though other effects can also be involved, the experimental results seem to indicate that the influence of the particle size on the average structural anisotropy noticeably contributes to the hardening observed for low . The influence of measuring temperature in size dependence of coercivity in nanostructured alloys has been analyzed. Some analogies and differences in respect of that observed in partially nanocrystallized samples have been found

Critical currents and superconductivity ferromagnetism coexistence in high-Tc oxides

CERN Document Server

Khene, Samir

2016-01-01

The book comprises six chapters which deal with the critical currents and the ferromagnetism-superconductivity coexistence in high-Tc oxides. It begins by gathering key data for superconducting state and the fundamental properties of the conventional superconductors, followed by a recap of the basic theories of superconductivity. It then discusses the differences introduced by the structural anisotropy on the Ginzburg-Landau approach and the Lawrence-Doniach model before addressing the dynamics of vortices and the ferromagnetism-superconductivity coexistence in high-Tc oxides, and provides an outline of the pinning phenomena of vortices in these materials, in particular the pinning of vortices by the spins. It elucidates the methods to improve the properties of superconducting materials for industrial applications. This optimization aims at obtaining critical temperatures and densities of critical currents at the maximum level possible. Whereas the primary objective is the basic mechanisms pushing the superco...

Performance of Halbach magnet arrays with finite coercivity

DEFF Research Database (Denmark)

Insinga, Andrea Roberto; Bahl, C.R.H.; Bjørk, Rasmus

2016-01-01

of the magnetic material and the fact that the coercivity is not infinite will limit the attainable field. The presented method is able to predict when and where demagnetization will occur, and these predictions are compared with the analytical solution for the case of infinite coercivity. However, the approach...... presented here also allows quantification of the decrease in flux density and homogeneity for a partially demagnetized magnet. Moreover, the problem of how to realize a Halbach cylinder geometry using a mix of materials with different coercivities without altering the overall performance is addressed. Being......A numerical method to study the effect of finite coercivity on the Halbach cylinder geometry is presented. Despite the fact that the analytical solution available for this geometry does not set any limit to the maximum air gap flux density achievable, in real life the non-linear response...

Formation and characterization of magnetic barium ferrite hollow fibers with low coercivity via co-electrospun

Energy Technology Data Exchange (ETDEWEB)

Liu, Gui-fang, E-mail: guifang777@163.com; Zhang, Zi-dong, E-mail: 1986zzd@163.com; Dang, Feng, E-mail: dangfeng@sdu.edu.cn; Cheng, Chuan-bing, E-mail: 807033063@qq.com; Hou, Chuan-xin, E-mail: 710313782@qq.com; Liu, Si-da, E-mail: superliustar@hotmail.com

2016-08-15

BaFe{sub 12}O{sub 19} fibers and hollow fibers were successfully prepared by electrospun and co-electrospun. A very interesting result appeared in this study that hollow fibers made by co-electrospun showed low coercivity values of a few hundred oersteds, compared with the coercivity values of more than thousand oersteds for the fibers made by electrospun. So the hollow fibers with high saturation magnetization (M{sub s}) and while comparatively low coercivity (H{sub c}) exhibited strong magnetism and basically showed soft character. And this character for hollow fibers will lead to increase of the permeability for the samples which is favorable for impedance matching in microwave absorption. So these hollow fibers are promised to have use in a number of applications, such as switching and sensing applications, electromagnetic materials, microwave absorber. - Highlights: • BaFe{sub 12}O{sub 19} fibers were prepared via electrospinning successfully. • The coercivity has a value of a few hundred oersteds for the hollow fibers made by coaxial electrospun. • BaFe{sub 12}O{sub 19} with high saturation magnetization and low coercivity shows great potential in microwave absorbing application.

Temperature-Dependent Coercive Field Measured by a Quantum Dot Strain Gauge.

Science.gov (United States)

Chen, Yan; Zhang, Yang; Keil, Robert; Zopf, Michael; Ding, Fei; Schmidt, Oliver G

2017-12-13

Coercive fields of piezoelectric materials can be strongly influenced by environmental temperature. We investigate this influence using a heterostructure consisting of a single crystal piezoelectric film and a quantum dots containing membrane. Applying electric field leads to a physical deformation of the piezoelectric film, thereby inducing strain in the quantum dots and thus modifying their optical properties. The wavelength of the quantum dot emission shows butterfly-like loops, from which the coercive fields are directly derived. The results suggest that coercive fields at cryogenic temperatures are strongly increased, yielding values several tens of times larger than those at room temperature. We adapt a theoretical model to fit the measured data with very high agreement. Our work provides an efficient framework for predicting the properties of ferroelectric materials and advocating their practical applications, especially at low temperatures.

Performance of Halbach magnet arrays with finite coercivity

International Nuclear Information System (INIS)

Insinga, A.R.; Bahl, C.R.H.; Bjørk, R.; Smith, A.

2016-01-01

A numerical method to study the effect of finite coercivity on the Halbach cylinder geometry is presented. Despite the fact that the analytical solution available for this geometry does not set any limit to the maximum air gap flux density achievable, in real life the non-linear response of the magnetic material and the fact that the coercivity is not infinite will limit the attainable field. The presented method is able to predict when and where demagnetization will occur, and these predictions are compared with the analytical solution for the case of infinite coercivity. However, the approach presented here also allows quantification of the decrease in flux density and homogeneity for a partially demagnetized magnet. Moreover, the problem of how to realize a Halbach cylinder geometry using a mix of materials with different coercivities without altering the overall performance is addressed. Being based on a numerical approach, the presented method can be employed to analyze the demagnetization effects due to coercivity for any geometry, even when the analytical solution is not available. - Highlights: • The effect of the finite coercivity on the performance of the Halbach cylinder geometry is analyzed • FEM predictions of demagnetization are in agreement with the analytical calculations. • Performance in the non-linear regime is quantified by the average and uniformity of the field • We show which regions in the geometry are more likely to experience non-linear behavior. • We provide a recipe for the fabrication of a multi-material Halbach cylinder

Temperature dependence of the coercive field of gas atomized Fe{sub 73.5}Si{sub 13.5}B{sub 9}Nb{sub 3}Cu{sub 1}

Energy Technology Data Exchange (ETDEWEB)

Garcia-Escorial, A., E-mail: age@cenim.csic.es [CENIM-CSIC, Avda, Gregorio del Amo, 8, 28040 Madrid (Spain); Lieblich, M. [CENIM-CSIC, Avda, Gregorio del Amo, 8, 28040 Madrid (Spain); Hernando, A.; Aragon, A.; Marin, P. [Instituto de Magnetismo Aplicado, IMA, P.O. Box 155, 28230 Madrid (Spain)

2012-09-25

Highlights: Black-Right-Pointing-Pointer An anomalous thermal dependence of the coercive field of gas atomized Fe{sub 73.5}Si{sub 13.5}B{sub 9}Nb{sub 3}Cu{sub 1} powder particles under 25 {mu}m powder particle, increasing Hc as temperature increases. Black-Right-Pointing-Pointer It is proposed that Cu rich regions at inter-grain boundaries could act as exchange decoupling regions contributing to the thermal increase of coercivity. Black-Right-Pointing-Pointer This anomalous thermal dependence points out that tailoring microstructure and size, by controlling the cooling rate of more adequate multiphase systems, could be a promising procedure to develop soft or hard magnets, avoiding Rare Earths metals that is nowadays an important target for the engineering of magnetic materials. - Abstract: In this work, the dependence of the coercive field of Fe{sub 73.5}Si{sub 13.5}B{sub 9}Nb{sub 3}Cu{sub 1} gas atomized powder with the temperature for different particle sizes has been studied, observing an anomalous behavior in the under 25 powder particle size fraction. This unusual behavior is related with the microstructure of the powder, and is attributed to the presence of a multiphase magnetic system, with non-magnetic regions decoupling the ferromagnetic domains.

Effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles

International Nuclear Information System (INIS)

Tong Liuniu; Wang Yichao; He Xianmei; Han Huaibin; Xia Ailin; Hu Jinlian

2012-01-01

We explore the effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles synthesized by the sol-gel method. X-ray diffraction and x-ray photoelectron spectroscopy data show evidence that Cr has been incorporated into the wurtzite ZnO lattice as Cr 2+ ions substituting for Zn 2+ ions without any detectable secondary phase in as-synthesized Zn 0.97 Cr 0.03 O nanopowders. The room temperature magnetization measurements reveal a large enhancement of saturation magnetization M s as well as an increase of coercivity of H 2 -annealed Zn 0.97 Cr 0.03 O:H samples. It is found that the field-cooled magnetization curves as a function of temperature from 40 to 400 K can be well fitted by a combination of a standard Bloch spin-wave model and Curie–Weiss law. The values of the fitted parameters of the ferromagnetic exchange interaction constant a and the Curie constant C of H 2 -annealed Zn 0.97 Cr 0.03 O:H nanoparticles are almost doubled upon H 2 -annealing. Photoluminescence measurements show evidence that the shallow donor defect or/and defect complexes such as hydrogen occupying an oxygen vacancy H o may play an important role in the origin of H 2 -annealing induced enhancement of ferromagnetism in Cr-H codoped ZnO nanoparticles. - Graphical Abstract: The H 2 -annealing induced enhancement of room temperature ferromagnetism in Cr-doped ZnO nanoparticles is observed. It is found that the field-cooled M-T curves can be well fitted by a combination of a standard Bloch spin-wave model and Curie–Weiss law. The values of the fitted parameters of the ferromagnetic exchange interaction constant a and the Curie constant C of H 2 -annealed Zn 0.97 Cr 0.03 O:H nanoparticles are almost doubled upon H 2 -annealing. The PL data show evidence that the hydrogen related shallow donor defect or/and defect complexes may be responsible for it. Display Omitted Highlights: ► The H 2 -annealing induced a large enhancement of

On the Issue of the Concept "Coercive Criminality"

Directory of Open Access Journals (Sweden)

Pestereva Y. S.

2014-04-01

Full Text Available The article deals with the actual problems relating to the concept of coercive criminality. Here is determined the lexical scope of the concept "coercion"; the philosophical and criminal law contents of the researched term are compared; the types of the coercive criminality are determined.

Coercivity and induced magnetic anisotropy by stress and/or field annealing in Fe- and Co- based (Finemet-type) amorphous alloys

International Nuclear Information System (INIS)

Miguel, C.; Zhukov, A.; Val, J.J. del; Gonzalez, J.

2005-01-01

Uniaxial magnetic anisotropy has been induced in amorphous Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 (Fe-rich) and (Co 77 Si 13.5 B 9.5 ) 90 Fe 7 Nb 3 (Co-rich) ferromagnetic alloys by annealing under stress and/or magnetic field. Such anisotropy plays a crucial role on the magnetization process and, consequently, determine the future applications of these materials. The mechanisms involved on the origin of such induced magnetic anisotropy showed significant differences between Fe-rich and Co-rich amorphous alloys. This work provides a comparative study of the coercive field and induced magnetic anisotropy in Fe-rich and Co-rich (Finemet) amorphous alloys treated by stress and/or field

Coercive Diplomacy: Countering War-Threatening Crises and Armed Conflicts

DEFF Research Database (Denmark)

Jakobsen, Peter Viggo

2015-01-01

Nowadays states rarely resort to war to defeat each other or to address war-threatening crises and armed conflicts. Instead, coercive diplomacy has emerged as their strategy of choice when persuasion and other non-military instruments fall short. Coercive diplomacy involves the use of military...... threats and/or limited force (sticks) coupled with inducements and assurances (carrots) in order to influence the opponent to do something it would prefer not to. States use coercive diplomacy in the hope of achieving their objectives without having to resort to full-scale war. This chapter presents...... the strategy of coercive diplomacy and its requirements for success and shows how states have employed it to manage crises and conflicts during the three strategic eras that the world has passed through since the end of the Cold War....

Conductance spectra of asymmetric ferromagnet/ferromagnet/ferromagnet junctions

Science.gov (United States)

Pasanai, K.

2017-01-01

A theory of tunneling spectroscopy of ferromagnet/ferromagnet/ferromagnet junctions was studied. We applied a delta-functional approximation for the interface scattering properties under a one-dimensional system of a free electron approach. The reflection and transmission probabilities were calculated in the ballistic regime, and the conductance spectra were then calculated using the Landauer formulation. The magnetization directions were set to be either parallel (P) or anti-parallel (AP) alignments, for comparison. We found that the conductance spectra was suppressed when increasing the interfacial scattering at the interfaces. Moreover, the electron could exhibit direct transmission when the thickness was rather thin. Thus, there was no oscillation in this case. However, in the case of a thick layer the conductance spectra oscillated, and this oscillation was most prominent when the middle layer thickness increased. In the case of direct transmission, the conductance spectra of P and AP systems were definitely suppressed with increased exchange energy of the middle ferromagnet. This also refers to an increase in the magnetoresistance of the junction. In the case of oscillatory behavior, the positions of the resonance peaks were changed as the exchange energy was changed.

High coercivity in Fe-Nb-B-Dy bulk nanocrystalline magnets

Energy Technology Data Exchange (ETDEWEB)

Ziolkowski, Grzegorz; Chrobak, Artur; Klimontko, Joanna [Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007, Katowice (Poland); Chrobak, Dariusz; Rak, Jan [Institute of Materials Science, University of Silesia, 75 Pulku Piechoty 1, 41-500, Chorzow (Poland); Zivotsky, Ondrej; Hendrych, Ales [Department of Physics, VSB-TU Ostrava, Ostrava (Czech Republic)

2016-11-15

The paper refers to structural and magnetic properties of the (Fe{sub 80}Nb{sub 6}B{sub 14}){sub 1-x}Dy{sub x} (x = 0.08, 0.10, 0.12, 0.16) bulk nanocrystalline alloys prepared by making use of the vacuum suction casting technique. The samples are in a form of rods with different diameters d = 1.5, 1, and 0.5 mm. The phase structure was investigated by XRD technique and reveals an occurrence of magnetically hard Dy{sub 2}Fe{sub 14}B as well as other relatively soft Dy-Fe, Fe-B, and Fe phases dependently on the Dy content. The alloys show hard magnetic properties with high coercive field up to 5.5 T (for x = 0.12 and d = 0.5 mm). The observed magnetic hardening effect with the increase of cooling rate (decrease of sample diameter d) can be attributed to a formation of ultra-hard magnetic objects as well as increasing role of low dimensional microstructure. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Faculty Perceptions of and Experiences with Students' Use of Coercive Power

Science.gov (United States)

Kuhn, Kristine L.

2016-01-01

The purpose of this basic qualitative study was to understand how faculty perceive and experience students' use of coercive power in faculty-student relationships. Interviews were used to gather data from faculty members who had experienced students' use of coercive power. Data reveal that students' use of coercive power can negatively impact…

Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

International Nuclear Information System (INIS)

Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

2013-01-01

Highlights: ► Ferromagnetic materials guide the flux distribution of the PMG to bulk positions. ► With ferromagnetic materials, guidance performance can be enhanced greatly. ► A new HTS Maglev system with onboard ferromagnetic materials is designed. ► The design can meet large guidance force requirements for practical applications. -- Abstract: Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves

Angular dependence of coercivity derived from alignment dependence of coercivity in Nd-Fe-B sintered magnets

Directory of Open Access Journals (Sweden)

Yutaka Matsuura

2018-01-01

Full Text Available Experimental results of the alignment dependence of the coercivity in Nd-Fe-B sintered magnets showed that the angle of magnetization reversal for anisotropically aligned magnets was bigger than that obtained from the theoretical results calculated using the postulation that every grain independently reverses its magnetization direction following the 1/cos θ law. The angles of reversed magnetization (θ1 for Nd13.48Co0.55B5.76Febal. with alignment α=0.95 and for Nd12.75Dy0.84B5.81Co0.55Febal. with α=0.96 were 30° and 36°, respectively, which were very similar to that of an ideal magnet with a Gaussian distribution (σ=31° and 44°, respectively of the grain alignment. In this model, we postulated that every grain independently reversed according to the 1/cos θ law. The calculation results for the angular dependence of the coercivity using the values θ1=ω1(0°=30°, σ=31° and θ1=ω1(0°=36°, σ=44° could qualitatively and convincingly explain the observed angular dependence of the coercivity of Nd14.2B6.2Co1.0Febal. and Nd14.2Dy0.3B6.2Co1.0Febal.. It is speculated that the magnetic domain wall is pinned at grains tilted away from the easy magnetization direction, and when the magnetic domain wall de-pins from the tilted grains, the magnetic domain wall jumps through several grains. We suggest that the coercive force of the aligned magnet behaves like a low-aligned magnet owing to the magnetization reversal of the crust of the grains induced by the pinning and subsequent jumping of the magnetic domain wall.

Angular dependence of coercivity derived from alignment dependence of coercivity in Nd-Fe-B sintered magnets

Science.gov (United States)

Matsuura, Yutaka; Nakamura, Tetsuya; Sumitani, Kazushi; Kajiwara, Kentaro; Tamura, Ryuji; Osamura, Kozo

2018-01-01

Experimental results of the alignment dependence of the coercivity in Nd-Fe-B sintered magnets showed that the angle of magnetization reversal for anisotropically aligned magnets was bigger than that obtained from the theoretical results calculated using the postulation that every grain independently reverses its magnetization direction following the 1/cos θ law. The angles of reversed magnetization (θ1) for Nd13.48Co0.55B5.76Febal. with alignment α=0.95 and for Nd12.75Dy0.84B5.81Co0.55Febal. with α=0.96 were 30° and 36°, respectively, which were very similar to that of an ideal magnet with a Gaussian distribution (σ=31° and 44°, respectively) of the grain alignment. In this model, we postulated that every grain independently reversed according to the 1/cos θ law. The calculation results for the angular dependence of the coercivity using the values θ1=ω1(0°)=30°, σ=31° and θ1=ω1(0°)=36°, σ=44° could qualitatively and convincingly explain the observed angular dependence of the coercivity of Nd14.2B6.2Co1.0Febal. and Nd14.2Dy0.3B6.2Co1.0Febal.. It is speculated that the magnetic domain wall is pinned at grains tilted away from the easy magnetization direction, and when the magnetic domain wall de-pins from the tilted grains, the magnetic domain wall jumps through several grains. We suggest that the coercive force of the aligned magnet behaves like a low-aligned magnet owing to the magnetization reversal of the crust of the grains induced by the pinning and subsequent jumping of the magnetic domain wall.

Investigation of coercivity for electroplated Fe-Ni thick films

Science.gov (United States)

Yanai, T.; Eguchi, K.; Koda, K.; Kaji, J.; Aramaki, H.; Takashima, K.; Nakano, M.; Fukunaga, H.

2018-05-01

We have already reported Fe-Ni firms with good soft magnetic properties prepared by using an electroplating method. In our previous studies, we prepared the Fe-Ni films from citric-acid-based baths (CA-baths) and ammonium-chloride-based ones (AC-baths), and confirmed that the coercivity for the AC-baths was lower than that for the CA-baths. In the present study, we investigated reasons for the lower coercivity for the AC-baths to further improve the soft magnetic properties. From an observation of magnetic domains of the Fe22Ni78 films, we found that Fe22Ni78 film for AC-bath had a magnetic anisotropy in the width direction, and also found that the coercivity in the width direction was lower than the longitudinal one for the AC-bath. As an annealing for a stress relaxation in the films reduced the difference in the coercivity, we considered that the anisotropy is attributed to the magneto-elastic effect.

Epitaxial ferromagnetic Fe3Si on GaAs(111)A with atomically smooth surface and interface

International Nuclear Information System (INIS)

Liu, Y. C.; Hung, H. Y.; Kwo, J.; Chen, Y. W.; Lin, Y. H.; Cheng, C. K.; Hong, M.; Tseng, S. C.; Hsu, C. H.; Chang, M. T.; Lo, S. C.

2015-01-01

Single crystal ferromagnetic Fe 3 Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe 3 Si/GaAs(111) yielded a saturation moment of 990 emu/cm 3 with a small coercive field ≤1 Oe at room temperature

Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

Energy Technology Data Exchange (ETDEWEB)

Jin, Zhenghe; Kim, Ki Wook [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Nori, Sudhakar; Lee, Yi-Fang; Narayan, Jagdish [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Kumar, D. [Department of Mechanical Engineering, North Carolina A & T State University, Greensboro, North Carolina 27411 (United States); Wu, Fan [Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey 08540 (United States); Prater, J. T. [Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709 (United States)

2015-10-28

We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, H{sub c} = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.

Optimizing magneto-optical effects in the ferromagnetic semiconductor GaMnAs

International Nuclear Information System (INIS)

Riahi, H.; Thevenard, L.; Maaref, M.A.; Gallas, B.; Lemaître, A.; Gourdon, C

2015-01-01

A trilayer of the ferromagnetic semiconductor GaMnAs, a SiO 2 buffer layer and a piezoelectric ZnO layer, is investigated in view of its use in device implementation to study surface acoustic wave-assisted magnetization switching. The magneto-optical properties: Kerr rotation and ellipticity and magnetic contrast in Kerr microscopy images are investigated as a function of temperature. While the ZnO layer prevents any good quality imaging of magnetic domains, we show that with the SiO 2 layer only the polar Kerr rotation and the magnetic contrast are increased by a factor of 2. This result is in good quantitative agreement with calculations using an optical interference model and could be further improved. The detrimental effects of the dielectric layers capping on the Curie temperature and coercive field of the GaMnAs layer can be kept to a reasonable level. - Highlights: • GaMnAs/SiO 2 /ZnO studied for surface acoustic wave assisted magnetization switching. • The Kerr rotation and magneticcontrast increase by a factor 2 with SiO 2 on GaMnAs. • Good quantitative agreement with an optical interference model. • Little detrimental effect of SiO 2 and ZnO on the ferromagnetic properties of GaMnAs

Room temperature p-type conductivity and coexistence of ferroelectric order in ferromagnetic Li doped ZnO nanoparticles

KAUST Repository

Awan, Saif Ullah

2014-10-28

Memory and switching devices acquired new materials which exhibit ferroelectric and ferromagnetic order simultaneously. We reported multiferroic behavior in Zn1-yLiyO(0.00≤y≤0.10) nanoparticles. The analysis of transmission electron micrographs confirmed the hexagonal morphology and wurtzite crystalline structure. We investigated p-type conductivity in doped samples and measured hole carriers in range 2.4×1017/cc to 7.3×1017/cc for different Li contents. We found that hole carriers are responsible for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5kV/cm (0.11 μC/cm2) and 2.8kV/cm (0.15 μC/cm2) for y=0.08 and y=0.10 samples. We propose that the mechanism of Li induced ferroelectricity in ZnO is due to indirect dipole interaction via hole carriers. We investigated that if the sample has hole carriers ≥5.3×1017/cc, they can mediate the ferroelectricity. Ferroelectric and ferromagnetic measurements showed that higher electric polarization and larger magnetic moment is attained when the hole concentration is larger and vice versa. Our results confirmed the hole dependent coexistence of ferromagnetic and ferroelectric behavior at room temperature, which provide potential applications for switchable and memory devices.

Synthesis, morphology and microstructure of pomegranate-like hematite ({alpha}-Fe{sub 2}O{sub 3}) superstructure with high coercivity

Energy Technology Data Exchange (ETDEWEB)

Tadic, Marin, E-mail: marint@vinca.rs [Condensed Matter Physics Laboratory, Vinca Institute, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia); Citakovic, Nada [Military Academy, Generala Pavla Jurisica Sturma 33, University of Belgrade, 11000 Belgrade (Serbia); Panjan, Matjaz [Jozef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia); Stanojevic, Boban [Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, University of Belgrade (Serbia); Markovic, Dragana [Condensed Matter Physics Laboratory, Vinca Institute, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia); Jovanovic, Dorde [Center for Solid State Physics and New Materials, Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia); Spasojevic, Vojislav [Condensed Matter Physics Laboratory, Vinca Institute, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia)

2012-12-05

Highlights: Black-Right-Pointing-Pointer We found superior magnetic properties of the hematite ({alpha}-Fe{sub 2}O{sub 3}). Black-Right-Pointing-Pointer TEM and HRTEM images show a pomegranate-like superstructure. Black-Right-Pointing-Pointer Magnetic measurements display high coercivity H{sub C} = 4350 Oe at the room temperature. - Abstract: We found novel and superior magnetic properties of the hematite ({alpha}-Fe{sub 2}O{sub 3}) that originate from an internal microstructure of particles and strong inter-particle interactions between nanocrystal sub-units. The hematite particles were synthesized by thermal decomposition of iron (III) nitrate without any template or surfactant. The purity, size, crystallinity, morphology, microstructure and magnetic features of the as-prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and SQUID magnetometry. An XRD study reveals a pure phase of {alpha}-Fe{sub 2}O{sub 3} whereas TEM shows {alpha}-Fe{sub 2}O{sub 3} spheres with a diameter of about 150 nm. RS also shows high quality and purity of the sample. Moreover, TEM and HRTEM images show a pomegranate-like superstructure and evidence that the spherical particles are composed of individual well-crystallized nanoparticle sub-units (self-assembled nanoparticles) with a size of about 20 nm. Magnetic measurements display hysteretic behavior at the room temperature with remanent magnetization M{sub r} = 0.731 emu/g, saturation magnetization M{sub S} = 6.83 emu/g and coercivity H{sub C} = 4350 Oe, as well as the Morin transition at T{sub M} = 261 K. These results and comparison with those in the literature reveal that the sample has extremely high coercivity. The magnetic properties of the sample are discussed in relation to morphology, internal microstructure, surface

Microstructure evolution and coercivity enhancement in Nd-Fe-B thin films diffusion-processed by R-Al alloys (R=Nd, Pr)

Science.gov (United States)

Xie, Yigao; Yang, Yang; Zhang, Tongbo; Fu, Yanqing; Jiang, Qingzheng; Ma, Shengcan; Zhong, Zhenchen; Cui, Weibin; Wang, Qiang

2018-05-01

Diffusion process by Nd-Al and Pr-Al alloys was compared and investigated in Nd-Fe-B thin films. Enhanced coercivity 2.06T and good squareness was obtained by using Pr85Al15 and Nd85Al15 alloys as diffusion sources. But the coercivity of diffusion-processed thin films by Pr70Al30 and Pr55Al45 alloys decreased to 2.04T and 1.82T. High ambient coercivity of 2.26T was achieved in diffusion-processed thin film by Nd70Al30 leading to an improved coercivity thermal stability because Nd2Fe14B grains were enveloped by Nd-rich phase as seen by transmission electron microscopy Nd-loss image. Meanwhile, microstructure-dependent parameters α and Neff were improved. However, high content of Al in diffusion-processed thin film by Nd55Al45 lead to degraded texture and coercivity.

Coercivity of magneto-optical media by spin dynamics

International Nuclear Information System (INIS)

Suits, J.C.

1990-01-01

Spin dynamics computer simulations have been carried out to study the effect of pinning on domain-wall motion in TbFeCo-like media. These calculations were done on a 30x30x1 mesh, where the spin direction at each lattice site was calculated with the Landau--Lifshitz--Gilbert equation. The simulations were made in an IBM 3090 mainframe--personal computer environment where the result of the calculation is a movie that runs at three frames/second on an AT and shows graphically the domain-wall--defect interaction. The domain wall is caused to move in an external field toward a defect, and the maximum field that pins the domain wall was observed. The defects have finite length and zero magnetization, which correspond to voids or nonmagnetic second phase in the media. The simulation shows that small defects on the order of 100 A in size can pin walls with pinning strength appropriate to the coercivity of magneto-optical media, i.e., local coercivities in the range 1--10 kOe. For sufficiently high fields a single wall may break up into two separate sections at the defect, and then join together beyond the defect to become a single wall again. For rectangular defects, the coercivity depends strongly and nearly linearly on defect length (parallel to the domain-wall surface) and only weakly on defect width for widths greater than about 50 A (perpendicular to the wall surface)

Coercive Sanctions and International Conflicts: A Sociological Theory

DEFF Research Database (Denmark)

Jaeger, Mark Daniel

international sanctions work, and more substantially, what are the social conditions within sanctions conflicts that are conducive to either cooperation or non-cooperation? Arguing that coercive sanctions and international conflicts are socially-constructed facts, the book explores the processes involved......Perhaps the most common question raised in the literature on coercive international sanctions is: "Do sanctions work?" Unsurprisingly, the answer to such a sweeping question remains inconclusive. Instead of asking whether sanctions work, this book addresses a more basic question: How do coercive......, and to its potential transformation. Thus it is premature to ‘predict’ the political effectiveness of sanctions simply on the basis of their economic impact. The book presents analyses of the sanctions conflicts between China and Taiwan and over Iran’s nuclear program, illustrating how negative sanctions...

Conductance spectra of asymmetric ferromagnet/ferromagnet/ferromagnet junctions

Energy Technology Data Exchange (ETDEWEB)

Pasanai, K., E-mail: krisakronmsu@gmail.com

2017-01-15

A theory of tunneling spectroscopy of ferromagnet/ferromagnet/ferromagnet junctions was studied. We applied a delta-functional approximation for the interface scattering properties under a one-dimensional system of a free electron approach. The reflection and transmission probabilities were calculated in the ballistic regime, and the conductance spectra were then calculated using the Landauer formulation. The magnetization directions were set to be either parallel (P) or anti-parallel (AP) alignments, for comparison. We found that the conductance spectra was suppressed when increasing the interfacial scattering at the interfaces. Moreover, the electron could exhibit direct transmission when the thickness was rather thin. Thus, there was no oscillation in this case. However, in the case of a thick layer the conductance spectra oscillated, and this oscillation was most prominent when the middle layer thickness increased. In the case of direct transmission, the conductance spectra of P and AP systems were definitely suppressed with increased exchange energy of the middle ferromagnet. This also refers to an increase in the magnetoresistance of the junction. In the case of oscillatory behavior, the positions of the resonance peaks were changed as the exchange energy was changed. - Highlights: • The conductance spectra of a FM/FM/FM junction were calculated. • The conductance spectra were suppressed by the exchange energy. • The exchange energy and the potential strength play similar roles in the junctions.

Conductance spectra of asymmetric ferromagnet/ferromagnet/ferromagnet junctions

International Nuclear Information System (INIS)

Pasanai, K.

2017-01-01

A theory of tunneling spectroscopy of ferromagnet/ferromagnet/ferromagnet junctions was studied. We applied a delta-functional approximation for the interface scattering properties under a one-dimensional system of a free electron approach. The reflection and transmission probabilities were calculated in the ballistic regime, and the conductance spectra were then calculated using the Landauer formulation. The magnetization directions were set to be either parallel (P) or anti-parallel (AP) alignments, for comparison. We found that the conductance spectra was suppressed when increasing the interfacial scattering at the interfaces. Moreover, the electron could exhibit direct transmission when the thickness was rather thin. Thus, there was no oscillation in this case. However, in the case of a thick layer the conductance spectra oscillated, and this oscillation was most prominent when the middle layer thickness increased. In the case of direct transmission, the conductance spectra of P and AP systems were definitely suppressed with increased exchange energy of the middle ferromagnet. This also refers to an increase in the magnetoresistance of the junction. In the case of oscillatory behavior, the positions of the resonance peaks were changed as the exchange energy was changed. - Highlights: • The conductance spectra of a FM/FM/FM junction were calculated. • The conductance spectra were suppressed by the exchange energy. • The exchange energy and the potential strength play similar roles in the junctions.

Coercivity enhancement of HDDR-processed Nd-Fe-B permanent magnet with the rapid hot-press consolidation process

Energy Technology Data Exchange (ETDEWEB)

Nozawa, N. [Magnetic Materials Research Laboratory, NEOMAX Company, Hitachi Metals Ltd., Osaka 618-0013 (Japan); Sepehri-Amin, H. [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan); Magnetic Materials Center, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Ohkubo, T. [Magnetic Materials Center, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Hono, K. [Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan); Magnetic Materials Center, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Nishiuchi, T. [Magnetic Materials Research Laboratory, NEOMAX Company, Hitachi Metals Ltd., Osaka 618-0013 (Japan); Hirosawa, S., E-mail: Satoshi_Hirosawa@hitachi-metals.co.j [Magnetic Materials Research Laboratory, NEOMAX Company, Hitachi Metals Ltd., Osaka 618-0013 (Japan)

2011-01-15

High coercivity, fully dense anisotropic permanent magnets of submicron grain sizes were produced by rapid hot-press consolidation of hydrogenation-disproportionation-desorption-recombination (HDDR) processed Nd-Fe-Co-B powders. In the hot-press process, the coercivity of the consolidated material showed a sharp minimum prior to full densification. Thereafter, it reached a value 25% higher than that of the initial powder. Scanning electron microscopy and transmission electron microscopy observations revealed that the variation in H{sub cJ} was caused by a redistribution of Nd along the grain boundaries during hot pressing and that the high coercivity was attributable to the formation of thin, continuous Nd-rich phase along the grain boundaries.

Carrier concentration induced ferromagnetism in semiconductors

International Nuclear Information System (INIS)

Story, T.

2007-01-01

In semiconductor spintronics the key materials issue concerns ferromagnetic semiconductors that would, in particular, permit an integration (in a single multilayer heterostructure) of standard electronic functions of semiconductors with magnetic memory function. Although classical semiconductor materials, such as Si or GaAs, are nonmagnetic, upon substitutional incorporation of magnetic ions (typically of a few atomic percents of Mn 2+ ions) and very heavy doping with conducting carriers (at the level of 10 20 - 10 21 cm -3 ) a ferromagnetic transition can be induced in such diluted magnetic semiconductors (also known as semimagnetic semiconductors). In the lecture the spectacular experimental observations of carrier concentration induced ferromagnetism will be discussed for three model semiconductor crystals. p - Ga 1-x Mn x As currently the most actively studied and most perspective ferromagnetic semiconductor of III-V group, in which ferromagnetism appears due to Mn ions providing both local magnetic moments and acting as acceptor centers. p - Sn 1-x Mn x Te and p - Ge 1-x Mn x Te classical diluted magnetic semiconductors of IV-VI group, in which paramagnet-ferromagnet and ferromagnet-spin glass transitions are found for very high hole concentration. n - Eu 1-x Gd x Te mixed magnetic crystals, in which the substitution of Gd 3+ ions for Eu 2+ ions creates very high electron concentration and transforms antiferromagnetic EuTe (insulating compound) into ferromagnetic n-type semiconductor alloy. For each of these materials systems the key physical features will be discussed concerning: local magnetic moments formation, magnetic phase diagram as a function of magnetic ions and carrier concentration as well as Curie temperature and magnetic anisotropy engineering. Various theoretical models proposed to explain the effect of carrier concentration induced ferromagnetism in semiconductors will be briefly discussed involving mean field approaches based on Zener and RKKY

Coercivity of the Nd–Fe–B hot-deformed magnets diffusion-processed with low melting temperature glass forming alloys

Energy Technology Data Exchange (ETDEWEB)

Seelam, U.M.R. [Elements Strategy Initiative Center for Magnetic Materials (ESICMM), National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Liu, Lihua [Elements Strategy Initiative Center for Magnetic Materials (ESICMM), National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan); Akiya, T.; Sepehri-Amin, H.; Ohkubo, T. [Elements Strategy Initiative Center for Magnetic Materials (ESICMM), National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Sakuma, N.; Yano, M.; Kato, A. [Advanced Material Engineering Division, Toyota Motor Corporation, Susono 410-1193 (Japan); Hono, K., E-mail: kazuhiro.hono@nims.go.jp [Elements Strategy Initiative Center for Magnetic Materials (ESICMM), National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan)

2016-08-15

Nd- and Pr-based alloys with bulk glass forming ability and low melting temperatures, Nd{sub 60}Al{sub 10}Ni{sub 10}Cu{sub 20} and Pr{sub 60}Al{sub 10}Ni{sub 10}Cu{sub 20}, were used for grain boundary diffusion process to enhance the coercivity of hot-deformed magnets. The coercivity increment was proportional to the weight gain after the diffusion process. For the sample with 64% weight gain, the coercivity increased up to 2.8 T, which is the highest value for bulk Nd–Fe–B magnets that do not contain heavy rare-earth elements, Dy or Tb. Approximately half of the intergranular regions were amorphous and the remaining regions were crystalline. Magnetic isolation of the Nd{sub 2}Fe{sub 14}B grains by the Nd-rich amorphous/crystalline intergranular phases is attributed to the large coercivity enhancement. The coercivity does not change after the crystallization of the intergranular phase, indicating that the coercivity is not influenced by the strain at the interface with the crystalline intergranular phase. - Highlights: • Bulk-glass forming alloys were infiltrated into hot-deformed Nd–Fe–B magnets. • Very high coercivity of 2.8 T was attained without heavy rare-earth elements. • Approximately half of the inter-granular regions were amorphous. • Crystallization of amorphous intergranular phase does not change coercivity.

Control of coercive field in lithium niobate crystals with repeated polarization reversal

International Nuclear Information System (INIS)

Ro, Jung Hoon; Jeong, Doun; Park, Taeyong; Kim, Chulhan; Kwon, Soon-Bok; Cha, Myoungsik; Choi, Byeong Cheol; Yu, Nanei; Kurimura, Sunao; Jeon, Gyerok

2005-01-01

In this study, the amount of decrease in coercive field of congruent lithium niobate during repeated poling and back-poling was measured. The polarization is reversed in 300 ms and then back-poled during the rest period. The coercive field can be decreased around 1 kV/mm with a repeated poling interval of 5 s. As the interval prolonged, the poling field decrease became smaller, and a stretched exponential function is suggested for the experimental fitting resulting in a set of meaningful parameters. These values are essential for the design of high quality domain engineering

Epitaxial ferromagnetic Fe{sub 3}Si on GaAs(111)A with atomically smooth surface and interface

Energy Technology Data Exchange (ETDEWEB)

Liu, Y. C.; Hung, H. Y.; Kwo, J., E-mail: chsu@nsrrc.org.tw, E-mail: raynien@phys.nthu.edu.tw, E-mail: mhong@phys.ntu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chen, Y. W.; Lin, Y. H.; Cheng, C. K.; Hong, M., E-mail: chsu@nsrrc.org.tw, E-mail: raynien@phys.nthu.edu.tw, E-mail: mhong@phys.ntu.edu.tw [Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Tseng, S. C.; Hsu, C. H., E-mail: chsu@nsrrc.org.tw, E-mail: raynien@phys.nthu.edu.tw, E-mail: mhong@phys.ntu.edu.tw [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Chang, M. T.; Lo, S. C. [Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China)

2015-09-21

Single crystal ferromagnetic Fe{sub 3}Si(111) films were grown epitaxially on GaAs(111)A by molecular beam epitaxy. These hetero-structures possess extremely low surface roughness of 1.3 Å and interfacial roughness of 1.9 Å, measured by in-situ scanning tunneling microscope and X-ray reflectivity analyses, respectively, showing superior film quality, comparing to those attained on GaAs(001) in previous publications. The atomically smooth interface was revealed by the atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) images using the correction of spherical aberration (Cs)-corrected electron probe. Excellent crystallinity and perfect lattice match were both confirmed by high resolution x-ray diffraction. Measurements of magnetic property for the Fe{sub 3}Si/GaAs(111) yielded a saturation moment of 990 emu/cm{sup 3} with a small coercive field ≤1 Oe at room temperature.

τ-MnAl with high coercivity and saturation magnetization

Directory of Open Access Journals (Sweden)

J. Z. Wei

2014-12-01

Full Text Available In this paper, high purity τ-Mn54Al46 and Mn54−xAl46Cxalloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD, powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm-1, coercivity of 0.5 T, and a maximum energy product of (BHmax = 24.7 kJm-3 were achieved for the pure Mn54Al46 powders without carbon doping. The carbon substituted Mn54−xAl46Cx, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 μB which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 μB at a volume expansion rate of ΔV/V ≈ 20%.

Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

Energy Technology Data Exchange (ETDEWEB)

Si, M. S.; Gao, Daqiang, E-mail: gaodq@lzu.edu.cn, E-mail: xueds@lzu.edu.cn; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng, E-mail: gaodq@lzu.edu.cn, E-mail: xueds@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Liu, Yushen [Jiangsu Laboratory of Advanced Functional Materials and College of Physics and Engineering, Changshu Institute of Technology, Changshu 215500 (China); Deng, Xiaohui [Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008 (China); Zhang, G. P. [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States)

2014-05-28

Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

High-field susceptibility in ferromagnetic NpOs2

International Nuclear Information System (INIS)

Dunlap, B.D.; Aldred, A.T.; Lam, D.J.; Davidson, G.R.

1975-01-01

NpOs 2 is known to be a ferromagnet with a Curie temperature of 7.5 0 K. Previous bulk magnetization measurements indicated a field-induced magnetization even well below the transition temperature. By a measurement of the local high-field susceptibility, using the Moessbauer effect in 237 Np, a susceptibility of (1.2 +- 0.2) x 10 -2 emu/mole at 1.6 0 K is obtained, in general agreement with the bulk measurement. Such a large susceptibility is best understood by a model f itinerant magnetism, although other properties of the material indicate localized behavior

Ultrahigh coercivity and core-shell microstructure achieved in oriented Nd-Fe-B thin films diffusion-processed with Dy-based alloys

Energy Technology Data Exchange (ETDEWEB)

Zhang, Tongbo; Zhou, Xiaoqian; Yu, Dedong; Fu, Yanqing; Cui, Weibin [Northeastern University, Key Laboratory of Electromagnetic Processing of Materials (EPM), Ministry of Education, Shenyang (China); Northeastern University, Department of Physics and Chemistry of Materials, School of Materials Science and Engineering, Shenyang (China); Li, Guojian; Wang, Qiang [Northeastern University, Key Laboratory of Electromagnetic Processing of Materials (EPM), Ministry of Education, Shenyang (China)

2017-01-15

Ultrahigh ambient coercivities of ∝4 T were achieved in Nd-Fe-B benchmark thin film with coercivity of 1.06 T by diffusion-processing with Dy, Dy{sub 70}Cu{sub 30} and Dy{sub 80}Ag{sub 20} alloy layer. High texture and good squareness were obtained. In triple-junction regions, Dy element was found to be immiscible with Nd element. Microstructure observation indicated the typical gradient elementary distribution. Unambiguous core/shell microstructure was characterized by transition electron microscopy. Due to the enhanced ambient coercivity, the coercivity temperature stability was also substantially increased. (orig.)

A new type of soft ferromagnetic alloys: RFe12-xGex

International Nuclear Information System (INIS)

Lachevre, V.; Barbara, B.; Fruchart, D.; Pontonnier, L.

1998-01-01

Ternary iron-rich rare earth germanides RFe 12-x Ge x with R=Y, La, Ce, Nd, Sm, Gd, Dy, Ho and Er reveal soft ferromagnetic properties. The structure, the microstructure and the soft magnetic properties of these materials have been studied versus the germanium content and the nature of the rare earth element. In the as-cast materials, at least three crystallized phases have been identified: α-Fe(Ge), RFe 2 Ge 2 and traces of Fe 3 Ge. The typical grain size is of some tens of micrometer. The Curie temperature of these alloys is rather high (i.e. >770 K). The transition temperature as well as the saturation magnetization are found to strongly depend on the nature of the R element. The rapidly quenched alloys appear fully homogenized compared with the as-cast materials and the grain size decreases to about one micrometer. Although X-ray diffraction patterns have shown that the two major phases remain present, the magnetic characteristics are fairly dependent on the earth rare element. For all the investigated materials, measurements of the hysterical behaviour reveal a very low coercivity level, i.e. H c <10 Oe. (orig.)

Stabilization of the high coercivity ε-Fe2O3 phase in the CeO2–Fe2O3/SiO2 nanocomposites

International Nuclear Information System (INIS)

Mantlikova, A.; Poltierova Vejpravova, J.; Bittova, B.; Burianova, S.; Niznansky, D.; Ardu, A.; Cannas, C.

2012-01-01

We have investigated the processes leading to the formation of the Fe 2 O 3 and CeO 2 nanoparticles in the SiO 2 matrix in order to stabilize the ε-Fe 2 O 3 as the major phase. The samples with two different concentrations of the Fe were prepared by sol–gel method, subsequently annealed at different temperatures up to 1100 °C, and characterized by the Mössbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe 2 O 3 phases under various conditions of preparation was investigated, starting with the preferential appearance of the γ-Fe 2 O 3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major ε-Fe 2 O 3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable α-Fe 2 O 3 phase. A continuous increase of the particle size of the CeO 2 nanocrystals with increasing annealing temperature was also observed. - Graphical abstract: The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic γ-Fe 2 O 3 phase with negligible coercivity to the high coercivity ε-Fe 2 O 3 phase has been observed. Highlights: ► Research of the stabilization of the high coercivity ε-Fe 2 O 3 in CeO 2 –Fe 2 O 3 /SiO 2 . ► Samples with two different concentrations of Fe and three annealing temperatures. ► Phase transition γ→ε→(β)→α with increasing annealing temperature and particle size. ► Elimination of the superparamagnetic phases in samples with higher content of Fe. ► Best conditions for high coercivity ε-Fe 2 O 3 —higher Fe content and T A =1100°C.

Feasibility of introducing ferromagnetic materials to onboard bulk high-T{sub c} superconductors to enhance the performance of present maglev systems

Energy Technology Data Exchange (ETDEWEB)

Deng, Zigang, E-mail: zgdeng@gmail.com [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); State Key Laboratory of Traction Power (TPL), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Wang, Jiasu [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Zheng, Jun; Zhang, Ya [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); State Key Laboratory of Traction Power (TPL), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Wang, Suyu [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China)

2013-02-14

Highlights: ► Ferromagnetic materials guide the flux distribution of the PMG to bulk positions. ► With ferromagnetic materials, guidance performance can be enhanced greatly. ► A new HTS Maglev system with onboard ferromagnetic materials is designed. ► The design can meet large guidance force requirements for practical applications. -- Abstract: Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

Optimizing magneto-optical effects in the ferromagnetic semiconductor GaMnAs

Energy Technology Data Exchange (ETDEWEB)

Riahi, H., E-mail: hassenriahi1987@gmail.com [Laboratoire Matériaux Molécules et Applications, IPEST, Université de Carthage, La Marsa (Tunisia); Thevenard, L. [CNRS, UMR7588, Institut des Nanosciences de Paris, 4 place Jussieu, 75005 Paris (France); Sorbonne Universités, UPMC Université Paris 06, UMR7588, 4 place Jussieu, 75005 Paris (France); Maaref, M.A. [Laboratoire Matériaux Molécules et Applications, IPEST, Université de Carthage, La Marsa (Tunisia); Gallas, B. [CNRS, UMR7588, Institut des Nanosciences de Paris, 4 place Jussieu, 75005 Paris (France); Sorbonne Universités, UPMC Université Paris 06, UMR7588, 4 place Jussieu, 75005 Paris (France); Lemaître, A. [Laboratoire de Photonique et de Nanostructures – CNRS, Route de Nozay, 91460 Marcoussis (France); Gourdon, C [CNRS, UMR7588, Institut des Nanosciences de Paris, 4 place Jussieu, 75005 Paris (France); Sorbonne Universités, UPMC Université Paris 06, UMR7588, 4 place Jussieu, 75005 Paris (France)

2015-12-01

A trilayer of the ferromagnetic semiconductor GaMnAs, a SiO{sub 2} buffer layer and a piezoelectric ZnO layer, is investigated in view of its use in device implementation to study surface acoustic wave-assisted magnetization switching. The magneto-optical properties: Kerr rotation and ellipticity and magnetic contrast in Kerr microscopy images are investigated as a function of temperature. While the ZnO layer prevents any good quality imaging of magnetic domains, we show that with the SiO{sub 2} layer only the polar Kerr rotation and the magnetic contrast are increased by a factor of 2. This result is in good quantitative agreement with calculations using an optical interference model and could be further improved. The detrimental effects of the dielectric layers capping on the Curie temperature and coercive field of the GaMnAs layer can be kept to a reasonable level. - Highlights: • GaMnAs/SiO{sub 2}/ZnO studied for surface acoustic wave assisted magnetization switching. • The Kerr rotation and magneticcontrast increase by a factor 2 with SiO{sub 2} on GaMnAs. • Good quantitative agreement with an optical interference model. • Little detrimental effect of SiO{sub 2} and ZnO on the ferromagnetic properties of GaMnAs.

Coercive properties of elliptic-parabolic operator

International Nuclear Information System (INIS)

Duong Min Duc.

1987-06-01

Using a generalized Poincare inequality, we study the coercive properties of a class of elliptic-parabolic partial differential equations, which contains many degenerate elliptic equations considered by the other authors. (author). 16 refs

Large time-dependent coercivity and resistivity modification under sustained voltage application in a Pt/Co/AlOx/Pt junction.

NARCIS (Netherlands)

Brink, van den A.; van der Heijden, M.A.J.; Swagten, H.J.M.; Koopmans, B.

2015-01-01

The coercivity and resistivity of a Pt/Co/AlOx/Pt junction are measured under sustained voltage application. High bias voltages of either polarity are determined to cause a strongly enhanced, reversible coercivity modification compared to low voltages. Time-resolved measurements show a logarithmic

Josephson junctions with ferromagnetic interlayer

International Nuclear Information System (INIS)

Wild, Georg Hermann

2012-01-01

We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO x /Pd 0.82 Ni 0.18 /Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to π-coupling is observed for a thickness d F =6 nm of the ferromagnetic Pd 0.82 Ni 0.18 interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd 0.82 Ni 0.18 has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.

Josephson junctions with ferromagnetic interlayer

Energy Technology Data Exchange (ETDEWEB)

Wild, Georg Hermann

2012-03-04

We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO{sub x}/Pd{sub 0.82}Ni{sub 0.18}/Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to {pi}-coupling is observed for a thickness d{sub F}=6 nm of the ferromagnetic Pd{sub 0.82}Ni{sub 0.18} interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd{sub 0.82}Ni{sub 0.18} has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.

Coercivity enhancement and thermal-stability improvement in the melt-spun NdFeB ribbons by grain boundary diffusion

Science.gov (United States)

Xie, Jiajun; Yuan, Chao; Luo, Yang; Yang, Yuanfei; Hu, Bin; Yu, Dunbo; Yan, Wenlong

2018-01-01

Rapidly quenched NdFeB ribbons with high coercivity were obtained by Nd70Cu30 diffusion process. Samples with a high coercivity of 22.02 kOe at room temperature were obtained after grain boundary diffusion with 20 wt% Nd70Cu30 alloys. The NdCu diffusion process promoted grain growth in the ribbons, and grain boundary phases were formed with Cu segregation among NdFeB grains. Coercivity above 10 kOe at 150 °C was achieved in the bonded magnets with NdCu content over 10 wt%. The flux loss of bonded magnets was reduced by ∼32% at 120 °C after diffusion treatment with only a small amount (2 wt%) of NdCu.

Graphic User Interface for Monte Carlo Simulation of Ferromagnetic/Antiferromagnetic Manganite Bilayers

Directory of Open Access Journals (Sweden)

Hector Barco-Ríos

2011-06-01

Full Text Available The manganites have been widely studied because of their important properties as colossal magnetoresistance and exchange bias that are important phenomena used in many technological applications. For this reason, in this work, a study of the exchange bias effect present in La2/3Ca1/3MnO3/La1/3Ca2/3MnO3. This study was carried out by using the Monte Carlo method and the Metropolis Algorithm. In order to make easy this study, a graphic user interface was built alloying a friendly interaction. The interface permits to control the thickness of Ferromagnetic and Antiferromagnetic layer, temperatures the magnetic field, the number of Monte Carlo steps and the exchange parameters. Results obtained reflected the influence of all of these parameters on the exchange bias and coercive fields.

Coercivity Recovery Effect of Sm-Fe-Cu-Al Alloy on Sm2Fe17N3 Magnet

Science.gov (United States)

Otogawa, Kohei; Asahi, Toru; Jinno, Miho; Yamaguchi, Wataru; Takagi, Kenta; Kwon, Hansang

2018-03-01

The potential of a Sm-Fe-Cu-Al binder for improvement of the magnetic properties of Sm2Fe17N3 was examined. Transmission electron microscope (TEM) observation of a Sm-Fe-Cu-Al alloy-bonded Sm2Fe17N3 magnet which showed high coercivity revealed that the Sm-Fe-Cu-Al alloy had an effect of removing the surface oxide layer of the Sm2 Fe17N3 grains. However, the Sm-Fe-Cu-Al binder was contaminated by carbon and nitrogen, which originated from the organic solvent used as the milling medium during pulverization. To prevent carbon and nitrogen contamination, the Sm-Fe- Cu-Al alloy was added directly on the surface of the Sm2Fe17N3 grains by sputtering. Comparing the recovered coercivity per unit amount of the added binder the uncontaminated binder-coated sample had a higher coercivity recovery effect than the milled binder-added sample. These results suggested that sufficient addition of the contamination-free Sm-Fe-Cu-Al binder has the possibility to reduce the amount of binder necessary to produce a high coercive Sm2Fe17N3 magnet.

Coercive force features in stressed epitaxial ferrite-garnet films

International Nuclear Information System (INIS)

Dubinko, S.V.; Nedviga, A.S.; Vishnevskij, V.G.; Shaposhnikov, A.N.; Yagupov, V.S.; Nesteruk, A.G.; Prokopov, A.R.

2005-01-01

One has investigated into effect of a relative mismatching of periods of lattices of a film and of a substrate within 0.5-0.85% range on behavior of the coercive force of (Bi, Sm, Lu, Ca) 3 (Fe, Sc, Ga, Al) 5 O 12 composition ferrite garnet epitaxial films (FGEF) synthesized at (111) orientation gadolinium-gallium garnet substrates. One has revealed that the FGEF coercive force at increase of the relative mismatching of periods of lattices of a film and of a substrate increases at first, while when reaching the maximum value it begins to decrease. The coercive force maximum value is shown to result from the periodical localized stresses. The period of the localized stresses is determined by the value of mismatching of periods of lattices of a film and of a substrate [ru

Towards ferromagnet/superconductor junctions on graphene

International Nuclear Information System (INIS)

Pakkayil, Shijin Babu

2015-01-01

Ever since A. Aspect et al. performed the famous 1982 experiment to prove the violation of Bell's inequality, there have been suggestions to conduct the same experiment in a solid state system. Some of those proposals involve superconductors as the source of entangled electron pair and spin depended interfaces as the optical analogue of polariser/filter. Semiconductors can serve as the best medium for such an experiment due to their long relaxation lengths. So far there are no reports on a ferromagnet/superconductor junctions on a semiconductor even though such junctions has been successfully realised in metallic systems. This thesis reports the successful fabrication of ferromagnet/superconductor junction along with characterising measurements in a perfectly two dimensional zero-gap semiconductor known as graphene. Since it's discovery in 2004, graphene has attracted prodigious interest from both academia and industry due to it's inimitable physical properties: very high mobility, high thermal and electrical conductivity, a high Young's modulus and impermeability. Graphene is also expected to have very long spin relaxation length and high spin life time because of it's low spin orbit coupling. For this reason and since researchers are always looking for novel materials and devices to comply with the high demands for better and faster data storage devices, graphene has emanated as a brand new material system for spin based devices. The very first spin injection and detection in graphene was realised in 2007 and ever since, the focal point of the research has been to improve the spin transport properties. A part of this thesis discusses a new fabrication recipe which has a high yield for successfully contacting graphene with a ferromagnet. A high starting yield for ferromagnetic contacts is a irremissible condition for combining superconducting contacts to the device to fabricate ferromagnet/superconductor junctions. Any fabrication recipe

Towards ferromagnet/superconductor junctions on graphene

Energy Technology Data Exchange (ETDEWEB)

Pakkayil, Shijin Babu

2015-07-01

Ever since A. Aspect et al. performed the famous 1982 experiment to prove the violation of Bell's inequality, there have been suggestions to conduct the same experiment in a solid state system. Some of those proposals involve superconductors as the source of entangled electron pair and spin depended interfaces as the optical analogue of polariser/filter. Semiconductors can serve as the best medium for such an experiment due to their long relaxation lengths. So far there are no reports on a ferromagnet/superconductor junctions on a semiconductor even though such junctions has been successfully realised in metallic systems. This thesis reports the successful fabrication of ferromagnet/superconductor junction along with characterising measurements in a perfectly two dimensional zero-gap semiconductor known as graphene. Since it's discovery in 2004, graphene has attracted prodigious interest from both academia and industry due to it's inimitable physical properties: very high mobility, high thermal and electrical conductivity, a high Young's modulus and impermeability. Graphene is also expected to have very long spin relaxation length and high spin life time because of it's low spin orbit coupling. For this reason and since researchers are always looking for novel materials and devices to comply with the high demands for better and faster data storage devices, graphene has emanated as a brand new material system for spin based devices. The very first spin injection and detection in graphene was realised in 2007 and ever since, the focal point of the research has been to improve the spin transport properties. A part of this thesis discusses a new fabrication recipe which has a high yield for successfully contacting graphene with a ferromagnet. A high starting yield for ferromagnetic contacts is a irremissible condition for combining superconducting contacts to the device to fabricate ferromagnet/superconductor junctions. Any fabrication recipe

Relaxor ferroelectricity, ferromagnetic and optical second harmonic properties in lanthanum lithium niobate (La0.05Li0.85NbO3) nanoparticles

Science.gov (United States)

Díaz-Moreno, Carlos A.; Ding, Yu; Li, Chunqiang; Portelles, Jorge; Heiras, J.; Hurtado-Macias, A.; Farias, J. R.; González-Hernández, J.; Yacamán, M. J.; López, Jorge

2017-07-01

Relaxor ferroelectricity, ferromagnetism and Second Harmonic Generation properties were founded and studied as a function of a reduction heat treatment at 650 °C in a Ar-5%H2 atmosphere in stoichiometric La0.05Li0.85NbO3 nanoparticles of 40 nm. A diffuse dielectric anomaly related with relaxor behavior from 25 °C to 800 °C in a frequency range from 100 Hz to 1 MHz was founded. It also shows ferromagnetic anhysterestic type and ferroelectric hysteresis loops at room temperature with a magnetic spin remnant of 2.5 × 10-3 emu/g and polarization saturation of 0.235 μC/cm2, remnant polarization of 0.141 μC/cm2, coercive field of 1.35 kV/cm, respectively. It shows very good second harmonic generation signal at 450 nm and 500 nm. High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy and Raman spectroscopy, indicate an ABO3 perovskite structure, new electronic binding energy structure for La (5s, 4d), Li (1s), Nb (4s, 3d, 4p) and oxygen (1s, 2s) and new vibrations modes on octahedron NbO6 related to multiferroic single phase nanoparticles, respectively.

Relaxor ferroelectricity, ferromagnetic and optical second harmonic properties in lanthanum lithium niobate (La0.05Li0.85NbO3) nanoparticles

International Nuclear Information System (INIS)

Díaz-Moreno, Carlos A.; Ding, Yu; Li, Chunqiang; Portelles, Jorge; Heiras, J.; Hurtado-Macias, A.; Farias, J.R.; González-Hernández, J.; Yacamán, M.J.

2017-01-01

Relaxor ferroelectricity, ferromagnetism and Second Harmonic Generation properties were founded and studied as a function of a reduction heat treatment at 650 °C in a Ar-5%H 2 atmosphere in stoichiometric La 0.05 Li 0.85 NbO 3 nanoparticles of 40 nm. A diffuse dielectric anomaly related with relaxor behavior from 25 °C to 800 °C in a frequency range from 100 Hz to 1 MHz was founded. It also shows ferromagnetic anhysterestic type and ferroelectric hysteresis loops at room temperature with a magnetic spin remnant of 2.5 × 10 −3 emu/g and polarization saturation of 0.235 μC/cm 2 , remnant polarization of 0.141 μC/cm 2 , coercive field of 1.35 kV/cm, respectively. It shows very good second harmonic generation signal at 450 nm and 500 nm. High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy and Raman spectroscopy, indicate an ABO 3 perovskite structure, new electronic binding energy structure for La (5s, 4d), Li (1s), Nb (4s, 3d, 4p) and oxygen (1s, 2s) and new vibrations modes on octahedron NbO 6 related to multiferroic single phase nanoparticles, respectively.

Excitonic Wigner crystal and high T sub c ferromagnetism in RB sub 6

CERN Document Server

Kasuya, T

2000-01-01

The mechanisms for the high T sub c ferromagnetism in La-doped divalent hexaborides DB sub 6 are studied in detail comparing with similar family materials, in particular with YbB sub 6 , EuB sub 6 and Ce monopnictides. It is shown that in DB sub 6 the light-electron-heavy-hole paired excitonic states form the Wigner crystal, or Wigner glass in actual materials, in which the conventional intersite electron exchange interactions similar to that in Ni dominate the pair singlet formation due to the intra pair mixing causing a ferromagnetic spin glass-like ordering of electron spins. In the La-doped system La sub x D sub 1 sub - sub x B sub 6 , the population of molecular La impurity states with giant moments increases as x approaches the optimal value x sub 0 approx 0.005 for high T sub c providing vacant states for the roton-like fluctuations, which cause the high T sub c at the boundary of the delocalization of electron carriers. Therefore, the critical La concentration for delocalization coincides with the opt...

Angular dependence of the coercivity and remanence of ordered arrays of Co nanowires

International Nuclear Information System (INIS)

Lavín, R.; Gallardo, C.; Palma, J.L.; Escrig, J.; Denardin, J.C.

2012-01-01

The angular dependence of the coercivity and remanence of ordered hexagonal arrays of Co nanowires prepared using anodic aluminum oxide templates was investigated. The experimental evolution of coercivity as a function of the angle, in which the external field is applied, is interpreted considering micromagnetic simulations. Depending on the angle between the axis of the wire and the applied magnetic field direction our results show that the magnetization reversal mode changes from vortex to a transverse domain wall. Besides, we observed that the dipolar interactions cause a reduction in coercive fields, mainly in the direction of easy magnetization of the nanowires. Good agreement between numerical and experimental data is obtained. - Highlights: ► Angular dependence of the coercivity and remanence of Co nanowire arrays. ► Results show that the magnetization reversal mode changes from vortex to a transverse domain wall. ► Dipolar interactions cause a reduction in coercive fields, which is the strongest in the direction of easy magnetization of the nanowire.

Passive high-frequency devices based on superlattice ferromagnetic nanowires

International Nuclear Information System (INIS)

Ye, B.; Li, F.; Cimpoesu, D.; Wiley, J.B.; Jung, J.-S.; Stancu, A.; Spinu, L.

2007-01-01

In this paper we propose to tailor the bandwidth of a microwave filter by exploitation of shape anisotropy of nanowires. In order to achieve this control of shape anisotropy, we considered superlattice wires containing varying-sized ferromagnetic regions separated by nonferromagnetic regions. Superlattice wires of Ni and Au with a nominal diameter of 200 nm were grown using standard electrodeposition techniques. The microwave properties were probed using X-band (9.8 GHz) ferromagnetic resonance (FMR) experiments performed at room temperature. In order to investigate the effectiveness of the shape anisotropy on the superlattice nanowire based filter the FMR spectrum of superlattice structure is compared to the FMR spectra of nanowires samples with constant length

Spin-orbit torque induced magnetization switching in heavy metal/ferromagnet multilayers with bilayer of heavy metals

Science.gov (United States)

Bekele, Zelalem Abebe; Meng, Kangkang; Zhao, Bing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Jiang, Yong

2017-08-01

Symmetry breaking provides new insight into the physics of spin-orbit torque (SOT) and the switching without a magnetic field could lead to significant impact. In this work, we demonstrate the robust zero-field SOT switching of a perpendicular ferromagnet (FM) layer where the symmetry is broken by a bilayer of heavy metals (HMs) with the strong spin-orbit coupling (SOC). We observed the change of coercivity value by 31% after inserting Co2FeAl in the multilayer structure. These two HM layers (Ta and Pt) are used to strengthen the SOC by linear combination. With different angles between the magnetization and the current (i.e. parallel and anti-parallel), the structures show different switching behaviors such as clockwise or counterclockwise.

Coercivity enhancement in HDDR near-stoichiometric ternary Nd–Fe–B powders

International Nuclear Information System (INIS)

Wan, Fangming; Han, Jingzhi; Zhang, Yinfeng; Wang, Changsheng; Liu, Shunquan; Yang, Jinbo; Yang, Yingchang; Sun, Aizhi; Yang, Fuqiang; Song, Renbo

2014-01-01

Anisotropic HDDR near-stoichiometric ternary Nd–Fe–B powders have been prepared. The coercivity of the powders was improved from 208.6 to 980.1 kA/m by the subsequent diffusion treatment using the Pr–Cu alloy. For comparison, Nd 11.5 Fe 80.7 B 6.1 Pr 1.2 Cu 0.5 alloy, in which Pr and Cu elements were directly added into the original Nd–Fe–B alloy, was also treated by the same HDDR process and the coercivity was only 557.3 kA/m. Microstructural investigations showed that a large area of (Nd, Pr)-rich phases concentrated at triangle regions in the HDDR Nd 11.5 Fe 80.7 B 6.1 Pr 1.2 Cu 0.5 powders, while the (Nd, Pr)-rich phases distributed uniformly in the diffusion treated powders. The uniform grain boundary layer can pin the motion of domain wall more effectively, resulting in a higher coercivity in diffusion treated HDDR Nd–Fe–B powders. - Highlights: • Anisotropic HDDR near-stoichiometric ternary Nd–Fe–B powders have been prepared. • The coercivity of the powders was improved from 2.62 to 12.31 kOe by the diffusion of Pr–Cu alloy. • The uniform grain boundary layer leads to a higher coercivity in diffusion treated powders

Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses

Energy Technology Data Exchange (ETDEWEB)

Tekgül, Atakan, E-mail: atakantekgul@gmail.com [Akdeniz University, Physics Department, Science Faculty, TR-07058 Antalya (Turkey); Uludag University, Physics Department, Science and Literature Faculty, TR-16059 Bursa (Turkey); Alper, Mürsel [Uludag University, Physics Department, Science and Literature Faculty, TR-16059 Bursa (Turkey); Kockar, Hakan [Balikesir University, Physics Department, Science and Literature Faculty, TR-10145 Balikesir (Turkey)

2017-01-01

The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3 nm to 10 nm using electrodeposition. By now, the thinnest Cu (0.5 nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current–time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of −0.3 and −1.5 V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600 kA/m from 3 to 8 nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8 nm of the CoFe layer thickness. It is seen that the thin Cu layer (fixed at 0.5 nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance (GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices. - Highlights: • The much thinner (0.5 nm) Cu layer was used to obtain the GMR effect on the electrodeposited CoFe/Cu multilayers. • All samples exhibited GMR and the maximum GMR value was 5.5%. • The M{sub s} and the H{sub c} changed with increasing magnetic layer thickness.

High-coercivity Nd-Fe-B magnets obtained with the electrophoretic deposition of submicron TbF3 followed by the grain-boundary diffusion process

International Nuclear Information System (INIS)

Soderžnik, Marko; Korent, Matic; Žagar Soderžnik, Kristina; Katter, Matthias; Üstüner, Kaan; Kobe, Spomenka

2016-01-01

Using a grain-boundary diffusion process (GBDP) involving the electrophoretic deposition (EPD) of submicron TbF 3 powder, we substantially increased the coercivity of sintered Nd-Fe-B permanent magnets. The experiments used magnets with low heavy-rare-earth (HRE) content (HRE = 1.2 wt%) and a coercivity of 790 kA/m (at 75 °C). After experiencing optimized conditions at 875 °C for 10 h and subsequent annealing at 500 °C for 1 h, the coercivity was increased to 1536 kA/m (at 75 °C). This value is 1.94 times higher than that for a sintered magnet, without post-sintering heat treatment. Furthermore, a vibration test revealed satisfactory adhesion of the TbF 3 powder to the surface of the magnet with no detected reduction in coercivity. Using field emission gun scanning electron microscopy (FEG-SEM) with an energy dispersive spectroscope (EDS), we confirmed the formation of various secondary intergranular phases and the core-shell-type microstructure, which increases the coercivity. The Tb content in the magnet, exposed to the EPD-based GBDP, was controlled by inductively coupled plasma optical electron spectroscopy (ICP-OES). The additional Tb detected in the magnet due to the described technology was only 0.12 wt%.

Magnet properties of Mn70Ga30 prepared by cold rolling and magnetic field annealing

International Nuclear Information System (INIS)

Ener, Semih; Skokov, Konstantin P.; Karpenkov, Dmitriy Yu.; Kuz'min, Michael D.; Gutfleisch, Oliver

2015-01-01

The remanence and coercivity of arc melted Mn 70 Ga 30 can be substantially improved by cold rolling. For best performance the rolled material should be annealed at T=730 K in the presence of a magnetic field of 1 T. The so-obtained magnet has a remanence of 0.239 T and a coercivity of 1.24 T at room temperature. The underlying reason for the high coercivity and remanence is the increase of the content of a metastable ferrimagnetic D0 22 phase at the expense of the normally stable anti-ferromagnetic D0 19 . Magnetic field significantly increases the nucleation rate of the ferromagnetic D0 22 phase that leads to grain size refinement and as a consequence of improving remanence and coercive field. - Highlights: • Alternative synthesis method for D0 22 phase formation in Mn–Ga is developed. • Effect of cold rolling and annealing on magnetic properties of Mn 70 Ga 30 is examined. • Small magnetic fields are sufficient to accelerate nucleation of the D0 22 phase

Coercivity enhancement of sintered Nd-Fe-B magnets by chemical bath deposition of TbCl{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Guo, Shuai, E-mail: gshuai@nimte.ac.cn; Zhang, Xiaofeng; Ding, Guangfei; Chen, Renjie; Yan, Aru [Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Lee, Don [Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); University of Dayton, Dayton, Ohio 45469 (United States)

2014-05-07

The chemical bath deposition (CBD) and the grain boundary diffusion method were combined to diffuse the heavy rare earth for obtain the thick magnets with high coercivity and low heavy rare earth. The jet mill powders were soaked into the alcohol solution of 0.2 wt. % TbCl{sub 3}. A thin layer of TbCl{sub 3} was wrapped to the surface of (PrNd){sub 2}Fe{sub 14}B powder particles. The coercivity of magnet is increased from 11.89 kOe to 14.72 kOe without significant reduction of remanence after grain boundary diffusion in the sintering and the annealing processes. The temperature coefficients of the remanence and the coercivity are improved by the substitution of PrNd by Tb in the surface of grains. The highly accelerated temperature/humidity stress test (HAST) results indicate that the CBD magnet has poor corrosion resistance, attributing to the present of Cl atoms in the grain boundaries.

Highly magnetic Co nanoparticles fabricated by X-ray radiolysis

Science.gov (United States)

Clifford, Dustin M.; Castano, Carlos E.; Rojas, Jessika V.

2018-03-01

Advanced routes for the synthesis of nanomaterials, such as ferromagnetic nanoparticles, are being explored that are easy to perform using cost-effective and non-toxic precursors. Radiolytic syntheses based on the use of X-rays as ionizing radiation are promising towards this effort. X-rays were used to produce highly magnetic cobalt nanoparticles (NPs), stable in air up to 200 °C, from the radiolysis of water. Crystal structure analysis by XRD indicates a mixture of Cofcc, 63%, and Cohcp, 37%, phases. Magnetic analysis by VSM gave a saturation magnetization (Ms) 136 emu/g at 1 T and coercivity (Hc) = 325 Oe when the reaction solution was purged with N2 while an air-purged treatment resulted in Co NPs having 102 emu/g with a coercivity (Hc) 270 Oe. Overall, the reduction of Co2+ occurred in an aqueous reaction environment without addition of chemical reductants resulting in Co NPs with size distribution from 20 to 140 nm. This clean approach at ambient temperature produced highly magnetic Co NPs that may be used for switching devices (i.e. reed switches) or as additives for alloys that require high Curie points.

Novel room temperature ferromagnetic semiconductors

Energy Technology Data Exchange (ETDEWEB)

Gupta, Amita [KTH Royal Inst. of Technology, Stockholm (Sweden)

2004-06-01

Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous

Angular dependence of the coercivity and remanence of ordered arrays of Co nanowires

Energy Technology Data Exchange (ETDEWEB)

Lavin, R. [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Av. Ecuador 3493, Santiago (Chile); Facultad de Ingenieria, Universidad Diego Portales, UDP, Ejercito 441, Santiago (Chile); Gallardo, C.; Palma, J.L. [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Av. Ecuador 3493, Santiago (Chile); Escrig, J. [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Av. Ecuador 3493, Santiago (Chile); Center for the Development of Nanoscience and Nanotechnology, CEDENNA, Av. Ecuador 3493, Santiago (Chile); Denardin, J.C., E-mail: jcdenardin@gmail.com [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Av. Ecuador 3493, Santiago (Chile); Center for the Development of Nanoscience and Nanotechnology, CEDENNA, Av. Ecuador 3493, Santiago (Chile)

2012-08-15

The angular dependence of the coercivity and remanence of ordered hexagonal arrays of Co nanowires prepared using anodic aluminum oxide templates was investigated. The experimental evolution of coercivity as a function of the angle, in which the external field is applied, is interpreted considering micromagnetic simulations. Depending on the angle between the axis of the wire and the applied magnetic field direction our results show that the magnetization reversal mode changes from vortex to a transverse domain wall. Besides, we observed that the dipolar interactions cause a reduction in coercive fields, mainly in the direction of easy magnetization of the nanowires. Good agreement between numerical and experimental data is obtained. - Highlights: Black-Right-Pointing-Pointer Angular dependence of the coercivity and remanence of Co nanowire arrays. Black-Right-Pointing-Pointer Results show that the magnetization reversal mode changes from vortex to a transverse domain wall. Black-Right-Pointing-Pointer Dipolar interactions cause a reduction in coercive fields, which is the strongest in the direction of easy magnetization of the nanowire.

Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

Science.gov (United States)

Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

2013-02-01

Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

Magnetic profiles in ferromagnetic/superconducting superlattices.

Energy Technology Data Exchange (ETDEWEB)

te Velthuis, S. G. E.; Hoffmann, A.; Santamaria, J.; Materials Science Division; Univ. Complutense de Madrid

2007-02-28

The interplay between ferromagnetism and superconductivity has been of longstanding fundamental research interest to scientists, as the competition between these generally mutually exclusive types of long-range order gives rise to a rich variety of physical phenomena. A method of studying these exciting effects is by investigating artificially layered systems, i.e. alternating deposition of superconducting and ferromagnetic thin films on a substrate, which enables a straight-forward combination of the two types of long-range order and allows the study of how they compete at the interface over nanometer length scales. While originally studies focused on low temperature superconductors interchanged with metallic ferromagnets, in recent years the scope has broadened to include superlattices of high T{sub c} superconductors and colossal magnetoresistance oxides. Creating films where both the superconducting as well as the ferromagnetic layers are complex oxide materials with similar crystal structures (Figure 1), allows the creation of epitaxial superlattices, with potentially atomically flat and ordered interfaces.

Magnetic and microstructural investigation of high-coercivity net-shape Nd–Fe–B-type magnets produced from spark-plasma-sintered melt-spun ribbons blended with DyF{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Žagar, Kristina, E-mail: kristina.zagar@ijs.si; Kocjan, Andraž; Kobe, Spomenka

2016-04-01

Nanostructured Nd–Fe–B-type materials produced by melt-spinning (MS) are used in a variety of applications in the electronics, automotive, and sensor industries. The very rapid MS process leads to flake-like powders with metastable, nanoscale, Nd{sub 2}Fe{sub 14}B grains. These powders are then formed into net-shaped, isotropic, polymer-bonded magnets, or they are hot formed into fully dense, metallic magnets that are isotropic and anisotropic. These fully dense magnets are usually produced with a conventional hot press without the inclusion of additives prior to the hot pressing. As a result, their properties, particularly the coercivity (H{sub ci}), are insufficient at automotive-relevant temperatures of 100–150 °C since the material H{sub ci} has a large temperature coefficient. In this study, we instead add a thin layer of DyF{sub 3} to the melt-spun ribbons prior to their hot consolidation in order to enhance the coercivity through a diffusion-based, partial substitution of the Nd by Dy. This is accomplished by applying extremely rapid, spark-plasma sintering to minimize any growth of the nanoscale Nd{sub 2}Fe{sub 14}B grains during consolidation. The result is a very high-coercivity magnet with drastically reduced amounts of heavy rare earths that is suitable for high-temperature applications. This work clearly demonstrates how rapidly formed, metastable states can provide us with properties that are unobtainable with conventional techniques. - Highlights: • We produced high coercivity magnets with drastically reduced amounts of HRE. • Microstructural analysis was conducted of the “free” and “wheel” side of Dy-treated Nd{sub 2}Fe{sub 14}B ribbons. • Dy-diffusion mechanism into ribbons depending on processing parameters is shown.

Doping effect on ferromagnetism, ferroelectricity and dielectric constant in sol-gel derived Bi1-xNdxFe1-yCoyO3 nanoceramics

Science.gov (United States)

Das, Sananda; Sahoo, R. C.; Bera, K. P.; Nath, T. K.

2018-04-01

Doping at the post-transition metal site by trivalent rare-earth ions and 3d transition metal site by transition metal ions in perovskite lattice has observed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report large ferromagnetism and enhanced dielectric constant (at ∼100 Hz) in chemically synthesized single phase multiferroic Bi1-xNdxFe1-yCoyO3 (x = 0, 0.10; y = 0, 0.10) nanoparticles (average particles size ∼45 nm). We have also examined the ferroelectric nature of our chemically synthesized samples. The Rietveld refinement of the XRD data reveals the structural symmetry breaking from distorted rhombohedral R3c structure of BiFeO3 to the triclinic P1 structure in Bi0.9Nd0.1Fe0.9Co0.1O3 (BNFCO) without having any iron rich impurity phase. The magnetization in these nanoceramics most likely originates from the coexistence of mixed valence states of Fe ion (Fe2+ and Fe3+). A high room temperature dielectric constant (∼1050) has been observed at 100 Hz of BNFCO sample. The frequency dependent anomalies near Neel temperature of antiferromagnet in temperature variation of dielectric study have been observed for all the doped and co-doped samples exhibiting typical characteristic of relaxor ferroelectrics. A spectacular enhancement of remanent magnetization MR (∼7.2 emu/gm) and noticeably large coercivity HC (∼17.4 kOe) at 5 K have been observed in this BNFCO sample. Such emergence of ferromagnetic ordering indicates the canting of the surface spins at the surface boundaries because of the reduction of particle size in nanodimension. We have also observed P-E hysteresis loops with a remanent polarization of 26 μC/cm2 and coercive field of 5.6 kV/cm of this sample at room temperature. From impedance spectroscopy study the estimated activation energy of 0.41 eV suggests the semiconducting nature of our nanoceramic BNCFO sample.

On the possibility of room temperature ferromagnetism on chunk-shape BaSnO3/ZnO core/shell nanostructures

Science.gov (United States)

Rajamanickam, N.; Jayakumar, K.; Ramachandran, K.

2018-04-01

Core/shell BaSnO3/ZnO (BS-ZO) nanostructures were prepared by oxalate precipitation method and wet-chemical method. BaSnO3 (BSO) cubic perovskite structure and ZnO hexagonal wurtzite structure were confirmed by X-ray diffraction (XRD). The crystallite sizes is 23 nm, 29 nm and 27 nm for BSO, ZnO and BS-ZO, respectively. Chunk-shape and cuboids morphology observed from scanning electron microscopy (SEM) analysis. The magnetic properties were studied by VSM for bare and core-shell nano systems and the room temperature ferromagnetism observed for core-shell nanostructures. The BSO/ZnO shows enhanced coercivity and saturated magnetization as compared with BSO and ZnO nanostructures.

Linear and non-linear energy barriers in systems of interacting single-domain ferromagnetic particles

International Nuclear Information System (INIS)

Petrila, Iulian; Bodale, Ilie; Rotarescu, Cristian; Stancu, Alexandru

2011-01-01

A comparative analysis between linear and non-linear energy barriers used for modeling statistical thermally-excited ferromagnetic systems is presented. The linear energy barrier is obtained by new symmetry considerations about the anisotropy energy and the link with the non-linear energy barrier is also presented. For a relevant analysis we compare the effects of linear and non-linear energy barriers implemented in two different models: Preisach-Neel and Ising-Metropolis. The differences between energy barriers which are reflected in different coercive field dependence of the temperature are also presented. -- Highlights: → The linear energy barrier is obtained from symmetry considerations. → The linear and non-linear energy barriers are calibrated and implemented in Preisach-Neel and Ising-Metropolis models. → The temperature and time effects of the linear and non-linear energy barriers are analyzed.

Coercivity enhancement of hot-deformed Nd-Fe-B magnets by the eutectic grain boundary diffusion process

International Nuclear Information System (INIS)

Liu, Lihua; Sepehri-Amin, H.; Ohkubo, T.; Yano, M.; Kato, A.; Shoji, T.; Hono, K.

2016-01-01

Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd 90 Al 10 exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd 70 Cu 30 exhibited the highest coercivity of 0.7 T at 200 ° C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd 2 Fe 14 B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd 2 Fe 14 B grains were observed in the sample processed with Nd 90 Al 10 , which explains its inferior thermal stability of coercivity compared to the sample processed with Nd 70 Cu 30 . The coercivity enhancement and poor thermal stability of the coercivity of the Nd 90 Al 10 diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy. - Highlights: • Coercivity of hot-deformed Nd-Fe-B magnets is enhanced by the infiltration of various R-TM eutectic alloys. • The sample infiltrated with Nd 90 Al 10 shows the highest coercivity of 2.5 T at room temperature. • At 200 °C, Nd 70 Cu 30 diffusion-processed sample possesses the highest coercivity of 0.7 T.

Relaxor ferroelectricity, ferromagnetic and optical second harmonic properties in lanthanum lithium niobate (La{sub 0.05}Li{sub 0.85}NbO{sub 3}) nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Díaz-Moreno, Carlos A., E-mail: cdiazmoreno@utep.edu [Department of Physics of University of Texas at El Paso, 500 W. University Ave, El Paso, TX 79968 (United States); Ding, Yu; Li, Chunqiang [Department of Physics of University of Texas at El Paso, 500 W. University Ave, El Paso, TX 79968 (United States); Portelles, Jorge [Facultad de Física, Universidad de La Habana, San lázaro y L, 10400 (Cuba); Universidad Nacional Autónoma de México, Centro de Nanociencias y Nanotecnología, km 107 Carretera Tijuana-Ensenada, Ensenada, B.C. 22860 (Mexico); Heiras, J. [Universidad Nacional Autónoma de México, Centro de Nanociencias y Nanotecnología, km 107 Carretera Tijuana-Ensenada, Ensenada, B.C. 22860 (Mexico); Hurtado-Macias, A. [Centro de Investigación en Materiales Avanzados S.C., Miguel de Cervantes #120, Complejo Industrial Chihuahua, Chihuahua, C.P. 31109 (Mexico); Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249 (United States); Farias, J.R. [Instituto de Ingeniería y Tecnología, UACJ, Avenida del Charro #450 N. Cd. Juárez, Chihuahua, C.P. 32310 (Mexico); González-Hernández, J. [Centro de Ingeniería y Desarrollo Industrial, Santiago de Querétaro 76130, Qro (Mexico); Yacamán, M.J. [Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249 (United States); and others

2017-07-01

Relaxor ferroelectricity, ferromagnetism and Second Harmonic Generation properties were founded and studied as a function of a reduction heat treatment at 650 °C in a Ar-5%H{sub 2} atmosphere in stoichiometric La{sub 0.05}Li{sub 0.85}NbO{sub 3} nanoparticles of 40 nm. A diffuse dielectric anomaly related with relaxor behavior from 25 °C to 800 °C in a frequency range from 100 Hz to 1 MHz was founded. It also shows ferromagnetic anhysterestic type and ferroelectric hysteresis loops at room temperature with a magnetic spin remnant of 2.5 × 10{sup −3} emu/g and polarization saturation of 0.235 μC/cm{sup 2}, remnant polarization of 0.141 μC/cm{sup 2}, coercive field of 1.35 kV/cm, respectively. It shows very good second harmonic generation signal at 450 nm and 500 nm. High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy and Raman spectroscopy, indicate an ABO{sub 3} perovskite structure, new electronic binding energy structure for La (5s, 4d), Li (1s), Nb (4s, 3d, 4p) and oxygen (1s, 2s) and new vibrations modes on octahedron NbO{sub 6} related to multiferroic single phase nanoparticles, respectively.

Damping Dependence of Reversal Magnetic Field on Co-based Nano-Ferromagnetic with Thermal Activation

Directory of Open Access Journals (Sweden)

Nadia Ananda Herianto

2015-02-01

Full Text Available Currently, hard disk development has used HAMR technology that applies heat to perpendicular media until near Curie temperature, then cools it down to room temperature. The use of HAMR technology is significantly influence by Gilbert damping constants. Damping affects the magnetization reversal and coercivity field. Simulation is used to evaluate magnetization reversal by completing Landau-Lifshitz-Gilbert explicit equation. A strong ferromagnetic cobalt based material with size 50×50×20 nm3 is used which parameters are anisotropy materials 3.51×106 erg/cm3, magnetic saturation 5697.5 G, exchange constant 1×10-7 erg/cm, and various Gilbert damping from 0.09 to 0.5. To observe the thermal effect, two schemes are used which are Reduced Barrier Writing and Curie Point Writing. As a result, materials with high damping is able to reverse the magnetizations faster and reduce the energy barrier. Moreover, it can lower the minimum field to start the magnetizations reversal, threshold field, and probability rate. The heating near Curie temperature has succeeded in reducing the reversal field to 1/10 compared to writing process in absence of thermal field.

Effect of Mg{sup 2+} and Ti{sup 4+} dopants on the structural, magnetic and high-frequency ferromagnetic properties of barium hexaferrite

Energy Technology Data Exchange (ETDEWEB)

Shams, Mohammad H. [Department of Physics, University of Isfahan, Hezar Jarib Street, Isfahan 81746-73441 (Iran, Islamic Republic of); Rozatian, Amir S.H., E-mail: a.s.h.rozatian@phys.ui.ac.ir [Department of Physics, University of Isfahan, Hezar Jarib Street, Isfahan 81746-73441 (Iran, Islamic Republic of); Yousefi, Mohammad H. [Department of Physics, University of Isfahan, Hezar Jarib Street, Isfahan 81746-73441 (Iran, Islamic Republic of); Valíček, Jan [Institute of Physics, Faculty of Mining and Geology, VŠB – Technical University of Ostrava, 17. Listopadu 15, 70833 Ostrava-Poruba (Czech Republic); Šepelák, Vladimir [Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen (Germany); Slovak Academy of Sciences, Watsonova 45, 04001 Košice (Slovakia)

2016-02-01

The doped barium hexaferrite, BaFe{sub 12−x}(Mg{sub 0.5}Ti{sub 0.5}){sub x}O{sub 19} with 1≤x≤5, is synthesized by a solid state ceramic method. Its crystalline structure, morphology, as well as static and dynamic magnetic properties are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry, and vector network analysis, respectively. The cation distribution of Mg{sup 2+} and Ti{sup 4+} in the hexagonal structure of BaFe{sub 12−x}(Mg{sub 0.5}Ti{sub 0.5}){sub x}O{sub 19} is investigated by {sup 57}Fe Mössbauer spectroscopy. The effect of Mg{sup 2+} and Ti{sup 4+} dopants on static and high-frequency magnetic properties of the ferrite is studied. - Highlights: • The BaFe{sub 12−x}(MgTi){sub 0.5x}O{sub 19} (x =1– 5) are synthesized by a solid state reaction method. • The Mg{sup 2+} and Ti{sup 4+} dopants take positions 12k for x=1 and 4f{sub 1} and 4f{sub 2} for x=5. • The coercivity and magnetization are decreased with an increase in Mg–Ti content. • The ferromagnetic resonance frequency is decreased with increase of x. • The FMR is shifted to lower frequencies due to the reduction of the anisotropy field.

Molecular ferromagnetism

International Nuclear Information System (INIS)

Epstein, A.J.

1990-01-01

This past year has been one of substantial advancement in both the physics and chemistry of molecular and polymeric ferromagnets. The specific heat studies of (DMeFc)(TCNE) have revealed a cusp at the three-dimensional ferromagnetic transition temperature with a crossover to primarily 1-D behavior at higher temperatures. This paper discusses these studies

Comparative study of magnetic properties and the anticancer effect of superparamagnetic and ferromagnetic iron oxide nanoparticles in the nanocomplex with doxorubicin

International Nuclear Information System (INIS)

Orel, V.E.; Shevchenko, A.D.; Rikhal's'kij, O.Yu.; Romanov, A.V.; Orel, Yi.V.; Lukyin, S.M.; Burlaka, A.P.; Venger, Je.F.

2015-01-01

Mechano-magneto-chemically synthesized magnetic nanocomplex (MNC) of superparamagnetic iron oxide Fe 3 O 4 nanoparticles (NP) and anticancer drug doxorubicin (DR) had significantly lower saturation magnetic moment and magnetic hysteresis loop area as compared to the MNC of ferro- magnetic NP. However, the last was characterized by lower coercivity. MNC of superparamagnetic NP and DR had g-factors of 2.00, 2.30, and 4.00. MNC of ferromagnetic NP and DR had the g-factor of 2.50, and the integrated intensity of electron spin resonance signals was by 61% greater. Superparamagnetic iron oxide Fe 3 O 4 NP in MNC with DR initiated a greater antitumor effect during magnetic nanotherapy of animals with carcinosarcoma Walker-256 as compared to the MNC composed of ferromagnetic NP and DR. In the future, superparamagnetic iron oxide Fe 3 O 4 NP as a part of the nanocomplex with DR can be used in theranostics - a methodology that combines magnetic resonance diagnostics and magnetic nanotherapy using MNC both as therapeutic and diagnostic agents

Spin-dependent transport and functional design in organic ferromagnetic devices

Directory of Open Access Journals (Sweden)

Guichao Hu

2017-09-01

Full Text Available Organic ferromagnets are intriguing materials in that they combine ferromagnetic and organic properties. Although challenges in their synthesis still remain, the development of organic spintronics has triggered strong interest in high-performance organic ferromagnetic devices. This review first introduces our theory for spin-dependent electron transport through organic ferromagnetic devices, which combines an extended Su–Schrieffer–Heeger model with the Green’s function method. The effects of the intrinsic interactions in the organic ferromagnets, including strong electron–lattice interaction and spin–spin correlation between π-electrons and radicals, are highlighted. Several interesting functional designs of organic ferromagnetic devices are discussed, specifically the concepts of a spin filter, multi-state magnetoresistance, and spin-current rectification. The mechanism of each phenomenon is explained by transmission and orbital analysis. These works show that organic ferromagnets are promising components for spintronic devices that deserve to be designed and examined in future experiments.

Coercivity enhancement of Nd–Fe–B sintered magnets with intergranular adding (Pr, Dy, Cu)−H{sub x} powders

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yujing; Ma, Tianyu, E-mail: maty@zju.edu.cn; Liu, Xiaolian; Liu, Pan; Jin, Jiaying; Zou, Junding; Yan, Mi, E-mail: mse_yanmi@zju.edu.cn

2016-02-01

Forming Nd{sub 2}Fe{sub 14}B/(Nd, Dy){sub 2}Fe{sub 14}B core–shell structure by intergranular adding Dy-containing sources into Nd–Fe–B sintered magnets is effective to improve coercivity and to minimize remanence loss simultaneously. However, the excessive Dy located in the intergranular regions has nearly no hard magnetic contribution, causing its low utilization efficiency. In this work, diluted Dy powders (Pr{sub 37}Dy{sub 30}Cu{sub 33})–H{sub x} were prepared and incorporated into Nd–Fe–B sintered magnets via a dual-alloy approach. The coercivity increases rapidly from 15.0 to 18.2 kOe by 21.3% with 2.0 wt% (Pr, Dy, Cu)–H{sub x} addition (the equivalent Dy is only 0.32 at%). The deduced coercivity incremental ratio is 10.0 kOe per unit Dy at%. Dehydrogenation reaction of (Pr, Dy, Cu)–H{sub x} occurs during sintering, which favors Dy diffusion towards the 2:14:1 phase grains as well as smoothing the grain boundaries (GBs). The enhanced local anisotropic field and the well decoupled 2:14:1 phase grains contribute to such rapid coercivity enhancement. This work suggests that adding diluted Dy hydrides is promising for fabricating high coercivity Nd–Fe–B sintered magnets with less heavy rare-earth consumption. - Highlights: • (Pr, Dy, Cu)–H{sub x} hydride powders were introduced into Nd–Fe–B sintered magnets. • Rapid coercivity enhancement from 15.0 kOe to 18.2 kOe with only 0.32 at% Dy was realized. • High utilization efficiency of Dy was achieved due to its promoted diffusion process. • Wettability and mobility of grain boundary phase was improved.

The origin of the coercivity reduction of Nd–Fe–B sintered magnet annealed below an optimal temperature

International Nuclear Information System (INIS)

Akiya, T.; Sasaki, T.T.; Ohkubo, T.; Une, Y.; Sagawa, M.; Kato, H.; Hono, K.

2013-01-01

In order to understand the origin of the coercivity reduction in a sintered Nd–Fe–B magnet that is annealed below an optimal annealing temperature, we performed focused ion beam/scanning electron microscopy tomography of post-sinter annealed magnets. A number of grain boundary cracks were observed between Nd 2 Fe 14 B grains and Nd-rich phases in the sample annealed below the optimal temperature. We deduced micromagnetic parameters α and N eff by fitting the temperature dependence of the coercivity. While α was constant regardless of the annealing conditions, N eff increased in the sample annealed below the optimal temperature with the reduced coercivity. This indicates that the reduction of the coercivity is due to the local stray field at the cracks. - Highlights: • We performed FIB/SEM tomography of post-sinter annealed magnets. • A number of grain boundary cracks were observed in the low-coercivity sample. • Parameters α and N eff were deduced from the temperature dependence of coercivity. • While α was constant, N eff increased in the low-coercivity sample. • The reduction of the coercivity is due to the local stray field at the cracks

Excess use of coercive measures in psychiatry among migrants compared with native Danes

DEFF Research Database (Denmark)

Nørredam, Marie Louise; Garcia-Lopez, A; Keiding, N

2010-01-01

Norredam M, Garcia-Lopez A, Keiding N, Krasnik A. Excess use of coercive measures in psychiatry among migrants compared with native Danes.Objective: To investigate differences in risk of compulsory admission and other coercive measures in psychiatric emergencies among refugees and immigrants comp...

Relation between Nd2Fe14B grain alignment and coercive force decrease ratio in NdFeB sintered magnets

International Nuclear Information System (INIS)

Matsuura, Yutaka; Hoshijima, Jun; Ishii, Rintaro

2013-01-01

It was found that the coercive force of NdFeB sintered magnets decreases as the Nd 2 Fe 14 B grain alignment improves. Because of this phenomenon, studies looked at the relation between this alignment and the coercive force decrease ratio. In experiments, it was expected that the coercive force of perfectly aligned magnet reached 0.7 of coercive force in istotropically aligned magnet. When it is postulated that the coercive force is determined by the Stoner–Wohlfarth model, coercive force increases as the alignment improves and it becomes difficult to explain our experimental data. On the other hand, when the coercive force is determined by magnetic domain wall motion, the coercive force decreases as the alignment improves and the coercive force of the perfectly aligned magnet reaches 1/√(2) of the isotropically aligned magnet. This tendency and value was very close to our data. It strongly suggests that the coercive force of NdFeB sintered magnets is determined by the domain wall motion. - Highlights: ► Coercive force of NdFeB sintered magnets decreases as grains alignment improves. ► Coercive force decrease ratio reaches −30% at the perfect aligned magnet. ►These experimental results are different from the Stoner–Wohlfarth model. ► The magnetic domain wall motion could explain this coercive force decrease ratio

Angular dependence of coercivity in isotropically aligned Nd-Fe-B sintered magnets

Science.gov (United States)

Matsuura, Yutaka; Nakamura, Tetsuya; Sumitani, Kazushi; Kajiwara, Kentaro; Tamura, Ryuji; Osamura, Kozo

2018-05-01

In order to understand the coercivity mechanism in Nd-Fe-B sintered magnets, the angular dependence of the coercivity of an isotropically aligned Nd15Co1.0B6Febal. sintered magnet was investigated through magnetization measurements using a vibrating sample magnetometer. These results are compared with the angular dependence calculated under the assumption that the magnetization reversal of each grain follows the Kondorskii law or, in other words, the 1/cos θ law for isotropic alignment distributions. The calculated angular dependence of the coercivity agrees very well with the experiment for magnetic fields applied between angles of 0 and 60°, and it is expected that the magnetization reversal occurs in each grain individually followed the 1/cos θ law. In contrast, this agreement between calculation and experiment is not found for anisotropic Nd-Fe-B samples. This implies that the coercivity of the aligned magnets depends upon the de-pinning of the domain walls from pinning sites. When the de-pinning occurs, it is expected that the domain walls are displaced through several grains at once.

Magnetic and microstructural investigation of high-coercivity net-shape Nd-Fe-B-type magnets produced from spark-plasma-sintered melt-spun ribbons blended with DyF3

Science.gov (United States)

Žagar, Kristina; Kocjan, Andraž; Kobe, Spomenka

2016-04-01

Nanostructured Nd-Fe-B-type materials produced by melt-spinning (MS) are used in a variety of applications in the electronics, automotive, and sensor industries. The very rapid MS process leads to flake-like powders with metastable, nanoscale, Nd2Fe14B grains. These powders are then formed into net-shaped, isotropic, polymer-bonded magnets, or they are hot formed into fully dense, metallic magnets that are isotropic and anisotropic. These fully dense magnets are usually produced with a conventional hot press without the inclusion of additives prior to the hot pressing. As a result, their properties, particularly the coercivity (Hci), are insufficient at automotive-relevant temperatures of 100-150 °C since the material Hci has a large temperature coefficient. In this study, we instead add a thin layer of DyF3 to the melt-spun ribbons prior to their hot consolidation in order to enhance the coercivity through a diffusion-based, partial substitution of the Nd by Dy. This is accomplished by applying extremely rapid, spark-plasma sintering to minimize any growth of the nanoscale Nd2Fe14B grains during consolidation. The result is a very high-coercivity magnet with drastically reduced amounts of heavy rare earths that is suitable for high-temperature applications. This work clearly demonstrates how rapidly formed, metastable states can provide us with properties that are unobtainable with conventional techniques.

Modification of interlayer exchange coupling in Fe/V/Fe trilayers using hydrogen

Energy Technology Data Exchange (ETDEWEB)

Skoryna, J., E-mail: jskoryna@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17 St., 60-179 Poznań (Poland); Marczyńska, A. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17 St., 60-179 Poznań (Poland); Lewandowski, M. [NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85 St., 61-614 Poznań (Poland); Smardz, L. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17 St., 60-179 Poznań (Poland)

2015-10-05

Highlights: • Magnetic films and multilayers. • Thin films. • Hydrogen absorbing materials. • Magnetic measurements. • Exchange coupling. - Abstract: Fe/V/Fe trilayers with constant-thickness Fe and step-like wedged V sublayers were prepared at room temperature using UHV magnetron sputtering. The bottom Fe layer grows onto oxidised Si(1 0 0) substrate and shows relatively high coercivity. The top Fe layer grows on vanadium spacer and shows considerably lower coercivity. The planar growth of the Fe and V sublayers was confirmed in-situ by X-ray photoelectron spectroscopy. Results show that the Fe sublayers are weakly exchange coupled for d{sub V} > 1.4 nm. Results on the coercivity studies as a function of the V interlayer thickness show near d{sub V} ∼ 1.95 nm (∼2.45 nm) weak antiferromagnetic (ferromagnetic) coupling, respectively. The hydrogenation of the Fe/V/Fe trilayers leads to increase of the strength of the ferromagnetic interlayer exchange coupling.

A harsh parenting team? Maternal reports of coparenting and coercive parenting interact in association with children's disruptive behaviour.

Science.gov (United States)

Latham, Rachel M; Mark, Katharine M; Oliver, Bonamy R

2017-05-01

Parenting and coparenting are both important for children's adjustment, but their interaction has been little explored. Using a longitudinal design and considering two children per family, we investigated mothers' and fathers' perceptions of coparenting as moderators of associations between their coercive parenting and children's disruptive behaviour. Mothers and fathers from 106 'intact' families were included from the Twins, Family and Behaviour study. At Time 1 (M child age  = 3 years 11 months, SD child age  = 4.44 months) parents reported on their coercive parenting and children's disruptive behaviour via questionnaire; at Time 2 (M child age  = 4 years 8 months, SD child age  = 4.44 months) perceptions of coparenting and the marital relationship were collected by telephone interview. Questionnaire-based reports of children's disruptive behaviour were collected at follow-up (M child age  = 5 years 11 months, SD child age  = 5.52 months). Multilevel modelling was used to examine child-specific and family-wide effects. Conservative multilevel models including both maternal and paternal perceptions demonstrated that maternal perceptions of coparenting and overall coercive parenting interacted in their prediction of parent-reported child disruptive behaviour. Specifically, accounting for perceived marital quality, behavioural stability, and fathers' perceptions, only in the context of perceived higher quality coparenting was there a positive association between mother-reported overall coercive parenting and children's disruptive behaviour at follow-up. When combined with highly coercive parenting, maternal perceptions of high quality coparenting may be detrimental for children's adjustment. © 2016 Association for Child and Adolescent Mental Health.

Coercivity enhancement of hot-deformed Nd-Fe-B magnets by the eutectic grain boundary diffusion process

Energy Technology Data Exchange (ETDEWEB)

Liu, Lihua [Elements Strategy Initiative Center for Magnetic Materials, National Institute of Materials Science, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305-8577 (Japan); Sepehri-Amin, H.; Ohkubo, T. [Elements Strategy Initiative Center for Magnetic Materials, National Institute of Materials Science, Tsukuba 305-0047 (Japan); Yano, M.; Kato, A.; Shoji, T. [Toyota Motor Corporation, Advanced Material Engineering Div., Susono 410-1193 (Japan); Hono, K., E-mail: kazuhiro.hono@nims.go.jp [Elements Strategy Initiative Center for Magnetic Materials, National Institute of Materials Science, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305-8577 (Japan)

2016-05-05

Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd{sub 90}Al{sub 10} exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd{sub 70}Cu{sub 30} exhibited the highest coercivity of 0.7 T at 200 {sup °}C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd{sub 2}Fe{sub 14}B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd{sub 2}Fe{sub 14}B grains were observed in the sample processed with Nd{sub 90}Al{sub 10}, which explains its inferior thermal stability of coercivity compared to the sample processed with Nd{sub 70}Cu{sub 30}. The coercivity enhancement and poor thermal stability of the coercivity of the Nd{sub 90}Al{sub 10} diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy. - Highlights: • Coercivity of hot-deformed Nd-Fe-B magnets is enhanced by the infiltration of various R-TM eutectic alloys. • The sample infiltrated with Nd{sub 90}Al{sub 10} shows the highest coercivity of 2.5 T at room temperature. • At 200 °C, Nd{sub 70}Cu{sub 30} diffusion-processed sample possesses the highest coercivity of 0.7 T.

Anisotropy and Microstructure of High Coercivity Rare Earth Iron Permanent Magnets, List of Papers Published

Science.gov (United States)

1989-01-01

hardly influences both the pared by three different production technologies, absolute value of HA and its temperature dependence. The permanent magnets...ing reverse domains [2]. pared from 99.5% pure cast material supplied by The application of these magnets has been Rare Earth Products. The...the c/ re 3b Fig.. E ncrographs showingthe celular precipitation structure of precipitation hardened SmCo 2:17 magnets (a). In low coercivity magnets

Recoil curve properties and coercive force decrease ratio in NdFeB sintered magnets

Energy Technology Data Exchange (ETDEWEB)

Matsuura, Yutaka, E-mail: Yutaka_Matsuura@hitachi-metals.co.jp; Kitai, Nobuyuki; Ishii, Rintaro; Natsumeda, Toshimitsu; Hoshijima, Jun

2013-11-15

It is examined that whether a reverse domain and magnetic domain wall exist in a lower demagnetization area than the coercive force and whether the observed demagnetization ratio curve can be explained using the alignment distribution function or not. From measurements of the recoil curve in the low demagnetization field, it was confirmed that minor demagnetization occurred in every demagnetization field and magnets of every grade of coercive force. The alignment distribution of Nd{sub 2}Fe{sub 14}B grains was also measured by electron back-scattering diffraction (EBSD). The alignments and the coercive force decrease ratios were calculated using these alignment distributions. These data were compared against the results obtained from magnetization measurements. From EBSD data, it was found that the alignment distributions of magnets used in this experiment were close to a Gaussian distribution. It was also found that there was no difference in the alignment distribution between magnets with Dy and without Dy, even though the coercive force decrease ratios were Dy dependent. The calculated alignments using the alignment distribution functions were close to the values of magnetization measurements. However, it was found that the calculated coercive force decrease ratios were different from the results obtained from magnetization measurement. - Highlights: • Reverse magnetic domains already exist lower magnetic field than coercive force. • Demagnetization happens not only from surface but also from inside of magnets. • Calculated alignment agrees well with that of the magnetic properties measurement. • Coercive force decrease ratio could not explain from alignment distribution. • We could not find any difference with and without Dy magnets in alignment distribution.

Optical orientation in ferromagnet/semiconductor hybrids

International Nuclear Information System (INIS)

Korenev, V L

2008-01-01

The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin–spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism

Optical orientation in ferromagnet/semiconductor hybrids

Science.gov (United States)

Korenev, V. L.

2008-11-01

The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin-spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism.

Optical Orientation in Ferromagnet/Semiconductor Hybrids

OpenAIRE

Korenev, V. L.

2008-01-01

The physics of optical pumping of semiconductor electrons in the ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of the ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of the semiconductor. Spin-spin interactions near the interface ferromagnet/semiconductor play crucial role in the optical readout and the manipulation of ferromagnetism.

Interplay between the ferromagnetic and ferroelectric phases on the magnetic and impedance analysis of (x)Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3}–(1 − x)CoFe{sub 2}O{sub 4} composites

Energy Technology Data Exchange (ETDEWEB)

Atif, M., E-mail: matif_80@yahoo.com [Functional Materials Lab, Department of Physics, Air University, PAF Complex E-9, Islamabad (Pakistan); Nadeem, M. [EMMG, Physics Division, Directorate of Science, PINSTECH, P.O. Nilore, Islamabad (Pakistan)

2015-02-25

Highlights: • Dense microstructure with a good dispersion of two phases is achieved. • Ferromagnetic behaviour with high coercivity for 0.5PZT–0.5CFO is observed. • Two relaxation processes are identified by two crystallographic phases. • Huge dielectric constant with low dielectric loss for x = 0.5 is reported. • Using SPH model, p-type carriers are responsible for the conduction mechanism. - Abstract: Magnetoelectric (ME) composites with the composition (x)PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} + (1 − x)CoFe{sub 2}O{sub 4} where x = 0.0, 0.5 and 1.0 are synthesized by ball milling method. X-ray diffraction (XRD) analysis revealed the presence of both PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} (PZT) and CoFe{sub 2}O{sub 4} (CFO) pure phases in the PZT–CFO composite. Scanning electron micrographs (SEM) showed distribution of constituent phases throughout the sample. Magnetic hysteresis loop showed ferromagnetic like behaviour of the composite with a coercive field larger than cobalt ferrite. Impedance (Z′ and Z″) and electrical modulus (M′ and M″) spectra suggested two distinct electrical responses which are observed in the temperature range of 300–370 K. These contributions are arising due to the coexistence of two relaxation processes: one is attributed to the high resistive (PZT) phase; while the second one is due to the comparatively conductive (CFO) phase in the PZT–CFO composite, respectively. The electrical conduction and dipolar relaxation are dominated by small polaron hopping (SPH) model, whereas the activation energies calculated from SPH model suggested that p-type carriers are responsible for the conduction in the PZT–CFO composite. Furthermore, ion hopping and conduction mechanism are discussed using an ac conductivity analysis.

Ferromagnetism versus slow paramagnetic relaxation in Fe-doped Li3N

Science.gov (United States)

Fix, M.; Jesche, A.; Jantz, S. G.; Bräuninger, S. A.; Klauss, H.-H.; Manna, R. S.; Pietsch, I. M.; Höppe, H. A.; Canfield, P. C.

2018-02-01

We report on isothermal magnetization, Mössbauer spectroscopy, and magnetostriction as well as temperature-dependent alternating-current (ac) susceptibility, specific heat, and thermal expansion of single crystalline and polycrystalline Li2(Li1 -xFex) N with x =0 and x ≈0.30 . Magnetic hysteresis emerges at temperatures below T ≈50 K with coercivity fields of up to μ0H =11.6 T at T =2 K and magnetic anisotropy energies of 310 K (27 meV). The ac susceptibility is strongly frequency-dependent (f =10 -10 000 Hz) and reveals an effective energy barrier for spin reversal of Δ E ≈1100 K (90 meV). The relaxation times follow Arrhenius behavior for T >25 K . For T <10 K , however, the relaxation times of τ ≈1010 s are only weakly temperature-dependent, indicating the relevance of a quantum tunneling process instead of thermal excitations. The magnetic entropy amounts to more than 25 J molFe-1 K-1, which significantly exceeds R ln 2 , the value expected for the entropy of a ground-state doublet. Thermal expansion and magnetostriction indicate a weak magnetoelastic coupling in accordance with slow relaxation of the magnetization. The classification of Li2(Li1 -xFex) N as ferromagnet is stressed and contrasted with highly anisotropic and slowly relaxing paramagnetic behavior.

Energy gap of ferromagnet-superconductor bilayers

Energy Technology Data Exchange (ETDEWEB)

Halterman, Klaus; Valls, Oriol T

2003-10-15

The excitation spectrum of clean ferromagnet-superconductor bilayers is calculated within the framework of the self-consistent Bogoliubov-de Gennes theory. Because of the proximity effect, the superconductor induces a gap in the ferromagnet spectrum, for thin ferromagnetic layers. The effect depends strongly on the exchange field in the ferromagnet. We find that as the thickness of the ferromagnetic layer increases, the gap disappears, and that its destruction arises from those quasiparticle excitations with wave vectors mainly along the interface. We discuss the influence that the interface quality and Fermi energy mismatch between the ferromagnet and superconductor have on the calculated energy gap. We also evaluate the density of states in the ferromagnet, and we find it in all cases consistent with the gap results.

High Power Laser Beam Welding of Thick-walled Ferromagnetic Steels with Electromagnetic Weld Pool Support

Science.gov (United States)

Fritzsche, André; Avilov, Vjaceslav; Gumenyuk, Andrey; Hilgenberg, Kai; Rethmeier, Michael

The development of modern high power laser systems allows single pass welding of thick-walled components with minimal distortion. Besides the high demands on the joint preparation, the hydrostatic pressure in the melt pool increases with higher plate thicknesses. Reaching or exceeding the Laplace pressure, drop-out or melt sagging are caused. A contactless electromagnetic weld support system was used for laser beam welding of thick ferromagnetic steel plates compensating these effects. An oscillating magnetic field induces eddy currents in the weld pool which generate Lorentz forces counteracting the gravity forces. Hysteresis effects of ferromagnetic steels are considered as well as the loss of magnetization in zones exceeding the Curie temperature. These phenomena reduce the effective Lorentz forces within the weld pool. The successful compensation of the hydrostatic pressure was demonstrated on up to 20 mm thick plates of duplex and mild steel by a variation of the electromagnetic power level and the oscillation frequency.

Magnet properties of Mn{sub 70}Ga{sub 30} prepared by cold rolling and magnetic field annealing

Energy Technology Data Exchange (ETDEWEB)

Ener, Semih, E-mail: ener@fm.tu-darmstadt.de [Materials Science, Technische Universität Darmstadt, 64287 Darmstadt (Germany); Skokov, Konstantin P. [Materials Science, Technische Universität Darmstadt, 64287 Darmstadt (Germany); Karpenkov, Dmitriy Yu. [Materials Science, Technische Universität Darmstadt, 64287 Darmstadt (Germany); Faculty of Physics, Tver State University, 170100 Tver (Russian Federation); Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Kuz' min, Michael D. [Materials Science, Technische Universität Darmstadt, 64287 Darmstadt (Germany); Gutfleisch, Oliver [Materials Science, Technische Universität Darmstadt, 64287 Darmstadt (Germany); Fraunhofer IWKS, Project Group for Material Cycles and Resource Strategy, 63457 Hanau (Germany)

2015-05-15

The remanence and coercivity of arc melted Mn{sub 70}Ga{sub 30} can be substantially improved by cold rolling. For best performance the rolled material should be annealed at T=730 K in the presence of a magnetic field of 1 T. The so-obtained magnet has a remanence of 0.239 T and a coercivity of 1.24 T at room temperature. The underlying reason for the high coercivity and remanence is the increase of the content of a metastable ferrimagnetic D0{sub 22} phase at the expense of the normally stable anti-ferromagnetic D0{sub 19}. Magnetic field significantly increases the nucleation rate of the ferromagnetic D0{sub 22} phase that leads to grain size refinement and as a consequence of improving remanence and coercive field. - Highlights: • Alternative synthesis method for D0{sub 22} phase formation in Mn–Ga is developed. • Effect of cold rolling and annealing on magnetic properties of Mn{sub 70}Ga{sub 30} is examined. • Small magnetic fields are sufficient to accelerate nucleation of the D0{sub 22} phase.

Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

Directory of Open Access Journals (Sweden)

Hamidreza Emamipour

2013-01-01

Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

Magnetization reversal mechanism and coercivity enhancement in three-dimensional granular Nd-Fe-B magnets studied by micromagnetic simulations

Science.gov (United States)

Lee, Jae-Hyeok; Choe, Jinhyeok; Hwang, Shinwon; Kim, Sang-Koog

2017-08-01

We studied the mechanism of magnetization reversals and coercivity enhancements in three-dimensional (3D) granular Nd-Fe-B permanent magnets using finite-element micromagnetic simulations. The magnetization reversals in the hard magnets consisting of hard-phase grains separated by relatively soft-phase grain boundaries were analyzed with reference to the simulation results for the magnetic field-dependent distributions of the local magnetizations. The saturation magnetization of the grain-boundary phase plays a crucial role in the transition between nucleation- and domain-wall-propagation-controlled reversal processes. The smaller the saturation magnetization of the grain-boundary phase is, the more preferable is the nucleation-controlled process, which results in a larger coercivity. The exchange stiffness of the grain-boundary phase determines the preferred paths of domain-wall propagations, whether inward into grains or along the grain boundaries for relatively small and large exchange stiffness, respectively. However, the exchange stiffness of the grain-boundary phase alone does not significantly contribute to coercivity enhancement in cases where the size of hard-phase grains is much greater than the exchange length. This work paves the way for the design of high-performance hard magnets of large coercivity and maximum-energy-product values.

Parental Perceptions of the Use of Coercive Measures on Children with Developmental Disabilities

Science.gov (United States)

Saloviita, Timo; Pirttimaa, Raija; Kontu, Elina

2016-01-01

Background: Children with developmental disabilities who exhibit challenging behaviour are potentially subject to the use of coercive interventions. The aim of the study was to investigate the prevalence of the use of coercive measures by authorities, according to parents' reports. Materials and Methods: A postal survey was distributed, as a total…

The effect of sputter-deposition conditions on the coercive force in amorphous rare-earth - transition-metal thin films

International Nuclear Information System (INIS)

Davies, C.F.; Somekh, R.E.; Evetts, J.E.; Storey, P.A.

1988-01-01

The origins of the coercive force in amorphous rare earth - transition metal films have been investigated, the results being discussed in terms of how the growth conditions of the sputter-deposited films determine the pinning features which cause the coercive force. The authors have studied the variation of coercive force with film thickness and developed a model which enables a local pinning force per unit area to be deduced. This suggests that it should be possible to increase the coercive force by breaking up the microstructure with a multi-layered structure. An increase in coercive force obtained by making such structures with tungsten is described. They also report on the reduction in coercive force obtained when the films are deposited in the presence of a perpendicular magnetic field

Depolarization corrections to the coercive field in thin-film ferroelectrics

International Nuclear Information System (INIS)

Dawber, M; Chandra, P; Littlewood, P B; Scott, J F

2003-01-01

Empirically, the coercive field needed to reverse the polarization in a ferroelectric increases with decreasing film thickness. For ferroelectric films of 100 μm to 100 nm in thickness the coercive field has been successfully described by a semi-empirical scaling law. Accounting for depolarization corrections, we show that this scaling behaviour is consistent with field measurements of ultrathin ferroelectric capacitors down to one nanometre in film thickness. Our results also indicate that the minimum film thickness, determined by a polarization instability, can be tuned by the choice of electrodes, and recommendations for next-generation ferroelectric devices are discussed. (letter to the editor)

Depolarization corrections to the coercive field in thin-film ferroelectrics

CERN Document Server

Dawber, M; Littlewood, P B; Scott, J F

2003-01-01

Empirically, the coercive field needed to reverse the polarization in a ferroelectric increases with decreasing film thickness. For ferroelectric films of 100 mu m to 100 nm in thickness the coercive field has been successfully described by a semi-empirical scaling law. Accounting for depolarization corrections, we show that this scaling behaviour is consistent with field measurements of ultrathin ferroelectric capacitors down to one nanometre in film thickness. Our results also indicate that the minimum film thickness, determined by a polarization instability, can be tuned by the choice of electrodes, and recommendations for next-generation ferroelectric devices are discussed. (letter to the editor)

Enhanced coercivity in α-(Fe,Co)/(Nd,Pr)2Fe14B nanocomposite magnets via interfacial modification

International Nuclear Information System (INIS)

Li Wei; Li Lanlan; Li Xiaohong; Sun Hongyu; Zhang Xiangyi

2008-01-01

We have prepared α-(Fe,Co)/(Nd,Pr) 2 Fe 14 B nanocomposite magnets having a high coercivity H c = 7.5 kOe and a large energy product (BH) max = 22.7 MGOe by interfacial modification using an intergranular amorphous phase, as compared with the corresponding values obtained without the intergranular phase, H c = 5.5 kOe and (BH) max = 16.1 MGOe. The enhanced coercivity is attributed to the increase in the nucleation field for magnetization reversal due to interfacial modification. This demonstrates a counter-intuitive approach for enhancing the magnetic properties of nanocomposite magnets

Enhancement of coercivity with reduced grain size in CoCrPt film grown by pulsed laser deposition

International Nuclear Information System (INIS)

Liang, Q.; Hu, X.F.; Li, H.Q.; He, X.X.; Wang, Xiaoru; Zhang, W.

2006-01-01

We report a pulsed laser deposition (PLD) growth of VMn/CoCrPt bilayer with a magnetic coercivity (H c ) of 2.2 kOe and a grain size of 12 nm. The effects of VMn underlayer on magnetic properties of CoCrPt layer were studied. The coercivity, H c , and squareness, S, of VMn/CoCrPt bilayer, is dependent on the thickness of VMn. The grain size of the CoCrPt film can also be modified by laser parameters. High laser fluence used for CoCrPt deposition produces a smaller grain size. Enhanced H c and reduced grain size in VMn/CoCrPt is explained by more pronounced surface phase segregation during deposition at high laser fluence

Variable substrate temperature deposition of CoFeB film on Ta for manipulating the perpendicular coercive forces

Energy Technology Data Exchange (ETDEWEB)

Lakshmanan, Saravanan; Rao, Subha Krishna [Nanotechnology Research Centre, SRM University, Kattankulathur, Chennai 603203 (India); Muthuvel, Manivel Raja [Defence Metallurgical Research Laboratory (DMRL), Hyderabad 500058 (India); Chandrasekaran, Gopalakrishnan [Nanotechnology Research Centre, SRM University, Kattankulathur, Chennai 603203 (India); Therese, Helen Annal, E-mail: helen.a@ktr.srmuniv.ac.in [Nanotechnology Research Centre, SRM University, Kattankulathur, Chennai 603203 (India)

2017-08-01

Highlights: • Ta/CoFeB(50 nm)/Ta thin films were deposited at various substrate temperatures (T{sub s}). • CoFeB films deposited at T{sub s} such as RT, 450 °C, 475 °C and 500 °C exhibited perpendicular coercivity. • CoFeB deposited at 475 °C displayed a higher coercivity of 315 Oe and a low M{sub s} of 169 emu/cc. • The enhanced crystallization of CoFeB at the Ta/CoFeB interface results in higher H{sub c} (⟂). - Abstract: Magnetization of Ta/CoFeB/Ta trilayer films with thick layer of CoFeB deposited under different substrate temperatures (T{sub s}) via ultra-high vacuum DC sputtering technique has been measured with the applied magnetic field parallel and perpendicular to the plane of the film respectively to study the perpendicular coercive forces of the film. The samples were further analyzed for its structural, topological, morphological, and electrical transport properties. The core chemical states for the elements present in the CoFeB thin film were analyzed by XPS studies. Magnetization studies reveal the existence of perpendicular coercive forces in CoFeB films deposited only at certain temperatures such as RT, 450 °C, 475 °C and 500 °C. CoFeB film deposited at 475 °C exhibited a maximum coercivity of 315 Oe and a very low saturation magnetization (M{sub s}) of 169 emu/cc in perpendicular direction. This pronounced effect in perpendicular coercive forces observed for CoFeB475 could be attributed to the effect of temperature in enhancing the crystallization of the film at the Ta/CoFeB interfaces. However at temperatures higher than 475 °C the destruction of the Ta/CoFeB interface due to intermixing of Ta and CoFeB results in the disappearance of magnetic anisotropy.

Heat dissipation due to ferromagnetic resonance in a ferromagnetic metal monitored by electrical resistance measurement

International Nuclear Information System (INIS)

Yamanoi, Kazuto; Yokotani, Yuki; Kimura, Takashi

2015-01-01

The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated

Relation between Nd{sub 2}Fe{sub 14}B grain alignment and coercive force decrease ratio in NdFeB sintered magnets

Energy Technology Data Exchange (ETDEWEB)

Matsuura, Yutaka, E-mail: Yutaka_Matsuura@hitachi-metals.co.jp [Hitachi Metals Ltd., NEOMAX Division, 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka 618-0013 (Japan); Hoshijima, Jun; Ishii, Rintaro [Hitachi Metals Ltd., NEOMAX Division, 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka 618-0013 (Japan)

2013-06-15

It was found that the coercive force of NdFeB sintered magnets decreases as the Nd{sub 2}Fe{sub 14}B grain alignment improves. Because of this phenomenon, studies looked at the relation between this alignment and the coercive force decrease ratio. In experiments, it was expected that the coercive force of perfectly aligned magnet reached 0.7 of coercive force in istotropically aligned magnet. When it is postulated that the coercive force is determined by the Stoner–Wohlfarth model, coercive force increases as the alignment improves and it becomes difficult to explain our experimental data. On the other hand, when the coercive force is determined by magnetic domain wall motion, the coercive force decreases as the alignment improves and the coercive force of the perfectly aligned magnet reaches 1/√(2) of the isotropically aligned magnet. This tendency and value was very close to our data. It strongly suggests that the coercive force of NdFeB sintered magnets is determined by the domain wall motion. - Highlights: ► Coercive force of NdFeB sintered magnets decreases as grains alignment improves. ► Coercive force decrease ratio reaches −30% at the perfect aligned magnet. ►These experimental results are different from the Stoner–Wohlfarth model. ► The magnetic domain wall motion could explain this coercive force decrease ratio.

Variable substrate temperature deposition of CoFeB film on Ta for manipulating the perpendicular coercive forces

Science.gov (United States)

Lakshmanan, Saravanan; Rao, Subha Krishna; Muthuvel, Manivel Raja; Chandrasekaran, Gopalakrishnan; Therese, Helen Annal

2017-08-01

Magnetization of Ta/CoFeB/Ta trilayer films with thick layer of CoFeB deposited under different substrate temperatures (Ts) via ultra-high vacuum DC sputtering technique has been measured with the applied magnetic field parallel and perpendicular to the plane of the film respectively to study the perpendicular coercive forces of the film. The samples were further analyzed for its structural, topological, morphological, and electrical transport properties. The core chemical states for the elements present in the CoFeB thin film were analyzed by XPS studies. Magnetization studies reveal the existence of perpendicular coercive forces in CoFeB films deposited only at certain temperatures such as RT, 450 °C, 475 °C and 500 °C. CoFeB film deposited at 475 °C exhibited a maximum coercivity of 315 Oe and a very low saturation magnetization (Ms) of 169 emu/cc in perpendicular direction. This pronounced effect in perpendicular coercive forces observed for CoFeB475 could be attributed to the effect of temperature in enhancing the crystallization of the film at the Ta/CoFeB interfaces. However at temperatures higher than 475 °C the destruction of the Ta/CoFeB interface due to intermixing of Ta and CoFeB results in the disappearance of magnetic anisotropy.

STM observations of ferromagnetic clusters

International Nuclear Information System (INIS)

Wawro, A.; Kasuya, A.

1998-01-01

Co, Fe and Ni clusters of nanometer size, deposited on silicon and graphite (highly oriented pyrolytic graphite), were observed by a scanning tunneling microscope. Deposition as well as the scanning tunneling microscope measurements were carried out in an ultrahigh vacuum system at room temperature. Detailed analysis of Co cluster height was done with the scanning tunneling microscope equipped with a ferromagnetic tip in a magnetic field up to 70 Oe. It is found that bigger clusters (few nanometers in height) exhibit a dependence of their apparent height on applied magnetic field. We propose that such behaviour originates from the ferromagnetic ordering of cluster and associate this effect to spin polarized tunneling. (author)

Magnetic nesting and co-existence of ferromagnetism and superconductivity

International Nuclear Information System (INIS)

Elesin, V.F.; Kapaev, V.V.; Kopaev, Yu.V.

2004-01-01

In the case of providing for the magnetic nesting conditions of the electron spin dispersion law the co-existence of ferromagnetism and superconductivity is possible by any high magnetization. The co-existence of ferromagnetism and superconductivity in the layered cuprate compounds of the RuSr 2 GdCu 2 O 8 -type is explained on this basis, wherein due to the nonstrict provision of the magnetic nesting condition there exists the finite but sufficiently high critical magnetization [ru

Magnetic response in the vicinity of magnetic compensation: a case study in spin ferromagnetic Sm1-xGdxAl2 intermetallic alloys

International Nuclear Information System (INIS)

Venkatesh, S; Vaidya, Ulhas; Rakhecha, Veer Chand; Ramakrishnan, S; Grover, A K

2010-01-01

A compensated magnetic state in an ideally homogeneous system with long range magnetic order is characterized by a net zero magnetization (M) throughout the sample (macroscopic). In the pristine state of the sample (i.e. with no external field, H = 0), this implies that at the magnetic compensation temperature (T comp ) we must have M = 0 at H = 0 irrespective of any thermal and magnetic history of the sample and any underlying physics. This simple fact voids the usual identification (and interpretation) of M-H loop parameters at and in the vicinity of magnetic compensation temperature, specifically the coercivity, the remanence, and the exchange bias characteristics. The physics of coercivity and exchange bias continues to be fully relevant, but its manifestation in an M-H loop would get camouflaged at (and near) a magnetic compensation because M→0 at H = 0. We present an experimental elucidation of the above premise through a case study in the spin ferromagnetic Sm 1-x Gd x Al 2 alloys [x = 0.01-0.06], where the specimens with x ≤ 0.03 show compensation below the Curie temperature T c , while those with x ≥ 0.03 have rather small magnetization due to near cancellation of opposing contributions, but are otherwise devoid of compensation. The experiments comprised low field (near zero) as well as high field (70 kOe) magnetization measurements from the paramagnetic state down to 5 K in the ordered regime (T c ∼ 125 K) and isothermal M-H loop studies on the remnant magnetic state of polycrystalline samples.

Coercivity enhancement of Dy-free Nd–Fe–B sintered magnets by intergranular adding Ho{sub 63.4}Fe{sub 36.6} alloy

Energy Technology Data Exchange (ETDEWEB)

Liang, Liping; Ma, Tianyu, E-mail: maty@zju.edu.cn; Wu, Chen; Zhang, Pei; Liu, Xiaolian; Yan, Mi, E-mail: mse_yanmi@zju.edu.cn

2016-01-01

High coercivity Nd–Fe–B sintered magnets serving in high-temperature environments always consume expensive and scarce heavy rare-earth Dy, which has simulated considerable interest to reduce Dy usage. In this work, coercivity of Dy-free magnets was investigated through intergranular adding eutectic Ho{sub 63.4}Fe{sub 36.6} powders. The coercivity increases gradually up to 4 wt% Ho{sub 63.4}Fe{sub 36.6} addition, however the remanence starts to deteriorate drastically as the addition is over 2.5 wt%. Coercivity above 18.0 kOe is obtained at the expense of a slight reduction in remanence through optimizing the addition amount and sintering conditions. The coercivity enhancement is explained through microstructural observations and elemental distribution analysis. (i) (Nd, Ho){sub 2}Fe{sub 14}B shell forms in the outer region of 2:14:1 phase grains, strengthening the local magnetic anisotropy filed, (ii) RE-rich grain boundary phase with low Fe content is thickened, weakening the magnetic coupling between adjacent 2:14:1 phase grains, and (iii) 2:14:1 phase grains are refined upon lowering sintering temperature, reducing the microstructural defects and the stray fields aroused from neighboring grains. - Highlights: • Eutectic Ho{sub 63.4}Fe{sub 36.6} powders were intergranular added to NdFeB sintered magnets. • The doped Dy-free magnet possessed coercivity of 18.0 kOe, remanence of 13.15 kGs. • (Nd, Ho){sub 2}Fe{sub 14}B shell formed in the surface of the matrix grains, increasing the H{sub A}. • Thick grain boundaries with low Fe content formed, decoupling the matrix grains. • By sintered at lower temperature, the matrix phase grains were refined.

Peculiar ferromagnetic insulator state in the low-hole-doped manganites

International Nuclear Information System (INIS)

Algarabel, P.A.; Teresa, J.M. de; Blasco, J.; Ibarra, M.R.; Kapusta, Cz.; Sikora, M.; Zajac, D.; Riedi, P.C.; Ritter, C.

2003-01-01

In this work we show the very different nature of the ferromagnetic state of the low-hole-doped manganites with respect to other manganites showing colossal magnetoresistance. High-field measurements definitively prove the coexistence of ferromagnetic-metallic and ferromagnetic-insulating regions even when the sample is magnetically saturated, with the ground state being inhomogeneous. We have investigated La 0.9 Ca 0.1 MnO 3 as a prototype compound. A wide characterization by means of magnetic and magnetotransport measurements, neutron diffraction, small-angle neutron scattering, and nuclear magnetic resonance has allowed us to establish that the ground state is based on the existence of disordered nanometric double-exchange metallic clusters that coexist with long-range superexchange-based ferromagnetic insulating regions. Under high magnetic field the system reaches magnetization saturation by aligning the magnetic clusters and the insulating matrix, but even if they grow in size, they do not reach the percolation limit

Nonlinear nuclear magnetic resonance in ferromagnets

International Nuclear Information System (INIS)

Nurgaliev, T.

1988-01-01

The properties of nonlinear nuclear magnetic resonance (NMR) have been studied theoretically by taking into account the interaction between NMR and FMR in the ferromagnets. The Landau-Lifshitz-Bloch equations, describing the electron and nuclear magnetization behaviour in ferromagnets are presented in an integral form for a weakly excited electronic system. The stationary solution of these equations has been analysed in the case of equal NMR and FMR frequencies: the criteria for the appearance of two stable dynamic states is found and the high-frequency magnetic susceptibility for these systems is investigated. 2 figs., 8 refs

Modulation of magnetic coercivity in Ni thin films by reversible control of strain

Energy Technology Data Exchange (ETDEWEB)

Lin, Wen-Chin, E-mail: wclin@ntnu.edu.tw [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Huang, Chia-Wei; Ting, Yi-Chieh; Lo, Fang-Yuh [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Chern, Ming-Yau [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China)

2015-05-01

In this study, we demonstrated the magnetoelectric control of magnetic thin films. (111)-textured Pd/Ni/Pd thin films were prepared on mica/lead zirconium titanate (PZT) substrates for the investigation. The reversible modulation of magnetic coercivity in Ni films was observed through the electric-voltage-controlled strain variation from the PZT substrate. For 14 nm Ni film, the applied electric field of ±350 V/m led to ±0.5% strain variation of PZT, which was transferred to ±0.4% strain variation of Pd/Ni/Pd thin films on mica, and resulted in ∓17 Oe (∓5% of the preliminary magnetic coercivity). The reversible modulation of magnetic coercivity is supposed to be caused by the voltage-controlled strain through the magneto-elastic effect. - Highlights: • The magnetoelectric control of the magnetic coercivity of Pd/Ni/Pd thin films was demonstrated. • The ±0.4% strain variation of 14 nm Ni thin films resulted in ±17 Oe change of H{sub c}. • The reversible modulation of H{sub c} is supposed to be caused by the magneto-elastic effect.

Hole-induced d"0 ferromagnetism enhanced by Na-doping in GaN

International Nuclear Information System (INIS)

Zhang, Yong; Li, Feng

2017-01-01

The d"0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature. - Highlights: • Hole-induced ferromagnetism in GaN is confirmed. • Both Ga Vacancy and Na-doping can introduce hole into GaN. • The concentration of Ga vacancy is too low to induce detectable ferromagnetism. • Na-doped GaN is a possible ferromagnet with a high curie-temperature.

An H1(Ph)-coercive discontinuous Galerkin formulation for the Poisson problem: 1D analysis

NARCIS (Netherlands)

Zee, van der K.G.; Brummelen, van E.H.; Borst, de R.

2006-01-01

Coercivity of the bilinear form in a continuum variational problem is a fundamental property for finite-element discretizations: By the classical Lax–Milgram theorem, any conforming discretization of a coercive variational problem is stable; i.e., discrete approximations are well-posed and possess

An H1(Ph)-Coercive Discontinuous Galerkin Formulation for The Poisson Problem : 1-D Analysis

NARCIS (Netherlands)

Van der Zee, K.G.; Van Brummelen, E.H.; De Borst, R.

2006-01-01

Coercivity of the bilinear form in a continuum variational problem is a fundamental property for finite-element discretizations: By the classical Lax–Milgram theorem, any conforming discretization of a coercive variational problem is stable; i.e., discrete approximations are well-posed and possess

High temperature structural and magnetic properties of cobalt nanorods

Energy Technology Data Exchange (ETDEWEB)

Ait Atmane, Kahina [Univ. Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR CNRS 7086, 15 rue J.-A. de Baief, 75205 Paris Cedex 13 (France); Zighem, Fatih [Laboratoire Leon Brillouin, CEA CNRS UMR 12, IRAMIS, CEA-Saclay, 91191 Gif sur Yvette (France); Soumare, Yaghoub [Univ. Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR CNRS 7086, 15 rue J.-A. de Baief, 75205 Paris Cedex 13 (France); Ibrahim, Mona; Boubekri, Rym [Universite de Toulouse, LPCNO, INSA CNRS UMR 5215, 135 av. de Rangueil, 31077 Toulouse Cedex 4 (France); Maurer, Thomas [Laboratoire Leon Brillouin, CEA CNRS UMR 12, IRAMIS, CEA-Saclay, 91191 Gif sur Yvette (France); Margueritat, Jeremie [Univ. Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR CNRS 7086, 15 rue J.-A. de Baief, 75205 Paris Cedex 13 (France); Piquemal, Jean-Yves, E-mail: jean-yves.piquemal@univ-paris-diderot.fr [Univ. Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR CNRS 7086, 15 rue J.-A. de Baief, 75205 Paris Cedex 13 (France); Ott, Frederic; Chaboussant, Gregory [Laboratoire Leon Brillouin, CEA CNRS UMR 12, IRAMIS, CEA-Saclay, 91191 Gif sur Yvette (France); Schoenstein, Frederic; Jouini, Noureddine [LSPM, CNRS UPR 9001, Universite Paris XIII, Institut Galilee, 99 av. J.-B. Clement, 93430 Villetaneuse (France); Viau, Guillaume, E-mail: gviau@insa-toulouse.fr [Universite de Toulouse, LPCNO, INSA CNRS UMR 5215, 135 av. de Rangueil, 31077 Toulouse Cedex 4 (France)

2013-01-15

We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ({approx}10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by {mu}{sub 0}H{sub C}=2(K{sub MC}+K{sub shape})/M{sub S} with K{sub MC} the magnetocrystalline anisotropy constant, K{sub shape} the shape anisotropy constant and M{sub S} the saturation magnetization. H{sub C} decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. - Graphical abstract: We present in this paper the structural and magnetic properties of high aspect ratio Co nanorods ({approx}10) at high temperatures (up to 623 K) using in-situ X-ray diffraction and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. Highlights: Black-Right-Pointing-Pointer Ferromagnetic Co nanorods are prepared using the polyol process. Black-Right-Pointing-Pointer The structural and texture properties of the Co nanorods are preserved up to 500 K. Black-Right-Pointing-Pointer The magnetic properties of the Co nanorods are irreversibly altered above 525 K.

In-plane electric field controlled ferromagnetism and anisotropic magnetoresistance in an LSMO/PMN-PT heterostructure

Science.gov (United States)

Guo, Qi; Xu, Xiaoguang; Wang, Fang; Lu, Yunhao; Chen, Jikun; Wu, Yanjun; Meng, Kangkang; Wu, Yong; Miao, Jun; Jiang, Yong

2018-06-01

We report the in-plane electric field controlled ferromagnetism of La2/3Sr1/3MnO3 (LSMO) films epitaxially deposited on [Pb(Mg1/3Nb2/3)O3]0.7-(PbTiO3)0.3 (PMN-PT) (001), (011) and (111) single crystal substrates. The in-plane coercivities (H c∥) and remanences of the LSMO films greatly depend on the in-plane electric field applied on the PMN-PT (001) and (011) substrates. The experimental change of H c∥ is consistent with the Stoner–Wohlfarth model and first principle calculation with the electric field varying from ‑10 to 10 kV cm‑1. Moreover, the Curie temperature and anisotropic magnetoresistance of the LSMO films can also be manipulated by an in-plane electric field. Finally, the LSMO/PMN-PT (001) heterostructure is designed to be a new kind of magnetic signal generator with the source of electric field.

Electric-field controlled ferromagnetism in MnGe magnetic quantum dots

Directory of Open Access Journals (Sweden)

Faxian Xiu

2011-03-01

Full Text Available Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (Tc>300 K and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs, materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS technology. Here, we review recent reports on the development of high-Curie temperature Mn0.05Ge0.95 quantum dots (QDs and successfully demonstrate electric-field control of ferromagnetism in the Mn0.05Ge0.95 quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS capacitor, the ferromagnetism of the channel layer (i.e. the Mn0.05Ge0.95 quantum dots was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

Ferromagnetism in doped or undoped spintronics nanomaterials

Science.gov (United States)

Qiang, You

2010-10-01

Much interest has been sparked by the discovery of ferromagnetism in a range of oxide doped and undoped semiconductors. The development of ferromagnetic oxide semiconductor materials with giant magnetoresistance (GMR) offers many advantages in spintronics devices for future miniaturization of computers. Among them, TM-doped ZnO is an extensively studied n-type wide-band-gap (3.36 eV) semiconductor with a tremendous interest as future mini-computer, blue light emitting, and solar cells. In this talk, Co-doped ZnO and Co-doped Cu2O semiconductor nanoclusters are successfully synthesized by a third generation sputtering-gas-aggregation cluster technique. The Co-doped nanoclusters are ferromagnetic with Curie temperature above room temperature. Both of Co-doped nanoclusters show positive magnetoresistance (PMR) at low temperature, but the amplitude of the PMRs shows an anomalous difference. For similar Co doping concentration at 5 K, PMR is greater than 800% for Co-doped ZnO but only 5% for Co-doped Cu2O nanoclusters. Giant PMR in Co-doped ZnO which is attributed to large Zeeman splitting effect has a linear dependence on applied magnetic field with very high sensitivity, which makes it convenient for the future spintronics applications. The small PMR in Co-doped Cu2O is related to its vanishing density of states at Fermi level. Undoped Zn/ZnO core-shell nanoparticle gives high ferromagnetic properties above room temperature due to the defect induced magnetization at the interface.

Determining the effect of grain size and maximum induction upon coercive field of electrical steels

Science.gov (United States)

Landgraf, Fernando José Gomes; da Silveira, João Ricardo Filipini; Rodrigues-Jr., Daniel

2011-10-01

Although theoretical models have already been proposed, experimental data is still lacking to quantify the influence of grain size upon coercivity of electrical steels. Some authors consider a linear inverse proportionality, while others suggest a square root inverse proportionality. Results also differ with regard to the slope of the reciprocal of grain size-coercive field relation for a given material. This paper discusses two aspects of the problem: the maximum induction used for determining coercive force and the possible effect of lurking variables such as the grain size distribution breadth and crystallographic texture. Electrical steel sheets containing 0.7% Si, 0.3% Al and 24 ppm C were cold-rolled and annealed in order to produce different grain sizes (ranging from 20 to 150 μm). Coercive field was measured along the rolling direction and found to depend linearly on reciprocal of grain size with a slope of approximately 0.9 (A/m)mm at 1.0 T induction. A general relation for coercive field as a function of grain size and maximum induction was established, yielding an average absolute error below 4%. Through measurement of B50 and image analysis of micrographs, the effects of crystallographic texture and grain size distribution breadth were qualitatively discussed.

Variables Associated with the Use of Coercive Measures on Psychiatric Patients in Spanish Penitentiary Centers

Directory of Open Access Journals (Sweden)

E. Girela

2014-01-01

Full Text Available We have studied the use of coercive medical measures (forced medication, isolation, and mechanical restraint in mentally ill inmates within two secure psychiatric hospitals (SPH and three regular prisons (RP in Spain. Variables related to adopted coercive measures were analyzed, such as type of measure, causes of indication, opinion of patient inmate, opinion of medical staff, and more frequent morbidity. A total of 209 patients (108 from SPH and 101 from RP were studied. Isolation (41.35% was the most frequent coercive measure, followed by mechanical restraint (33.17% and forced medication (25.48%. The type of center has some influence; specifically in RP there is less risk of isolation and restraint than in SPH. Not having had any previous imprisonment reduces isolation and restraint risk while increases the risk of forced medication, as well as previous admissions to psychiatric inpatient units does. Finally, the fact of having lived with a partner before imprisonment reduces the risk of forced medication and communication with the family decreases the risk of isolation. Patients subjected to a coercive measure exhibited a pronounced psychopathology and most of them had been subjected to such measures on previous occasions. The mere fact of external assessment of compliance with human rights slows down the incidence of coercive measures.

Variables associated with the use of coercive measures on psychiatric patients in Spanish penitentiary centers.

Science.gov (United States)

Girela, E; López, A; Ortega, L; De-Juan, J; Ruiz, F; Bosch, J I; Barrios, L F; Luna, J D; Torres-González, F

2014-01-01

We have studied the use of coercive medical measures (forced medication, isolation, and mechanical restraint) in mentally ill inmates within two secure psychiatric hospitals (SPH) and three regular prisons (RP) in Spain. Variables related to adopted coercive measures were analyzed, such as type of measure, causes of indication, opinion of patient inmate, opinion of medical staff, and more frequent morbidity. A total of 209 patients (108 from SPH and 101 from RP) were studied. Isolation (41.35%) was the most frequent coercive measure, followed by mechanical restraint (33.17%) and forced medication (25.48%). The type of center has some influence; specifically in RP there is less risk of isolation and restraint than in SPH. Not having had any previous imprisonment reduces isolation and restraint risk while increases the risk of forced medication, as well as previous admissions to psychiatric inpatient units does. Finally, the fact of having lived with a partner before imprisonment reduces the risk of forced medication and communication with the family decreases the risk of isolation. Patients subjected to a coercive measure exhibited a pronounced psychopathology and most of them had been subjected to such measures on previous occasions. The mere fact of external assessment of compliance with human rights slows down the incidence of coercive measures.

Temperature dependence of coercivity behavior in iron films on silicone oil surfaces

International Nuclear Information System (INIS)

Xu Xiaojun; Ye Quanlin; Ye Gaoxiang

2007-01-01

A new iron film system, deposited on silicone oil surfaces by vapor phase deposition method, has been fabricated and its microstructure as well as magnetic properties has been studied. It is found that the temperature dependence of the coercive field H c (T) of the films exhibits a peak around a critical temperature T crit =10-15 K: for the temperature T crit ,H c (T) increases with the temperature; if T>T crit , however, it decreases rapidly and then approaches a steady value as T further increases. Our study shows that, for T>T crit , the observed coercivity behavior is mainly dominated by the effect of the non-uniform single-domain particle size distribution, and for T crit , the anomalous coercivity behavior may be resulted from the surface anisotropy, the surface effect and the characteristic internal stress distribution in the films. The influence of the shape and size of the particles on the thermal dependence of the magnetization is also investigated

Effect of Complex Working Conditions on Nurses Who Exert Coercive Measures in Forensic Psychiatric Care.

Science.gov (United States)

Gustafsson, Niclas; Salzmann-Erikson, Martin

2016-09-01

Nurses who exert coercive measures on patients within psychiatric care are emotionally affected. However, research on their working conditions and environment is limited. The purpose of the current study was to describe nurses' experiences and thoughts concerning the exertion of coercive measures in forensic psychiatric care. The investigation was a qualitative interview study using unstructured interviews; data were analyzed with inductive content analysis. Results described participants' thoughts and experiences of coercive measures from four main categories: (a) acting against the patients' will, (b) reasoning about ethical justifications, (c) feelings of compassion, and (d) the need for debriefing. The current study illuminates the working conditions of nurses who exert coercive measures in clinical practice with patients who have a long-term relationship with severe symptomatology. The findings are important to further discuss how nurses and leaders can promote a healthier working environment. [Journal of Psychosocial Nursing and Mental Health Services, 54(9), 37-43.]. Copyright 2016, SLACK Incorporated.

Magnetic structure and microstructure of die-upset hard magnets RE13.75Fe80.25B6 (RE=Nd, Pr): A possible origin of high coercivity

International Nuclear Information System (INIS)

Volkov, V.V.; Zhu, Y.

1999-01-01

In situ transmission electron microscopy magnetizing experiments combined with Lorentz magnetic microscopy in Fresnel endash Foucault modes were used to characterize the magnetic structure of die-upset, high energy-product hard magnets Nd 13.75 Fe 80.25 B 6 and Pr 13.75 Fe 80.25 B 6 . Experimental observations indicate a well-aligned grain structure and quasiperiodic nonaligned open-quotes extended defectclose quotes layers transverse to press direction. The local remanence of the open-quotes defectclose quotes layers is far from saturation when the external field is removed. The layers are enriched with inclusions of approximate composition Nd 7 Fe 3 , generally with a polygonal shape, and are associated with the original ribbon interfaces. They may be responsible for a high coercivity mechanism, since the motion of reverse domains can be impeded by these layers, even when they are nucleated. Thus, a delayed nucleation of reversed domains seems to be a limiting factor for magnetization reversal and coercivity force. Both Lorentz magnetic imaging and high-resolution microscopy highlight the role of magnetocrystalline anisotropy for domain wall-grain boundary interactions and pinning. Local remanence was estimated directly from magnetic moment sensitive Foucault images. copyright 1999 American Institute of Physics

Exchange bias in nearly perpendicularly coupled ferromagnetic/ferromagnetic system

International Nuclear Information System (INIS)

Bu, K.M.; Kwon, H.Y.; Oh, S.W.; Won, C.

2012-01-01

Exchange bias phenomena appear not only in ferromagnetic/antiferromagnetic systems but also in ferromagnetic/ferromagnetic systems in which two layers are nearly perpendicularly coupled. We investigated the origin of the symmetry-breaking mechanism and the relationship between the exchange bias and the system's energy parameters. We compared the results of computational Monte Carlo simulations with those of theoretical model calculation. We found that the exchange bias exhibited nonlinear behaviors, including sign reversal and singularities. These complicated behaviors were caused by two distinct magnetization processes depending on the interlayer coupling strength. The exchange bias reached a maximum at the transition between the two magnetization processes. - Highlights: ► Exchange bias phenomena are found in perpendicularly coupled F/F systems. ► Exchange bias exhibits nonlinear behaviors, including sign reversal and singularities. ► These complicated behaviors were caused by two distinct magnetization processes. ► Exchange bias reached a maximum at the transition between the two magnetization processes. ► We established an equation to maximize the exchange bias in perpendicularly coupled F/F system.

Coercive and legitimate authority impact tax honesty: evidence from behavioral and ERP experiments.

Science.gov (United States)

Gangl, Katharina; Pfabigan, Daniela M; Lamm, Claus; Kirchler, Erich; Hofmann, Eva

2017-07-01

Cooperation in social systems such as tax honesty is of central importance in our modern societies. However, we know little about cognitive and neural processes driving decisions to evade or pay taxes. This study focuses on the impact of perceived tax authority and examines the mental chronometry mirrored in ERP data allowing a deeper understanding about why humans cooperate in tax systems. We experimentally manipulated coercive and legitimate authority and studied its impact on cooperation and underlying cognitive (experiment 1, 2) and neuronal (experiment 2) processes. Experiment 1 showed that in a condition of coercive authority, tax payments are lower, decisions are faster and participants report more rational reasoning and enforced compliance, however, less voluntary cooperation than in a condition of legitimate authority. Experiment 2 confirmed most results, but did not find a difference in payments or self-reported rational reasoning. Moreover, legitimate authority led to heightened cognitive control (expressed by increased MFN amplitudes) and disrupted attention processing (expressed by decreased P300 amplitudes) compared to coercive authority. To conclude, the neuronal data surprisingly revealed that legitimate authority may led to higher decision conflict and thus to higher cognitive demands in tax decisions than coercive authority. © The Author (2017). Published by Oxford University Press.

Nd and Sc co-doped BiFeO{sub 3} nanopowders displaying enhanced ferromagnetism at room temperature

Energy Technology Data Exchange (ETDEWEB)

Hernández, N., E-mail: netzahualpille.hernandeznv@uanl.edu.mx [Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Km. 10 Nueva carretera al Aeropuerto Internacional de Monterrey, PIIT Monterrey, CP 66600 Apodaca, Nuevo León (Mexico); González-González, V.A. [Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Km. 10 Nueva carretera al Aeropuerto Internacional de Monterrey, PIIT Monterrey, CP 66600 Apodaca, Nuevo León (Mexico); Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, Pedro de Alba S/N, San Nicolás de los Garza, Nuevo León 66450 (Mexico); Dzul-Bautista, I.B. [Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Km. 10 Nueva carretera al Aeropuerto Internacional de Monterrey, PIIT Monterrey, CP 66600 Apodaca, Nuevo León (Mexico); Gutiérrez, J.; Barandiarán, J.M. [Basque Center for Materials, Applications and Nanostructures (BCMaterials), Universidad del País Vasco (UPV/EHU), Parque Tecnológico de Bizkaia, Ed. 500, Derio 48160 (Spain); and others

2015-07-25

Highlights: • Will study the structure of materials obtained. • A well crystallized BiFeO{sub 3} doped material was obtained without further annealing. • The obtained nanoparticles have sizes less than 60 nm. • Enhanced ferromagnetic materials was obtained. - Abstract: We have developed a novel synthetic route for the preparation of single phase Nd{sub x}Bi{sub 1−x}Fe{sub 0.95}Sc{sub 0.05}O{sub 3} (NBFSO) nanopowder materials by a surfactant-assisted combustion-derived method. Rietveld fitting of the Powder X-ray diffraction data showed the nanopowder structure evolves from a distorted rhombohedral BiFeO{sub 3} crystalline structure (R3c, x = 0) to a orthorhombic structure (Pbnm, x = 0.10). Differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 200 °C. Transmission electron microscopy (TEM) images revealed the presence of clusters formed by fine nanoparticles less than 60 nm in diameter. From Raman spectroscopy, the change from rhombohedral structure to cubic structure was observed by a drastic intensity reduction of the A{sub 1}{sup −2} and A{sub 1}{sup −3} Raman modes, with the A{sub 1}{sup −1} and A{sub 1}{sup −2} modes gradually merging together, indicating the merge of the orthorhombic phase. Despite the antiferromagnetic nature of bulk BiFeO{sub 3}, the NBFSO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivities of 0.08 T and remanent magnetizations of 0.65–4.05 Am{sup 2}/kg when measured at room temperature. The increasing and uncompensated spins at the surface of nanoparticles and the canted internal spin by the tilt of FeO{sub 6} octahedral units and the structure transition appear to be the main reason for observed this ferromagnetic behavior.

Coexistence of weak ferromagnetism and ferroelectricity in the high pressure LiNbO3-type phase of FeTiO3.

Science.gov (United States)

Varga, T; Kumar, A; Vlahos, E; Denev, S; Park, M; Hong, S; Sanehira, T; Wang, Y; Fennie, C J; Streiffer, S K; Ke, X; Schiffer, P; Gopalan, V; Mitchell, J F

2009-07-24

We report the magnetic and electrical characteristics of polycrystalline FeTiO_{3} synthesized at high pressure that is isostructural with acentric LiNbO_{3} (LBO). Piezoresponse force microscopy, optical second harmonic generation, and magnetometry demonstrate ferroelectricity at and below room temperature and weak ferromagnetism below approximately 120 K. These results validate symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LBO structure.

Proliferation Persuasion. Coercive Bargaining with Nuclear Technology

Energy Technology Data Exchange (ETDEWEB)

Volpe, Tristan A. [George Washington Univ., Washington, DC (United States)

2015-08-31

Why do states wait for prolonged periods of time with the technical capacity to produce nuclear weapons? Only a handful of countries have ever acquired the sensitive nuclear fuel cycle technology needed to produce fissile material for nuclear weapons. Yet the enduring trend over the last five decades is for these states to delay or forgo exercising the nuclear weapons option provided by uranium enrichment or plutonium reprocessing capabilities. I show that states pause at this threshold stage because they use nuclear technology to bargain for concessions from both allies and adversaries. But when does nuclear latency offer bargaining benefits? My central argument is that challengers must surmount a dilemma to make coercive diplomacy work: the more they threaten to proliferate, the harder it becomes to reassure others that compliance will be rewarded with nuclear restraint. I identify a range of mechanisms able to solve this credibility problem, from arms control over breakout capacity to third party mediation and confidence building measures. Since each step towards the bomb raises the costs of implementing these policies, a state hits a sweet spot when it first acquires enrichment and/or reprocessing (ENR) technology. Subsequent increases in proliferation capability generate diminishing returns at the bargaining table for two reasons: the state must go to greater lengths to make a credible nonproliferation promise, and nuclear programs exhibit considerable path dependency as they mature over time. Contrary to the conventional wisdom about power in world politics, less nuclear latency thereby yields more coercive threat advantages. I marshal new primary source evidence from archives and interviews to identify episodes in the historical record when states made clear decisions to use ENR technology as a bargaining chip, and employ this theory of proliferation persuasion to explain how Japan, North Korea, and Iran succeeded and failed to barter concessions from the

Crystallization and atomic diffusion behavior of high coercive Ta/Nd-Fe-B/Ta-based permanent magnetic thin film

Energy Technology Data Exchange (ETDEWEB)

Tian, Na; Zhang, Xiao; You, Caiyin; Fu, Huarui [Xi' an University of Technology, School of Materials Science and Engineering, Xi' an (China); Shen, Qianlong [Logistics University of People' s Armed Police Force, Tianjin (China)

2017-06-15

A high coercivity of about 20.4 kOe was obtained through post-annealing the sputtered Ta/Nd-Fe-B/Ta-based permanent magnetic thin films. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the crystallization and atomic diffusion behaviors during post-annealing. The results show that the buffer and capping Ta layers prefered to intermix with Fe and B atoms, and Nd tends to be combined with O atoms. The preferred atomic combination caused the appearance of the soft magnetic phase of Fe-Ta-B, resulting in a kink of the second quadratic magnetic hysteresis loop. The preferred atomic diffusion and phase formation of the thin films were well explained in terms of the formation enthalpy of the various compounds. (orig.)

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.

Large coercivity in nanocrystalline TbMn6Sn6 permanent magnets prepared by mechanical milling

International Nuclear Information System (INIS)

Zhang Hongwei; Zhao Tongyun; Zhang Jian; Rong Chuanbing; Zhang Shaoying; Shen Baogen; Li Lu; Zhang Ligang

2003-01-01

Isotropic TbMn 6 Sn 6 was prepared by mechanical milling and subsequent annealing. Although the crystalline grain size was a little larger than 15 nm, no remanence enhancement resulting from intergrain exchange coupling was observed. The coercivity μ 0 H c = 0.96 T at 293 K was much larger than that expected from magnetocrystalline anisotropy. The smallest effective anisotropy constant is suggested to be 0.25 MJ m -3 when the coercivity mechanism is controlled by coherent rotation of magnetization in a single-domain grain. The contributions of shape anisotropy and magnetoelastic anisotropy are considered in order to explain the large coercivity in the magnets

Structure, coercive control, and autonomy promotion: A comparison of fathers' and mothers' food parenting strategies.

Science.gov (United States)

Pratt, Mercedes; Hoffmann, Debra; Taylor, Maija; Musher-Eizenman, Dara

2017-05-01

This study explored differences in mothers' and fathers' food parenting strategies, specifically coercive control, structure, and autonomy promotion, and whether parenting style and parental responsibility for food parenting related to the use of these strategies. Parents of children aged 2.5-7.5 years ( N = 497) reported about their parenting practices and food parenting strategies. Parenting style accounted for the majority of the variance in food parenting. Fathers were more authoritarian than mothers. Authoritarian and permissive parenting practices were related to more coercive strategies. Mothers reported more food parenting responsibility. Responsibility was related to less coercive practices and more autonomy promotion and structure.

Temperature limited heater utilizing non-ferromagnetic conductor

Science.gov (United States)

Vinegar,; Harold J. , Harris; Kelvin, Christopher [Houston, TX

2012-07-17

A heater is described. The heater includes a ferromagnetic conductor and an electrical conductor electrically coupled to the ferromagnetic conductor. The ferromagnetic conductor is positioned relative to the electrical conductor such that an electromagnetic field produced by time-varying current flow in the ferromagnetic conductor confines a majority of the flow of the electrical current to the electrical conductor at temperatures below or near a selected temperature.

Modeling of exchange bias in the antiferromagnetic (core)/ferromagnetic (shell) nanoparticles with specialized shapes

International Nuclear Information System (INIS)

Hu Yong; Liu Yan; Du An

2011-01-01

Zero-field-cooled (ZFC) and field-cooled (FC) hysteresis loops of egg- and ellipsoid-shaped nanoparticles with inverted ferromagnetic (FM)-antiferromagnetic (AFM) core-shell morphologies are simulated using a modified Monte Carlo method, which takes into account both the thermal fluctuations and energy barriers during the rotation of spin. Pronounced exchange bias (EB) fields and reduced coercivities are obtained in the FC hysteresis loops. The analysis of the microscopic spin configurations allows us to conclude that the magnetization reversal occurs by means of the nucleation process during both the ZFC and FC hysteresis branches. The nucleation takes place in the form of 'sparks' resulting from the energy competition and the morphology of the nanoparticle. The appearance of EB in the FC hysteresis loops is only dependent on that the movements of 'sparks' driven by magnetic field at both branches of hysteresis loops are not along the same axis, which is independent of the strength of AFM anisotropy. The tilt of 'spark' movement with respect to the symmetric axis implies the existence of additional unidirectional anisotropy at the AFM/FM interfaces as a consequence of the surplus magnetization in the AFM core, which is the commonly accepted origin of EB. Our simulations allow us to clarify the microscopic mechanisms of the observed EB behavior, not accessible in experiments. - Highlights: → A modified Monte Carlo method considers thermal fluctuations and energy barriers. → Egg and ellipsoid nanoparticles with inverted core-shell morphology are studied. → Pronounced exchange bias fields and reduced coercivities may be detected. → 'Sparks' representing nucleation sites due to energy competition are observed. → 'Sparks' can reflect or check directly and vividly the origin of exchange bias.

Strain-Induced Ferromagnetism in Antiferromagnetic LuMnO3 Thin Films

Science.gov (United States)

White, J. S.; Bator, M.; Hu, Y.; Luetkens, H.; Stahn, J.; Capelli, S.; Das, S.; Döbeli, M.; Lippert, Th.; Malik, V. K.; Martynczuk, J.; Wokaun, A.; Kenzelmann, M.; Niedermayer, Ch.; Schneider, C. W.

2013-07-01

Single phase and strained LuMnO3 thin films are discovered to display coexisting ferromagnetic and antiferromagnetic orders. A large moment ferromagnetism (≈1μB), which is absent in bulk samples, is shown to display a magnetic moment distribution that is peaked at the highly strained substrate-film interface. We further show that the strain-induced ferromagnetism and the antiferromagnetic order are coupled via an exchange field, therefore demonstrating strained rare-earth manganite thin films as promising candidate systems for new multifunctional devices.

Effect of Coercive Voltage and Charge Injection on Performance of a Ferroelectric-Gate Thin-Film Transistor

Directory of Open Access Journals (Sweden)

P. T. Tue

2013-01-01

Full Text Available We adopted a lanthanum oxide capping layer between semiconducting channel and insulator layers for fabrication of a ferroelectric-gate thin-film transistor memory (FGT which uses solution-processed indium-tin-oxide (ITO and lead-zirconium-titanate (PZT film as a channel layer and a gate insulator, respectively. Good transistor characteristics such as a high “on/off” current ratio, high channel mobility, and a large memory window of 108, 15.0 cm2 V−1 s−1, and 3.5 V were obtained, respectively. Further, a correlation between effective coercive voltage, charge injection effect, and FGT’s memory window was investigated. It is found that the charge injection from the channel to the insulator layer, which occurs at a high electric field, dramatically influences the memory window. The memory window’s enhancement can be explained by a dual effect of the capping layer: (1 a reduction of the charge injection and (2 an increase of effective coercive voltage dropped on the insulator.

Successful interventions on an organisational level to reduce violence and coercive interventions in in-patients with adjustment disorders and personality disorders.

Science.gov (United States)

Steinert, Tilman; Eisele, Frank; Goeser, Ulla; Tschoeke, Stefan; Uhlmann, Carmen; Schmid, Peter

2008-11-17

Self-directed and other violence as well as subsequent coercive interventions occur in a substantial proportion of patients with personality disorders during in-patient treatment. Different strategies may be required to reduce coercive interventions for patients of different diagnostic groups. We specialised one of our acute admission wards in the treatment of personality disorders and adjustment disorders (ICD-10 F4 and F6). Patients are not transferred to other acute wards in case of suicidal or violent behaviour. Violent behaviour and coercive interventions such as seclusion or restraint were recorded in the same way as in the rest of the hospital. We recorded the percentage of subjects affected by diagnostic group and average length of an intervention in the year before and after the change in organisational structure. The total number of coercive interventions decreased by 85% both among patients with an F4 and those with an F6 primary diagnosis. Violent behaviours decreased by about 50%, the proportion of involuntary committed patients decreased by 70%. The organisational change turned out to be highly effective without any additional cost of personnel or other resources.

Tuning coercivity in CoCrPt-SiO{sub 2} hard disk material

Energy Technology Data Exchange (ETDEWEB)

Strache, Thomas; Lenz, Kilian; Fassbender, Juergen [Forschungszentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, P.O. Box 51 01 19, 01314 Dresden (Germany); Tibus, Stefan [University of Konstanz, Department of Physics, 78457 Konstanz (Germany); Chemnitz University of Technology, Institute of Physics, 09107 Chemnitz (Germany); Springer, Felix [University of Konstanz, Department of Physics, 78457 Konstanz (Germany); Rohrmann, Hartmut [OC Oerlikon Balzers, AG Data Storage, P.O. Box 1000, 9496 Balzers (Liechtenstein); Albrecht, Manfred [Chemnitz University of Technology, Institute of Physics, 09107 Chemnitz (Germany)

2009-07-01

In order to increase the storage density of modern computer disk drives and to push the superparamagnetic limit to the smallest achievable bit sizes further, smaller grains with even larger magnetic anisotropies are required, which are accompanied by large coercive fields obstructing the writing process. One route to overcome this problem is to independently reduce the coercive field without altering anisotropy and remanence by tailoring the intergranular exchange in granular CoCrPt-SiO{sub 2} films. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry, also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy.

Spin-flip scattering effect on the current-induced spin torque in ferromagnet-insulator-ferromagnet tunnel junctions

International Nuclear Information System (INIS)

Zhu Zhengang; Su Gang; Jin Biao; Zheng Qingrong

2003-01-01

We have investigated the current-induced spin transfer torque of a ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τ Rx /I e (τ Rx is the spin-transfer torque acting on the right ferromagnet and I e is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τ Rx /I e is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τ Rx /I e versus the relevant orientation for different molecular fields

Giant magnetotransmission and magnetoreflection in ferromagnetic materials

International Nuclear Information System (INIS)

Telegin, A.V.; Sukhorukov, Yu.P.; Loshkareva, N.N.; Mostovshchikova, E.V.; Bebenin, N.G.; Gan'shina, E.A.; Granovsky, A.B.

2015-01-01

We present a brief review on magnetotransmission (magnetoabsorption) and magnetoreflection of natural (unpolarized) light in ferromagnetic chromium chalcogenide spinel, manganites with perovskite structure and thin-film metallic nanostructures in the middle infrared spectral range. The magnetooptical effects under discussion are of high interest for numerous and promising applications in the infrared optoelectronics. - Highlights: • Magnetotransmission and magnetoreflection of light in ferromagnetic are presented. • The effects are greater than common magnetooptical phenomena in the infrared. • The effects may have a different origin depending on a material or spectral range. • Possible applications of the magnetotransmission and magnetoreflection are discussed

Giant magnetotransmission and magnetoreflection in ferromagnetic materials

Energy Technology Data Exchange (ETDEWEB)

Telegin, A.V., E-mail: telegin@imp.uran.ru [M.N. Miheev Institute of Metal Physics of Ural Branch of RAS, 620137 Yekaterinburg (Russian Federation); Sukhorukov, Yu.P.; Loshkareva, N.N.; Mostovshchikova, E.V.; Bebenin, N.G. [M.N. Miheev Institute of Metal Physics of Ural Branch of RAS, 620137 Yekaterinburg (Russian Federation); Gan' shina, E.A.; Granovsky, A.B. [Moscow State University, 119991 Moscow (Russian Federation)

2015-06-01

We present a brief review on magnetotransmission (magnetoabsorption) and magnetoreflection of natural (unpolarized) light in ferromagnetic chromium chalcogenide spinel, manganites with perovskite structure and thin-film metallic nanostructures in the middle infrared spectral range. The magnetooptical effects under discussion are of high interest for numerous and promising applications in the infrared optoelectronics. - Highlights: • Magnetotransmission and magnetoreflection of light in ferromagnetic are presented. • The effects are greater than common magnetooptical phenomena in the infrared. • The effects may have a different origin depending on a material or spectral range. • Possible applications of the magnetotransmission and magnetoreflection are discussed.

Hard magnetic properties and coercivity mechanism of melt-spun Misch Metal-Fe-B alloy

Energy Technology Data Exchange (ETDEWEB)

Quan, Ningtao; Luo, Yang, E-mail: eluoyang@foxmail.com; Yan, Wenlong; Yuan, Chao; Yu, Dunbo; Sun, Liang; Lu, Shuo; Li, Hongwei; Zhang, Hongbin

2017-09-01

Highlights: • Melt-spun MM{sub 13}Fe{sub 81}B{sub 6} alloy shows that the distributions of the La, Ce, Pr, Nd, Fe and B elements is uniformly distributed, and the grain size is in the range of 30–40 nm, it can be seen that Pr-rich and La-rich phases concentrated on grain boundaries, which resulted in the coercivity augment with the increase of MMFe{sub 2} content, and the grain size is around 40–50 nm in MM{sub 16}Fe{sub 78}B{sub 6}. • There is a significant formation of MMFe{sub 2} with abundant Pr and La, and a small amount of Ce and Nd enriched at the interfacial region in MM{sub 16}Fe{sub 78}B{sub 6}, thus an inhomogeneous region was formed. It is considered that the inhomogeneous region is effective in increasing the coercivity. • The optimum-quenched MM{sub 13}Fe{sub 81}B{sub 6} alloy have been shown to exhibit a coercive force of 6.9 kOe and an energy product of 8.5 MGOe, which is superior to anisotropic ferrite magnets of 4.5 MGOe. - Abstract: Magnetic and structural properties of Misch Metal (MM)-Fe-B alloys, were examined in the melt-spun ribbons. Melt-spun MM-Fe-B samples were prepared at the surface velocities of 18–30 m/s. Crystalline structure and their room-temperature magnetization characteristics were analyzed, and the optimum surface velocity of 20 m/s and nominal composition of MM{sub 13}Fe{sub 81}B{sub 6} were obtained. Microstructural analyses indicate that the grain size is approximately 30–50 nm in the alloys with the optimum characteristics. In the MM{sub 16}Fe{sub 78}B{sub 6} alloys, Pr-rich and La-rich phases concentrated on grain boundaries, which resulted in the coercivity augment with the increase of MMFe{sub 2} content. Dependence of coercivity on applied magnetic field suggested that the mechanism of coercivity in moderate MM-content samples was inhomogeneous domain wall pinning type. The melt-spun ribbons in the optimum condition exhibit a coercive force of 6.9 kOe and an energy product of 8.5 MGOe, which can be used as

Relationships Between Shame, Restrictiveness, Authoritativeness, and Coercive Control in Men Mandated to a Domestic Violence Offenders Program.

Science.gov (United States)

Kaplenko, Hannah; Loveland, Jennifer E; Raghavan, Chitra

2018-04-01

Coercive control, a key element of intimate partner violence (IPV), is defined as an abuse dynamic that intends to strip the target of autonomy and liberty. While coercive control is gaining popularity in the research world, little is known about its correlates and causes. This study sought to examine how shame and men's need for dominance, measured by two trait indexes of dominance, restrictiveness and the need for authority, influence coercive control. The present study used a diverse sample of men (n = 134) who were mandated to attend a domestic violence offenders program. Findings suggest that shame plays a role in the commission of coercively controlling behavior both directly and partially through its influence on authority but not through restrictiveness. Implications for understanding IPV in a domestic violence offenders program are discussed.

The Physics of Ferromagnetism

CERN Document Server

Miyazaki, Terunobu

2012-01-01

This book covers both basic physics of ferromagnetism such as magnetic moment, exchange coupling, magnetic anisotropy and recent progress in advanced ferromagnetic materials. Special interests are focused on NdFeB permanent magnets and the materials studied in the field of spintronics. In the latter, development of tunnel magnetoresistance effect through so called giant magnetoresistance effect is explained.

Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

Directory of Open Access Journals (Sweden)

Stefan Kolenda

2016-11-01

Full Text Available Background: Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron–hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime.Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction.Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators.

Higher Education Policy in Australia: Corporate or Coercive Federalism?

Science.gov (United States)

Smart, Don

1991-01-01

Although the Hawke government's general strategy of corporate federalism may dominate educational policy in Australia, higher education (excluding teacher education) is an exception. Because the Commonwealth assumed full financial responsibility for higher education, it has increasingly employed coercive federalism or simply ignored the states.…

Empowerment, Coercive Persuasion and Organizational Learning: Do They Connect?

Science.gov (United States)

Schein, Edgar H.

1999-01-01

Individual learning in organizations can be de facto coercive persuasion when organizational learning and culture change require that learners develop appropriate attitudes and thinking. If the goal of organizational learning--innovative organizations--is accepted, moral choices that restrict individual freedom must be made. (SK)

One step facile synthesis of ferromagnetic magnetite nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Suppiah, Durga Devi; Abd Hamid, Sharifah Bee, E-mail: sharifahbee@um.edu.my

2016-09-15

The ferromagnetic properties of magnetite (Fe{sub 3}O{sub 4}) were influenced by the nanoparticle size, hence importance were given to the synthesis method. This paper clearly shows that magnetite nanoparticles were successfully synthesized by employing one step controlled precipitation method using a single salt (Iron(II) sulfate) iron precursor. The acquired titration curve from this method provides vital information on the possible reaction mechanism leading to the magnetite (Fe{sub 3}O{sub 4}) nanoparticles formation. Goethite (α-FeOOH) was obtained at pH 4, while the continuous addition of hydroxyl ions (OH{sup −}) forms iron hydroxides (Fe(OH){sub 2}). This subsequently reacts with the goethite, producing magnetite (Fe{sub 3}O{sub 4}) at pH 10. Spectroscopy studies validate the magnetite phase existence while structural and morphology analysis illustrates cubic shaped magnetite with an average size of 35 nm was obtained. The synthesized magnetite might be superparamagnetic though lower saturation magnetization (67.5 emu/g) measured at room temperature as compared to bulk magnetite. However the nanoparticles surface anisotropy leads to higher remanence (12 emu/g) and coercivity (117.7 G) making the synthesized magnetite an excellent candidate to be utilized in recording devices. The understanding of the magnetite synthesis mechanism can not only be used to achieve even smaller magnetite nanoparticles but also to prepare different types of iron oxides hydroxides using different iron precursor source. - Highlights: • Magnetite strong magnetism properties make it versatile in various applications including biomedical and electromagnetic materials. • Sulfate (SO{sub 4}{sup 2−}) anion plays a major role in the structure control of iron oxide during synthesis. • Phase pure magnetite nanoparticles with high magnetism properties can be obtained using a single salt (SO{sub 4}{sup 2−}) method.

Computational nano-materials design for high-TC ferromagnetism in wide-gap magnetic semiconductors

International Nuclear Information System (INIS)

Katayama-Yoshida, H.; Sato, K.; Fukushima, T.; Toyoda, M.; Kizaki, H.; Dinh, V.A.; Dederichs, P.H.

2007-01-01

We propose materials design of high-T C wide band-gap dilute magnetic semiconductors (DMSs) based on first-principles calculations by using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method. First, we discuss a unified physical picture of ferromagnetism in II-VI and III-V DMSs and show that DMS family is categorized into two groups depending on the electronic structure. One is the system where Zener's double exchange mechanism dominates in the ferromagnetic interaction, and in the other systems Zener's p-d exchange mechanism dominates. Next, we develop an accurate method for T C calculation for the DMSs and show that the mean field approximation completely fails to predict Curie temperature of DMS in particular for wide-gap DMS where the exchange interaction is short-ranged. The calculated T C of homogeneous DMSs by using the present method agrees very well with available experimental values. For more realistic material design, we simulate spinodal nano-decomposition by applying the Monte Carlo method to the Ising model with ab initio chemical pair interactions between magnetic impurities in DMS. It is found that by controlling the dimensionality of the decomposition various characteristic phases occur in DMS such as 3D Dairiseki-phase and 1D Konbu-phase, and it is suggested that super-paramagnetic blocking phenomena should be important to understand the magnetism of wide-gap DMS. Based on the present simulations for spinodal nano-decomposition, we propose a new crystal growth method of positioning by seeding and shape controlling method in 100 Tera-bit density of nano-magnets in the semiconductor matrix with high-T C (or high-T B )

Optimization of a superconducting linear levitation system using a soft ferromagnet

Science.gov (United States)

Agramunt-Puig, Sebastia; Del-Valle, Nuria; Navau, Carles; Sanchez, Alvaro

2013-04-01

The use of guideways that combine permanent magnets and soft ferromagnetic materials is a common practice in magnetic levitation transport systems (maglevs) with bulk high-temperature superconductors. Theoretical tools to simulate in a realistic way both the behavior of all elements (permanent magnets, soft ferromagnet and superconductor) and their mutual effects are helpful to optimize the designs of real systems. Here we present a systematic study of the levitation of a maglev with translational symmetry consisting of a superconducting bar and a guideway with two identic permanent magnets and a soft ferromagnetic material between them. The system is simulated with a numerical model based on the energy minimization method that allows to analyze the mutual interaction of the superconductor, assumed to be in the critical state, and a soft ferromagnet with infinite susceptibility. Results indicate that introducing a soft ferromagnet within the permanent magnets not only increases the levitation force but also improves the stability. Besides, an estimation of the relative sizes and shapes of the soft ferromagnet, permanent magnets and the superconductor in order to obtain large levitation force with full stability is provided.

Coercivity enhancements of Nd–Fe–B sintered magnets by diffusing DyHx along different axes

International Nuclear Information System (INIS)

Ma, Tianyu; Wang, Xuejiao; Liu, Xiaolian; Wu, Chen; Yan, Mi

2015-01-01

Diffusing heavy rare earth elements along the grain boundaries (GBs) for Nd 2 Fe 14 B-type sintered magnets serves as an effective method to enhance coercivity and to minimize remanence loss simultaneously. Considering the texture anisotropy of Nd-rich GB phases, the coercivity incremental difference by diffusing DyH x fine powders along or perpendicular to the  <0 0 1 >  easy axis (c-axis) has been investigated. The coercivity increases more rapidly to 20.61 kOe (5.76 kOe higher than that of the as-sintered state) when diffusing along the c-axis than that diffusing perpendicular to c-axis (18.85 kOe, 4.00 kOe higher than the as-sintered state). Microstructural investigation reveals that Dy diffuses more easily towards the magnet inner part when treating along the c-axis than that for the perpendicular case due to the anisotropic distribution of the Nd-rich phase. This is verified by a higher Dy content at equivalent diffusing depth and a much deeper final diffusion distance. The local Dy-containing fractions with a stronger anisotropy field are richer for the magnet treated along the c-axis, leading to the much rapider coercivity enhancement. This work reveals that diffusion heavy rare earth along the c-axis is more effective to enhance coercivity for aligned Nd–Fe–B sintered magnets. (paper)

How to obtain a magnetic hard-soft architecture by pulsed laser deposition

International Nuclear Information System (INIS)

Fix, T; Trassin, M; Hassan, R Sayed; Schmerber, G; Viart, N; Meny, C; Colis, S; Dinia, A

2007-01-01

In spin valve type systems, one ferromagnetic electrode must be magnetically hard to act as a reference layer while the other electrode must be magnetically soft to act as a sensor or storage layer. This magnetic hard-soft architecture can usually be obtained by four different methods: the use of two ferromagnets with different coercive fields (here CoFe 2 and Ni 80 Fe 20 ), the use of an underlayer enhancing the coercive field of one of the two ferromagnets (here Ta and Ru), the use of a ferromagnet coupled to a ferrimagnet or antiferromagnet (here NiO/CoFe 2 and CoFe 2 O 4 /CoFe 2 ), or the use of an artificial antiferromagnet (here CoFe 2 /Ru/CoFe 2 ). We show that at least the first and the third methods seem to work with pulsed laser deposition in the thermodynamic conditions used

Room-temperature ferromagnetism in cerium dioxide powders

Energy Technology Data Exchange (ETDEWEB)

Rakhmatullin, R. M., E-mail: rrakhmat@kpfu.ru; Pavlov, V. V.; Semashko, V. V.; Korableva, S. L. [Kazan Federal University, Institute of Physics (Russian Federation)

2015-08-15

Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

Optimization of a superconducting linear levitation system using a soft ferromagnet

International Nuclear Information System (INIS)

Agramunt-Puig, Sebastia; Del-Valle, Nuria; Navau, Carles; Sanchez, Alvaro

2013-01-01

Highlights: ► Study of the levitation of a superconducting bar over different magnetic guideways. ► A soft ferromagnet within permanent magnets improves levitation stability. ► We study the best geometry for large levitation force with full stability. -- Abstract: The use of guideways that combine permanent magnets and soft ferromagnetic materials is a common practice in magnetic levitation transport systems (maglevs) with bulk high-temperature superconductors. Theoretical tools to simulate in a realistic way both the behavior of all elements (permanent magnets, soft ferromagnet and superconductor) and their mutual effects are helpful to optimize the designs of real systems. Here we present a systematic study of the levitation of a maglev with translational symmetry consisting of a superconducting bar and a guideway with two identic permanent magnets and a soft ferromagnetic material between them. The system is simulated with a numerical model based on the energy minimization method that allows to analyze the mutual interaction of the superconductor, assumed to be in the critical state, and a soft ferromagnet with infinite susceptibility. Results indicate that introducing a soft ferromagnet within the permanent magnets not only increases the levitation force but also improves the stability. Besides, an estimation of the relative sizes and shapes of the soft ferromagnet, permanent magnets and the superconductor in order to obtain large levitation force with full stability is provided

Optimization of a superconducting linear levitation system using a soft ferromagnet

Energy Technology Data Exchange (ETDEWEB)

Agramunt-Puig, Sebastia; Del-Valle, Nuria; Navau, Carles, E-mail: carles.navau@uab.cat; Sanchez, Alvaro

2013-04-15

Highlights: ► Study of the levitation of a superconducting bar over different magnetic guideways. ► A soft ferromagnet within permanent magnets improves levitation stability. ► We study the best geometry for large levitation force with full stability. -- Abstract: The use of guideways that combine permanent magnets and soft ferromagnetic materials is a common practice in magnetic levitation transport systems (maglevs) with bulk high-temperature superconductors. Theoretical tools to simulate in a realistic way both the behavior of all elements (permanent magnets, soft ferromagnet and superconductor) and their mutual effects are helpful to optimize the designs of real systems. Here we present a systematic study of the levitation of a maglev with translational symmetry consisting of a superconducting bar and a guideway with two identic permanent magnets and a soft ferromagnetic material between them. The system is simulated with a numerical model based on the energy minimization method that allows to analyze the mutual interaction of the superconductor, assumed to be in the critical state, and a soft ferromagnet with infinite susceptibility. Results indicate that introducing a soft ferromagnet within the permanent magnets not only increases the levitation force but also improves the stability. Besides, an estimation of the relative sizes and shapes of the soft ferromagnet, permanent magnets and the superconductor in order to obtain large levitation force with full stability is provided.

Room Temperature Ferromagnetic Mn:Ge(001

Directory of Open Access Journals (Sweden)

George Adrian Lungu

2013-12-01

Full Text Available We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001, heated at relatively high temperature (starting with 250 °C. The samples were characterized by low energy electron diffraction (LEED, scanning tunneling microscopy (STM, high resolution transmission electron microscopy (HRTEM, X-ray photoelectron spectroscopy (XPS, superconducting quantum interference device (SQUID, and magneto-optical Kerr effect (MOKE. Samples deposited at relatively elevated temperature (350 °C exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001 crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001. The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

Enhanced coercivity in {alpha}-(Fe,Co)/(Nd,Pr){sub 2}Fe{sub 14}B nanocomposite magnets via interfacial modification

Energy Technology Data Exchange (ETDEWEB)

Li Wei; Li Lanlan; Li Xiaohong; Sun Hongyu; Zhang Xiangyi [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, 066004 Qinhuangdao (China)], E-mail: xyzh66@ysu.edu.cn

2008-08-07

We have prepared {alpha}-(Fe,Co)/(Nd,Pr){sub 2}Fe{sub 14}B nanocomposite magnets having a high coercivity H{sub c} = 7.5 kOe and a large energy product (BH){sub max} = 22.7 MGOe by interfacial modification using an intergranular amorphous phase, as compared with the corresponding values obtained without the intergranular phase, H{sub c} = 5.5 kOe and (BH){sub max} = 16.1 MGOe. The enhanced coercivity is attributed to the increase in the nucleation field for magnetization reversal due to interfacial modification. This demonstrates a counter-intuitive approach for enhancing the magnetic properties of nanocomposite magnets.

Josephson tunnel junctions with ferromagnetic interlayer

International Nuclear Information System (INIS)

Weides, M.P.

2006-01-01

Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al 2 O 3 tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or π coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, π) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-π Josephson junction. At a certain temperature this 0-π junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum Φ 0 . Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T → 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

Josephson tunnel junctions with ferromagnetic interlayer

Energy Technology Data Exchange (ETDEWEB)

Weides, M.P.

2006-07-01

Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

International Nuclear Information System (INIS)

Štrbík, V.; Beňačka, Š.; Gaži, Š.; Španková, M.; Šmatko, V.; Knoška, J.; Gál, N.; Chromik, Š.; Sojková, M.; Pisarčík, M.

2017-01-01

Highlights: • Superconductor-ferromagnet-superconductor nanojunction. • Nanojunctions prepared by Ga"3"+ focused ion beam patterning. • Indication of triplet Cooper pair component in junction superconducting current. • Qualitative agreement with theoretical model. - Abstract: The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa_2Cu_3O_x (YBCO) and half-metallic ferromagnet La_0_._6_7Sr_0_._3_3MnO_3 (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga"3"+ focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40 nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO_2.

Ferromagnetic pairing states on two-coupled chains

International Nuclear Information System (INIS)

Tanaka, Akinori

2008-01-01

We propose a concrete model which exhibits ferromagnetism and electron-pair condensation simultaneously. The model is defined on two chains and consists of the electron hopping term, the on-site Coulomb repulsion and a ferromagnetic interaction which describes ferromagnetic coupling between two electrons, one on a bond in a chain and the other on a site in the other chain. It is rigorously shown that the model has fully-polarized ferromagnetic pairing ground states. The higher dimensional version of the model is also presented

Electric-field assisted switching of magnetization in perpendicularly magnetized (Ga,Mn)As films at high temperatures

Science.gov (United States)

Wang, Hailong; Ma, Jialin; Yu, Xueze; Yu, Zhifeng; Zhao, Jianhua

2017-01-01

The electric-field effects on the magnetism in perpendicularly magnetized (Ga,Mn)As films at high temperatures have been investigated. An electric-field as high as 0.6 V nm-1 is applied by utilizing a solid-state dielectric Al2O3 film as a gate insulator. The coercive field, saturation magnetization and magnetic anisotropy have been clearly changed by the gate electric-field, which are detected via the anomalous Hall effect. In terms of the Curie temperature, a variation of about 3 K is observed as determined by the temperature derivative of the sheet resistance. In addition, electrical switching of the magnetization assisted by a fixed external magnetic field at 120 K is demonstrated, employing the gate-controlled coercive field. The above experimental results have been attributed to the gate voltage modulation of the hole density in (Ga,Mn)As films, since the ferromagnetism in (Ga,Mn)As is carrier-mediated. The limited modulation magnitude of magnetism is found to result from the strong charge screening effect introduced by the high hole concentration up to 1.10  ×  1021 cm-3, while the variation of the hole density is only about 1.16  ×  1020 cm-3.

Interaction of ultra soft magnetic materials with the high-T{sub c} superconductor YBCO

Energy Technology Data Exchange (ETDEWEB)

Stahl, Claudia; Treiber, Sebastian; Schuetz, Gisela [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Walker, Patrick [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany); Albrecht, Joachim [Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany)

2013-07-01

We have grown bilayers of optimally doped YBa{sub 2}Cu{sub 3}O{sub 7-δ} (YBCO) and ferromagnetic CoFeB on single-crystalline substrates by pulsed laser deposition and sputtering. These heterostructures are typically composed of about 100 nm YBCO and several 10 nm of CoFeB. Regarding the superconductor, the properties of the YBCO film change as a consequence of the vicinity of the ferromagnet. In detail we investigated the critical current density as a function of temperature, applied field and time as well as the transition temperature by SQUID magnetization measurements and quantitative magneto-optical measurements. The amorphous material CoFeB exhibits an in plane anisotropy and a very low coercivity. From magneto-optical images we find that the flux line lattice of the superconductor is mapped into the magnet and still visible as significant magnetic out-of-plane contrast at room temperature. We discuss this phenomenon as a new route to high-resolution mapping of the flux line distribution on a nanometer scale.

Unexpected large room-temperature ferromagnetism in porous Cu{sub 2}O thin films

Energy Technology Data Exchange (ETDEWEB)

Hou, Xue [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Sun, Huiyuan, E-mail: huiyuansun@126.com [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Liu, Lihu; Jia, Xiaoxuan; Liu, Huiyuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China)

2015-05-15

Porous Cu{sub 2}O films have been fabricated on porous anodic alumina substrates using DC-reactive magnetron sputtering with pure Cu targets, and unexpectedly large room temperature ferromagnetism has been observed in the films. The maximum saturation magnetic moment along the out-of-plane direction was as high as 94 emu/cm{sup 3}. Photoluminescence spectra show that the ferromagnetism originates with oxygen vacancies. The ferromagnetism could be adjusted by changing the concentration of oxygen vacancies through annealing in an oxygen atmosphere. These observations suggest that the origin of the ferromagnetism is due to coupling between oxygen vacancies with local magnetic moments in the porous Cu{sub 2}O films, which can occur either directly through exchange interactions between oxygen vacancies, or through the mediation of conduction electrons. Such a ferromagnet without the presence of any ferromagnetic dopant may find applications in spintronic devices. - Highlights: • Porous Cu{sub 2}O films were deposited on porous anodic alumina (PAA) substrates. • Significant room-temperature ferromagnetism has been observed in porous Cu{sub 2}O films. • Ferromagnetism of Cu{sub 2}O films exhibited different magnetic signals with the field. • The saturation magnetization is 94 emu/cm{sup 3} with an out-of-plane.

Formation of quadrupolar phase in non-Heisenberg ferromagnets with half-integer spin

International Nuclear Information System (INIS)

Fridman, Yu.A.; Kosmachev, O.A.; Spirin, D.V.

2005-01-01

Possibility of realization of quadrupolar phase in non-Heisenberg ferromagnet with magnetic ion spin 32 is studied. It is shown that such phase state exists only in ferromagnets with high value of biquadratic exchange when external magnetic field is not applied. Phase diagram of the system is built

Efficiency of homopolar generators without ferromagnetic circuit

International Nuclear Information System (INIS)

Kharitonov, V.V.

1982-01-01

E.m.f. and weights of homopolar generators (HG) without a ferromagnetic circuit and of similar generator with a ferromagnetic circuit are compared at equal armature diameters and armature rotative speed. HG without ferromagnetic cuircuit of disk and cylinder types with hot and superconducting excitation winding are considered. Areas of the most reasonable removal of a ferromagnetic circuit in the HG layout are found. The plots of relationships between the e.m.f. and HG weight that permit to estimate the efficiency of ''nonferrite'' HG constructions are presented

Coercivities of hot-deformed magnets processed from amorphous and nanocrystalline precursors

International Nuclear Information System (INIS)

Tang, Xin; Sepehri-Amin, H.; Ohkubo, T.; Hioki, K.; Hattori, A.; Hono, K.

2017-01-01

Hot-deformed magnets have been processed from amorphous and nanocrystalline precursors and their hard magnetic properties and microstructures have been investigated in order to explore the optimum process route. The hot-deformed magnets processed from an amorphous precursor exhibited the coercivity of 1.40 T that is higher than that processed from nanocrystalline powder, ∼1.28 T. The average grain size was larger in the magnets processed from amorphous precursor. Detailed microstructure analyses by aberration corrected scanning transmission electron microscopy revealed that the Nd + Pr concentrations in the intergranular phases were higher in the hot-deformed magnet processed from the amorphous precursor, which is considered to lead to the enhanced coercivity due to a stronger pinning force against magnetic domain wall motion.

Dimensionality Driven Enhancement of Ferromagnetic Superconductivity in URhGe

Science.gov (United States)

Braithwaite, Daniel; Aoki, Dai; Brison, Jean-Pascal; Flouquet, Jacques; Knebel, Georg; Nakamura, Ai; Pourret, Alexandre

2018-01-01

In most unconventional superconductors, like the high-Tc cuprates, iron pnictides, or heavy-fermion systems, superconductivity emerges in the proximity of an electronic instability. Identifying unambiguously the pairing mechanism remains nevertheless an enormous challenge. Among these systems, the orthorhombic uranium ferromagnetic superconductors have a unique position, notably because magnetic fields couple directly to ferromagnetic order, leading to the fascinating discovery of the reemergence of superconductivity in URhGe at a high field. Here we show that uniaxial stress is a remarkable tool allowing the fine-tuning of the pairing strength. With a relatively small stress, the superconducting phase diagram is spectacularly modified, with a merging of the low- and high-field superconducting states and a significant enhancement of the superconductivity. The superconducting critical temperature increases both at zero field and under a field, reaching 1 K, more than twice higher than at ambient pressure. This enhancement of superconductivity is shown to be directly related to a change of the magnetic dimensionality detected from an increase of the transverse magnetic susceptibility: In addition to the Ising-type longitudinal ferromagnetic fluctuations, transverse magnetic fluctuations also play an important role in the superconducting pairing.

Dynamic detection of spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance (Conference Presentation)

Science.gov (United States)

Crowell, Paul A.; Liu, Changjiang; Patel, Sahil; Peterson, Tim; Geppert, Chad C.; Christie, Kevin; Stecklein, Gordon; Palmstrøm, Chris J.

2016-10-01

A distinguishing feature of spin accumulation in ferromagnet-semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this new approach enables a measurement of short spin lifetimes (C. Liu, S. J. Patel, T. A. Peterson, C. C. Geppert, K. D. Christie, C. J. Palmstrøm, and P. A. Crowell, "Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance," Nature Communications 7, 10296 (2016). http://dx.doi.org/10.1038/ncomms10296

Investigation of cellular microstructure and enhanced coercivity in sputtered Sm2(CoCuFeZr)17 film

International Nuclear Information System (INIS)

Bhatt, Ranu; Schütz, G.; Bhatt, Pramod

2014-01-01

We have investigated the effect of annealing temperature on the microstructure and magnetic properties of Sm 2 (CoCuFeZr) 17 films prepared using ion beam sputtering at room temperature. The as-deposited film shows randomly oriented polycrystalline grains and exhibits small coercivity (H C ) of 0.04 T at room temperature. Post annealing of these films at 700 °C under Ar atmosphere shows significant changes in the microstructure transforming it to the development of cellular growth, concomitant with enhanced coercivity up to 1.3 T. The enhanced coercivity is explained using the domain wall pinning mechanism

Electrical and magnetic behavior of iron doped nickel titanate (Fe{sup 3+}/NiTiO{sub 3}) magnetic nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Lenin, Nayagam; Karthik, Arumugam; Sridharpanday, Mathu; Selvam, Mohanraj; Srither, Saturappan Ravisekaran; Arunmetha, Sundarmoorthy; Paramasivam, Palanisamy; Rajendran, Venkatachalam, E-mail: veerajendran@gmail.com

2016-01-01

Iron doped nickel titanate (Fe{sup 3+}/NiTiO{sub 3}) ferromagnetic nanoparticles with different concentrations of Fe (0.2, 0.4, and 0.6 mol) were synthesized using precipitation route with precursor source such as nickel nitrate and iron nitrate solutions. The prepared magnetic nanopowders were investigated through X-ray diffraction (XRD), Fourier transform infrared, scanning electron microscope, X-ray fluorescence, Brunauer–Emmett–Teller, vibrating sample magnetometer, and electrochemical impedance spectroscopy to explore the structural, ferromagnetic, and dielectric properties. The obtained XRD pattern shows formation of iron doped nickel titanate in orthorhombic structure. The crystallite size ranges from 57 to 21 nm and specific surface area ranges from 11 to 137 m{sup 2} g{sup −1}. The hysteresis loops of nanomagnetic materials show ferromagnetic behavior with higher magnitude of coercivity (H{sub c}) 867–462 Oe. The impedance analysis of ferromagnetic materials explores the ferro-dielectric behavior with enhanced properties of Fe{sup 3+}/NiTiO{sub 3} nanoparticles at higher Fe content. - Highlights: • Iron doped nickel titanate magnetic nanoparticles. • Ferromagnetic magnetism behavior with higher magnitude of coercivity. • Dielectric behavior of ferromagnetic nanoparticles with increase of Fe content.

Magnetic damping phenomena in ferromagnetic thin-films and multilayers

Science.gov (United States)

Azzawi, S.; Hindmarch, A. T.; Atkinson, D.

2017-11-01

Damped ferromagnetic precession is an important mechanism underpinning the magnetisation processes in ferromagnetic materials. In thin-film ferromagnets and ferromagnetic/non-magnetic multilayers, the role of precession and damping can be critical for spintronic device functionality and as a consequence there has been significant research activity. This paper presents a review of damping in ferromagnetic thin-films and multilayers and collates the results of many experimental studies to present a coherent synthesis of the field. The terms that are used to define damping are discussed with the aim of providing consistent definitions for damping phenomena. A description of the theoretical basis of damping is presented from early developments to the latest discussions of damping in ferromagnetic thin-films and multilayers. An overview of the time and frequency domain methods used to study precessional magnetisation behaviour and damping in thin-films and multilayers is also presented. Finally, a review of the experimental observations of magnetic damping in ferromagnetic thin-films and multilayers is presented with the most recent explanations. This brings together the results from many studies and includes the effects of ferromagnetic film thickness, the effects of composition on damping in thin-film ferromagnetic alloys, the influence of non-magnetic dopants in ferromagnetic films and the effects of combining thin-film ferromagnets with various non-magnetic layers in multilayered configurations.

Perfect GMR effect in gapped graphene-based ferromagnetic normal ferromagnetic junctions

Institute of Scientific and Technical Information of China (English)

Hossein Karbaschi; Gholam Reza Rashedi

2015-01-01

We investigate the quantum transport property in gapped graphene-based ferromagnetic/normal/ferromagnetic (FG/NG/FG) junctions by using the Dirac–Bogoliubov–de Gennes equation. The graphene is fabricated on SiC and BN substrates separately, so carriers in FG/NG/FG structures are considered as massive relativistic particles. Transmission prob-ability, charge, and spin conductances are studied as a function of exchange energy of ferromagnets (h), size of graphene gap, and thickness of normal graphene region (L) respectively. Using the experimental values of Fermi energy in the normal graphene part (EFN∼400 meV) and energy gap in graphene (260 meV for SiC and 50 meV for BN substrate), it is shown that this structure can be used for both spin-up and spin-down polarized current. The latter case has different behavior of gapped FG/NG/FG from that of gapless FG/NG/FG structures. Also perfect charge giant magnetoresistance is observed in a range of EFN−mv2F

Nonlinear nano-scale localized breather modes in a discrete weak ferromagnetic spin lattice

International Nuclear Information System (INIS)

Kavitha, L.; Parasuraman, E.; Gopi, D.; Prabhu, A.; Vicencio, Rodrigo A.

2016-01-01

We investigate the propagation dynamics of highly localized discrete breather modes in a weak ferromagnetic spin lattice with on-site easy axis anisotropy due to crystal field effect. We derive the discrete nonlinear equation of motion by employing boson mappings and p-representation. We explore the onset of modulational instability both analytically in the framework of linear stability analysis and numerically by means of molecular dynamics (MD) simulations, and a perfect agreement was demonstrated. It is also explored that how the antisymmetric nature of the canted ferromagnetic lattice supports highly localized discrete breather (DBs) modes as shown in the stability/instability windows. The energy exchange between low amplitude discrete breathers favours the growth of higher amplitude DBs, resulting eventually in the formation of few long-lived high amplitude DBs. - Highlights: • The effects of DM and anisotropy interaction on the DB modes are studied. • The antisymmetric nature of the canted ferromagnetic medium supports the DB modes. • Dynamics of ferromagnetic chain is governed by boson mappings and p-representation.

(Ga,Fe)Sb: A p-type ferromagnetic semiconductor

Energy Technology Data Exchange (ETDEWEB)

Tu, Nguyen Thanh; Anh, Le Duc; Tanaka, Masaaki [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Hai, Pham Nam [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-0033 (Japan)

2014-09-29

A p-type ferromagnetic semiconductor (Ga{sub 1−x},Fe{sub x})Sb (x = 3.9%–13.7%) has been grown by low-temperature molecular beam epitaxy (MBE) on GaAs(001) substrates. Reflection high energy electron diffraction patterns during the MBE growth and X-ray diffraction spectra indicate that (Ga,Fe)Sb layers have the zinc-blende crystal structure without any other crystallographic phase of precipitates. Magnetic circular dichroism (MCD) spectroscopy characterizations indicate that (Ga,Fe)Sb has the zinc-blende band structure with spin-splitting induced by s,p-d exchange interactions. The magnetic field dependence of the MCD intensity and anomalous Hall resistance of (Ga,Fe)Sb show clear hysteresis, demonstrating the presence of ferromagnetic order. The Curie temperature (T{sub C}) increases with increasing x and reaches 140 K at x = 13.7%. The crystal structure analyses, magneto-transport, and magneto-optical properties indicate that (Ga,Fe)Sb is an intrinsic ferromagnetic semiconductor.

Non-ferromagnetic overburden casing

Science.gov (United States)

Vinegar, Harold J.; Harris, Christopher Kelvin; Mason, Stanley Leroy

2010-09-14

Systems, methods, and heaters for treating a subsurface formation are described herein. At least one system for electrically insulating an overburden portion of a heater wellbore is described. The system may include a heater wellbore located in a subsurface formation and an electrically insulating casing located in the overburden portion of the heater wellbore. The casing may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the casing.

Anion vacancy-mediated ferromagnetism in atomic-thick Ni3N nanosheets

Science.gov (United States)

Xia, Baorui; Wang, Tongtong; Chi, Xiao; Yu, Xiaojiang; Liu, Peitao; Zhang, Jingyan; Xi, Shibo; Du, Yonghua; Gao, Daqiang

2017-12-01

Realizing spin and electronic behavior of two-dimensional ultrathin nanosheets is significant to construct next generation nanoelectronics. Here, atomic-thick Ni3N nanosheets with clear room temperature ferromagnetism and high saturation magnetization (1.2 emu/g) are reported. X-ray magnetic circular dichroism and first-principles calculation results give the evidence that the observed intrinsic ferromagnetism in Ni3N nanosheets originates from the surface N-deficiency, where alignments of localized large magnetic moments of Ni in the vicinity of the N defect can be aligned parallel to activate macroscopic ferromagnetism. These ultrathin Ni3N nanosheets show great potential application in next-generation electron devices.

Competing ferromagnetic and anti-ferromagnetic interactions in iron nitride ζ-Fe2N

Science.gov (United States)

Rao, K. Sandeep; Salunke, H. G.

2018-03-01

The paper discusses the magnetic state of zeta phase of iron nitride viz. ζ-Fe2N on the basis of spin polarized first principles electronic structure calculations together with a review of already published data. Results of our first principles study suggest that the ground state of ζ-Fe2N is ferromagnetic (FM) with a magnetic moment of 1.528μB on the Fe site. The FM ground state is lower than the anti-ferromagnetic (AFM) state by 8.44 meV and non-magnetic (NM) state by 191 meV per formula unit. These results are important in view of reports which claim that ζ-Fe2N undergoes an AFM transition below 10 K and others which do not observe any magnetic transition up to 4.2 K. We argue that the experimental results of AFM transition below 10 K are inconclusive and we propose the presence of competing FM and AFM superexchange interactions between Fe sites mediated by nitrogen atoms, which are consistent with Goodenough-Kanamori-Anderson rules. We find that the anti-ferromagnetically coupled Fe sites are outnumbered by ferromagnetically coupled Fe sites leading to a stable FM ground state. A Stoner analysis of the results also supports our claim of a FM ground state.

Peculiar long-range supercurrent in superconductor-ferromagnet-superconductor junction containing a noncollinear magnetic domain in the ferromagnetic region

Energy Technology Data Exchange (ETDEWEB)

Meng, Hao, E-mail: menghao1982@shu.edu.cn [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China); National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Wu, Xiuqiang [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Ren, Yajie [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China)

2015-01-14

We study the supercurrent in clean superconductor-ferromagnet-superconductor heterostructure containing a noncollinear magnetic domain in the ferromagnetic region. It is demonstrated that the magnetic domain can lead to a spin-flip scattering process, which reverses the spin orientations of the singlet Cooper pair and simultaneously changes the sign of the corresponding electronic momentum. If the ferromagnetic layers on both sides of magnetic domain have the same features, the long-range proximity effect will take place. That is because the singlet Cooper pair will create an exact phase-cancellation effect and gets an additional π phase shift as it passes through the entire ferromagnetic region. Then, the equal spin triplet pair only exists in the magnetic domain region and can not diffuse into the other two ferromagnetic layers. So, the supercurrent mostly arises from the singlet Cooper pairs, and the equal spin triplet pairs are not involved. This result can provide a approach for generating the long-range supercurrent.

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

Energy Technology Data Exchange (ETDEWEB)

Štrbík, V., E-mail: vladimir.strbik@savba.sk [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia); Beňačka, Š.; Gaži, Š.; Španková, M.; Šmatko, V. [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia); Knoška, J. [Center for Free-Electron Laser Science, DESY, Notkestraße 85, 22607, Hamburg (Germany); Department of Physics, University of Hamburg, Luruper Chaussee 149, 22607, Hamburg (Germany); Gál, N.; Chromik, Š.; Sojková, M.; Pisarčík, M. [Institute of Electrical Engineering, SAS, Dúbravská Cesta 9, Bratislava (Slovakia)

2017-02-15

Highlights: • Superconductor-ferromagnet-superconductor nanojunction. • Nanojunctions prepared by Ga{sup 3+} focused ion beam patterning. • Indication of triplet Cooper pair component in junction superconducting current. • Qualitative agreement with theoretical model. - Abstract: The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa{sub 2}Cu{sub 3}O{sub x} (YBCO) and half-metallic ferromagnet La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga{sup 3+} focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40 nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO{sub 2}.

Lattice effects on ferromagnetism in perovskite ruthenates

Science.gov (United States)

Cheng, J.-G.; Zhou, J.-S.; Goodenough, John B.

2013-01-01

Ferromagnetism and its evolution in the orthorhombic perovskite system Sr1–xCaxRuO3 have been widely believed to correlate with structural distortion. The recent development of high-pressure synthesis of the Ba-substituted Sr1–yBayRuO3 makes it possible to study ferromagnetism over a broader phase diagram, which includes the orthorhombic Imma and the cubic phases. However, the chemical substitutions introduce the A-site disorder effect on Tc, which complicates determination of the relationship between ferromagnetism and structural distortion. By clarifying the site disorder effect on Tc in several unique series of ruthenates in which the average bond length 〈A–O〉 remains the same but the bond-length variance varies, we are able to demonstrate a parabolic curve of Tc versus mean bond length 〈A–O〉. A much higher Tc ∼ 177 K than that found in orthorhombic SrRuO3 can be obtained from the curve at a bond length 〈A–O〉, which makes the geometric factor t = 〈A–O〉/(√2〈Ru–O〉) ∼ 1. This result reveals not only that the ferromagnetism in the ruthenates is extremely sensitive to the lattice strain, but also that it has an important implication for exploring the structure–property relationship in a broad range of oxides with perovskite or a perovskite-related structure. PMID:23904477

Ferromagnets as pure spin current generators and detectors

Science.gov (United States)

Qu, Danru; Miao, Bingfeng; Chien, Chia -Ling; Huang, Ssu -Yen

2015-09-08

Provided is a spintronics device. The spintronics can include a ferromagnetic metal layer, a positive electrode disposed on a first surface portion of the ferromagnetic metal layer, and a negative electrode disposed on a second surface portion of the ferromagnetic metal.

Coercivity scaling in antidot lattices in Fe, Ni, and NiFe thin films

Energy Technology Data Exchange (ETDEWEB)

Gräfe, Joachim, E-mail: graefe@is.mpg.de; Schütz, Gisela; Goering, Eberhard J., E-mail: goering@is.mpg.de

2016-12-01

Antidot lattices can be used to artificially engineer magnetic properties in thin films, however, a conclusive model that describes the coercivity enhancement in this class of magnetic nano-structures has so far not been found. We prepared Fe, Ni, and NiFe thin films and patterned each with 21 square antidot lattices with different geometric parameters and measured their hysteretic behavior. On the basis of this extensive dataset we are able to provide a model that can describe both the coercivity scaling over a wide range of geometric lattice parameters and the influence of different materials.

High coercivity, anisotropic, heavy rare earth-free Nd-Fe-B by Flash Spark Plasma Sintering.

Science.gov (United States)

Castle, Elinor; Sheridan, Richard; Zhou, Wei; Grasso, Salvatore; Walton, Allan; Reece, Michael J

2017-09-11

In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive "die upset" processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free Nd 30.0 Fe 61.8 Co 5.8 Ga 0.6 Al 0.1 B 0.9 melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m -1 ) and matched remanence (1.16 T) giving a BH max of 230 kJ m -3 .

Ferromagnetism in poly(N-perfluorophenylpyrrole)

Energy Technology Data Exchange (ETDEWEB)

Čík, G., E-mail: gabriel.cik@stuba.sk [Department of Environmental Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava (Slovakia); Šeršeň, F. [Institute of Chemistry, Faculty of Natural Sciences, Comenius University, 842 15 Bratislava (Slovakia); Dlháň, L. [Department of Inorganic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava (Slovakia); Zálupský, P. [Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava (Slovakia); Rapta, P. [Department of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava (Slovakia); Hrnčariková, K. [Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, 812 37 Bratislava (Slovakia); Plecenik, T. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 842 48 Bratislava (Slovakia)

2015-10-01

Magnetic properties of the synthesized poly(N-perfluorophenylpyrrole) were studied. The synthesized polymer dissolves in common organic solvents. By the zero-field cooling-field cooling method (ZFC–FC) we found that at low temperatures (T{sub b}<50 K) the synthetic polymer reaches a state with prevailing ferromagnetism. The synthesized polymer retained ferromagnetism even at 300 K. The anomalous magnetic behavior was explained in terms of spin–spin interaction of triplet polarons. As can be seen from the calculated spin density of SOMO and SOMO 1 such a state arise as a consequence of 1-D spin interactions of polarons. Based on the calculated and visualized spin density (SOMO) on the polymer chain such interactions can be explained by the theory of flat-band-ferromagnetism. - Highlights: • We synthesized a new conducting polymer poly(N-perfluorophenylpyrrole). • By the ZFC–FC and EPR methods we measured magnetic properties of the prepared polymer. • We discussed stability and interactions of the polarons in triplet states. • At low temperatures the synthesized polymer reached ferromagnetism.

Topological magnon bands in ferromagnetic star lattice

International Nuclear Information System (INIS)

Owerre, S A

2017-01-01

The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1–3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii–Moriya (DM) spin–orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases. (paper)

Topological magnon bands in ferromagnetic star lattice.

Science.gov (United States)

Owerre, S A

2017-05-10

The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1-3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases.

Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

Energy Technology Data Exchange (ETDEWEB)

Remes, Zdenek [Institute of Physics ASCR v.v.i., Cukrovarnicka 10, 162 00 Prague 6 (Czech Republic); Sun, Shih-Jye, E-mail: sjs@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Varga, Marian [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Chou, Hsiung [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Hsu, Hua-Shu [Department of Applied Physics, National Pingtung University of Education, Pingtung 900, Taiwan (China); Kromka, Alexander [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Horak, Pavel [Nuclear Physics Institute, 250 68 Rez (Czech Republic)

2015-11-15

The nanocrystalline diamond films turn to be ferromagnetic after implanting various nitrogen doses on them. Through this research, we confirm that the room-temperature ferromagnetism of the implanted samples is derived from the measurements of magnetic circular dichroism (MCD) and superconducting quantum interference device (SQUID). Samples with larger crystalline grains as well as higher implanted doses present more robust ferromagnetic signals at room temperature. Raman spectra indicate that the small grain-sized samples are much more disordered than the large grain-sized ones. We propose that a slightly large saturated ferromagnetism could be observed at low temperature, because the increased localization effects have a significant impact on more disordered structure. - Highlights: • Nitrogen implanted nanocrystalline diamond films exhibit ferromagnetism at room temperature. • Nitrogen implants made a Raman deviation from the typical nanocrystalline diamond films. • The ferromagnetism induced from the structure distortion is dominant at low temperature.

Valley and spin resonant tunneling current in ferromagnetic/nonmagnetic/ferromagnetic silicene junction

Directory of Open Access Journals (Sweden)

Yaser Hajati

2016-02-01

Full Text Available We study the transport properties in a ferromagnetic/nonmagnetic/ferromagnetic (FNF silicene junction in which an electrostatic gate potential, U, is attached to the nonmagnetic region. We show that the electrostatic gate potential U is a useful probe to control the band structure, quasi-bound states in the nonmagnetic barrier as well as the transport properties of the FNF silicene junction. In particular, by introducing the electrostatic gate potential, both the spin and valley conductances of the junction show an oscillatory behavior. The amplitude and frequency of such oscillations can be controlled by U. As an important result, we found that by increasing U, the second characteristic of the Klein tunneling is satisfied as a result of the quasiparticles chirality which can penetrate through a potential barrier. Moreover, it is found that for special values of U, the junction shows a gap in the spin and valley-resolve conductance and the amplitude of this gap is only controlled by the on-site potential difference, Δz. Our findings of high controllability of the spin and valley transport in such a FNF silicene junction may improve the performance of nano-electronics and spintronics devices.

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

KAUST Repository

Aravindh, S. Assa

2014-12-19

In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn 48O48 nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of ≤2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high TC in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV) obtained with the O vacancy. Density of states shows that Fermi level overlaps with Gd f states with the introduction of O vacancy, indicating the possibility of s-f coupling. These results will assist in understanding experimental findings in Gd-doped ZnO nanowires.

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

KAUST Repository

Aravindh, S. Assa; Schwingenschlö gl, Udo; Roqan, Iman S.

2014-01-01

In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn 48O48 nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of ≤2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high TC in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV) obtained with the O vacancy. Density of states shows that Fermi level overlaps with Gd f states with the introduction of O vacancy, indicating the possibility of s-f coupling. These results will assist in understanding experimental findings in Gd-doped ZnO nanowires.

Levitation properties of maglev systems using soft ferromagnets

Science.gov (United States)

Huang, Chen-Guang; Zhou, You-He

2015-03-01

Soft ferromagnets are widely used as flux-concentration materials in the design of guideways for superconducting magnetic levitation transport systems. In order to fully understand the influence of soft ferromagnets on the levitation performance, in this work we apply a numerical model based on the functional minimization method and the Bean’s critical state model to study the levitation properties of an infinitely long superconductor immersed in the magnetic field created by a guideway of different sets of infinitely long parallel permanent magnets with soft ferromagnets between them. The levitation force, guidance force, magnetic stiffness and magnetic pole density are calculated considering the coupling between the superconductor and soft ferromagnets. The results show that the levitation performance is closely associated with the permanent magnet configuration and with the location and dimension of the soft ferromagnets. Introducing the soft ferromagnet with a certain width in a few configurations always decreases the levitation force. However, for most configurations, the soft ferromagnets contribute to improve the levitation performance only when they have particular locations and dimensions in which the optimized location and thickness exist to increase the levitation force the most. Moreover, if the superconductor is laterally disturbed, the presence of soft ferromagnets can effectively improve the lateral stability for small lateral displacement and reduce the degradation of levitation force.

Study of coercive measures in prisons and secure psychiatric hospitals: the views of inmates and caregivers

Directory of Open Access Journals (Sweden)

A. Runte-Geidel

2014-06-01

Full Text Available Aim: The aim of the study was to ascertain the opinions of both inmates and staff of prison establishments about the use of coercive measures justified for clinical reasons for people with mental health problems and about the need to create protocols to regulate the application of these measures. Method: These opinions were gathered in a Qualitative Study with Focus Groups (prison inmates and prison staff from the Granada Penitentiary Centre and the Alicante Penitentiary Psychiatric Hospital, both in Spain. Results: The results showed that forced medication is the most commonly used coercive measure in these institutions. The inmates did not understand and rejected the use of this measure, above all because they were poorly informed about their illness and the medication required to treat it. The staff however defended the benefits of psychiatric medicine, even when administered without the patient's consent. Conclusions: Both inmates and staff agreed that it would be useful to have a protocol regulating the use of coercive measures. The study has also identified a number of important factors that could help to reduce the need for coercive measures or make their use unnecessary.

Angular dependence of coercivity with temperature in Co-based nanowires

Energy Technology Data Exchange (ETDEWEB)

Bran, C., E-mail: cristina.bran@icmm.csic.es [Institute of Materials Science of Madrid, CSIC, 28049 Madrid (Spain); Espejo, A.P. [Departamento de Física, Universidad de Santiago de Chile (USACH) and Center for the Development of Nanoscience and Nanotechnology (CEDENNA), Avenida Ecuador 3493, 9170124 Santiago (Chile); Palmero, E.M. [Institute of Materials Science of Madrid, CSIC, 28049 Madrid (Spain); Escrig, J. [Departamento de Física, Universidad de Santiago de Chile (USACH) and Center for the Development of Nanoscience and Nanotechnology (CEDENNA), Avenida Ecuador 3493, 9170124 Santiago (Chile); Vázquez, M. [Institute of Materials Science of Madrid, CSIC, 28049 Madrid (Spain)

2015-12-15

The magnetic behavior of arrays of Co and CoFe nanowire arrays has been measured in the temperature range between 100 and 300 K. We have paid particular attention to the angular dependence of magnetic properties on the applied magnetic field orientation. The experimental angular dependence of coercivity has been modeled according to micromagnetic analytical calculations, and we found that the propagation of a transversal domain wall mode gives the best fitting with experimental observations. That reversal mode holds in the whole measuring temperature range, for nanowires with different diameters and crystalline structure. Moreover, the quantitative strength of the magnetocrystalline anisotropy and its magnetization easy axis are determined to depend on the crystalline structure and nanowires diameter. The evolution of the magnetocrystalline anisotropy with temperature for nanowires with different composition gives rise to an opposite evolution of coercivity with increasing temperature: it decreases for CoFe while it increases for Co nanowire arrays.

Defect controlled room temperature ferromagnetism in Co-doped barium titanate nanocrystals

International Nuclear Information System (INIS)

Ray, Sugata; Kolen'ko, Yury V; Watanabe, Tomoaki; Yoshimura, Masahiro; Itoh, Mitsuru; Kovnir, Kirill A; Lebedev, Oleg I; Turner, Stuart; Erni, Rolf; Tendeloo, Gustaaf Van; Chakraborty, Tanushree

2012-01-01

Defect mediated high temperature ferromagnetism in oxide nanocrystallites is the central feature of this work. Here, we report the development of room temperature ferromagnetism in nanosized Co-doped barium titanate particles with a size of around 14 nm, synthesized by a solvothermal drying method. A combination of x-ray diffraction with state-of-the-art electron microscopy techniques confirms the intrinsic doping of Co into BaTiO 3 . The development of the room temperature ferromagnetism was tracked down to the different donor defects, namely hydroxyl groups at the oxygen site and oxygen vacancies and their relative concentrations at the surface and the core of the nanocrystal, which could be controlled by post-synthesis drying and thermal treatments.

Prediction of Intrinsic Ferromagnetic Ferroelectricity in a Transition-Metal Halide Monolayer

Science.gov (United States)

Huang, Chengxi; Du, Yongping; Wu, Haiping; Xiang, Hongjun; Deng, Kaiming; Kan, Erjun

2018-04-01

The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr3 monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr - Br6 units. As an example, we further show that (CrBr3)2Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices.

Does the sole description of a tax authority affect tax evasion?--the impact of described coercive and legitimate power.

Science.gov (United States)

Hartl, Barbara; Hofmann, Eva; Gangl, Katharina; Hartner-Tiefenthaler, Martina; Kirchler, Erich

2015-01-01

Following the classic economic model of tax evasion, taxpayers base their tax decisions on economic determinants, like fine rate and audit probability. Empirical findings on the relationship between economic key determinants and tax evasion are inconsistent and suggest that taxpayers may rather rely on their beliefs about tax authority's power. Descriptions of the tax authority's power may affect taxpayers' beliefs and as such tax evasion. Experiment 1 investigates the impact of fines and beliefs regarding tax authority's power on tax evasion. Experiments 2-4 are conducted to examine the effect of varying descriptions about a tax authority's power on participants' beliefs and respective tax evasion. It is investigated whether tax evasion is influenced by the description of an authority wielding coercive power (Experiment 2), legitimate power (Experiment 3), and coercive and legitimate power combined (Experiment 4). Further, it is examined whether a contrast of the description of power (low to high power; high to low power) impacts tax evasion (Experiments 2-4). Results show that the amount of fine does not impact tax payments, whereas participants' beliefs regarding tax authority's power significantly shape compliance decisions. Descriptions of high coercive power as well as high legitimate power affect beliefs about tax authority's power and positively impact tax honesty. This effect still holds if both qualities of power are applied simultaneously. The contrast of descriptions has little impact on tax evasion. The current study indicates that descriptions of the tax authority, e.g., in information brochures and media reports, have more influence on beliefs and tax payments than information on fine rates. Methodically, these considerations become particularly important when descriptions or vignettes are used besides objective information.

Does the sole description of a tax authority affect tax evasion?--the impact of described coercive and legitimate power.

Directory of Open Access Journals (Sweden)

Barbara Hartl

Full Text Available Following the classic economic model of tax evasion, taxpayers base their tax decisions on economic determinants, like fine rate and audit probability. Empirical findings on the relationship between economic key determinants and tax evasion are inconsistent and suggest that taxpayers may rather rely on their beliefs about tax authority's power. Descriptions of the tax authority's power may affect taxpayers' beliefs and as such tax evasion. Experiment 1 investigates the impact of fines and beliefs regarding tax authority's power on tax evasion. Experiments 2-4 are conducted to examine the effect of varying descriptions about a tax authority's power on participants' beliefs and respective tax evasion. It is investigated whether tax evasion is influenced by the description of an authority wielding coercive power (Experiment 2, legitimate power (Experiment 3, and coercive and legitimate power combined (Experiment 4. Further, it is examined whether a contrast of the description of power (low to high power; high to low power impacts tax evasion (Experiments 2-4. Results show that the amount of fine does not impact tax payments, whereas participants' beliefs regarding tax authority's power significantly shape compliance decisions. Descriptions of high coercive power as well as high legitimate power affect beliefs about tax authority's power and positively impact tax honesty. This effect still holds if both qualities of power are applied simultaneously. The contrast of descriptions has little impact on tax evasion. The current study indicates that descriptions of the tax authority, e.g., in information brochures and media reports, have more influence on beliefs and tax payments than information on fine rates. Methodically, these considerations become particularly important when descriptions or vignettes are used besides objective information.

A generalized view of self-citation: direct, co-author, collaborative, and coercive induced self-citation.

Science.gov (United States)

Ioannidis, John P A

2015-01-01

The phenomenon of self-citation can present in many different forms, including direct, co-author, collaborative, and coercive induced self-citation. It can also pertain to the citation of single scientists, groups of scientists, journals, and institutions. This article presents some case studies of extreme self-citation practices. It also discusses the implications of different types of self-citation. Self-citation is not necessarily inappropriate by default. In fact, usually it is fully appropriate but often it is even necessary. Conversely, inappropriate self-citation practices may be highly misleading and may distort the scientific literature. Coercive induced self-citation is the most difficult to discover. Coercive Induced self-citation may happen directly from reviewers of articles, but also indirectly from reviewers of grants, scientific advisors who steer a research agenda, and leaders of funding agencies who may espouse spending disproportionately large funds in research domains that perpetuate their own self-legacy. Inappropriate self-citation can be only a surrogate marker of what might be much greater distortions of the scientific corpus towards conformity to specific opinions and biases. Inappropriate self-citations eventually affect also impact metrics. Different impact metrics vary in the extent to which they can be gamed through self-citation practices. Citation indices that are more gaming-proof are available and should be more widely used. We need more empirical studies to dissect the impact of different types of inappropriate self-citation and to examine the effectiveness of interventions to limit them. Copyright © 2014. Published by Elsevier Inc.

Spin-dependent quasiparticle tunneling in junction superconductor-isolator-ferromagnetic

International Nuclear Information System (INIS)

Shlapak, Yu.V.; Shaternik, V.E.; Rudenko, E.M.

2001-01-01

The influence of Andreev reflection of quasiparticles in transparent tunnel junctions of superconductor-isolator-ferromagnetic on electric-current transport is studied within the framework of the Blonder-Tinkham-Klapwijk (BTK) model. It's obtained that current and signal-to-noise ratio can be increased for the memory cell by using in it the double-barrier tunnel junction ferromagnetic-isolator-superconductor-isolator-ferromagnetic instead off the usual tunnel junction ferromagnetic-isolator-ferromagnetic. The evolution of non-linear (tunnel-type) current-voltage characteristics with increasing of the junction transparency is described. (orig.)

Synthesis, characterization, properties, and applications of nanosized ferroelectric, ferromagnetic, or multiferroic materials

International Nuclear Information System (INIS)

Dhak, Debasis; Das, Soma; Communication Engineering.); Dhak, Prasanta

2015-01-01

Recently, there has been an enormous increase in research activity in the field of ferroelectrics and ferromagnetics especially in multiferroic materials which possess both ferroelectric and ferromagnetic properties simultaneously. However, the ferroelectric, ferromagnetic, and multiferroic properties should be further improved from the utilitarian and commercial viewpoints. Nanostructural materials are central to the evolution of future electronics and information technologies. Ferroelectrics and ferromagnetics have already been established as a dominant branch in electronics sector because of their diverse applications. The ongoing dimensional downscaling of materials to allow packing of increased numbers of components into integrated circuits provides the momentum for evolution of nanostructural devices. Nanoscaling of the above materials can result in a modification of their functionality. Furthermore, nanoscaling can be used to form high density arrays of nanodomain nanostructures, which is desirable for miniaturization of devices

Solutions to quasilinear equations of $N$-biharmonic type with degenerate coercivity

Directory of Open Access Journals (Sweden)

Sami Aouaoui

2014-10-01

Full Text Available In this article we show the existence of multiple solutions for quasilinear equations in divergence form with degenerate coercivity. Our strategy is to combine a variational method and an iterative technique to obtain the solutions.

Ferromagnetic and twin domains in LCMO manganites

International Nuclear Information System (INIS)

Jung, G.; Markovich, V.; Mogilyanski, D.; Beek, C. van der; Mukovskii, Y.M.

2005-01-01

Ferromagnetic and twin domains in lightly Ca-doped La 1-x Ca x MnO 3 single crystals have been visualized and investigated by means of the magneto-optical technique. Both types of domains became visible below the Curie temperature. The dominant structures seen in applied magnetic field are associated with magneto-crystalline anisotropy and twin domains. In a marked difference to the twin domains which appear only in applied magnetic field, ferromagnetic domains show up in zero applied field and are characterized by oppositely oriented spontaneous magnetization in adjacent domains. Ferromagnetic domains take form of almost periodic, corrugated strip-like structures. The corrugation of the ferromagnetic domain pattern is enforced by the underlying twin domains

Substrate bias effects on composition and coercivity of CoCrTa/Cr thin films on canasite and glass

Science.gov (United States)

Deng, Y.; Lambeth, D. N.; Sui, X.; Lee, L.-L.; Laughlin, D. E.

1993-05-01

CoCrTa/Cr thin films were prepared by rf diode sputtering onto canasite and glass substrates at various bias voltages from two targets of different compositions (Co82.8Cr14.6Ta2.6 and Co86Cr12Ta2). While Auger depth profile analysis indicates that there is some broadening at the CoCrTa-Cr interface, x-ray fluorescence spectroscopy reveals that changes in alloy composition due to the resputtering processes are even more prominent. For both targets, as the substrate bias increases the Co content in the films declines, and the magnetization decreases. The maximum film coercivity appears to correlate to the final film composition. By investigating the results from both targets, it is concluded that the coercivity reaches a maximum when the film composition is in the neighborhood of Co84Cr13Ta3. Thus, to optimize the coercivity different bias voltages are required for each target. Excessive substrate bias, however, leads to films with low magnetization and coercivity.

Coercivity enhancement in hot deformed Nd2Fe14B-type magnets by doping low-melting RCu alloys (R = Nd, Dy, Nd + Dy)

Science.gov (United States)

Lee, Y. I.; Huang, G. Y.; Shih, C. W.; Chang, W. C.; Chang, H. W.; You, J. S.

2017-10-01

Magnetic properties of the anisotropic NdFeB magnets prepared by hot pressing followed by die-upsetting NdFeB MQU-F powders doped with low-melting RCu alloy powders were explored, where RCu stands for Nd70Cu30, Dy70Cu30 and (Nd0.5Dy0.5)70Cu30, respectively. In addition, the post-annealing at 600 °C was employed to modify the microstructures and the magnetic properties of the hot deformed magnets. It is found that doping RCu alloy powders is effective in enhancing the coercivity of the hot deformed NdFeB magnets from 15.1 kOe to 16.3-19.5 kOe. For Nd70Cu30-doped magnets, the increment of coercivity is only 1.2 kOe. Meanwhile, Dy70Cu30-doped and (Nd0.5Dy0.5)70Cu30-doped magnets show an almost identical enhancement of coercivity of about 4.4 kOe. Importantly, the latter magnet shows a beneficial effect of reducing the usage of Dy from 1.6 wt% to 0.8 wt%. TEM analysis shows that nonmagnetic Nd, Dy and Cu appear at grain boundary and isolate the magnetic grains, leading to an enhancement of coercivity. Doping lower melting point Dy-lean (Nd0.5Dy0.5)70Cu30 powders into commercial MQU-F powders for making high coercivity hot deformed NdFeB magnets might be a potential and economic way for mass production.

Ferromagnetism carried by highly delocalized hybrid states in Sc-doped ZnO thin films

KAUST Repository

Benali Kanoun, Mohammed

2012-05-29

We present first-principles results for Sc-doped ZnOthin films. Neighboring Sc atoms in the surface and/or subsurface layers are found to be coupled ferromagnetically, where only two of the possible configurations induce spin polarization. In the first configuration, the polarization is carried by the Sc d states as expected for transition metaldoping. However, there is a second configuration which is energetically favorable. It is governed by polarized hybrid states of the Zns, O p, and Sc d orbitals. Such highly delocalized states can be an important ingredient for understanding the magnetism of dopedZnOthin films.

Ferromagnetic Swimmers - Devices and Applications

Science.gov (United States)

Hamilton, Joshua; Petrov, Peter; Winlove, C. Peter; Gilbert, Andrew; Bryan, Matthew; Ogrin, Feodor

2017-11-01

Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. We propose a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. Experimentally, these devices (3.6 mm) are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters and demonstrate stable propulsion over a wide range of Reynolds numbers. Manipulation of the external magnetic field resulted in robust control over the speed and direction of propulsion. We also demonstrate our ferromagnetic swimmer working as a macroscopic prototype of a microfluidic pump. By physically tethering the swimmer, instead of swimming, the swimmer generates a directional flow of liquid around itself.

Effects of Rashba and Dresselhaus spin-orbit couplings on itinerant ferromagnetism

Science.gov (United States)

Liu, Mengnan; Xu, Liping; Wan, Yong; Yan, Xu

2018-02-01

Based on Stoner model for itinerant ferromagnet, effects of spin-orbit coupling (SOC) on ferromagnetism were investigated at zero temperature. It was found that SOC will enhance the critical ferromagnetic exchange interaction for spontaneous magnetization, and then suppress ferromagnetism. In case of the coexistence of Rashba and Dresselhaus SOCs, the mixture of the two spin-orbit couplings showed stronger suppressed effect on ferromagnetism than only one kind of SOC alone. When the two SOCs mixed with equal magnitude, ferromagnetism in itinerant ferromagnet was suppressed to minimum.

Synthesis, characterization and Monte Carlo simulation of CoFe2O4/Polyvinylpyrrolidone nanocomposites: The coercivity investigation

International Nuclear Information System (INIS)

Mirzaee, Sh; Farjami shayesteh, S.; Mahdavifar, S; Hekmatara, S Hoda.

2015-01-01

To study the influence of polymer matrix on the effective magnetic anisotropy constant and coercivity of magnetic nanoparticles, we have synthesized the Cobalt ferrite/Polyvinylpyrrolidone (PVP) nanocomposites by co-precipitation method in four different processes. In addition the Monte Carlo simulation and law of approach to the saturation magnetization have been applied to achieve the anisotropy constants. The obtained experimental and theoretical results showed a decrease in anisotropy constant relative to the bulk cobalt ferrite. We have showed that the PVP matrix can interact with metal cations and made them approximately immobilized to participate in spinel structure. Hence different anisotropy constants or coercivity were obtained for synthesized nanocomposites. In addition, PVP matrix can attach to the surface of magnetic particles and make them approximately non-interacting. The synthesized samples have been characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Magnetic measurements were made at room temperature using a vibrating sample magnetometer (VSM). - Highlights: • We studied the effect of polymer matrix on the coercivity of the CoFe 2 O 4 /PVP nanocomposites. • The polymer matrix decreases the anisotropy of the nanocomposite system. • We have synthesized nanocomposites with approximately the same size, but significantly different coercivity. • We showed that the PVP/CoFe 2 O 4 nanocomposite has the considerable coercivity due to the spin hindrance. • Magnetic properties of nanocomposites simulated by Monte Carlo method

Novel superconducting state in ferromagnetic superconductor UCoGe. Microscopic coexistence of ferromagnetism and superconductivity probed by 59Co-NQR measurements

International Nuclear Information System (INIS)

Ishida, Kenji; Hattori, Taisuke; Ihara, Yoshihiko; Nakai, Yusuke; Sato, Noriaki K.; Deguchi, Kazuhiko; Tamura, Nobuyuki; Satoh, Isamu

2010-01-01

We have investigated the relationship between ferromagnetism and superconductivity in ferromagnetic superconductor UCoGe from 59 Co nuclear quadrupole resonance (NQR) measurements. Our experimental results indicate the microscopic coexistence of ferromagnetism and superconductivity in UCoGe, and suggest a 'self-induced vortex state' in its superconducting state. We also review NQR experiments, which play an important role in this study. (author)

Ferromagnetic Objects Magnetovision Detection System.

Science.gov (United States)

Nowicki, Michał; Szewczyk, Roman

2013-12-02

This paper presents the application of a weak magnetic fields magnetovision scanning system for detection of dangerous ferromagnetic objects. A measurement system was developed and built to study the magnetic field vector distributions. The measurements of the Earth's field distortions caused by various ferromagnetic objects were carried out. The ability for passive detection of hidden or buried dangerous objects and the determination of their location was demonstrated.

Effects of geometrical frustration on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice

Science.gov (United States)

Farkašovský, Pavol

2018-05-01

The small-cluster exact-diagonalization calculations and the projector quantum Monte Carlo method are used to examine the competing effects of geometrical frustration and interaction on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice. It is shown that the geometrical frustration stabilizes the ferromagnetic state at high electron concentrations ( n ≳ 7/4), where strong correlations between ferromagnetism and the shape of the noninteracting density of states are observed. In particular, it is found that ferromagnetism is stabilized for these values of frustration parameters, which lead to the single-peaked noninterating density of states at the band edge. Once, two or more peaks appear in the noninteracting density of states at the band edge the ferromagnetic state is suppressed. This opens a new route towards the understanding of ferromagnetism in strongly correlated systems.

Magnetic and electronic properties of half-metallic ferromagnetic Mn-stabilised zirconia

Energy Technology Data Exchange (ETDEWEB)

Maznichenko, Igor; Daene, Markus; Hergert, Wolfram; Mertig, Ingrid [Martin-Luther-Univ. Halle-Wittenberg, Inst. Phys., 06099 Halle (Germany); Ernst, Arthur; Ostanin, Sergey; Sandratskii, Leonid; Bruno, Patrick [Max-Planck-Inst. Mikrostrukturphys., Weinberg 2, 06120 Halle (Germany); Bergqvist, Lars [Dept. Phys., Uppsala Univ., Box 530, 751 21 Uppsala (Sweden); Hughes, Ian; Staunton, Julie [Dept. Phys., Univ. Warwick, Coventry CV4 7AL (United Kingdom); Kudrnovsky, Josef [Max-Planck-Inst. Mikrostrukturphys., Weinberg 2, 06120 Halle (Germany); Inst. Phys., Acad. Sci. of the Czech Republic, Na Slovance 2, 18221 Prague (Czech Republic)

2007-07-01

The investigations of the manganese stabilised cubic zirconia (Mn-SZ) show that this dilute magnetic semiconductors possess unique magnetic properties. Based on ab-initio electronic structure calculations which include the effects of thermally excited magnetic fluctuations, the autors predict Mn-SZ to be ferromagnetic for a wide range of Mn concentration up to high T{sub C}. It was found that this material, which is well known both as a diamond imitation and as a catalyst, is halfmetallic with majority and minority spin states of the Mn impurities lying in the wide band gap of zirconia. The high T{sub C} ferromagnetism is robust against oxygen vacancies and against the distribution of Mn impurities on the Zr fcc sublattice. This work responds to the question concerning the key electronic and structure factors behind an optimal doping. The autors propose this stable half-metallic ferromagnet to be a promising candidate for future spintronics applications.

High-output microwave detector using voltage-induced ferromagnetic resonance

International Nuclear Information System (INIS)

Shiota, Yoichi; Suzuki, Yoshishige; Miwa, Shinji; Tamaru, Shingo; Nozaki, Takayuki; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji

2014-01-01

We investigated the voltage-induced ferromagnetic resonance (FMR) with various DC bias voltage and input RF power in magnetic tunnel junctions. We found that the DC bias monotonically increases the homodyne detection voltage due to the nonlinear FMR originating in an asymmetric magnetization-potential in the free layer. In addition, the linear increase of an output voltage to the input RF power in the voltage-induced FMR is more robust than that in spin-torque FMR. These characteristics enable us to obtain an output voltage more than ten times than that of microwave detectors using spin-transfer torque

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

Energy Technology Data Exchange (ETDEWEB)

Aravindh, S. Assa; Schwingenschloegl, Udo, E-mail: udo.schwingenschloegl@kaust.edu.sa, E-mail: iman.roqan@kaust.edu.sa; Roqan, Iman S., E-mail: udo.schwingenschloegl@kaust.edu.sa, E-mail: iman.roqan@kaust.edu.sa [Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia)

2014-12-21

In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn{sub 48}O{sub 48} nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of ≤2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high T{sub C} in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV) obtained with the O vacancy. Density of states shows that Fermi level overlaps with Gd f states with the introduction of O vacancy, indicating the possibility of s-f coupling. These results will assist in understanding experimental findings in Gd-doped ZnO nanowires.

Giant superconductivity-induced modulation of the ferromagnetic magnetization in a cuprate-manganite superlattice.

Science.gov (United States)

Hoppler, J; Stahn, J; Niedermayer, Ch; Malik, V K; Bouyanfif, H; Drew, A J; Rössle, M; Buzdin, A; Cristiani, G; Habermeier, H-U; Keimer, B; Bernhard, C

2009-04-01

Artificial multilayers offer unique opportunities for combining materials with antagonistic orders such as superconductivity and ferromagnetism and thus to realize novel quantum states. In particular, oxide multilayers enable the utilization of the high superconducting transition temperature of the cuprates and the versatile magnetic properties of the colossal-magnetoresistance manganites. However, apart from exploratory work, the in-depth investigation of their unusual properties has only just begun. Here we present neutron reflectometry measurements of a [Y(0.6)Pr(0.4)Ba(2)Cu(3)O(7) (10 nm)/La(2/3)Ca(1/3)MnO(3) (10 nm)](10) superlattice, which reveal a surprisingly large superconductivity-induced modulation of the vertical ferromagnetic magnetization profile. Most surprisingly, this modulation seems to involve the density rather than the orientation of the magnetization and is highly susceptible to the strain, which is transmitted from the SrTiO(3) substrate. We outline a possible explanation of this unusual superconductivity-induced phenomenon in terms of a phase separation between ferromagnetic and non-ferromagnetic nanodomains in the La(2/3)Ca(1/3)MnO(3) layers.

Conceptual study of ferromagnetic pebbles for heat exhaust in fusion reactors with short power decay length

Directory of Open Access Journals (Sweden)

N. Gierse

2015-03-01

The key results of this study are that very high heat fluxes are accessible in the operation space of ferromagnetic pebbles, that ferromagnetic pebbles are compatible with tokamak operation and current divertor designs, that the heat removal capability of ferromagnetic pebbles increases as λq decreases and, finally, that for fusion relevant values of q∥ pebble diameters below 100 μm are required.

Effects of High-Energy Proton-Beam Irradiation on the Magnetic Properties of ZnO Nanorods

Energy Technology Data Exchange (ETDEWEB)

Park, Jun Kue; Kwon, Hyeok-Jung; Cho, Yong Sub [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-10-15

There are still many problem for the application due to its unstable magnetism state and too small magnetization values. Here we investigate magnetic properties of ZnO nanorods after high-energy proton-beam irradiation. Electron spin resonance (ESR) measurement on temperature was made to identify intrinsic or extrinsic defects as well as to observe magnetic ordering after irradiation. Understanding the effects of proton beam irradiation on magnetic behavior may help to shed light on the mechanism responsible for the magnetic ordering in this material. We have investigated proton-beam irradiation effects on the magnetic properties of ZnO nanorods. After irradiation a broad ESR line is observed, indicating emergence of ferromagnetic ordering up to room temperature. In M-H curve, stronger coercive field is observed after irradiation.

Spark-plasma-sintering magnetic field assisted compaction of Co{sub 80}Ni{sub 20} nanowires for anisotropic ferromagnetic bulk materials

Energy Technology Data Exchange (ETDEWEB)

Ouar, Nassima; Schoenstein, Frédéric; Mercone, Silvana; Farhat, Samir; Jouini, Noureddine [Laboratoire des Sciences des Procédés et des Matériaux, CNRS, LSPM—UPR 3407, Université Paris 13, Sorbonne-Paris-Cité, 99 Avenue J.-B. Clément, 93430 Villetaneuse (France); Villeroy, Benjamin [Institut de Chimie et des Matériaux Paris Est, CNRS, ICMPE—UMR 7182, Equipe de Chimie Métallurgique des Terres Rares, 2-8 rue Henri Dunant, 94320 Thiais Cedex (France); Leridon, Brigitte [Laboratoire de Physique et d’Étude des Matériaux, LPEM, ESPCI-ParisTech, CNRS, UPMC, 10 rue Vauquelin, F-75231 Paris Cedex 5 (France)

2013-10-28

We developed a two-step process showing the way for sintering anisotropic nanostructured bulk ferromagnetic materials. A new reactor has been optimized allowing the synthesis of several grams per batch of nanopowders via a polyol soft chemistry route. The feasibility of the scale-up has been successfully demonstrated for Co{sub 80}Ni{sub 20} nanowires and a massic yield of ∼97% was obtained. The thus obtained nanowires show an average diameter of ∼6 nm and a length of ∼270 nm. A new bottom-up strategy allowed us to compact the powder into a bulk nanostructured system. We used a spark-plasma-sintering technique under uniaxial compression and low temperature assisted by a permanent magnetic field of 1 T. A macroscopic pellet of partially aligned nanowire arrays has been easily obtained. This showed optimized coercive properties along the direction of the magnetic field applied during compaction (i.e., the nanowires' direction)

Structural and magnetic properties of granular CoPd multilayers

Science.gov (United States)

Vivas, L. G.; Figueroa, A. I.; Bartolomé, F.; Rubín, J.; García, L. M.; Deranlot, C.; Petroff, F.; Ruiz, L.; González-Calbet, J. M.; Brookes, N. B.; Wilhelm, F.; Rogalev, A.; Bartolomé, J.

2016-02-01

Multilayers of bimetallic CoPd alloyed and assembled nanoparticles, prepared by room temperature sequential sputtering deposition on amorphous alumina, were studied by means of high-resolution transmission electron microscopy, x-ray diffraction, SQUID-based magnetometry and x-ray magnetic circular dichroism. Alloying between Co and Pd in these nanoparticles gives rise to a high perpendicular magnetic anisotropy. Their magnetic properties are temperature dependent: at low temperature, the multilayers are ferromagnetic with a high coercive field; at intermediate temperature the behavior is of a soft-ferromagnet, and at higher temperature, the perpendicular magnetic anisotropy in the nanoparticles disappears. The magnetic orbital moment to spin moment ratio is enhanced compared with Co bare nanoparticles and Co fcc bulk.

Ferromagnetic Objects Magnetovision Detection System

Directory of Open Access Journals (Sweden)

Michał Nowicki

2013-12-01

Full Text Available This paper presents the application of a weak magnetic fields magnetovision scanning system for detection of dangerous ferromagnetic objects. A measurement system was developed and built to study the magnetic field vector distributions. The measurements of the Earth’s field distortions caused by various ferromagnetic objects were carried out. The ability for passive detection of hidden or buried dangerous objects and the determination of their location was demonstrated.

High-Temperature Ferromagnetism in Transition Metal Implanted Wide-Bandgap Semiconductors

Science.gov (United States)

2005-07-01

Mn)As and Its Heterostructures,” Acta Physica Polonica A, 94 (2):155–164 (August 1998). 79. Ohno, Y., D. K. Young, B. Beschoten, F. Matsukura, H. Ohno...reactive molecular-beam epitaxy,” Physical Review B , 67 (16):16205 (April 2003). 26. Dietl, T. “From Magnetic Polarons to Ferromagnetism,” Acta Physica ...samples,” Physica B , 308-310 :985–988 (December 2001). 15. Bradley, F. N. Materials for Magnetic Functions (First Edition). New York: Hayden, 1971. 16

Magnetization reversal of ferromagnetic nanoparticles induced by a stream of polarized electrons

Energy Technology Data Exchange (ETDEWEB)

Kozhushner, M.A.; Gatin, A.K.; Grishin, M.V.; Shub, B.R. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation); Kim, V.P.; Khomutov, G.B. [Faculty of Physics, Lomonosov Moscow State University, Lenin Gory 1-2, Moscow 119991 (Russian Federation); Ilegbusi, O.J. [University of Central Florida, 4000 Central Florida Boulevard, Orlando, FL 32816-2450 (United States); Trakhtenberg, L.I. [Semenov Institute of Chemical Physics of RAS, 4, Kosygin Street, Moscow 119991 (Russian Federation)

2016-09-15

The remagnetization of ferromagnetic Fe{sub 3}O{sub 4} nanoparticles of several thousand cubic nanometers by spin-polarized current is investigated. For this purpose, magnetite nanoparticles are synthesized and deposited on a conductive nonmagnetic substrate. The remagnetization is conducted in high-vacuum scanning tunneling microscope (STM). The STM tip from magnetized iron wire constitutes one electrode while the ferromagnetic nanoparticle on the graphite surface represents the second electrode. The measured threshold value of remagnetization current (I{sub thresh}=9 nA) is the lowest value of current at which remagnetization occurs. The change in nanoparticle magnetization is detected by the effect of giant magnetic resistance, specifically, the dependence of the weak polarized current (Iferromagnetic nanoclusters. The peculiarities of size dependence of the observed effects are explained. - Highlights: • Ferromagnetic nanoparticle in STM with ferromagnetic tip. • Change of the direction of nanoparticle magnetization by current I>I{sub cr}=9 nA. • GMR effect used to control change of magnetization.

Investigation of cellular microstructure and enhanced coercivity in sputtered Sm{sub 2}(CoCuFeZr){sub 17} film

Energy Technology Data Exchange (ETDEWEB)

Bhatt, Ranu, E-mail: rbhatt@barc.gov.in; Schütz, G. [Max Planck Institute for Intelligent Systems (formerly Max Planck Institute for Metals Research), Heisenbergstr. 3, 70569 Stuttgart (Germany); Bhatt, Pramod [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)

2014-03-14

We have investigated the effect of annealing temperature on the microstructure and magnetic properties of Sm{sub 2}(CoCuFeZr){sub 17} films prepared using ion beam sputtering at room temperature. The as-deposited film shows randomly oriented polycrystalline grains and exhibits small coercivity (H{sub C}) of 0.04 T at room temperature. Post annealing of these films at 700 °C under Ar atmosphere shows significant changes in the microstructure transforming it to the development of cellular growth, concomitant with enhanced coercivity up to 1.3 T. The enhanced coercivity is explained using the domain wall pinning mechanism.

Does the Sole Description of a Tax Authority Affect Tax Evasion? - The Impact of Described Coercive and Legitimate Power

Science.gov (United States)

Hartl, Barbara; Hofmann, Eva; Gangl, Katharina; Hartner-Tiefenthaler, Martina; Kirchler, Erich

2015-01-01

Following the classic economic model of tax evasion, taxpayers base their tax decisions on economic determinants, like fine rate and audit probability. Empirical findings on the relationship between economic key determinants and tax evasion are inconsistent and suggest that taxpayers may rather rely on their beliefs about tax authority’s power. Descriptions of the tax authority’s power may affect taxpayers’ beliefs and as such tax evasion. Experiment 1 investigates the impact of fines and beliefs regarding tax authority’s power on tax evasion. Experiments 2-4 are conducted to examine the effect of varying descriptions about a tax authority’s power on participants’ beliefs and respective tax evasion. It is investigated whether tax evasion is influenced by the description of an authority wielding coercive power (Experiment 2), legitimate power (Experiment 3), and coercive and legitimate power combined (Experiment 4). Further, it is examined whether a contrast of the description of power (low to high power; high to low power) impacts tax evasion (Experiments 2-4). Results show that the amount of fine does not impact tax payments, whereas participants’ beliefs regarding tax authority’s power significantly shape compliance decisions. Descriptions of high coercive power as well as high legitimate power affect beliefs about tax authority’s power and positively impact tax honesty. This effect still holds if both qualities of power are applied simultaneously. The contrast of descriptions has little impact on tax evasion. The current study indicates that descriptions of the tax authority, e.g., in information brochures and media reports, have more influence on beliefs and tax payments than information on fine rates. Methodically, these considerations become particularly important when descriptions or vignettes are used besides objective information. PMID:25923770

Out-of-plane coercive field of Ni80Fe20 antidot arrays

International Nuclear Information System (INIS)

Gao Chunhong; Chen Ke; Lue Ling; Zhao Jianwei; Chen Peng

2010-01-01

The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni 80 Fe 20 antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni 80 Fe 20 antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos θ| dependence. The angular dependence of out-of-plane coercivity of Ni 80 Fe 20 antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane.

Out-of-plane coercive field of Ni 80Fe 20 antidot arrays

Science.gov (United States)

Gao, Chunhong; Chen, Ke; Lü, Ling; Zhao, Jianwei; Chen, Peng

2010-11-01

The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni 80Fe 20 antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni 80Fe 20 antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos θ| dependence. The angular dependence of out-of-plane coercivity of Ni 80Fe 20 antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane.

Coercive Journal Self Citations, Impact Factor, Journal Influence and Article Influence

NARCIS (Netherlands)

C-L. Chang (Chia-Lin); M.J. McAleer (Michael)

2013-01-01

textabstractThis paper examines the issue of coercive journal self citations and the practical usefulness of two recent journal performance metrics, namely the Eigenfactor score, which may be interpreted as measuring “Journal Influence”, and the Article Influence score, using the Thomson Reuters ISI

Half-Metallic Ferromagnetism and Stability of Transition Metal Pnictides and Chalcogenides

Science.gov (United States)

Liu, Bang-Gui

It is highly desirable to explore robust half-metallic ferromagnetic materials compatible with important semiconductors for spintronic applications. A state-of-the-art full potential augmented plane wave method within the densityfunctional theory is reliable enough for this purpose. In this chapter we review theoretical research on half-metallic ferromagnetism and structural stability of transition metal pnictides and chalcogenides. We show that some zincblende transition metal pnictides are half-metallic and the half-metallic gap can be fairly wide, which is consistent with experiment. Systematic calculations reveal that zincblende phases of CrTe, CrSe, and VTe are excellent half-metallic ferromagnets. These three materials have wide half-metallic gaps, are low in total energy with respect to the corresponding ground-state phases, and, importantly, are structurally stable. Halfmetallic ferromagnetism is also found in wurtzite transition metal pnictides and chalcogenides and in transition-metal doped semiconductors as well as deformed structures. Some of these half-metallic materials could be grown epitaxially in the form of ultrathin .lms or layers suitable for real spintronic applications.

Transition Metal Dopants Essential for Producing Ferromagnetism in Metal Oxide Nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Johnson, Lydia; Thurber, Aaron P.; Anghel, Josh; Sabetian, Maryam; Engelhard, Mark H.; Tenne, D.; Hanna, Charles; Punnoose, Alex

2010-08-13

Recent claims that ferromagnetism can be produced in nanoparticles of metal oxides without the presence of transition metal dopants has been refuted in this work by investigating 62 high quality well-characterized nanoparticle samples of both undoped and Fe doped (0-10% Fe) ZnO. The undoped ZnO nanoparticles showed zero or negligible magnetization, without any dependence on the nanoparticle size. However, chemically synthesized Zn₁₋xFexO nanoparticles showed clear ferromagnetism, varying systematically with Fe concentration. Furthermore, the magnetic properties of Zn₁₋xFexO nanoparticles showed strong dependence on the reaction media used to prepare the samples. The zeta potentials of the Zn₁₋xFexO nanoparticles prepared using different reaction media were significantly different, indicating strong differences in the surface structure. Electron paramagnetic resonance studies clearly showed that the difference in the ferromagnetic properties of Zn₁₋xFexO nanoparticles with different surface structures originate from differences in the fraction of the doped Fe³⁺ ions that are coupled ferromagnetically.

Ferromagnetic spin coupling as the origin of 0.7 anomaly in quantum point contacts.

Science.gov (United States)

Aryanpour, K; Han, J E

2009-02-06

We study one-dimensional itinerant electron models with ferromagnetic coupling to investigate the origin of the 0.7 anomaly in quantum point contacts. Linear conductance calculations from the quantum Monte Carlo technique for spin interactions of different spatial range suggest that 0.7(2e;{2}/h) anomaly results from a strong interaction of low-density conduction electrons to ferromagnetic fluctuations formed across the potential barrier. The conductance plateau appears due to the strong incoherent scattering at high temperature when the electron traversal time matches the time scale of dynamic ferromagnetic excitations.

Magneto-optical Kerr-effect at low temperatures. Investigation of superconductor/ferromagnet heterostructures

Energy Technology Data Exchange (ETDEWEB)

Zahn, Patrick; Bayer, Jonas [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Institute for Innovative Surfaces FINO, Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany); Stahl, Claudia; Ruoss, Stephen; Graefe, Joachim; Schuetz, Gisela [Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart (Germany); Albrecht, Joachim [Institute for Innovative Surfaces FINO, Aalen University, Beethovenstrasse 1, 73430 Aalen (Germany)

2016-07-01

With XMCD microscopy it is possible to visualize the critical current density of the superconductor YBCO with high spatial resolution. Therefore, soft magnetic CoFeB is introduced as sensor layer. The magnetic stray fields of the supercurrents lead to a local reorientation of the magnetic moments in the ferromagnet, which are then imaged via X-ray microscopy. These experiments have to be carried out at the scanning X-ray microscope MAXYMUS at the synchrotron Bessy II in Berlin. For that purpose pre-characterization of the sensor is highly desirable: Magnetic interactions between the superconductor and the ferromagnetic sensor layer have been investigated at low temperatures using Kerr-effect measurements. Therefore hysteresis loops are obtained by a sophisticated magnet and field ramping setup within the NanoMOKE3 system. The results are used to optimize the ferromagnetic sensor layer for XMCD microscopy of superconductors.

Annealing induced low coercivity, nanocrystalline Co–Fe–Si thin films exhibiting inverse cosine angular variation

Energy Technology Data Exchange (ETDEWEB)

Hysen, T., E-mail: hysenthomas@gmail.com [Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India); Al-Harthi, Salim; Al-Omari, I.A. [Department of Physics, Sultan Qaboos University, PC 123, Muscat, Sultanate of Oman (Oman); Geetha, P.; Lisha, R. [Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India); Ramanujan, R.V. [School of Materials Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Sakthikumar, D. [Graduate School of Interdisciplinary New Science, Toyo University, Kawagoe, Saitama (Japan); Anantharaman, M.R., E-mail: mra@cusat.ac.in [Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India)

2013-09-15

Co–Fe–Si based films exhibit high magnetic moments and are highly sought after for applications like soft under layers in perpendicular recording media to magneto-electro-mechanical sensor applications. In this work the effect of annealing on structural, morphological and magnetic properties of Co–Fe–Si thin films was investigated. Compositional analysis using X-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a native oxide surface layer consisting of oxides of Co, Fe and Si on the surface. The morphology of the as deposited films shows mound like structures conforming to the Volmer–Weber growth model. Nanocrystallisation of amorphous films upon annealing was observed by glancing angle X-ray diffraction and transmission electron microscopy. The evolution of magnetic properties with annealing is explained using the Herzer model. Vibrating sample magnetometry measurements carried out at various angles from 0° to 90° to the applied magnetic field were employed to study the angular variation of coercivity. The angular variation fits the modified Kondorsky model. Interestingly, the coercivity evolution with annealing deduced from magneto-optical Kerr effect studies indicates a reverse trend compared to magetisation observed in the bulk. This can be attributed to a domain wall pinning at native oxide layer on the surface of thin films. The evolution of surface magnetic properties is correlated with morphology evolution probed using atomic force microscopy. The morphology as well as the presence of the native oxide layer dictates the surface magnetic properties and this is corroborated by the apparent difference in the bulk and surface magnetic properties. - Highlights: • The relation between grain size and magnetic properties in Co–Fe–Si thin films obeys the Herzer model. • Angular variation of coercivity is found to obey the Kondorsky model. • The MOKE measurements provide further evidence for domain wall pinning. �

Modification of critical current in HTSC tape conductors by a ferromagnetic layer

International Nuclear Information System (INIS)

Goemoery, F; Souc, J; Seiler, E; Vojenciak, M; Granados, X

2008-01-01

In some applications of tape conductors from high temperature superconductors (HTSC) the magnetic field is created by the transported current itself. This is e.g. the case of power transmission cables or current leads. Quite complex distribution of local magnetic field determines then the ability of the superconducting element to carry electrical current. We have investigated how much the critical current of a tape conductor can be changed by putting a ferromagnetic layer in the vicinity of the HTSC material. Numerical procedure has been developed to resolve the current and field distribution in such superconductor-ferromagnet composite tape. Theoretical predictions have been confirmed by experiments on sample made from Bi-2223/Ag composite tape. The critical current of such tape can be improved by placing a soft ferromagnetic material at the tape's edges. On the other hand, the calculations show that the ferromagnetic substrate of YBCO coated tape reduces its self-field critical current

Giant magnetic coercivity in YNi{sub 4}B-type SmNi{sub 3}TB (T=Mn–Cu) solid solutions

Energy Technology Data Exchange (ETDEWEB)

Yao, Jinlei; Yan, Chang [Research Center for Solid State Physics and Materials, School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009 (China); Yapaskurt, V.O. [Department of Petrology, Geological Faculty Moscow State University, Leninskie Gory, Moscow 119992 (Russian Federation); Morozkin, A.V., E-mail: morozkin@tech.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation)

2016-12-01

The effects of transition metal substitution for Ni on the magnetic properties of the YNi{sub 4}B-type SmNi{sub 4}B via SmNi{sub 3}TB (T=Mn, Fe, Co, Cu) solid solutions have been investigated. SmNi{sub 4}B, SmNi{sub 3}MnB, SmNi{sub 3}FeB, SmNi{sub 3}CoB and SmNi{sub 3}CuB show ferromagnetic ordering at 40 K, 210 K, 322 K, 90 K and 57 K and field sensitive metamagnetic-like transitions at 15 K, 100 K, 185 K, 55 K and 15 K in a magnetic field of 10 kOe, respectively. The magnetocaloric effects of SmNi{sub 3}TB (T=Mn–Cu) were calculated in terms of isothermal magnetic entropy change (ΔS{sub m}). The magnetic entropy ΔS{sub m} reaches value of –0.94 J/kg K at 40 K for SmNi{sub 4}B, –1.5 J/kg K at 205 K for SmNi{sub 3}MnB, –0.54 J/kg K at 320 K for SmNi{sub 3}FeB, –0.49 J/kg K at 90 K for SmNi{sub 3}CoB and –0.54 J/kg K at 60 K for SmNi{sub 3}CuB in field change of 0–50 kOe around the Curie temperature. They show positive ΔS{sub m} of +0.71 J/kg K at ~10 K for SmNi{sub 4}B, +1.69 J/kg K at 30 K for SmNi{sub 3}MnB, +0.89 J/kg K at 110 K for SmNi{sub 3}FeB, +1.08 J/kg K at 25 K for SmNi{sub 3}CoB and +1.12 J/kg K at 10 K for SmNi{sub 3}CuB in field change of 0–50 kOe around the low temperature metamagnetic-like transition. Below the field induced transition temperature (change of magnetic structure), SmNi{sub 3}TB (T=Mn–Cu) exhibits giant magnetic coercivity of 74 kOe at 5 K for SmNi{sub 4}B, 69 kOe at 20 K (90 kOe at 10 K) for SmNi{sub 3}MnB, 77 kOe at 60 K for SmNi{sub 3}FeB, 88 kOe at 20 K for SmNi{sub 3}CoB and 52 kOe at 5 K for SmNi{sub 3}CuB. - Highlights: • YNi{sub 4}B-type SmNi{sub 3}{Mn, Fe, Co, Ni, Cu}B exhibit the Curie points at 39–322 K. • SmNi{sub 3}{Mn, Fe, Co, Ni, Cu}B show field induced transition at 15–185 K. • SmNi{sub 3}MnB shows huge magnetic hysteresis with coercive field of 69 kOe at 20 K. • SmNi{sub 3}FeB shows huge magnetic hysteresis with coercive field of 77 kOe at 60 K. • SmNi{sub 3}CoB shows giant coercive

A Combined TEM/STEM and Micromagnetic Study of the Anisotropic Nature of Grain Boundaries and Coercivity in Nd-Fe-B Magnets

Directory of Open Access Journals (Sweden)

Gregor A. Zickler

2017-01-01

Full Text Available The nanoanalytical high resolution TEM/STEM investigation of the intergranular grain boundary phase of anisotropic sintered and rapidly quenched heavy rare earth-free Nd-Fe-B magnet materials revealed a difference in composition for grain boundaries parallel (large Fe-content and perpendicular (low Fe content to the alignment direction. This behaviour vanishes in magnets with a high degree of misorientation. The numerical finite element micromagnetic simulations are based on the anisotropic compositional behaviour of GBs and show a decrease of the coercive field with an increasing thickness of the grain boundary layer. The magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries parallel to the c-axis and secondly as Néel domain wall perpendicular to the c-axis into the adjacent hard magnetic grains. The increasing misalignment of grains leads to the loss of the anisotropic compositional behaviour and therefore to an averaged value of the grain boundary composition. In this case the simulations show an increase of the coercive field compared to the anisotropic magnet. The calculated coercive field values of the investigated magnet samples are in the order of μ0HcJ=1.8 T–2.1 T for a mean grain boundary thickness of 4 nm, which agrees perfectly with the experimental data.

Optimal thermoeconomic performance of an irreversible regenerative ferromagnetic Ericsson refrigeration cycle

International Nuclear Information System (INIS)

Xu, Zhichao; Guo, Juncheng; Lin, Guoxing; Chen, Jincan

2016-01-01

On the basis of the Langevin theory of classical statistical mechanics, the magnetization, entropy, and iso-field heat capacity of ferromagnetic materials are analyzed and their mathematical expressions are derived. An irreversible regenerative Ericsson refrigeration cycle by using a ferromagnetic material as the working substance is established, in which finite heat capacity rates of low and high temperature reservoirs, non-perfect regenerative heat of the refrigeration cycle, additional regenerative heat loss, etc. are taken into account. Based on the regenerative refrigeration cycle model, a thermoeconomic function is introduced as one objective function and optimized with respect to the temperatures of the working substance in the two iso-thermal processes. By means of numerical calculation, the effects of the effective factor of the heat exchangers in high/low temperature reservoir sides, efficiency of the regenerator, heat capacity rate of the low temperature reservoir, and applied magnetic field on the optimal thermoeconomic function as well as the corresponding cooling rate and coefficient of performance are revealed. The results obtained in this paper can provide some theoretical guidance for the optimal design of actual regenerative magnetic refrigerator cycle. - Highlights: • Thermodynamic performance of ferromagnetic material is analyzed. • An irreversible regenerative ferromagnetic Ericsson refrigeration cycle is set up. • The thermoeconomic objective function is introduced and optimized. • Impacts of the thermoeconomic and other parameters are discussed.

Prospects of high temperature ferromagnetism in (Ga, Mn)As semiconductors

Czech Academy of Sciences Publication Activity Database

Jungwirth, Tomáš; Wang, K. Y.; Mašek, Jan; Edmonds, K. W.; König, J.; Sinova, J.; Polini, M.; Goncharuk, Natalya; MacDonald, A. H.; Sawicki, M.; Campion, R. P.; Zhao, L.X.; Foxon, C. T.; Gallagher, B. L.

2005-01-01

Roč. 72, č. 16 (2005), 165204/1-165204/13 ISSN 1098-0121 R&D Projects: GA ČR(CZ) GA202/05/0575; GA MŠk(CZ) LC510 Grant - others:EU FENIKS(XE) EC:G5RD-CT-2001-00535; EPSRC(GB) GR/S81407/01; Welch Foundation(GB) DE-FG03-02ER45958; Deutsche Forschungsgemeinschaft(DE) SFB 491 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * spintronics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.185, year: 2005

Nonlinear anisotropic elliptic equations with variable exponents and degenerate coercivity

Directory of Open Access Journals (Sweden)

Hocine Ayadi

2018-02-01

Full Text Available In this article, we prove the existence and the regularity of distributional solutions for a class of nonlinear anisotropic elliptic equations with $p_i(x$ growth conditions, degenerate coercivity and $L^{m(\\cdot}$ data, with $m(\\cdot$ being small, in appropriate Lebesgue-Sobolev spaces with variable exponents. The obtained results extend some existing ones [8,10].

Ferromagnetic properties of Mn-doped AlN

International Nuclear Information System (INIS)

Li, H.; Bao, H.Q.; Song, B.; Wang, W.J.; Chen, X.L.; He, L.J.; Yuan, W.X.

2008-01-01

Mn-doped AlN polycrystalline powders with a wurtzite structure were synthesized by solid-state reactions. A red-orange band at 600 nm, due to Mn 3+ incorporated into the AlN lattice, is observed in the photoluminescence (PL) spectrum at room temperature (RT). Magnetic measurements show the samples possess hysteresis loops up to 300 K, indicating that the obtained powders are ferromagnetic at around RT. The Mn concentration-induced RT ferromagnetism is less than 1 at%. Our results confirm that the RT ferromagnetism can be realized in Mn-doped AlN

Flux penetration in a ferromagnetic/superconducting bilayer

Energy Technology Data Exchange (ETDEWEB)

Adamus, Z.; Cieplak, M.Z.; Abal' Oshev, A. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA/DSM/DRECAM, Laboratoire des Solides Irradies, F-91191 Gif Sur Yvette, (France); Konczykowski, M. [Ecole Polytech, CNRS - UMR 7642, F-91128 Palaiseau, (France); Cheng, X.M.; Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

2007-07-01

An array of miniature Hall sensors is used to study the magnetic flux penetration in a ferromagnetic/superconducting bilayer consisting of Nb as a superconducting layer and Co/Pt multilayer with perpendicular magnetic anisotropy as a ferromagnetic layer, separated by an amorphous Si layer to avoid the proximity effect. It is found that the magnetic domains in the ferromagnetic layer create a large edge barrier in the superconducting layer which delays flux penetration. The smooth flux profiles observed in the absence of magnetic pinning change into terraced profiles in the presence of domains. (authors)

Coercivity degradation caused by inhomogeneous grain boundaries in sintered Nd-Fe-B permanent magnets

Science.gov (United States)

Chen, Hansheng; Yun, Fan; Qu, Jiangtao; Li, Yingfei; Cheng, Zhenxiang; Fang, Ruhao; Ye, Zhixiao; Ringer, Simon P.; Zheng, Rongkun

2018-05-01

Quantitative correlation between intrinsic coercivity and grain boundaries in three dimensions is critical to further improve the performance of sintered Nd-Fe-B permanent magnets. Here, we quantitatively reveal the local composition variation across and especially along grain boundaries using the powerful atomic-scale analysis technique known as atom probe tomography. We also estimate the saturation magnetization, magnetocrystalline anisotropy constant, and exchange stiffness of the grain boundaries on the basis of the experimentally determined structure and composition. Finally, using micromagnetic simulations, we quantify the intrinsic coercivity degradation caused by inhomogeneous grain boundaries. This approach can be applied to other magnetic materials for the analysis and optimization of magnetic properties.

Ferromagnetic resonance frequency increase and resonance line broadening of a ferromagnetic Fe–Co–Hf–N film with in-plane uniaxial anisotropy by high-frequency field perturbation

International Nuclear Information System (INIS)

Seemann, K.; Leiste, H.; Krüger, K.

2013-01-01

Soft ferromagnetic Fe-Co-Hf-N films, produced by reactive r.f. magnetron sputtering, are useful to study the ferromagnetic resonance (FMR) by means of frequency domain permeability measurements up to the GHz range. Films with the composition Fe 33 Co 43 Hf 10 N 14 exhibit a saturation polarisation J s of around 1.35 T. They are consequently considered as being uniformly magnetised due to an in-plane uniaxial anisotropy of approximately μ 0 H u ≈4.5 m T after annealing them, e.g., at 400 °C in a static magnetic field for 1 h. Being exposed to a high-frequency field, the precession of magnetic moments leads to a marked frequency-dependent permeability with a sharp Lorentzian shaped imaginary part at around 2.33 GHz (natural resonance peak), which is in a very good agreement with the modified Landau–Lifschitz–Gilbert (LLG) differential equation. A slightly increased FMR frequency and a clear increase in the resonance line broadening due to an increase of the exciting high-frequency power (1–25.1 mW), considered as an additional perturbation of the precessing system of magnetic moments, could be discovered. By solving the homogenous LLG differential equation with respect to the in-plane uniaxial anisotropy, it was revealed that the high-frequency field perturbation impacts the resonance peak position f FMR and resonance line broadening Δf FMR characterised by a completed damping parameter α=α eff +Δα. Adapted from this result, the increase in f FMR and decrease in lifetime of the excited level of magnetic moments associated with Δf FMR , similar to a spin-½ particle in a static magnetic field, was theoretically elaborated as well as compared with experimental data. - Highlights: • Impact on the resonance frequency and resonance line by the high-frequency power. • Theoretic approach by solving the LLG differential equation. • Experimental verification and magnon processes. • Theoretical and experimental determination of the resonance state

Ferromagnetic artificial pinning centers in multifilamentary superconducting wires

International Nuclear Information System (INIS)

Wang, J.Q.; Rizzo, N.D.; Prober, D.E.

1997-01-01

The authors fabricated multifilamentary NbTi wires with ferromagnetic (FM) artificial pinning centers (APCs) to enhance the critical current density (J c ) in magnetic fields. They used a bundle and draw technique to process the APC wires with either Ni or Fe as the pinning centers. Both wires produced higher J c in the high field range (5-9 T) than previous non-magnetic APC wires similarly processed, even though the authors have not yet optimized pin percentage. Using a magnetometer they found that the pins remained ferromagnetic for the wires with maximum J c . However, they did observe a substantial loss of FM material for the wires where the pin diameter approached 3 nm. Thus, they expect further enhancement of J c with better pin quality

Design and installation of a ferromagnetic wall in tokamak geometry

International Nuclear Information System (INIS)

Hughes, P. E.; Levesque, J. P.; Rivera, N.; Mauel, M. E.; Navratil, G. A.

2015-01-01

Low-activation ferritic steels are leading material candidates for use in next-generation fusion development experiments such as a prospective component test facility and DEMO power reactor. Understanding the interaction of plasmas with a ferromagnetic wall will provide crucial physics for these facilities. In order to study ferromagnetic effects in toroidal geometry, a ferritic wall upgrade was designed and installed in the High Beta Tokamak–Extended Pulse (HBT-EP). Several material options were investigated based on conductivity, magnetic permeability, vacuum compatibility, and other criteria, and the material of choice (high-cobalt steel) is characterized. Installation was accomplished quickly, with minimal impact on existing diagnostics and overall machine performance, and initial results demonstrate the effects of the ferritic wall on plasma stability

Design and installation of a ferromagnetic wall in tokamak geometry

Energy Technology Data Exchange (ETDEWEB)

Hughes, P. E., E-mail: peh2109@columbia.edu; Levesque, J. P.; Rivera, N.; Mauel, M. E.; Navratil, G. A. [Columbia University Plasma Physics Laboratory, Columbia University, 102 S.W. Mudd, 500 W. 120th St., New York, New York 10027 (United States)

2015-10-15

Low-activation ferritic steels are leading material candidates for use in next-generation fusion development experiments such as a prospective component test facility and DEMO power reactor. Understanding the interaction of plasmas with a ferromagnetic wall will provide crucial physics for these facilities. In order to study ferromagnetic effects in toroidal geometry, a ferritic wall upgrade was designed and installed in the High Beta Tokamak–Extended Pulse (HBT-EP). Several material options were investigated based on conductivity, magnetic permeability, vacuum compatibility, and other criteria, and the material of choice (high-cobalt steel) is characterized. Installation was accomplished quickly, with minimal impact on existing diagnostics and overall machine performance, and initial results demonstrate the effects of the ferritic wall on plasma stability.

Understanding the Room Temperature Ferromagnetism in GaN Nanowires with Pd Doping

International Nuclear Information System (INIS)

Manna, S; De, S K

2011-01-01

We report the first synthesis and characterization of 4d transition metal palladium-doped GaN nanowires (NWs). Room temperature ferromagnetism has been observed in high quality Vapor Liquid Solid (VLS) epitaxy grown undoped n-type GaN nanowires. It was proposed that this type of magnetism is due to defects which are not observed in Bulk GaN because of large formation energy of defects in bulk GaN. Here we have successfully doped 4d transition metal Pd in GaN NWs. We find fairly strong and long-range ferromagnetic coupling between Pd substituted for Ga in GaN . The results suggest that 4d metals such as Pd may also be considered as candidates for ferromagnetic dopants in semiconductors.

Magnetic excitations in ferromagnetic semiconductors

International Nuclear Information System (INIS)

Furdyna, J.K.; Liu, X.; Zhou, Y.Y.

2009-01-01

Magnetic excitations in a series of GaMnAs ferromagnetic semiconductor films were studied by ferromagnetic resonance (FMR). Using the FMR approach, multi-mode spin wave resonance spectra have been observed, whose analysis provides information on magnetic anisotropy (including surface anisotropy), distribution of magnetization precession within the GaMnAs film, dynamic surface spin pinning (derived from surface anisotropy), and the value of exchange stiffness constant D. These studies illustrate a combination of magnetism and semiconductor physics that is unique to magnetic semiconductors

An active magnetic bearing with high Tc superconducting coils and ferromagnetic cores

International Nuclear Information System (INIS)

Brown, G.V.; DiRusso, E.; Provenza, A.J.

1996-01-01

A proof-of-feasibility demonstration showed that high-T c , superconductor (HTS) coils can be used in a high-load, active magnetic bearing in LN 2 . A homopolar radial bearing with commercially wound HTS (Bi 2223) bias and control coils produced over 890 N (200 lb) radial load capacity (measured nonrotating) and supported a shaft to 14000 rpm. The goal was to show that HTS coils can operate stably with ferromagnetic cores in a feedback controlled system at a current density similar to that for Cu in LN 2 . The bias coil, wound with nontwisted, multifilament HTS conductor, dissipated negligible power for its direct current. The control coils, wound with monofilament HTS sheathed in Ag, dissipated negligible power for direct current. AC losses increased rapidly with frequency and quadratically with AC amplitude. Above about 2 Hz, the effective resistance of the control coils exceeds that of the silver which is in electrical parallel with the oxide superconductor. These results show that twisted multifilament conductor is not needed for stable levitation but may be desired to reduce control power for sizable dynamic loads

Single-magnon tunneling through a ferromagnetic nanochain

International Nuclear Information System (INIS)

Petrov, E.G.; Ostrovsky, V.

2010-01-01

Magnon transmission between ferromagnetic contacts coupled by a linear ferromagnetic chain is studied at the condition when the chain exhibits itself as a tunnel magnon transmitter. It is shown that dependently on magnon energy at the chain, a distant intercontact magnon transmission occurs either in resonant or off-resonant tunneling regime. In the first case, a transmission function depends weakly on the number of chain sites whereas at off-resonant regime the same function manifests an exponential drop with the chain length. Change of direction of external magnetic field in one of ferromagnetic contacts blocks a tunnel transmission of magnon.

Power Structure in Family and Coercive Trends Consequence of it Based on Women’s Emotional Energy and Economic Situation in Abdanan

Directory of Open Access Journals (Sweden)

مریم مختاری

2014-01-01

Full Text Available This research carried out with the purpose of determining role of women’s emotional energy and economic situation in power structure in family and coercive trends consequence of it in Abdanan. Subject of power in family is one of the considered  problems in Sociology. In this way role of two differential factors (emotional energy and economic situation is thinkful. Research method was survey and population were all of married women in Abdanan that were selected 400women as a sample size with performance of multy stage cluster sampling. A researcher-made questionnaire was used for data collection. In this research power structure considered as a mediator variable. Research finging showed that there is significant and direct relation between emotional energy and power structure in family but there isn’t significant relation between economic situation and power structure in family. Relation between variables and coercive trends as a dependent variable is expressive of significant and direct relation between emotional energy and coercive trends. There is significant and reverse relation between economic situation and coercive trends and also significant and direct relation between power structure in family and coercive trends.

Dynamical response of vibrating ferromagnets

CERN Document Server

Gaganidze, E; Ziese, M

2000-01-01

The resonance frequency of vibrating ferromagnetic reeds in a homogeneous magnetic field can be substantially modified by intrinsic and extrinsic field-related contributions. Searching for the physical reasons of the field-induced resonance frequency change and to study the influence of the spin glass state on it, we have measured the low-temperature magnetoelastic behavior and the dynamical response of vibrating amorphous and polycrystalline ferromagnetic ribbons. We show that the magnetoelastic properties depend strongly on the direction of the applied magnetic field. The influence of the re-entrant spin glass transition on these properties is discussed. We present clear experimental evidence that for applied fields perpendicular to the main area of the samples the behavior of ferromagnetic reeds is rather independent of the material composition and magnetic state, exhibiting a large decrease of the resonance frequency. This effect can be very well explained with a model based on the dynamical response of t...

Raman characterization of bulk ferromagnetic nanostructured graphite

International Nuclear Information System (INIS)

Pardo, Helena; Divine Khan, Ngwashi; Faccio, Ricardo; Araújo-Moreira, F.M.; Fernández-Werner, Luciana

2012-01-01

Raman spectroscopy was used to characterize bulk ferromagnetic graphite samples prepared by controlled oxidation of commercial pristine graphite powder. The G:D band intensity ratio, the shape and position of the 2D band and the presence of a band around 2950 cm -1 showed a high degree of disorder in the modified graphite sample, with a significant presence of exposed edges of graphitic planes as well as a high degree of attached hydrogen atoms.

Predicting sexual coercion in early adulthood: The transaction among maltreatment, gang affiliation, and adolescent socialization of coercive relationship norms.

Science.gov (United States)

Ha, Thao; Kim, Hanjoe; Christopher, Caroline; Caruthers, Allison; Dishion, Thomas J

2016-08-01

This study tested a transactional hypothesis predicting early adult sexual coercion from family maltreatment, early adolescent gang affiliation, and socialization of adolescent friendships that support coercive relationship norms. The longitudinal study of a community sample of 998 11-year-olds was intensively assessed in early and middle adolescence and followed to 23-24 years of age. At age 16-17 youth were videotaped with a friend, and their interactions were coded for coercive relationship talk. Structural equation modeling revealed that maltreatment predicted gang affiliation during early adolescence. Both maltreatment and gang affiliation strongly predicted adolescent sexual promiscuity and coercive relationship norms with friends at age 16-17 years. Adolescent sexual promiscuity, however, did not predict sexual coercion in early adulthood. In contrast, higher levels of observed coercive relationship talk with a friend predicted sexual coercion in early adulthood for both males and females. These findings suggest that peers have a socialization function in the development of norms prognostic of sexual coercion, and the need to consider peers in the promotion of healthy relationships.

Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

International Nuclear Information System (INIS)

Zhu, Yunpeng; Wang, Gang; Liu, Liyuan; Yang, Xinsheng; Zhao, Yong

2015-01-01

Abstract : HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate. - Highlight: • A continuous Hall sensor array system has been designed. • The inhomogeneity of YBCO tape with ferromagnetic substrate can be detected by HAS. • Finite element method is an effective method for calibrating the remanent field.

Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

Energy Technology Data Exchange (ETDEWEB)

Zhu, Yunpeng; Wang, Gang; Liu, Liyuan [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Yang, Xinsheng, E-mail: xsyang@swjtu.edu.cn [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Zhao, Yong [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wale, Sydney 2052, NSW (Australia)

2015-12-15

Abstract : HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate. - Highlight: • A continuous Hall sensor array system has been designed. • The inhomogeneity of YBCO tape with ferromagnetic substrate can be detected by HAS. • Finite element method is an effective method for calibrating the remanent field.

Dynamic temperature field in the ferromagnetic plate induced by moving high frequency inductor

Directory of Open Access Journals (Sweden)

Milošević-Mitić Vesna

2014-01-01

Full Text Available The subject of the paper is the temperature distribution in the thin metallic ferromagnetic plate influenced by moving linear high frequency induction heater. As a result of high frequency electromagnetic field, conducting currents appear in the part of the plate. Distribution of the eddy-current power across the plate thickness is obtained by use of complex analysis. The influences of the heater frequency, magnetic field intensity and plate thickness on the heat power density were discussed. By treating this power as a moving heat source, differential equations governing distribution of the temperature field are formulated. Temperature across the plate thickness is assumed to be in linear form. Differential equations are analytically solved by using integral-transform technique, Fourier finite-sine and finite-cosine transform and Laplace transform. The influence of the heater velocity to the plate temperature is presented on numerical examples based on theoretically obtained results. [Projekat Ministarstva nauke Republike Srbije, br. TR 35040 i br. TR 35011

Magnetic excitons in singlet-ground-state ferromagnets

DEFF Research Database (Denmark)

Birgeneau, R.J.; Als-Nielsen, Jens Aage; Bucher, E.

1971-01-01

The authors report measurements of the dispersion of singlet-triplet magnetic excitons as a function of temperature in the singlet-ground-state ferromagnets fcc Pr and Pr3Tl. Well-defined excitons are observed in both the ferromagnetic and paramagnetic regions, but with energies which are nearly...

Ferromagnetism carried by highly delocalized hybrid states in Sc-doped ZnO thin films

KAUST Repository

Benali Kanoun, Mohammed; Goumri-Said, Souraya; Manchon, Aurelien; Schwingenschlö gl, Udo

2012-01-01

We present first-principles results for Sc-doped ZnOthin films. Neighboring Sc atoms in the surface and/or subsurface layers are found to be coupled ferromagnetically, where only two of the possible configurations induce spin polarization

Ferromagnetic bond of Li{sub 10} cluster: An alternative approach in terms of effective ferromagnetic sites

Energy Technology Data Exchange (ETDEWEB)

Donoso, Roberto; Fuentealba, Patricio, E-mail: pfuentea@hotmail.es, E-mail: cardena@macul.ciencias.uchile.cl; Cárdenas, Carlos, E-mail: pfuentea@hotmail.es, E-mail: cardena@macul.ciencias.uchile.cl [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Centro para el Desarrollo de la Nanociencia y la Nanotecnología (CEDENNA), Avda. Ecuador 3493, Santiago 9170124 (Chile); Rössler, Jaime [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Llano-Gil, Sandra [Faculty of Engineering, Food Engineering Program, Corporación Universitaria Lasallista, Caldas, Antioquia (Colombia)

2016-09-07

In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li{sub 10} and Li{sub 8} clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

Fabrication and properties of multiferroic nanocomposite films

KAUST Repository

Al-Nassar, Mohammed Y.; Ivanov, Yurii P.; Kosel, Jü rgen

2015-01-01

A new type of multiferroic polymer nanocomposite is presented, which exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature. The multiferroic nanocomposite consists of a ferroelectric copolymer poly(vinylindene fluoride-trifluoroethylene) [P(VDF-TrFE)] and high aspect ratio ferromagnetic nickel (Ni) nanowires (NWs), which were grown inside anodic aluminum oxide membranes. The fabrication of nanocomposite films with Ni NWs embedded in P(VDF-TrFE) has been successfully carried out via a simple low-temperature spin-coating technique. Structural, ferromagnetic, and ferroelectric properties of the developed nanocomposite have been investigated. The remanent and saturation polarization as well as the coercive field of the ferroelectric phase are slightly affected by the incorporation of the NWs as well as the thickness of the films. While the former two decrease, the last increases by adding the NWs or increasing the thickness. The ferromagnetic properties of the nanocomposite films are found to be isotropic.

Exchange coupling in metallic multilayers with a top FeRh layer

Energy Technology Data Exchange (ETDEWEB)

Yamada, S., E-mail: yamada@ee.es.osaka-u.ac.jp; Kanashima, T.; Hamaya, K., E-mail: hamaya@ee.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531 (Japan); Tanikawa, K. [Department of Electronics, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan); Hirayama, J. [Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531 (Japan); Department of Electronics, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan); Taniyama, T. [Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)

2016-05-15

We study magnetic properties of metallic multilayers with FeRh/ferromagnet interfaces grown by low-temperature molecular beam epitaxy. Room-temperature coercivity of the ferromagnetic layers is significantly enhanced after the growth of FeRh, proving the existence of the exchange coupling between the antiferromagnetic FeRh layer and the ferromagnetic layer. However, exchange bias is not clearly observed probably due to the presence of disordered structures, which result from the lattice strain at the FeRh/ferromagnet interfaces due to the lattice mismatch. We infer that the lattice matched interface between FeRh and ferromagnetic layers is a key parameter for controlling magnetic switching fields in such multilayer systems.

Sex-Symmetric Effects of Coercive Behaviors on Mental Health? Not Exactly

Science.gov (United States)

Prospero, Moises

2009-01-01

The present study tested a section of the model of coercion in intimate partner violence (IPV) by investigating the relationships among coercion, IPV and mental health symptoms. The study's sample consisted of 573 culturally diverse university students (age M = 21.4) who completed a survey that measured past IPV victimization, coercive behaviors,…

Voltage control of ferromagnetic resonance

Directory of Open Access Journals (Sweden)

Ziyao Zhou

2016-06-01

Full Text Available Voltage control of magnetism in multiferroics, where the ferromagnetism and ferroelectricity are simultaneously exhibiting, is of great importance to achieve compact, fast and energy efficient voltage controllable magnetic/microwave devices. Particularly, these devices are widely used in radar, aircraft, cell phones and satellites, where volume, response time and energy consumption is critical. Researchers realized electric field tuning of magnetic properties like magnetization, magnetic anisotropy and permeability in varied multiferroic heterostructures such as bulk, thin films and nanostructure by different magnetoelectric (ME coupling mechanism: strain/stress, interfacial charge, spin–electromagnetic (EM coupling and exchange coupling, etc. In this review, we focus on voltage control of ferromagnetic resonance (FMR in multiferroics. ME coupling-induced FMR change is critical in microwave devices, where the electric field tuning of magnetic effective anisotropic field determines the tunability of the performance of microwave devices. Experimentally, FMR measurement technique is also an important method to determine the small effective magnetic field change in small amount of magnetic material precisely due to its high sensitivity and to reveal the deep science of multiferroics, especially, voltage control of magnetism in novel mechanisms like interfacial charge, spin–EM coupling and exchange coupling.

Room temperature ferromagnetism in a phthalocyanine based carbon material

International Nuclear Information System (INIS)

Honda, Z.; Sato, K.; Sakai, M.; Fukuda, T.; Kamata, N.; Hagiwara, M.; Kida, T.

2014-01-01

We report on a simple method to fabricate a magnetic carbon material that contains nitrogen-coordinated transition metals and has a large magnetic moment. Highly chlorinated iron phthalocyanine was used as building blocks and potassium as a coupling reagent to uniformly disperse nitrogen-coordinated iron atoms on the phthalocyanine based carbon material. The iron phthalocyanine based carbon material exhibits ferromagnetic properties at room temperature and the ferromagnetic phase transition occurs at T c  = 490 ± 10 K. Transmission electron microscopy observation, X-ray diffraction analysis, and the temperature dependence of magnetization suggest that the phthalocyanine molecules form three-dimensional random networks in the iron phthalocyanine based carbon material

Room temperature ferromagnetism in a phthalocyanine based carbon material

Energy Technology Data Exchange (ETDEWEB)

Honda, Z., E-mail: honda@fms.saitama-u.ac.jp; Sato, K.; Sakai, M.; Fukuda, T.; Kamata, N. [Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570 (Japan); Hagiwara, M.; Kida, T. [KYOKUGEN (Center for Quantum Science and Technology under Extreme Conditions), Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)

2014-02-07

We report on a simple method to fabricate a magnetic carbon material that contains nitrogen-coordinated transition metals and has a large magnetic moment. Highly chlorinated iron phthalocyanine was used as building blocks and potassium as a coupling reagent to uniformly disperse nitrogen-coordinated iron atoms on the phthalocyanine based carbon material. The iron phthalocyanine based carbon material exhibits ferromagnetic properties at room temperature and the ferromagnetic phase transition occurs at T{sub c} = 490 ± 10 K. Transmission electron microscopy observation, X-ray diffraction analysis, and the temperature dependence of magnetization suggest that the phthalocyanine molecules form three-dimensional random networks in the iron phthalocyanine based carbon material.

Dirac Magnons in Honeycomb Ferromagnets

Directory of Open Access Journals (Sweden)

Sergey S. Pershoguba

2018-01-01

Full Text Available The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009RMPHAT0034-686110.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014ADPHAH0001-873210.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX_{3} (X=F, Cl, Br and I, that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956PHRVAO0031-899X10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956PHRVAO0031-899X10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr_{3} [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in

Dirac Magnons in Honeycomb Ferromagnets

Science.gov (United States)

Pershoguba, Sergey S.; Banerjee, Saikat; Lashley, J. C.; Park, Jihwey; Ågren, Hans; Aeppli, Gabriel; Balatsky, Alexander V.

2018-01-01

The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009), 10.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014), 10.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX3 (X =F , Cl, Br and I), that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956), 10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956), 10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr3 [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in Ferromagnetic CrBr3 Studied by Inelastic Neutron Scattering: Spin-Wave Correlation

An electromagnetically actuated fiber optic switch using magnetized ferromagnetic materials

Science.gov (United States)

Pandojirao-S, Praveen; Dhaubanjar, Naresh; Phuyal, Pratibha C.; Chiao, Mu; Chiao, J.-C.

2008-03-01

This paper presents the design, fabrication and testing of a fiber optic switch actuated electromagnetically. The ferromagnetic gel coated optical fiber is actuated using external electromagnetic fields. The ferromagnetic gel consists of ferromagnetic powders dispersed in epoxy. The fabrication utilizes a simple cost-effective coating setup. A direct fiberto-fiber alignment eliminates the need for complementary optical parts and the displacement of fiber switches the laser coupling. The magnetic characteristics of magnetized ferromagnetic materials are performed using alternating gradient magnetometer and the magnetic hysteresis curves are measured for different ferromagnetic materials including iron, cobalt, and nickel. Optical fiber switches with various fiber lengths are actuated and their static and dynamic responses for the same volume of ferromagnetic gel are summarized. The highest displacement is 1.345 mm with an input current of 260mA. In this paper, the performance of fiber switches with various coating materials is presented.

Neutron depolarization study of static and dynamic magnetic properties of ferromagnets

International Nuclear Information System (INIS)

Stuesser, N.

1986-01-01

In this thesis neutron depolarization experiments are performed on amorphous and crystalline ferromagnetic materials. The subjects studied are concerned with 'domain structure in magnetically weak uniaxial amorphous ferromagnetic ribbons', 'static critical behaviour at the ferromagnetic-paramagnetic phase transition', 'small magnetic anisotropy in nickel near T c ', and 'magnetization reversal in conducting ferromagnets'. 87 refs.; 37 figs.; 3 tabs

Transport properties of Josephson contacts with ferromagnetic tunnel barriers; Transporteigenschaften von Josephson-Kontakten mit ferromagnetischer Tunnelbarriere

Energy Technology Data Exchange (ETDEWEB)

Sprungmann, Dirk

2010-01-28

The combination of the Josephson and the proximity effect is possible by the introduction of a ferromagnetic barrier into a Josephson contact resulting in a so called π coupling. The supra current through these contacts is flowing in the reverse direction. Specific new electronic circuits such as phase shifting devices are possible, for instance for high-speed analog-digital transducers. In the frame of this thesis SIFS Josephson contacts were studied, with a barrier consisting of a thin insulating Al2Ox barrier layer and a ferromagnetic thin film. For the ferromagnetic material weak ferromagnetic Ni(0.6)Cu(0.4), the strong ferromagnetic Fe(0.25)Co(0.75) and the ternary Heusler alloys Co2MnSn and Cu2MnAl were used. Josephson contacts with π coupling were realized with the NiCu alloy, triplet superconductivity seems to appear with the Heusler systems.

Tunnel barrier and noncollinear magnetization effects on shot noise in ferromagnetic/semiconductor/ferromagnetic heterojunctions

International Nuclear Information System (INIS)

An Xingtao; Liu Jianjun

2008-01-01

Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers

Wellhead with non-ferromagnetic materials

Energy Technology Data Exchange (ETDEWEB)

Hinson, Richard A [Houston, TX; Vinegar, Harold J [Bellaire, TX

2009-05-19

Wellheads for coupling to a heater located in a wellbore in a subsurface formation are described herein. At least one wellhead may include a heater located in a wellbore in a subsurface formation; and a wellhead coupled to the heater. The wellhead may be configured to electrically couple the heater to one or more surface electrical components. The wellhead may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the wellhead. Systems and methods for using such wellheads for treating a subsurface formation are described herein.

Development and processing temperature dependence of ferromagnetism in Zn0.98Co0.02O

International Nuclear Information System (INIS)

Hays, J.; Thurber, A.; Reddy, K. M.; Punnoose, A.; Engelhard, M. H.

2006-01-01

We report the development of room-temperature ferromagnetism (FM), with coercivity H c =2000 Oe and saturation magnetization M s ∼0.01 emu/g, in chemically synthesized powders of Zn 0.98 Co 0.02 O processed at 150 deg. C, and paramagnetism with antiferromagnetic interactions between the Co 2+ spins (S=3/2) in samples processed at higher temperatures 200≤T P ≤900 deg. C. X-ray diffraction data show a decrease in the lattice parameters a and c with T P , indicating a progressive incorporation of 0.58A sized tetrahedral Co 2+ at the substitutional sites of 0.60 A sized Zn 2+ . Diffuse reflectance spectra show three well defined absorption edges at 660, 615, and 568 nm due to the d-d crystal field transitions 4 A 2 (F)→ 2 E(G), 4 A 2 (F)→ 4 T 1 (P), and 4 A 2 (F)→ 2 T 1 (G) of high spin (S=3/2)Co 2+ in a tetrahedral crystal field, whose intensities increase with processing temperature. X-ray photoelectron spectroscopy shows that the doped Co 2+ ions in the 150 deg. C processed samples are located mostly on the surface of the particles and they disperse into the entire volume of the particles when processed at higher temperatures. The observations suggest that the FM most likely results from Co 2+ attached to the surface sites and it is lost in well dispersed samples formed at T P >150 deg. C

Effect of Cu addition on coercivity and interfacial state of Nd-Fe-B/Nd-rich thin films

International Nuclear Information System (INIS)

Matsuura, M; Sugimoto, S; Fukada, T; Tezuka, N; Goto, R

2010-01-01

This study provides the effect of Cu addition on coercivity (H cJ ) and interfacial microstructure in Nd-Fe-B/Nd-rich thin films. All films were deposited by using ultra high vacuum (UHV) magnetron sputtering, and the Nd-Fe-B layer was oxidized under several atmospheres with different oxygen content. Then, the films were annealed at 250-550 0 C under UHV. The films oxidized in low vacuum (10 -2 -10 -5 Pa) (under low oxygen state) exhibited the recovery of H cJ by the annealing at 450 0 C. On the contrary, the H cJ of the films oxidized in Ar (under high oxygen state) decreased with increasing annealing temperature. However, the H cJ increased drastically at the temperatures above 550 0 C. In addition, the Cu added films, which were annealed at temperatures above 350 0 C, showed higher coercivities than the films without Cu addition. The XRD analysis suggested the existence of C-Nd 2 O 3 phase in the Cu added films annealed at 550 0 C. It can be considered that the Cu addition decreases the eutectic temperature of Nd-rich phase and influences the interfacial state between Nd 2 Fe 14 B and Nd-rich phase.

Temperature dependence of coercive field and fatigue in poly(vinylidene fluoride-trifluoroethylene) copolymer ultra-thin films

International Nuclear Information System (INIS)

Zhang Xiuli; Xu Haisheng; Zhang Yanni

2011-01-01

The experimental intrinsic coercive field of ferroelectric poly(vinylidene fluoride-trifluoethylene) copolymer films, with both bottom and top gold electrodes is measured at a wide temperature range. In the lower temperature region from -20 to 25 deg. C, the temperature dependence of coercive field shows good agreement with the prediction by the Landau-Ginzburg (LG) mean-field theory. In the higher temperature region from 25 to 80 deg. C, the coercive field shows a slow decrease with the increased temperature, where the LG theory is not applicable any more. The temperature-dependent changes in the polymer chains have been analysed. A reversible 'inherent fatigue' is observed from the partially recovered remanent polarization after re-annealing a fatigued P(VDF-TrFE) film. FTIR spectra indicate that the interchain spacing does not change from 10 to 10 7 switching cycles while the degree of all-trans ferroelectric phase decreases gradually with applied switching cycles. After a re-annealing treatment, ferroelectric phase recovers and dipoles at the boundary of crystallites acquire much higher energy.

Differentiating between Confrontive and Coercive Kinds of Parental Power-Assertive Disciplinary Practices

Science.gov (United States)

Baumrind, Diana

2012-01-01

In this essay, I differentiate between coercive and confrontive kinds of power assertion to elucidate the significantly different effects on children's well-being of authoritarian and authoritative styles of parental authority. Although both parenting styles (in contrast to the permissive style) are equally demanding, forceful, and…

Tunneling magnetoresistance in junctions composed of ferromagnets and time-reversal invariant topological superconductors

International Nuclear Information System (INIS)

Yan, Zhongbo; Wan, Shaolong

2016-01-01

Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance. (paper)

Investigation of superparamagnetism in pure and chromium substituted cobalt nanoferrite

Energy Technology Data Exchange (ETDEWEB)

Raghasudha, M., E-mail: raghasudha_m@yahoo.co.in [Department of Chemistry, University College of Science, Osmania University, Hyderabad 500007, Telangana (India); Ravinder, D. [Department of Physics, University College of Science, Osmania University, Hyderabad 500007, Telangana (India); Veerasomaiah, P. [Department of Chemistry, University College of Science, Osmania University, Hyderabad 500007, Telangana (India)

2016-12-15

Nanostructured magnetic materials with the chemical composition CoFe{sub 2}O{sub 4} and CoCr{sub 0.9}Fe{sub 1.1}O{sub 4} were synthesized through Citrate-gel chemical synthesis with a crystallite size of 6.5 nm and 10.7 nm respectively. Structural characterization of the samples was performed by X-ray diffraction analysis and magnetic properties were studied using Vibrating Sample Magnetometer (VSM). Magnetization measurements as a function of applied magnetic field ±10 T at various temperatures 5 K, 25 K, 310 K and 355 K were carried out. Field cooled (FC) and Zero field cooled (ZFC) magnetization measurements under a magnetic field of 100 Oe for temperature ranging from 5–400 K were studied. The blocking temperature (T{sub b}) for both the ferrites was observed to be around 355 K. Below blocking temperature they showed ferromagnetic behavior and above which they are superparamagnetic in nature that favors their application in the biomedical field. The substitution of paramagnetic Cr{sup 3+} ions for magnetic Fe{sup 3+} ion in cobalt ferrite has resulted in a decrease in magnetization and the coercivity of the samples. CoCr{sub 0.9}Fe{sub 1.1}O{sub 4} nanoferrites with observed low coercivity of 338 Oe make them desirable in high frequency transformers due to their very soft magnetic behavior. - Highlights: • Particle size of CoFe{sub 2}O{sub 4} and CoCr{sub 0.9}Fe{sub 1.1}O{sub 4} is 6.5 nm and 10.7 nm respectively. • At 5 K and 25 K the materials were ferromagnetic in nature with high coercivity. • Materials show superparamagnetic behavior above room temperature. • Blocking temperature is at around 355 K where coercivity and remanence are zero. • Materials are suitable for hyperthermia cancer therapy.

Room-temperature ferromagnetism in hydrogenated ZnO nanoparticles

Science.gov (United States)

Xue, Xudong; Liu, Liangliang; Wang, Zhu; Wu, Yichu

2014-01-01

The effect of hydrogen doping on the magnetic properties of ZnO nanoparticles was investigated. Hydrogen was incorporated by annealing under 5% H2 in Ar ambient at 700 °C. Room-temperature ferromagnetism was induced in hydrogenated ZnO nanoparticles, and the observed ferromagnetism could be switched between "on" and "off" states through hydrogen annealing and oxygen annealing process, respectively. It was found that Zn vacancy and OH bonding complex (VZn + OH) was crucial to the observed ferromagnetism by using the X-ray photoelectron spectroscopy and positron annihilation spectroscopy analysis. Based on first-principles calculations, VZn + OH was favorable to be presented due to the low formation energy. Meanwhile, this configuration could lead to a magnetic moment of 0.57 μB. The Raman and photoluminescence measurements excluded the possibility of oxygen vacancy as the origin of the ferromagnetism.

Micromagnetic simulation of exchange coupled ferri-/ferromagnetic heterostructures

Energy Technology Data Exchange (ETDEWEB)

Oezelt, Harald, E-mail: harald.oezelt@fhstp.ac.at [Industrial Simulation, St. Pölten University of Applied Sciences, Matthias Corvinus-Straße 15, A-3100 St. Pölten (Austria); Kovacs, Alexander; Reichel, Franz; Fischbacher, Johann; Bance, Simon [Industrial Simulation, St. Pölten University of Applied Sciences, Matthias Corvinus-Straße 15, A-3100 St. Pölten (Austria); Gusenbauer, Markus [Center for Integrated Sensor Systems, Danube University Krems, Viktor Kaplan-Straße 2, A-2700 Wiener Neustadt (Austria); Schubert, Christian; Albrecht, Manfred [Institute of Physics, Chemnitz University of Technology, Reichenhainer Straße 70, D-09126 Chemnitz (Germany); Institute of Physics, University of Augsburg, Universitätsstraße 1, D-86159 Augsburg (Germany); Schrefl, Thomas [Industrial Simulation, St. Pölten University of Applied Sciences, Matthias Corvinus-Straße 15, A-3100 St. Pölten (Austria); Center for Integrated Sensor Systems, Danube University Krems, Viktor Kaplan-Straße 2, A-2700 Wiener Neustadt (Austria)

2015-05-01

Exchange coupled ferri-/ferromagnetic heterostructures are a possible material composition for future magnetic storage and sensor applications. In order to understand the driving mechanisms in the demagnetization process, we perform micromagnetic simulations by employing the Landau–Lifshitz–Gilbert equation. The magnetization reversal is dominated by pinning events within the amorphous ferrimagnetic layer and at the interface between the ferrimagnetic and the ferromagnetic layer. The shape of the computed magnetization reversal loop corresponds well with experimental data, if a spatial variation of the exchange coupling across the ferri-/ferromagnetic interface is assumed. - Highlights: • We present a model for exchange coupled ferri-/ferromagnetic heterostructures. • We incorporate the microstructural features of the amorphous ferrimagnet. • A distribution of interface exchange coupling is assumed to fit experimental data. • The reversal is dominated by pinning within the ferrimagnet and at the interface.

Onset of itinerant ferromagnetism associated with semiconductor ...

Indian Academy of Sciences (India)

In this paper, the magnetic and transport properties of the TiNb1−CoSn solid solution compounds with half Heusler cubic MgAgAs-type structure have been studied. This work shows the onset of ferromagnetism associated with a semiconductor to metal transition. The transition occurs directly from ferromagnetic metal to ...

Understanding lattice defects to influence ferromagnetic order of ZnO nanoparticles by Ni, Cu, Ce ions

Energy Technology Data Exchange (ETDEWEB)

Verma, Kuldeep Chand, E-mail: dkuldeep.physics@gmail.com [Department of Physics, Panjab University, Chandigarh 160014 (India); Kotnala, R.K., E-mail: rkkotnala@gmail.com [CSIR-National Physical Laboratory, New Delhi 110012 (India)

2017-02-15

Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-T{sub c} ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism. - Graphical abstract: The lattice defects/vacancies attributed by Ni and Ce ions in the wurtzite ZnO structure are responsible in high T{sub c} -ferromagnetism due to long-range magnetic

Coercivity enhancement in Nd-Fe-B sintered permanent magnet by Dy nanoparticles doping

Energy Technology Data Exchange (ETDEWEB)

Liu, W.Q., E-mail: liuweiqiang77@hotmail.co [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Sun, H. [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Yi, X.F. [Anhui Earth-panda Advance Magnetic Material Co., Ltd., Anhui 231500 (China); Liu, X.C.; Zhang, D.T. [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Yue, M., E-mail: yueming@bjut.edu.c [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Zhang, J.X. [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China)

2010-07-02

Nd-Fe-B permanent magnets with a small amount of Dysprosium (Dy) nanoparticles doping were prepared by conventional sintered method, and the microstructure and magnetic properties of the magnets were studied. Investigation shows that the coercivity rises gradually, while the remanence decreases simultaneously with increased Dy doping amount. As a result, the magnet with 1.5 wt.% Dy exhibits optimal magnetic properties. Further investigation presumed that Dy is enriched as (Nd, Dy){sub 2}Fe{sub 14}B phase in the surface region of the Nd{sub 2}Fe{sub 14}B matrix grains indicated by the enhancement of the magneto-crystalline anisotropy field of the Nd{sub 2}Fe{sub 14}B phase. As a result, the magnet doped with a small amount of Dy nanoparticles possesses remarkably enhanced coercivity without sacrificing its magnetization noticeably.

High-coercivity minerals from North African Humid Period soil material deposited in Lake Yoa (Chad)

Science.gov (United States)

Just, J.; Kroepelin, S.; Wennrich, V.; Viehberg, F. A.; Wagner, B.; Rethemeyer, J.; Karls, J.; Melles, M.

2015-12-01

The Holocene is a period of fundamental climatic change in North Africa. Humid conditions during the so-called African Humid Period (AHP) have favored the formation of big lake systems. Only very few of these lakes persist until today. One of them is Lake Yoa (19°03'N/20°31'E) in the Ounianga Basin, Chad, which maintains its water level by ground water inflow. Here we present the magnetic characteristics together with proxies for lacustrine productivity and biota of a sediment core (Co1240) from Lake Yoa, retrieved in 2010 within the framework of the Collaborative Research Centre 806 - Our Way to Europe (Deutsche Forschungsgemeinschaft). Magnetic properties of AHP sediments show strong indications for reductive diagenesis. An up to ~ 80 m higher lake level is documented by lacustrine deposits in the Ounianga Basin, dating to the early phase of the AHP. The higher lake level and less strong seasonality restricted deep mixing of the lake. Development of anoxic conditions consequently lead to the dissolution of iron oxides. An exception is an interval with high concentration of high-coercivity magnetic minerals, deposited between 7800 - 8120 cal yr BP. This interval post-dates the 8.2 event, which was dry in Northern Africa and probably caused a reduced vegetation cover. We propose that the latter resulted in the destabilization of soils around Lake Yoa. After the re-establishment of humid conditions, these soil materials were eroded and deposited in the lake. Magnetic minerals appear well preserved in the varved Late Holocene sequence, indicating (sub-) oxic conditions in the lake. This is surprising, because the occurrence of varves is often interpreted as an indicator for anoxic conditions of the lake water. However, the salinity of lake water rose strongly after the AHP. We therefore hypothesize that the conservation of varves and absence of benthic organisms rather relates to the high salinity than to anoxic conditions.

Superconductivity near ferromagnetism in MgCNi3

International Nuclear Information System (INIS)

Rosner, H.; Weht, R.; Johannes, M.; Pickett, W.E.; Tosatti, E.

2001-06-01

Superconductivity and ferromagnetism have been believed to be incompatible over any extended temperature range until certain specific examples - RuSr 2 GdCu 2 O 8 and UGe 2 - have arisen in the past 2-3 years. The discovery of superconductivity above 8 K in MgCNi 3 , which is primarily the ferromagnetic element Ni and is strongly exchange-enhanced, provides a probable new and different example. This compound is shown here to be near ferromagnetism, requiring only hole-doping by 12% substitution of Mg by Na or Li. This system will provide the means to probe coupling, and possible coexistence, of these two forms of collective behavior without the requirement of pressure. (author)

Room temperature ferromagnetism in Mn-doped NiO nanoparticles

Science.gov (United States)

Layek, Samar; Verma, H. C.

2016-01-01

Mn-doped NiO nanoparticles of the series Ni1-xMnxO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.

Formation of DNA-network embedding ferromagnetic Cobalt nano-particles

Science.gov (United States)

Kanki, Teruo; Tanaka, Hidekazu; Shirakawa, Hideaki; Sacho, Yu; Taniguchi, Masateru; Lee, Hea-Yeon; Kawai, Tomoji; Kang, Nam-Jung; Chen, Jinwoo

2002-03-01

Formation of DNA-network embedding ferromagnetic Cobalt nano-particles T. Kanki, Hidekazu. Tanaka, H. Shirakawa, Y. Sacho, M. Taniguchi, H. Lee, T. Kawai The Institute of Scientific and Industrial Research, Osaka University, Japan and Nam-Jung Kang, Jinwoo Chen Korea Advanced Institute of Science and Technology (KAIST), Korea DNA can be regarded as a naturally occurring and highly specific functional biopolymer and as a fine nano-wire. Moreover, it was found that large-scale DNA networks can be fabricated on mica surfaces. By using this network structure, we can expect to construct nano-scale assembly of functional nano particle, for example ferromagnetic Co nano particles, toward nano scale spin-electronics based on DNA circuits. When we formed DNA network by 250mg/ml DNA solution of poly(dG)-poly(dC) including ferromagnetic Co nano particles (diameter of 12nm), we have conformed the DNA network structure embedding Co nano-particles (height of about 12nm) by atomic force microscopy. On the other hand, we used 100mg/ml DNA solution, DNA can not connect each other, and many Co nano-particles exist without being embedded.

Two-fold origin of the deformation-induced ferromagnetism in bulk Fe60Al40 (at.%) alloys

International Nuclear Information System (INIS)

Menendez, E; Surinach, S; Baro, M D; Sort, J; Liedke, M O; Fassbender, J; Nogues, J

2008-01-01

The transition from the atomically ordered B2-phase to the chemically disordered A2-phase and the concomitant deformation-induced ferromagnetism have been investigated in bulk polycrystalline Fe 60 Al 40 (at.%) alloys subjected to compression processes. A detailed correlation between structural, magnetic and mechanical properties reveals that the generated ferromagnetism depends on the stress level but is virtually independent of the loading rate. The mechanisms governing the induced ferromagnetism also vary as the stress level is increased. Namely, in the low-stress regime both lattice cell expansion and atomic intermixing play a role in the induced ferromagnetic behavior. Conversely, lattice expansion seems to become the main mechanism contributing to the generated ferromagnetism in the high-stress regime. Furthermore, a correlation is also observed between the order-disorder transition and the mechanical hardness. Hence, a combination of magnetic and mechanical measurements can be used, in synergetic manner, to investigate this deformation-induced phase transition.

Innovative soft magnetic multilayers with enhanced in-plane anisotropy and ferromagnetic resonance frequency for integrated RF passive devices

Science.gov (United States)

Falub, Claudiu V.; Bless, Martin; Hida, Rachid; MeduÅa, Mojmír; Ammann, Arnold

2018-04-01

We present an innovative, economical method for manufacturing soft magnetic materials that may pave the way for integrated thin film magnetic cores with dramatically improved properties. Soft magnetic multilayered thin films based on the Fe-28%Co20%B (at.%) and Co-4.5%Ta4%Zr (at.%) amorphous alloys are deposited on 8" bare Si and Si/200nm-thermal-SiO2 wafers in an industrial, high-throughput Evatec LLS EVO II magnetron sputtering system. The multilayers consist of stacks of alternating 80-nm-thick ferromagnetic layers and 4-nm-thick Al2O3 dielectric interlayers. Since in our dynamic sputter system the substrate cage rotates continuously, such that the substrates face different targets alternatively, each ferromagnetic sublayer in the multilayer consists of a fine structure comprising alternating CoTaZr and FeCoB nanolayers with very sharp interfaces. We adjust the thickness of these individual nanolayers between 0.5 and 1.5 nm by changing the cage rotation speed and the power of each gun, which is an excellent mode to engineer new, composite ferromagnetic materials. Using X-ray reflectometry (XRR) we reveal that the interfaces between the FeCoB and CoTaZr nanolayers are perfectly smooth with roughness of 0.2-0.3 nm. Kerr magnetometry and B-H looper measurements for the as-deposited samples show that the coercivity of these thin films is very low, 0.2-0.3 Oe, and gradually scales up with the thickness of FeCoB nanolayers, i.e. with the increase of the overall Fe content from 0 % (e.g. CoTaZr-based multilayers) to 52 % (e.g. FeCoB-based multilayers). We explain this trend in the random anisotropy model, based on considerations of grain size growth, as revealed by glancing angle X-ray diffraction (GAXRD), but also because of the increase of magnetostriction with the increase of Fe content as shown by B-H looper measurements performed on strained wafers. The unexpected enhancement of the in-plane anisotropy field from 18.3 Oe and 25.8 Oe for the conventional Co

Innovative soft magnetic multilayers with enhanced in-plane anisotropy and ferromagnetic resonance frequency for integrated RF passive devices

Directory of Open Access Journals (Sweden)

Claudiu V. Falub

2018-04-01

Full Text Available We present an innovative, economical method for manufacturing soft magnetic materials that may pave the way for integrated thin film magnetic cores with dramatically improved properties. Soft magnetic multilayered thin films based on the Fe-28%Co20%B (at.% and Co-4.5%Ta4%Zr (at.% amorphous alloys are deposited on 8” bare Si and Si/200nm-thermal-SiO2 wafers in an industrial, high-throughput Evatec LLS EVO II magnetron sputtering system. The multilayers consist of stacks of alternating 80-nm-thick ferromagnetic layers and 4-nm-thick Al2O3 dielectric interlayers. Since in our dynamic sputter system the substrate cage rotates continuously, such that the substrates face different targets alternatively, each ferromagnetic sublayer in the multilayer consists of a fine structure comprising alternating CoTaZr and FeCoB nanolayers with very sharp interfaces. We adjust the thickness of these individual nanolayers between 0.5 and 1.5 nm by changing the cage rotation speed and the power of each gun, which is an excellent mode to engineer new, composite ferromagnetic materials. Using X-ray reflectometry (XRR we reveal that the interfaces between the FeCoB and CoTaZr nanolayers are perfectly smooth with roughness of 0.2-0.3 nm. Kerr magnetometry and B-H looper measurements for the as-deposited samples show that the coercivity of these thin films is very low, 0.2-0.3 Oe, and gradually scales up with the thickness of FeCoB nanolayers, i.e. with the increase of the overall Fe content from 0 % (e.g. CoTaZr-based multilayers to 52 % (e.g. FeCoB-based multilayers. We explain this trend in the random anisotropy model, based on considerations of grain size growth, as revealed by glancing angle X-ray diffraction (GAXRD, but also because of the increase of magnetostriction with the increase of Fe content as shown by B-H looper measurements performed on strained wafers. The unexpected enhancement of the in-plane anisotropy field from 18.3 Oe and 25.8 Oe for the

The ferromagnetic-spin glass transition in PdMn alloys: symmetry breaking of ferromagnetism and spin glass studied by a multicanonical method.

Science.gov (United States)

Kato, Tomohiko; Saita, Takahiro

2011-03-16

The magnetism of Pd(1-x)Mn(x) is investigated theoretically. A localized spin model for Mn spins that interact with short-range antiferromagnetic interactions and long-range ferromagnetic interactions via itinerant d electrons is set up, with no adjustable parameters. A multicanonical Monte Carlo simulation, combined with a procedure of symmetry breaking, is employed to discriminate between the ferromagnetic and spin glass orders. The transition temperature and the low-temperature phase are determined from the temperature variation of the specific heat and the probability distributions of the ferromagnetic order parameter and the spin glass order parameter at different concentrations. The calculation results reveal that only the ferromagnetic phase exists at x glass phase exists at x > 0.04, and that the two phases coexist at intermediate concentrations. This result agrees semi-quantitatively with experimental results.

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

International Nuclear Information System (INIS)

Philippe, M P; Wéra, L; Fagnard, J-F; Vanderheyden, B; Vanderbemden, P; Ainslie, M D; Dennis, A R; Shi, Y-H; Cardwell, D A

2015-01-01

Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y–Ba–Cu–O high temperature superconductor to form superconductor/ferromagnet hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*, saturation of the ferromagnet occurs, and above d*, a weak thickness-dependence is observed. The influence of the ferromagnet is observed even if its saturation magnetization is lower than the trapped flux density of the superconductor. Conversely, thin ferromagnetic discs can be driven to full saturation even though the outer magnetic field is much smaller than their saturation magnetization. (paper)

Analysis of ultra-narrow ferromagnetic domain walls

Energy Technology Data Exchange (ETDEWEB)

Jenkins, Catherine; Paul, David

2012-01-10

New materials with high magnetic anisotropy will have domains separated by ultra-narrow ferromagnetic walls with widths on the order of a few unit cells, approaching the limit where the elastic continuum approximation often used in micromagnetic simulations is accurate. The limits of this approximation are explored, and the static and dynamic interactions with intrinsic crystalline defects and external driving elds are modeled. The results developed here will be important when considering the stability of ultra-high-density storage media.

Biaxial stress driven tetragonal symmetry breaking and high-temperature ferromagnetic semiconductor from half-metallic CrO2

Science.gov (United States)

Xiao, Xiang-Bo; Liu, Bang-Gui

2018-03-01

It is highly desirable to combine the full spin polarization of carriers with modern semiconductor technology for spintronic applications. For this purpose, one needs good crystalline ferromagnetic (or ferrimagnetic) semiconductors with high Curie temperatures. Rutile CrO2 is a half-metallic spintronic material with Curie temperature 394 K and can have nearly full spin polarization at room temperature. Here, we find through first-principles investigation that when a biaxial compressive stress is applied on rutile CrO2, the density of states at the Fermi level decreases with the in-plane compressive strain, there is a structural phase transition to an orthorhombic phase at the strain of -5.6 % , and then appears an electronic phase transition to a semiconductor phase at -6.1 % . Further analysis shows that this structural transition, accompanying the tetragonal symmetry breaking, is induced by the stress-driven distortion and rotation of the oxygen octahedron of Cr, and the half-metal-semiconductor transition originates from the enhancement of the crystal field splitting due to the structural change. Importantly, our systematic total-energy comparison indicates the ferromagnetic Curie temperature remains almost independent of the strain, near 400 K. This biaxial stress can be realized by applying biaxial pressure or growing the CrO2 epitaxially on appropriate substrates. These results should be useful for realizing full (100%) spin polarization of controllable carriers as one uses in modern semiconductor technology.

Influence of lattice defects on criticality of Potts ferromagnet

International Nuclear Information System (INIS)

Souza Costa, U.M. de.

1985-01-01

The critical properties of the q-state Potts ferromagnet and the anisotropic Heisenberg model on hypercubic lattices (d = 2,3); emphasis is given to the free surface and the interface effects, the Real Space Renormalization Group approach. The criticality of the quenched bond-mixed q-state Potts ferromagnet on square lattice is discussed. It is shown that, the crossover from the pure fixed point to the random one occurs, while q increases, through a pitchfork bifurcation; the relation-ship with the Harris criterion is analyzed. High precision numerical values for the critical temperatures corresponding to arbitrary concentrations of the coupling constants J sub(1) and J sub(2), and arbitrary ratios J sub(1)/J sub(2) are presented.(author)

Magnetization reversal and coercivity of Fe3Se4 nanowire arrays

Science.gov (United States)

Li, D.; Li, S. J.; Zhou, Y. T.; Bai, Y.; Zhu, Y. L.; Ren, W. J.; Long, G.; Zeng, H.; Zhang, Z. D.

2015-05-01

The microstructure and magnetic properties of Fe3Se4 nanowire (NW) arrays in anodic aluminum oxide (AAO) porous membrane are studied. Cross-sectional SEM and plane-view TEM images show that the mean wire diameter (dw) and the center-to-center spacing (D) of Fe3Se4 nanowires are about 220 nm and 330 nm, respectively. The field-cooled magnetization dependent on the temperature indicates a Curie temperature around 334 K for the Fe3Se4 nanowires. The coercivities of Fe3Se4 nanowires at 10 K, obtained from the in-plane and out-of-plane hysteresis loops, are as high as 22.4 kOe and 23.3 kOe, which can be understood from the magnetocrystalline anisotropy and the magnetization reversal process.

Research Update: Strain and composition effects on ferromagnetism of Mn0.05Ge0.95 quantum dots

Directory of Open Access Journals (Sweden)

Liming Wang

2016-04-01

Full Text Available Mn0.05Ge0.95 quantum dots (QDs samples were grown by molecular beam epitaxy on Si substrates and 15-nm-thick fully strained Si0.8Ge0.2 virtual substrates, respectively. The QDs samples grown on the Si0.8Ge0.2 virtual substrates show a significant ferromagnetism with a Curie temperature of 227 K, while the QDs samples grown on the Si substrates are non-ferromagnetic. Microstructures of the QDs samples were characterized by high resolution transmission electron microscopy and synchrotron radiation X-ray diffraction. Interdependence between microstructure and ferromagnetism of Mn-doped Ge QDs was investigated. For the QDs sample grown on the strained Si0.8Ge0.2 virtual substrate, although the ferromagnetic phase Mn5Ge3 clusters were found to be formed in small dome-shaped dots, the significant ferromagnetism observed in that sample is attributed to ferromagnetic phase Mn-doped large dome-shaped Ge QDs, rather than to the ferromagnetic phase Mn5Ge3 clusters. The fully strained Si0.8Ge0.2 virtual substrates would result in a residual strain into the QDs and an increase in Ge composition in the QDs. Both consequences favor the formations of ferromagnetic phase Mn-doped Ge QDs from points of view of quantum confinement effect as well as Mn doping at substitutional sites.

Room temperature ferromagnetism in Mn-doped NiO nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Layek, Samar, E-mail: samarlayek@gmail.com; Verma, H.C.

2016-01-01

Mn-doped NiO nanoparticles of the series Ni{sub 1−x}Mn{sub x}O (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum. - Highlights: • Mn-doped NiO nanoparticles are prepared by a simple hydrothermal method. • Unit cell volume decreases with increasing doping concentration. • Mn-doping leads to room temperature ferromagnetism in NiO nanoparticles. • Magnetization is highest for 2% Mn-doping. • Above 2%, magnetization decreases with increasing doping.

Room temperature ferromagnetism in Mn-doped NiO nanoparticles

International Nuclear Information System (INIS)

Layek, Samar; Verma, H.C.

2016-01-01

Mn-doped NiO nanoparticles of the series Ni_1_−_xMn_xO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum. - Highlights: • Mn-doped NiO nanoparticles are prepared by a simple hydrothermal method. • Unit cell volume decreases with increasing doping concentration. • Mn-doping leads to room temperature ferromagnetism in NiO nanoparticles. • Magnetization is highest for 2% Mn-doping. • Above 2%, magnetization decreases with increasing doping.

High-pressure catalytic chemical vapor deposition of ferromagnetic ruthenium-containing carbon nanostructures

Energy Technology Data Exchange (ETDEWEB)

Khavrus, Vyacheslav O., E-mail: V.Khavrus@ifw-dresden.de; Ibrahim, E. M. M.; Bachmatiuk, Alicja; Ruemmeli, Mark H.; Wolter, A. U. B.; Hampel, Silke; Leonhardt, Albrecht [IFW Dresden (Germany)

2012-06-15

We report on the high-pressure catalytic chemical vapor deposition (CCVD) of ruthenium nanoparticles (NPs) and single-walled carbon nanotubes (SWCNTs) by means of gas-phase decomposition of acetonitrile and ruthenocene in a tubular quartz flow reactor at 950 Degree-Sign C and at elevated pressures (between 2 and 8 bar). The deposited material consists of Ru metal cores with sizes ranging between 1 and 3 nm surrounded by a carbon matrix. The high-pressure CCVD seems to be an effective route to obtain composite materials containing metallic NPs, Ru in this work, inside a nanostructured carbon matrix protecting them from oxidation in ambient air. We find that in contradiction to the weak paramagnetic properties characterizing bulk ruthenium, the synthesized samples are ferromagnetic as predicted for nanosized particles of nonmagnetic materials. At low pressure, the very small ruthenium catalyst particles are able to catalyze growth of SWCNTs. Their yield decreases with increasing reaction pressure. Transmission electron microscopy, selected area energy-dispersive X-ray analysis, Raman spectroscopy, and magnetic measurements were used to analyze and confirm properties of the synthesized NPs and nanotubes. A discussion on the growth mechanism of the Ru-containing nanostructures is presented.

Coercive force changes in Sm(CoFeCuZr)z during step-like heat treatments

International Nuclear Information System (INIS)

Puzanova, T.Z.; Shchegoleva, N.N.; Sakhnova, L.V.; Majkov, V.G.; Shur, Ya.S.; Nikolaeva, N.V.

1987-01-01

Sm(Co 0.67 Fe 0.22 Cu 0.08 Zr 0.03 ) 8.35 alloy, contaning two homogeneous solid solutions SmM 6.85 and SmM 7.75 (M=Co, Fe, Cu, Zr) after high-temperature treatment, is investigated. It is shown, that after isothermal tempering at 800 deg C, SmM 6.85 and SmM 7.75 are close by microstructure and their coercive forces change in a different way during step-like cooling within 700-400 deg C interval. Possibility of producing material, single-phase in magnetic relation, is discussed

Large-scale calculation of ferromagnetic spin systems on the pyrochlore lattice

Energy Technology Data Exchange (ETDEWEB)

Soldatov, Konstantin, E-mail: soldatov_ks@students.dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Nefedev, Konstantin, E-mail: nefedev.kv@dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Institute of Applied Mathematics, Far Eastern Branch, Russian Academy of Science, Vladivostok (Russian Federation); Komura, Yukihiro [CIJ-solutions, Chuo-ku, Tokyo 103-0023 (Japan); Okabe, Yutaka, E-mail: okabe@phys.se.tmu.ac.jp [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan)

2017-02-19

We perform the high-performance computation of the ferromagnetic Ising model on the pyrochlore lattice. We determine the critical temperature accurately based on the finite-size scaling of the Binder ratio. Comparing with the data on the simple cubic lattice, we argue the universal finite-size scaling. We also calculate the classical XY model and the classical Heisenberg model on the pyrochlore lattice. - Highlights: • Calculations of the ferromagnetic models on the pyrochlore lattice were performed. • Precise critical temperatures were determined using Binder ratio finite-size scaling. • The universal finite-size scaling was argued.

Room-temperature ferromagnetism in hydrogenated ZnO nanoparticles

International Nuclear Information System (INIS)

Xue, Xudong; Liu, Liangliang; Wang, Zhu; Wu, Yichu

2014-01-01

The effect of hydrogen doping on the magnetic properties of ZnO nanoparticles was investigated. Hydrogen was incorporated by annealing under 5% H 2 in Ar ambient at 700 °C. Room-temperature ferromagnetism was induced in hydrogenated ZnO nanoparticles, and the observed ferromagnetism could be switched between “on” and “off” states through hydrogen annealing and oxygen annealing process, respectively. It was found that Zn vacancy and OH bonding complex (V Zn  + OH) was crucial to the observed ferromagnetism by using the X-ray photoelectron spectroscopy and positron annihilation spectroscopy analysis. Based on first-principles calculations, V Zn  + OH was favorable to be presented due to the low formation energy. Meanwhile, this configuration could lead to a magnetic moment of 0.57 μ B . The Raman and photoluminescence measurements excluded the possibility of oxygen vacancy as the origin of the ferromagnetism

Attitude of young psychiatrists toward coercive measures in psychiatry: a case vignette study in Japan

Directory of Open Access Journals (Sweden)

Wake Yosuke

2009-09-01

Full Text Available Abstract Background Every psychiatrist must pay careful attention to avoid violating human rights when initiating coercive treatments such as seclusion and restraint. However, these interventions are indispensable in clinical psychiatry, and they are often used as strategies to treat agitated patients. In this study, we investigated young psychiatrists' attitudes toward psychiatric coercive measures. Methods A total of 183 young psychiatrists participated as subjects in our study. A questionnaire with a case vignette describing a patient with acute psychosis was sent to the study subjects via the Internet or by mail. This questionnaire included scoring the necessity for hospitalization, and the likelihood of prescribing seclusion and/or restraint, on a 9-point Likert scale (with 9 indicating strong agreement. Results There was general agreement among the study subjects that the case should be admitted to a hospital (8.91 ± 0.3 and secluded (8.43 ± 1.0. The estimated length of hospitalization was 13.53 ± 6.4 weeks. Regarding the likelihood of prescribing restraint, results showed great diversity (5.14 ± 2.5 on 9-point scale; psychiatrists working at general hospitals scored significantly higher (6.25 ± 2.5 than those working at university hospitals (5.02 ± 2.3 or psychiatric hospitals (4.15 ± 2.6. A two-group comparison of the length of inpatient care revealed a significant difference between those psychiatrists who scored 1-3 (n = 55, 14.22 ± 7.4 wks and those who scored 7-9 (n = 62, 12.22 ± 4.0 regarding the need to use restraint. Conclusion Our results may reflect the current dilemma in Japanese psychiatry wherein psychiatrists must initiate coercive measures to shorten hospitalization stays. This study prompted its subject psychiatrists to consider coercive psychiatric treatments.

Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide

KAUST Repository

Li, Yangyang

2017-12-16

Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.

Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide

KAUST Repository

Li, Yangyang; Weng, Yakui; Yin, Xinmao; Yu, Xiaojiang; Sarath Kumar, S. R.; Wehbe, Nimer; Wu, Haijun; Alshareef, Husam N.; Pennycook, Stephen J.; Breese, Mark B. H.; Chen, Jingsheng; Dong, Shuai; Wu, Tao

2017-01-01

Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.

Investigation of energy losses in low-coercivity resin-bonded magnets in alternating magnetic fields

Science.gov (United States)

Milov, E. V.; Sipin, I. A.; Milov, V. N.; Andreenko, A. S.; Balan, I. A.

2017-01-01

Energy losses during alternating remagnetization of low-coercitivity resin-bonded magnets and commercially produced electrical steels were studied experimentally. The studies were conducted on several samples of resin-bonded magnets with different manufacturing technologies and samples of electrical steel sheets of various thicknesses. The static and dynamic magnetic properties of the samples were measured on a vibration magnetometer and a specially designed apparatus, respectively. It was found that the studied samples of bonded magnets have a relatively high level of hysteresis losses associated with high coercivity, which reaches a value of 4-5 Oe. At the same time, the remagnetization losses due to the Foucault currents in the bonded magnets are considerably lower than in electrical steels. The measurement results show that bonded magnets at high frequencies of remagnetization, especially in high-rpm motors, can be competitive in comparison with electrical steels.

Oxygen vacancy-induced ferromagnetism in un-doped ZnO thin films

Science.gov (United States)

Zhan, Peng; Wang, Weipeng; Liu, Can; Hu, Yang; Li, Zhengcao; Zhang, Zhengjun; Zhang, Peng; Wang, Baoyi; Cao, Xingzhong

2012-02-01

ZnO films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.

A method for measuring exchange stiffness in ferromagnetic films

International Nuclear Information System (INIS)

Girt, Erol; Huttema, W.; Montoya, E.; Kardasz, B.; Eyrich, C.; Heinrich, B.; Mryasov, O. N.; Dobin, A. Yu.; Karis, O.

2011-01-01

An exchange stiffness, A ex , in ferromagnetic films is obtained by fitting the M(H) dependence of two ferromagnetic layers antiferromagnetically coupled across a nonmagnetic spacer layer with a simple micromagnetic model. In epitaxial and textured structures this method allows measuring A ex between the crystallographic planes perpendicular to the growth direction of ferromagnetic films. Our results show that A ex between [0001] planes in textured Co grains is 1.54 ± 0.12 x 10 -11 J/m.

Magnetic characterisation of large grain, bulk Y–Ba–Cu–O superconductor–soft ferromagnetic alloy hybrid structures

International Nuclear Information System (INIS)

Philippe, M.P.; Fagnard, J.-F.; Kirsch, S.; Xu, Z.; Dennis, A.R.; Shi, Y.-H.; Cardwell, D.A.; Vanderheyden, B.; Vanderbemden, P.

2014-01-01

Highlights: • Large grain, bulk YBaCuO superconductor (SC) combined with ferromagnetic elements. • The flux lines curve outwards through the ferromagnet in the remanent state. • The trapped field in the SC is enhanced by the presence of the ferromagnet. • The effects of the SC and the ferromagnet add when the ferromagnet is saturated. - Abstract: Large grain, bulk Y–Ba–Cu–O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In the present work, we investigate how the trapped field of such magnets can be improved by combining bulk YBCO with a soft FeNi, ferromagnetic alloy. This involves machining the alloy into components of various shapes, such as cylinders and rings, which are attached subsequently to the top surface of a solid, bulk HTS cylinder. The effect of these modifications on the magnetic hysteresis curve and trapped field of the bulk superconductor at 77 K are then studied using pick-up coil and Hall probe measurements. The experimental data are compared to finite element modelling of the magnetic flux distribution using Campbell’s algorithm. Initially we establish the validity of the technique involving pick-up coils wrapped around the bulk superconductor to obtain its magnetic hysteresis curve in a non-destructive way and highlight the difference between the measured signal and the true magnetization of the sample. We then consider the properties of hybrid ferromagnet/superconductor (F/S) structures. Hall probe measurements, together with the results of the model, establish that flux lines curve outwards through the ferromagnet, which acts, effectively, like a magnetic short circuit. Magnetic hysteresis curves show that the effects of the superconductor and the ferromagnet simply add when the ferromagnet is saturated fully by the applied field. The trapped field of the hybrid structure is always larger than that of the

Study of the magnetic microstructure of high-coercivity sintered SmCo5 permanent magnets with the conventional Bitter pattern technique and the colloid-SEM method

International Nuclear Information System (INIS)

Szmaja, Witold

2007-01-01

The magnetic microstructure of high-coercivity sintered SmCo 5 permanent magnets was studied with the conventional Bitter pattern technique, and also for the first time with the colloid-scanning electron microscopy (colloid-SEM) method. Both techniques were supported by digital image acquisition, enhancement and analysis. Thanks to this, it was possible to obtain high-contrast and clear images of the magnetic microstructure and to analyze them in detail, and consequently also to achieve improvements over earlier results. In the thermally demagnetized state the grains were composed of magnetic domains. On the surface perpendicular to the alignment axis, the main domains forming a maze pattern and surface reverse spikes were observed. Investigations on the surface parallel to the alignment axis, especially by the colloid-SEM technique, provided a detailed insight into the orientation of grains. The alignment of grains was good, but certainly not perfect; there were also strongly misaligned grains, although generally very rare. In most cases the domain structures within grains were independent of their neighbors, but in some cases (not so rare) the domain walls were observed to continue through the grain boundaries, indicating significant magnetostatic interaction between neighboring grains. Studies of the behavior of the magnetic microstructure under the influence of an external magnetic field, performed for the first time on the surface parallel to the alignment axis (with the conventional Bitter pattern method), showed that the domain walls move easily within the grains and that the magnetization reversal mechanism is mainly related to the nucleation and growth of reverse domains, i.e. that sintered SmCo 5 magnets are nucleation-dominated systems. Groupwise magnetization reversal of adjacent magnetically coupled grains was observed, an unfavorable effect for high-coercivity magnets. Images obtained by the colloid-SEM technique and the conventional Bitter pattern

Room-temperature ferromagnetism in hydrogenated ZnO nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Xue, Xudong; Liu, Liangliang; Wang, Zhu; Wu, Yichu, E-mail: ycwu@whu.edu.cn [School of Physics and Technology, Hubei Nuclear Solid Physics Key Laboratory, Wuhan University, Wuhan 430072 (China)

2014-01-21

The effect of hydrogen doping on the magnetic properties of ZnO nanoparticles was investigated. Hydrogen was incorporated by annealing under 5% H{sub 2} in Ar ambient at 700 °C. Room-temperature ferromagnetism was induced in hydrogenated ZnO nanoparticles, and the observed ferromagnetism could be switched between “on” and “off” states through hydrogen annealing and oxygen annealing process, respectively. It was found that Zn vacancy and OH bonding complex (V{sub Zn} + OH) was crucial to the observed ferromagnetism by using the X-ray photoelectron spectroscopy and positron annihilation spectroscopy analysis. Based on first-principles calculations, V{sub Zn} + OH was favorable to be presented due to the low formation energy. Meanwhile, this configuration could lead to a magnetic moment of 0.57 μ{sub B}. The Raman and photoluminescence measurements excluded the possibility of oxygen vacancy as the origin of the ferromagnetism.

Ferromagnetic shape memory materials

Science.gov (United States)

Tickle, Robert Jay

Ferromagnetic shape memory materials are a new class of active materials which combine the properties of ferromagnetism with those of a diffusionless, reversible martensitic transformation. These materials have been the subject of recent study due to the unusually large magnetostriction exhibited in the martensitic phase. In this thesis we report the results of experiments which characterize the magnetic and magnetomechanical properties of both austenitic and martensitic phases of ferromagnetic shape memory material Ni2MnGa. In the high temperature cubic phase, anisotropy and magnetostriction constants are determined for a range of temperatures from 50°C down to the transformation temperature, with room temperature values of K1 = 2.7 +/- 104 ergs/cm3 and lambda100 = -145 muepsilon. In the low temperature tetragonal phase, the phenomenon of field-induced variant rearrangement is shown to produce anomalous results when traditional techniques for determining anisotropy and magnetostriction properties are employed. The requirement of single variant specimen microstructure is explained, and experiments performed on such a specimen confirm a uniaxial anisotropy within each martensitic variant with anisotropy constant Ku = 2.45 x 106 ergs/cm3 and a magnetostriction constant of lambdasv = -288 +/- 73 muepsilon. A series of magnetomechanical experiments investigate the effects of microstructure bias, repeated field cycling, varying field ramp rate, applied load, and specimen geometry on the variant rearrangement phenomenon in the martensitic phase. In general, the field-induced strain is found to be a function of the variant microstructure. Experiments in which the initial microstructure is biased towards a single variant state with an applied load generate one-time strains of 4.3%, while those performed with a constant bias stress of 5 MPa generate reversible strains of 0.5% over a period of 50 cycles. An increase in the applied field ramp rate is shown to reduce the

Resistive switching via the converse magnetoelectric effect in ferromagnetic multilayers on ferroelectric substrates.

Science.gov (United States)

Pertsev, N A; Kohlstedt, H

2010-11-26

A voltage-controlled resistive switching is predicted for ferromagnetic multilayers and spin valves mechanically coupled to a ferroelectric substrate. The switching between low- and high-resistance states results from the strain-driven magnetization reorientations by about 90°, which are shown to occur in ferromagnetic layers with a high magnetostriction and weak cubic magnetocrystalline anisotropy. Such reorientations, not requiring external magnetic fields, can be realized experimentally by applying moderate electric field to a thick substrate (bulk or membrane type) made of a relaxor ferroelectric having ultrahigh piezoelectric coefficients. The proposed multiferroic hybrids exhibiting giant magnetoresistance may be employed as electric-write nonvolatile magnetic memory cells with nondestructive readout.

Intrinsic and spatially nonuniform ferromagnetism in Co-doped ZnO films

Science.gov (United States)

Tseng, L. T.; Suter, A.; Wang, Y. R.; Xiang, F. X.; Bian, P.; Ding, X.; Tseng, A.; Hu, H. L.; Fan, H. M.; Zheng, R. K.; Wang, X. L.; Salman, Z.; Prokscha, T.; Suzuki, K.; Liu, R.; Li, S.; Morenzoni, E.; Yi, J. B.

2017-09-01

Co doped ZnO films have been deposited by a laser-molecular beam epitaxy system. X-ray diffraction and UV spectra analysis show that Co effectively substitutes the Zn site. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy analysis indicate that there are no clusters. Co dopants are uniformly distributed in ZnO film. Ferromagnetic ordering is observed in all samples deposited under an oxygen partial pressure, PO2=10-3 , 10-5, and 10-7 torr, respectively. However, the magnetization of PO2=10-3 and 10-5 is very small at room temperature. At low temperature, the ferromagnetic ordering is enhanced. Muon spin relaxation (μ SR ) measurements confirm the ferromagnetism in all samples, and the results are consistent with magnetization measurements. From μ SR and TEM analysis, the film deposited under PO2=10-7 torr shows intrinsic ferromagnetism. However, the volume fraction of the ferromagnetism phase is approximately 70%, suggesting that the ferromagnetism is not carrier mediated. Resistivity versus temperature measurements indicate Efros variable range hopping dominates the conductivity. From the above results, we can confirm that a bound magnetic polaron is the origin of the ferromagnetism.

Magnon-photon interaction in ferromagnets

International Nuclear Information System (INIS)

Shrivastava, K.N.

1980-01-01

A magnon-photon interaction for the magnetic vector of the electromagnetic wave perpendicular to the direction of magnetization in a ferromagnet is constructed with the use of Bogoliubov transformation. The resulting magnon-photon interaction is found to contain several interesting new radiation effects. The self-energy of the magnon is calculated and life times arising from the radiation scattering are predicted. The magnon frequency shift due to the radiation field is found. One of the terms arising from the one-magnon one-photon scattering gives a line width that is in reasonable agreement with the experimentally measured value of ferromagnetic resonance line width in yttrium iron garnet. (orig.)

Angular and geometry dependence of coercivity and remanence nickel nanotube isolated

Energy Technology Data Exchange (ETDEWEB)

Gomes, J.L.; Davila, Y.G.; Garcia, R.P.; Del Toro, A.D.; Martins, I.G.; Hernandez, E.P. [Universidade Federal de Pernambuco (UFPE), PE (Brazil)

2016-07-01

, where we vary the angle of the magnetic field applied to the ferromagnetic system. We investigated the role of geometry in the coercivity and remanence of hysteresis curves, where we analyze the types of magnetization reversal modes that can appear in isolated nanotube system. (author)

Ferromagnetic Film on a Superconducting Substrate

OpenAIRE

Bulaevskii, L. N.; Chudnovsky, E. M.

2000-01-01

We study the equilibrium domain structure and magnetic flux around a ferromagnetic (FM) film with perpendicular magnetization M_0 on a superconducting (SC) substrate. At 4{\\pi}M_0> 1. Here \\lambda_L is the London penetration length. For 4{\\pi}M_0 > H_{c1} and l_{N} in excess of about 35 {\\lambda}_{L}, the domains are connected by SC vortices. We argue that pinning of vortices by magnetic domains in FM/SC multilayers can provide high critical currents.

Itinerant Ferromagnetism in Ultracold Fermi Gases

DEFF Research Database (Denmark)

Heiselberg, Henning

2012-01-01

Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC. Thermodyna......Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC...

Test of the fast thin-film ferromagnetic shutters for ultracold neutrons

International Nuclear Information System (INIS)

Pokotilovskij, Yu.N.; Novopol'tsev, M.I.; Geltenbort, P.

2008-01-01

Test of thin-film ferromagnetic shutters of two types for ultracold neutrons has been performed. The first type is based on neutron reflection from the sequence of successively placed thin ferromagnetic layers with oppositely directed magnetization. The second one is based on neutron refraction in ferromagnetic foils inserted in the beam

Subjective experience of coercion in psychiatric care: a study comparing the attitudes of patients and healthy volunteers towards coercive methods and their justification.

Science.gov (United States)

Mielau, J; Altunbay, J; Gallinat, J; Heinz, A; Bermpohl, F; Lehmann, A; Montag, C

2016-06-01

Under certain conditions, coercive interventions in psychotic patients can help to regain insight and alleviate symptoms, but can also traumatize subjects. This study explored attitudes towards psychiatric coercive interventions in healthy individuals and persons suffering from schizophrenia, schizoaffective or bipolar disorder. The impact of personal history of coercive treatment on preferences concerning clinical management of patients unable to consent was investigated. Six case vignettes depicting scenarios of ethical dilemmas and demanding decisions in favour of or against coercive interventions were presented to 60 healthy volunteers and 90 patients. Structured interviews focusing on experienced coercion were performed in conjunction with the Coercion Experience Scale and the Admission Experience Survey. Symptom severity, psychosocial functioning and insight into illness were assessed as influencing variables. Student's t tests compared patients' and controls' judgments, followed by regression analyses to define the predictive value of symptoms and measures of coercion on judgments regarding the total patient sample and patients with experience of fixation. Patients and non-psychiatric controls showed no significant difference in their attitudes towards involuntary admission and forced medication. Conversely, patients more than controls significantly disapproved of mechanical restraint. Subjective experience of coercive interventions played an important role for the justification of treatment against an individual's "natural will". Factors influencing judgments on coercion were overall functioning and personal experience of treatment effectiveness and fairness. Qualitative and quantitative aspects of perceived coercion, in addition to insight into illness, predicted judgments of previously fixated patients. Results underline the importance of the quality of practical implementation and care, if coercive interventions cannot be avoided.

Out-of-plane coercive field of Ni{sub 80}Fe{sub 20} antidot arrays

Energy Technology Data Exchange (ETDEWEB)

Chunhong, Gao [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China); Ke, Chen [Chongqing Electric Power College, Chongqing (China); Ling, Lue; Jianwei, Zhao [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China); Chen Peng, E-mail: pchen@swu.edu.c [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China)

2010-11-15

The out-of-plane magnetic anisotropy and out-of-plane magnetization reversal process of nanoscale Ni{sub 80}Fe{sub 20} antidot arrays deposited by magnetron sputtering technique on an anodic aluminum oxide (AAO) membrane are investigated. The angular dependence of out-of-plane remanent magnetization of Ni{sub 80}Fe{sub 20} antidot arrays shows that the maximum remanence is in-plane and the squareness of the out-of-plane hysteresis loop follow a |cos {theta}| dependence. The angular dependence of out-of-plane coercivity of Ni{sub 80}Fe{sub 20} antidot arrays shows that the maximum coercivity lies on the surface of a cone with its symmetric axis normal to the sample plane, which indicates a transition of magnetic reversal from curling to coherent rotation when changing the angle between the applied magnetic field and the sample plane.

The fabrication and the coercivity mechanism of segmented (Ni/Fe)m composite nanowire arrays

International Nuclear Information System (INIS)

Xue, D S; Shi, H G; Si, M S

2004-01-01

Arrays of segmented (Ni/Fe) m (m = 1,2,3,4,5) composite nanowires about 3 μm in length and with aspect ratios of about 60 were electrodeposited on anodic porous alumina templates using a dual bath. The structure, morphology and magnetic properties of the samples were characterized by means of x-ray diffraction, transmission electron microscopy and vibrating sample magnetometry, respectively. It is found that Fe(110) and Ni(111) orientations along nanowire axis are preferred. The large aspect ratio of the composite nanowires reveals a strong shape magnetic anisotropy. As the number of the Ni/Fe composite segments m increases, the coercivity of the nanowire arrays, with the magnetic field applied parallel to the wire, gradually increases. The coercivity variation of the segmented composite nanowires is closely related to the effective exchange coupling between the Ni and Fe segments

Theory for disordered phase in Heisenberg and non-Heisenberg two-dimensional S=1 ferromagnets

International Nuclear Information System (INIS)

Spirin, D.V.; Fridman, Yu.A.

2003-01-01

We apply a modification of self-consistent spin-wave theory to investigation of two-dimensional S=1 isotropic Heisenberg and non-Heisenberg ferromagnets at nonzero temperatures. We use Hubbard operators method and bosonization technique. We calculated chemical potential and found dependence of correlation length on temperature. Specific heat has Schottky-type peak and decreases at high temperatures. Disordered phase in non-Heisenberg ferromagnet is also studied. The results for such a model differ from those of Heisenberg one

Proximity effects in ferromagnet/superconductor structures

International Nuclear Information System (INIS)

Yu, H.L.; Sun, G.Y.; Yang, L.Y.; Xing, D.Y.

2004-01-01

The Nambu spinor Green's function approach is applied to study proximity effects in ferromagnet/superconductor (FM/SC) structures. They include the induced superconducting order parameter and density of states (DOS) with superconducting feature on the FM side, and spin-dependent DOS within the energy gap on the SC side. The latter indicates an appearance of gapless superconductivity and a coexistence of ferromagnetism and superconductivity in a small regime near the interface. The influence of exchange energy in FM and barrier strength at interface on the proximity effects is discussed

Perpendicular magnetic anisotropy of amorphous ferromagnetic CoSiB/[Pt,Au] multilayer

International Nuclear Information System (INIS)

Jeong, S.; Yim, H. I.

2012-01-01

Perpendicular magnetic anisotropy is being widely studied as a possible candidate for a high density spin-transfer torque magnetic random access memory. The key issues of a high-density spin-transfer torque magnetic random access memory are decreasing the switching current and the high thermal stability. In order to solve these problems, two approaches are suggested: One is the development a new amorphous ferromagnetic material as a pinned layer for a multilayer with a low saturated magnetization (M s ) value because of the interface roughness between the two layers. The other is a search for the most suitable materials with high perpendicular magnetic anisotropy in order to have high thermal stability. In this work, we present an amorphous ferromagnetic Co 75 Si 15 B 10 material and compare the magnetic properties of a [CoSiB (0.3, 0.4, 0.5 nm)/Pt (1.4 nm)] 5 multilayer and new combinations [CoSiB (0.3, 0.4, 0.5 nm)/Au (1.5 nm)] 5 .

Possible mechanism for d0 ferromagnetism mediated by intrinsic defects

KAUST Repository

Zhang, Zhenkui

2014-01-01

We examine the effects of several intrinsic defects on the magnetic behavior of ZnS nanostructures using hybrid density functional theory to gain insights into d0 ferromagnetism. Previous studies have predicted that the magnetism is due to a coupling between partially filled defect states. By taking into account the electronic correlations, we find an additional splitting of the defect states in Zn vacancies and thus the possibility of gaining energy by preferential filling of hole states, establishing ferromagnetism between spin polarized S 3p holes. We demonstrate a crucial role of neutral S vacancies in promoting ferromagnetism between positively charged S vacancies. S dangling bonds on the nanoparticle surface also induce ferromagnetism. This journal is

Investigation of a Mesoporous Silicon Based Ferromagnetic Nanocomposite

Directory of Open Access Journals (Sweden)

Roca AG

2009-01-01

Full Text Available Abstract A semiconductor/metal nanocomposite is composed of a porosified silicon wafer and embedded ferromagnetic nanostructures. The obtained hybrid system possesses the electronic properties of silicon together with the magnetic properties of the incorporated ferromagnetic metal. On the one hand, a transition metal is electrochemically deposited from a metal salt solution into the nanostructured silicon skeleton, on the other hand magnetic particles of a few nanometres in size, fabricated in solution, are incorporated by immersion. The electrochemically deposited nanostructures can be tuned in size, shape and their spatial distribution by the process parameters, and thus specimens with desired ferromagnetic properties can be fabricated. Using magnetite nanoparticles for infiltration into porous silicon is of interest not only because of the magnetic properties of the composite material due to the possible modification of the ferromagnetic/superparamagnetic transition but also because of the biocompatibility of the system caused by the low toxicity of both materials. Thus, it is a promising candidate for biomedical applications as drug delivery or biomedical targeting.

Heat Transport in Graphene Ferromagnet-Insulator-Superconductor Junctions

Institute of Scientific and Technical Information of China (English)

LI Xiao-Wei

2011-01-01

We study heat transport in a graphene ferromagnet-insulator-superconducting junction. It is found that the thermal conductance of the graphene ferromagnet-insulator-superconductor (FIS) junction is an oscillatory function of the barrier strength x in the thin-barrier limit. The gate potential U0 decreases the amplitude of thermal conductance oscillation. Both the amplitude and phase of the thermal conductance oscillation varies with the exchange energy Eh. The thermal conductance of a graphene FIS junction displays the usual exponential dependence on temperature, reflecting the s-wave symmetry of superconducting graphene.%@@ We study heat transport in a graphene ferromagnet-insulator-superconducting junction.It is found that the thermal conductance of the graphene ferromagnet-insulator-superconductor(FIS)junction is an oscillatory function of the barrier strength X in the thin-barrier limit.The gate potential Uo decreases the amplitude of thermal conductance oscillation.Both the amplitude and phase of the thermal conductance oscillation varies with the exchange energy Eh.The thermal conductance of a graphene FIS junction displays the usual exponential dependence on temperature, reflecting the s-wave symmetry of superconducting graphene.

Ultrathin Epitaxial Ferromagneticγ-Fe2O3Layer as High Efficiency Spin Filtering Materials for Spintronics Device Based on Semiconductors

KAUST Repository

Li, Peng

2016-06-01

In spintronics, identifying an effective technique for generating spin-polarized current has fundamental importance. The spin-filtering effect across a ferromagnetic insulating layer originates from unequal tunneling barrier heights for spin-up and spin-down electrons, which has shown great promise for use in different ferromagnetic materials. However, the low spin-filtering efficiency in some materials can be ascribed partially to the difficulty in fabricating high-quality thin film with high Curie temperature and/or partially to the improper model used to extract the spin-filtering efficiency. In this work, a new technique is successfully developed to fabricate high quality, ferrimagnetic insulating γ-Fe2O3 films as spin filter. To extract the spin-filtering effect of γ-Fe2O3 films more accurately, a new model is proposed based on Fowler–Nordheim tunneling and Zeeman effect to obtain the spin polarization of the tunneling currents. Spin polarization of the tunneled current can be as high as −94.3% at 2 K in γ-Fe2O3 layer with 6.5 nm thick, and the spin polarization decays monotonically with temperature. Although the spin-filter effect is not very high at room temperature, this work demonstrates that spinel ferrites are very promising materials for spin injection into semiconductors at low temperature, which is important for development of novel spintronics devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Magnetic coercivity and intensity of Mars crust: Dichotomy formation via unicellular convection mechanism

Czech Academy of Sciences Publication Activity Database

Kletetschka, Günther; Acuna, M. H.; Connerney, J. E.; Wasilewski, P. J.; Ness, F. N.

2005-01-01

Roč. 86, č. 52 (2005), GP43A-0884 ISSN 0096-3941. [American Geophysical Union Fall Meeting. 05.12.2005-05.12.2005, San Francisco] Institutional research plan: CEZ:AV0Z30130516 Keywords : magnetic coercivity * magnetic intesity * plate tectonics Subject RIV: BM - Solid Matter Physics ; Magnetism

Magnetic and structural studies on nanostructured Gd/Cr multilayer films

International Nuclear Information System (INIS)

Gadioli, G.Z.; Rouxinol, F.P.; Gelamo, R.V.; Cardoso, L.P.; Gama, S.; Bica de Moraes, M.A.

2013-01-01

Investigations of magnetic phases, transition temperatures and coercivity were performed in multilayered Gd/Cr films as a function of the crystalline state and morphology of the Gd layers. The films were deposited by dc magnetron sputtering at three substrate temperatures, T s , (room temperature, 300 and 500 °C). The Gd and Cr thicknesses were of 10 and 30 nm, respectively. Two series of three films were prepared. In one of the series, the films had a single Gd/Cr bilayer; in the other, 15 bilayers. The discontinuous or granular nature of the Gd layers was revealed by scanning electron microscopy Grazing incidence angle x-ray diffraction was used to investigate the crystalline state of the Gd and Cr layers. These techniques revealed that grain average size and crystalline order increase with increasing T s . From dc magnetic measurements, the co-existence of ferromagnetic and superferromagnetic phases in the Gd layers was observed, and Curie transition temperatures, T C , were determined. High coercive fields at low temperature (2 K) were measured in hysteresis cycles. Field-cooled and zero field-cooled magnetizations as functions of temperature curves exhibited, for some of the samples, a low temperature peak suggesting a freezing transition to a cluster glass state. This was confirmed by complementary ac-susceptibility measurements carried out as a function of temperature, for various frequencies of the ac field. Some results of this work – the decline in T C for decreasing Gd grain size, the high coercive field and its dependence on particle size, and the behavior of the magnetization at low temperatures for the sample deposited at room temperature – are discussed in terms of finite size and surface effects in nanosized particles. - Highlights: • Sputter-deposited Gd/Cr multilayer films with nanostructured Gd layers • Ferromagnetic and superferromagnetic phases are observed. • Ferromagnetic phase dependent of the deposition temperature • Improved

Suppression of the ferromagnetic state by disorder in the Kondo lattice

International Nuclear Information System (INIS)

Crisan, M.; Popoviciu, C.

1992-01-01

This paper reports that ferromagnetic ground state of a Kondo lattice with a low concentration of conduction electrons is ferromagnetic. Assuming the existence of disorder in the Fermi liquid of the conduction electrons the authors show that the ferromagnetic state can be suppressed by the effect of the spin fluctuations of the disordered Fermi liquid

Superparamagnetism and coercivity in HCP-Co nanoparticles dispersed in silica matrix

Energy Technology Data Exchange (ETDEWEB)

Julian Fernandez, C. de E-mail: dejulian@padova.infm.it; Mattei, G.; Sangregorio, C.; Battaglin, C.; Gatteschi, D.; Mazzoldi, P

2004-05-01

The magnetic properties of Co HCP nanoparticles dispersed in a silica matrix with sizes between 2{+-}0.7 and 5{+-}2.2 nm were investigated. The temperature dependence of zero-field cooled and field cooled magnetizations and of the coercive field were analyzed considering the thermal activated demagnetization process. Enhanced anisotropy was observed for the 2 nm nanoparticles, while the demagnetization process of the larger ones is dominated by interparticle interactions.

Fabrication and Magnetic Properties of Fe65Co35–ZnO Nano-Granular Films

Directory of Open Access Journals (Sweden)

Wang Guowei

2010-01-01

Full Text Available Abstract A series of nano-granular films composed of magnetic metal (Fe65Co35 granules with a few nanometers in size and semiconductor oxide (ZnO have been fabricated by a magnetron sputtering method, and excellent soft magnetic properties have been achieved in a wide metal volume fraction (x range for as-deposited samples due to the exchange coupling between FeCo granules (a ferromagnetic interaction in nano-scale. In a wide range (0.53 < x < 0.71, the films exhibit coercivity H C not exceeding 15 Oe, along with high resistivity. Especially for the sample with x = 0.67, coercivities in hard and easy axes are 1.43 and 7.08 Oe, respectively, 4πM S = 9.85 kg, and ρ reaches 2.06 × 103 μΩ cm. The dependence of complex permeability μ = μ′ − jμ″ on frequency shows that the real part μ′ is more than 100 below 1.83 GHz and that the ferromagnetic resonance frequency reaches 2.31 GHz, implying the promising for high frequency application. The measured negative temperature coefficient of resistivity reveals that may be the weak localized electrons existing in samples mediate the exchange coupling.

Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li_{1-x}Fe_x)N

OpenAIRE

Jesche, A.; McCallum, R. W.; Thimmaiah, S.; Jacobs, J. L.; Taufour, V.; Kreyssig, A.; Houk, R. S.; Bud'ko, S. L.; Canfield, P. C.

2014-01-01

Large magnetic anisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic hysteresis in Li2(Li1-xFex)N. An extrapolated, magnetic anisotropy field of 220 Tesla and a coercivity field of over 11 Tesla at 2 Kelvin outperform all known hard-ferromagnets and single-molecule magnets (SMMs). Steps in the hysteresis loops and relaxation phenome...

Dielectric and magnetic characterizations of capacitor structures with an ionic liquid/MgO barrier and a ferromagnetic Pt electrode

Directory of Open Access Journals (Sweden)

D. Hayakawa

2016-11-01

Full Text Available The dielectric and magnetic properties of electric double layer (EDL capacitor structures with a perpendicularly magnetized Pt/Co/Pt electrode and an insulating cap layer (MgO are investigated. An electric field is applied through a mixed ionic liquid/MgO barrier to the surface of the top Pt layer, at which the magnetic moment is induced by the ferromagnetic proximity effect. The basic dielectric properties of the EDL capacitor are studied by varying the thickness of the MgO cap layer. The results indicate that the capacitance, i.e., the accumulated charge density at the Pt surface, is reduced with increasing the MgO thickness. From the MgO thickness dependence of the capacitance value, the effective dielectric constant of the ionic liquid is evaluated. Almost no electric field effect on the magnetic moment, the coercivity, or the Curie temperature is confirmed in the top Pt layer with the thickness of 1.3 nm, regardless of the presence or absence of the MgO cap layer, whereas the a clear change in the magnetic moment is observed when the top Pt layer is replaced by a Pd layer of 1.7 nm.

Effect of shear stress on electromagnetic behaviors in superconductor-ferromagnetic bilayer structure

Science.gov (United States)

Yong, Huadong; Zhao, Meng; Jing, Ze; Zhou, Youhe

2014-09-01

In this paper, the electromagnetic response and shielding behaviour of superconductor-ferromagnetic bilayer structure are studied. The magnetomechanical coupling in ferromagnetic materials is also considered. Based on the linear piezomagnetic coupling model and anti-plane shear deformation, the current density and magnetic field in superconducting strip are obtained firstly. The effect of shear stress on the magnetization of strip is discussed. Then, we consider the magnetic cloak for superconductor-ferromagnetic bilayer structure. The magnetic permeability of ferromagnetic material is obtained for perfect cloaking in uniform magnetic field with magnetomechanical coupling in ferromagnet. The simulation results show that the electromagnetic response in superconductors will change by applying the stress only to the ferromagnetic material. In addition, the performance of invisibility of structure for non-uniform field will be affected by mechanical stress. It may provide a method to achieve tunability of superconducting properties with mechanical loadings.

Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid

Science.gov (United States)

Korenev, V. L.; Akimov, I. A.; Zaitsev, S. V.; Sapega, V. F.; Langer, L.; Yakovlev, D. R.; Danilov, Yu. A.; Bayer, M.

2012-07-01

Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.

Bifunctional ferromagnetic Eu-Gd-Bi-codoped hybrid organo-silica red emitting phosphors synthesized by a modified Pechini sol-gel method

Energy Technology Data Exchange (ETDEWEB)

Abo-Naf, S.M., E-mail: sm.abo-naf@nrc.sci.eg [Glass Research Department, National Research Centre (NRC), El-Buhouth Str., Dokki, 12622 Cairo (Egypt); Abdel-Hameed, S.A.M.; Marzouk, M.A. [Glass Research Department, National Research Centre (NRC), El-Buhouth Str., Dokki, 12622 Cairo (Egypt); Hamdy, Y.M. [Spectroscopy Department, National Research Centre (NRC), El-Buhouth Str., Dokki, 12622 Cairo (Egypt)

2017-06-15

Red phosphor, composed of Eu-Gd-Bi-codoped hybrid organo-silica glass, has been synthesized via a modified Pechini sol-gel process. The synthesized hybrid glass was analyzed with powder X-ray diffraction (XRD), differential thermal analysis coupled with thermogravimetry (DTA-TG) and Fourier transform infrared (FTIR) spectroscopy. XRD and DTA-TG confirmed its amorphous structure up to 1000 °C. Magnetic behavior of the produced phosphor was investigated using vibrating specimen magnetometer (VSM) and the obtained results revealed its unsaturated ferromagnetic behavior. Photoluminescence (PL) properties of the obtained phosphor have been investigated under near-UV excitation at 395 nm. The influence of calcination temperature on the PL intensity and its decay behavior as well as on the ferromagnetic characteristics has been studied to determine the optimal reaction temperature of the phosphor. The PL emission spectra show the characteristic emission bands of Eu{sup 3+} ions in the wavelength range from 580 to 700 nm. These emission spectra have been dominated by the electric dipole {sup 5}D{sub 0}→{sup 7}F{sub 2} transition of the Eu{sup 3+} peaked at 610–620 nm producing the red light emission of the phosphors. It was found that the phosphor performance, expressed by its PL intensity and life time, could be significantly improved by increasing of the heat treatment temperature up to 900 °C. Also, calcination at 900 °C for 6 h greatly increased both of the magnetization and retentivity, while decreased the coercivity value. The organic phenomenon of metal citrate-ethylene glycol chelation and its degradation by calcination were well followed by FTIR spectroscopy. The obtained results are promising and could afford a basis for designing of efficient red phosphors for displays, lighting and bifunctional biosensors for biomedical applications. - Highlights: • Eu-Gd-Bi-codoped hybrid organo-silica phosphor was synthesized by sol-gel method. • Inorganic Eu

Coercivity of Nd-Fe-B hot-deformed magnets produced by the spark plasma sintering method

Directory of Open Access Journals (Sweden)

Tetsuji Saito

2017-05-01

Full Text Available The effects of Nd-Cu alloy powder addition on the microstructures and magnetic properties of Nd-Fe-B hot-deformed magnets produced by the spark plasma sintering (SPS method were investigated. The addition of a small amount of Nd-Cu alloy powder, up to 2%, significantly increased the coercivity of the Nd-Fe-B hot-deformed magnets without deteriorating the crystallographic alignment of the Nd2Fe14B phase. The Nd-Fe-B hot-deformed magnet with 2% Nd-Cu alloy powder had the same remanence value as the Nd-Fe-B hot-deformed magnet without Nd-Cu alloy powder addition, but the magnet with 2% Nd-Cu alloy powder exhibited higher coercivity and a higher maximum energy product than the magnet without Nd-Cu alloy powder addition.

Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure

Science.gov (United States)

Cai, Kaiming; Yang, Meiyin; Ju, Hailang; Wang, Sumei; Ji, Yang; Li, Baohe; Edmonds, Kevin William; Sheng, Yu; Zhang, Bao; Zhang, Nan; Liu, Shuai; Zheng, Houzhi; Wang, Kaiyou

2017-07-01

All-electrical and programmable manipulations of ferromagnetic bits are highly pursued for the aim of high integration and low energy consumption in modern information technology. Methods based on the spin-orbit torque switching in heavy metal/ferromagnet structures have been proposed with magnetic field, and are heading toward deterministic switching without external magnetic field. Here we demonstrate that an in-plane effective magnetic field can be induced by an electric field without breaking the symmetry of the structure of the thin film, and realize the deterministic magnetization switching in a hybrid ferromagnetic/ferroelectric structure with Pt/Co/Ni/Co/Pt layers on PMN-PT substrate. The effective magnetic field can be reversed by changing the direction of the applied electric field on the PMN-PT substrate, which fully replaces the controllability function of the external magnetic field. The electric field is found to generate an additional spin-orbit torque on the CoNiCo magnets, which is confirmed by macrospin calculations and micromagnetic simulations.

Ferromagnetism in proton irradiated 4H-SiC single crystal

Directory of Open Access Journals (Sweden)

Ren-Wei Zhou

2015-04-01

Full Text Available Room-temperature ferromagnetism is observed in proton irradiated 4H-SiC single crystal. An initial increase in proton dose leads to pronounced ferromagnetism, accompanying with obvious increase in vacancy concentration. Further increase in irradiation dose lowers the saturation magnetization with the decrease in total vacancy defects due to the defects recombination. It is found that divacancies are the mainly defects in proton irradiated 4H-SiC and responsible for the observed ferromagnetism.

Dependence of the polar Kerr angle and coercivity on repeat distance in sequentially prepared Tb/FeCo films

International Nuclear Information System (INIS)

Shin, S.

1991-01-01

Multilayer thin films of Tb and FeCo were prepared by sequential thermal evaporation of Tb and Fe 90 Co 10 alloy on glass substrates at ambient temperature in a vacuum of about 1 x 10 -6 Torr. The repeat distance of the films was varied from 3.5 to 175 A while maintaining the composition constant for all samples. Low-angle x-ray diffraction and Auger electron spectroscopy showed that a multilayer structure was achieved for films fabricated with a repeat distance Λ≥31.5 A. The polar Kerr rotation angle and coercivity of the samples were obtained by measuring the polar Kerr hysteresis loop using a 632.8-nm HeNe laser. It was observed that for the samples having a multilayer structure, the remnant Kerr angle and coercivity monotonically decreased with increasing repeat distance, and eventually disappeared for Λ≥70 A. For the samples showing a nonmultilayer structure, the remnant Kerr angle was independent of repeat distance. However, the coercivity increased with repeat distance until a broad maximum was obtained around Λ congruent 14--21 A

Ferromagnetic quantum critical fluctuations and anomalous coexistence of ferromagnetism and superconductivity in UCoGe revealed by Co-NMR and NQR studies

International Nuclear Information System (INIS)

Ohta, Tetsuya; Nakai, Yusuke; Ihara, Yoshihiko; Ishida, Kenji; Deguchi, Kazuhiko; Sato, Noriaki K.; Satoh, Isamu

2008-01-01

Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies were carried out for the recently discovered UCoGe, in which the ferromagnetic and superconducting (SC) transitions are reported to occur at T Curie - 3 K and T S - 0.8 K, in order to investigate the coexistence of ferromagnetism and superconductivity as well as the normal-state and SC properties from a microscopic point of view. From the nuclear spin-lattice relaxation rate 1/T 1 and Knight-shift measurements, we confirm that ferromagnetic fluctuations that possess a quantum critical character are present above T Curie and also the occurrence of a ferromagnetic transition at 2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal state show that UCoGe is an itinerant ferromagnet similar to ZrZn 2 and YCo 2 . The onset SC transition is identified at T S - 0.7 K, below which 1/T 1 arising from 30% of the volume fraction starts to decrease due to the opening of the SC gap. This component of 1/T 1 , which follows a T 3 dependence in the temperature range 0.3-0.1 K, coexists with the magnetic components of 1/T 1 showing a √T dependence below T S . From the NQR measurements in the SC state, we suggest that the self-induced vortex state is realized in UCoGe. (author)

Ferromagnetic Josephson Junctions for Cryogenic Memory

Science.gov (United States)

Niedzielski, Bethany M.; Gingrich, Eric C.; Khasawneh, Mazin A.; Loloee, Reza; Pratt, William P., Jr.; Birge, Norman O.

2015-03-01

Josephson junctions containing ferromagnetic materials are of interest for both scientific and technological purposes. In principle, either the amplitude of the critical current or superconducting phase shift across the junction can be controlled by the relative magnetization directions of the ferromagnetic layers in the junction. Our approach concentrates on phase control utilizing two junctions in a SQUID geometry. We will report on efforts to control the phase of junctions carrying either spin-singlet or spin-triplet supercurrent for cryogenic memory applications. Supported by Northorp Grumman Corporation and by IARPA under SPAWAR Contract N66001-12-C-2017.

Modelling the power losses in the ferromagnetic materials

Directory of Open Access Journals (Sweden)

Detka Kalina

2017-07-01

Full Text Available In this paper, the problem of describing power losses in ferromagnetic materials is considered. The limitations of Steinmetz formula are shown and a new analytical description of losses in a considered material is proposed. The correctness of the developed description is demonstrated experimentally by comparing the results of calculation with the catalogue characteristics for different ferromagnetic materials.

Superparamagnetism and coercivity in HCP-Co nanoparticles dispersed in silica matrix

International Nuclear Information System (INIS)

Julian Fernandez, C. de; Mattei, G.; Sangregorio, C.; Battaglin, C.; Gatteschi, D.; Mazzoldi, P.

2004-01-01

The magnetic properties of Co HCP nanoparticles dispersed in a silica matrix with sizes between 2±0.7 and 5±2.2 nm were investigated. The temperature dependence of zero-field cooled and field cooled magnetizations and of the coercive field were analyzed considering the thermal activated demagnetization process. Enhanced anisotropy was observed for the 2 nm nanoparticles, while the demagnetization process of the larger ones is dominated by interparticle interactions

Spin Heat Accumulation Induced by Tunneling from a Ferromagnet

NARCIS (Netherlands)

Vera-Marun, I.J.; Wees, B.J. van; Jansen, R.

2014-01-01

An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the

Spin-transfer torque in tunnel junctions with ferromagnetic layer of finite thickness

International Nuclear Information System (INIS)

Wilczynski, M.

2011-01-01

Two components of the spin torque exerted on a free ferromagnetic layer of finite thickness and a half-infinite ferromagnetic electrode in single tunnel junctions have been calculated in the spin-polarized free-electron-like one-band model. It has been found that the torque oscillates with the thickness of ferromagnetic layer and can be enhanced in the junction with the special layer thickness. The bias dependence of torque components also significantly changes with layer thickness. It is non-symmetric for the normal torque, in contrast to the symmetric junctions with two identical half-infinite ferromagnetic electrodes. The asymmetry of the bias dependence of the normal component of the torque can be also observed in the junctions with different spin splitting of the electron bands in the ferromagnetic electrodes. - Research highlights: → The torque oscillates with the thickness of ferromagnetic layer. → Bias dependence of the torque changes with the layer thickness. → Bias dependence of the normal torque can be asymmetric.

Modelling characteristics of ferromagnetic cores with the influence of temperature

International Nuclear Information System (INIS)

Górecki, K; Rogalska, M; Zarȩbski, J; Detka, K

2014-01-01

The paper is devoted to modelling characteristics of ferromagnetic cores with the use of SPICE software. Some disadvantages of the selected literature models of such cores are discussed. A modified model of ferromagnetic cores taking into account the influence of temperature on the magnetizing characteristics and the core losses is proposed. The form of the elaborated model is presented and discussed. The correctness of this model is verified by comparing the calculated and the measured characteristics of the selected ferromagnetic cores.

Synthesis of high saturation magnetic iron oxide nanomaterials via low temperature hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Bhavani, P.; Rajababu, C.H. [Department of Materials Science & Nanotechnology, Yogivemana University, Vemanapuram 516003, Kadapa (India); Arif, M.D. [Environmental Magnetism Laboratory, Indian Institute of Geomagnetism (IIG), Navi Mumbai 410218, Mumbai (India); Reddy, I. Venkata Subba [Department of Physics, Gitam University, Hyderabad Campus, Rudraram, Medak 502329 (India); Reddy, N. Ramamanohar, E-mail: manoharphd@gmail.com [Department of Materials Science & Nanotechnology, Yogivemana University, Vemanapuram 516003, Kadapa (India)

2017-03-15

Iron oxide nanoparticles (IONPs) were synthesized through a simple low temperature hydrothermal approach to obtain with high saturation magnetization properties. Two series of iron precursors (sulfates and chlorides) were used in synthesis process by varying the reaction temperature at a constant pH. The X-ray diffraction pattern indicates the inverse spinel structure of the synthesized IONPs. The Field emission scanning electron microscopy and high resolution transmission electron microscopy studies revealed that the particles prepared using iron sulfate were consisting a mixer of spherical (16–40 nm) and rod (diameter ~20–25 nm, length <100 nm) morphologies that synthesized at 130 °C, while the IONPs synthesized by iron chlorides are found to be well distributed spherical shapes with size range 5–20 nm. On other hand, the IONPs synthesized at reaction temperature of 190 °C has spherical (16–46 nm) morphology in both series. The band gap values of IONPs were calculated from the obtained optical absorption spectra of the samples. The IONPs synthesized using iron sulfate at temperature of 130 °C exhibited high saturation magnetization (M{sub S}) of 103.017 emu/g and low remanant magnetization (M{sub r}) of 0.22 emu/g with coercivity (H{sub c}) of 70.9 Oe{sub ,} which may be attributed to the smaller magnetic domains (d{sub m}) and dead magnetic layer thickness (t). - Highlights: • Comparison of iron oxide materials prepared with Fe{sup +2}/Fe{sup +3} sulfates and chlorides at different temperatures. • We prepared super-paramagnetic and soft ferromagnetic magnetite nanoparticles. • We report higher saturation magnetization with lower coercivity.

Pseudo spin-valve behavior in oxide ferromagnet/superconductor/ferromagnet trilayers

International Nuclear Information System (INIS)

Pang, B.S.H.; Bell, C.; Tomov, R.I.; Durrell, J.H.; Blamire, M.G.

2005-01-01

La 0.7 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7-δ /La 0.67 Sr 0.33 MnO 3 heterostructural devices with double coercivity have been fabricated. The superconducting critical current (I c ) and critical temperature in both parallel (P) and antiparallel (AP) magnetic configurations remained unchanged within our measurement limits. This observation is contrary to results obtained elsewhere using similar metallic systems. A pseudo spin-valve magnetoresistive (MR) characteristic was observed at bias current (I bias )∼I c at temperatures below the onset of superconductivity. The effect increased with decreasing temperature and I bias and can be explained using the assumption of the electron spin-charge separation

Ferromagnet / superconductor oxide superlattices

Science.gov (United States)

Santamaria, Jacobo

2006-03-01

The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic

Graphene-ferromagnet interfaces: hybridization, magnetization and charge transfer.

Science.gov (United States)

Abtew, Tesfaye; Shih, Bi-Ching; Banerjee, Sarbajit; Zhang, Peihong

2013-03-07

Electronic and magnetic properties of graphene-ferromagnet interfaces are investigated using first-principles electronic structure methods in which a single layer graphene is adsorbed on Ni(111) and Co(111) surfaces. Due to the symmetry matching and orbital overlap, the hybridization between graphene pπ and Ni (or Co) d(z(2)) states is very strong. This pd hybridization, which is both spin and k dependent, greatly affects the electronic and magnetic properties of the interface, resulting in a significantly reduced (by about 20% for Ni and 10% for Co) local magnetic moment of the top ferromagnetic layer at the interface and an induced spin polarization on the graphene layer. The calculated induced magnetic moment on the graphene layer agrees well with a recent experiment. In addition, a substantial charge transfer across the graphene-ferromagnet interfaces is observed. We also investigate the effects of thickness of the ferromagnet slab on the calculated electronic and magnetic properties of the interface. The strength of the pd hybridization and the thickness-dependent interfacial properties may be exploited to design structures with desirable magnetic and transport properties for spintronic applications.

Ferromagnetic resonance in low interacting permalloy nanowire arrays

Energy Technology Data Exchange (ETDEWEB)

Raposo, V.; Zazo, M.; Flores, A. G.; Iñiguez, J. [Departamento de Física Aplicada, University of Salamanca, E-37071 Salamanca (Spain); Garcia, J.; Vega, V.; Prida, V. M. [Departamento de Física, Universidad de Oviedo, E-33007 Oviedo (Spain)

2016-04-14

Dipolar interactions on magnetic nanowire arrays have been investigated by various techniques. One of the most powerful techniques is the ferromagnetic resonance spectroscopy, because the resonance field depends directly on the anisotropy field strength and its frequency dependence. In order to evaluate the influence of magnetostatic dipolar interactions among ferromagnetic nanowire arrays, several densely packed hexagonal arrays of NiFe nanowires have been prepared by electrochemical deposition filling self-ordered nanopores of alumina membranes with different pore sizes but keeping the same interpore distance. Nanowires’ diameter was changed from 90 to 160 nm, while the lattice parameter was fixed to 300 nm, which was achieved by carefully reducing the pore diameter by means of Atomic Layer Deposition of conformal Al{sub 2}O{sub 3} layers on the nanoporous alumina templates. Field and frequency dependence of ferromagnetic resonance have been studied in order to obtain the dispersion diagram which gives information about anisotropy, damping factor, and gyromagnetic ratio. The relationship between resonance frequency and magnetic field can be explained by the roles played by the shape anisotropy and dipolar interactions among the ferromagnetic nanowires.

Nonlinear wave propagation through a ferromagnet with damping in ...

Indian Academy of Sciences (India)

magnetic waves in a ferromagnet can be reduced to an integro-differential equation. Keywords. Solitons; integro-differential equations; reductive perturbation method. PACS Nos 41.20 Jb; 05.45 Yv; 03.50 De; 78.20 Ls. 1. Introduction. The phenomenon of propagation of electromagnetic waves in ferromagnets are not only.

Spectrum of ferromagnetic transition metal magnetic excitations and neutron scattering

International Nuclear Information System (INIS)

Kuzemskij, A.L.

1979-01-01

Quantum statistical models of ferromagnetic transition metals as well as methods of their solutions are reviewed. The correspondence of results on solving these models and the data on scattering thermal neutrons in ferromagnetic is discussed

The paramagnetic properties of ferromagnetic mixed-spin chain system

International Nuclear Information System (INIS)

Hu, Ai-Yuan; Wu, Zhi-Min; Cui, Yu-Ting; Qin, Guo-Ping

2015-01-01

The double-time Green's function method is used to investigate the paramagnetic properties of ferromagnetic mixed-spin chain system within the random-phase approximation and Anderson–Callen's decoupling approximation. The analytic expressions of the transverse susceptibility, longitudinal susceptibility and correlation length are obtained under transverse and longitudinal magnetic field. Using the analytic expressions of the transverse and longitudinal susceptibility to fit the experimental results, our results well agree with experimental data and the results from the high temperature series expansion within a simple Padé approximation. - Highlights: • We investigate the magnetic properties of a ferromagnetic mixed-spin chain system. • We use the double-time temperature-dependent Green's function technique. • Different single-ion anisotropy values for different spin values are considered. • Our results agree with experimental data and the results from the other theoretical methods

Growth of room temperature ferromagnetic Ge1-xMnx quantum dots on hydrogen passivated Si (100) surfaces

Science.gov (United States)

Gastaldo, Daniele; Conta, Gianluca; Coïsson, Marco; Amato, Giampiero; Tiberto, Paola; Allia, Paolo

2018-05-01

A method for the synthesis of room-temperature ferromagnetic dilute semiconductor Ge1-xMnx (5 % < x < 8 %) quantum dots by molecular beam epitaxy by selective growth on hydrogen terminated silicon (100) surface is presented. The functionalized substrates, as well as the nanostructures, were characterized in situ by reflection high-energy electron diffraction. The quantum dots density and equivalent radius were extracted from field emission scanning electron microscope pictures, obtained ex-situ. Magnetic characterizations were performed by superconducting quantum interference device vibrating sample magnetometry revealing that ferromagnetic order is maintained up to room temperature: two different ferromagnetic phases were identified by the analysis of the field cooled - zero field cooled measurements.

Piezo-voltage control of magnetization orientation in a ferromagnetic semiconductor

Energy Technology Data Exchange (ETDEWEB)

Althammer, M.; Brandlmaier, A.; Gepraegs, S.; Opel, M.; Gross, R. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany); Bihler, C.; Brandt, M.S. [Walter Schottky Institut, Technische Universitaet Muenchen, 85748 Garching (Germany); Schoch, W.; Limmer, W. [Institut fuer Halbleiterphysik, Universitaet Ulm, 89069 Ulm (Germany); Goennenwein, S.T.B.

2008-06-15

The possibility to control magnetic properties via electrical fields is investigated in a piezoelectric actuator/ferromagnetic semiconductor thin film hybrid structure. Using anisotropic magnetoresistance techniques, the magnetic anisotropy and the magnetization orientation within the plane of the ferromagnetic film are measured quantitatively. The experiments reveal that the application of an electrical field to the piezoelectric actuator allows to continuously and reversibly rotate the magnetization orientation in the ferromagnet by about 70 . (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Magnon-induced superconductivity in a topological insulator coupled to ferromagnetic and antiferromagnetic insulators

Science.gov (United States)

Hugdal, Henning G.; Rex, Stefan; Nogueira, Flavio S.; Sudbø, Asle

2018-05-01

We study the effective interactions between Dirac fermions on the surface of a three-dimensional topological insulator due to the proximity coupling to the magnetic fluctuations in a ferromagnetic or antiferromagnetic insulator. Our results show that the magnetic fluctuations can mediate attractive interactions between Dirac fermions of both Amperean and BCS types. In the ferromagnetic case, we find pairing between fermions with parallel momenta, so-called Amperean pairing, whenever the effective Lagrangian for the magnetic fluctuations does not contain a quadratic term. The pairing interaction also increases with increasing Fermi momentum and is in agreement with previous studies in the limit of high chemical potential. If a quadratic term is present, the pairing is instead of BCS type above a certain chemical potential. In the antiferromagnetic case, BCS pairing occurs when the ferromagnetic coupling between magnons on the same sublattice exceeds the antiferromagnetic coupling between magnons on different sublattices. Outside this region in parameter space, we again find that Amperean pairing is realized.

Long range anti-ferromagnetic spin model for prebiotic evolution

International Nuclear Information System (INIS)

Nokura, Kazuo

2003-01-01

I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states

Enhancement of the coercivity in Co-Ni layered double hydroxides by increasing basal spacing.

Science.gov (United States)

Zhang, Cuijuan; Tsuboi, Tomoya; Namba, Hiroaki; Einaga, Yasuaki; Yamamoto, Takashi

2016-09-14

The magnetic properties of layered double hydroxides (LDH) containing transition metal ions can still develop, compared with layered metal hydroxide salts which exhibit structure-dependent magnetism. In this article, we report the preparation of a hybrid magnet composed of Co-Ni LDH and n-alkylsulfonate anions (Co-Ni-CnSO3 LDH). As Co-Ni LDH is anion-exchangeable, we can systematically control the interlayer spacing by intercalating n-alkylsulfonates with different carbon numbers. The magnetic properties were examined with temperature- and field-dependent magnetization measurements. As a result, we have revealed that the coercive field depends on the basal spacing. It is suggested that increasing the basal spacing varies the competition between the in-plane superexchange interactions and long-range out-of-plane dipolar interactions. Moreover, a jump in the coercive field at around 20 Å of the basal spacing is assumed to be the modification of the magnetic ordering in Co-Ni-CnSO3 LDH.

The enhanced coercivity for the magnetite/silica nanocomposite at room temperature

International Nuclear Information System (INIS)

Wu Mingzai; Xiong Ying; Peng Zhenmeng; Jiang Nan; Qi Haiping; Chen Qianwang

2004-01-01

Magnetite/silica nanocomposite was synthesized by a facile solvothermal processing at 150 deg. C for about 10 h. X-ray diffraction (XRD) analysis revealed the effect of annealing on the crystallinity of silica. Transmission electron microscopy (TEM) images showed the good dispersion of magnetite in the silica matrix. Magnetic properties of the nanocomposite were characterized by vibration sample magnetometer (VSM), and the enhanced coercivity was explained by the intrinsic anisotropy of the particles enhanced by the interparticle dipolar fields

Influence of microstructural change of the interface between Nd2Fe14B and Nd-O phases on coercivity of Nd-Fe-B films by oxidation and subsequent low-temperature annealing

International Nuclear Information System (INIS)

Matsuura, Masashi; Tezuka, Nobuki; Sugimoto, Satoshi; Goto, Ryota

2011-01-01

This study provides the influence of microstructural change of the interface between Nd 2 Fe 14 B and Nd-O phases on coercivity of Nd-Fe-B thin films during annealing at low temperature (∼350 deg. C). All films were prepared by using ultra high vacuum (UHV) magnetron sputtering, and the Nd-Fe-B layer was oxidized under Ar gas atmosphere (O 2 content; ∼2 Vol.ppm). Then, the films were annealed at 250-350 deg. C under UHV condition. After oxidation, the coercivity of Nd-Fe-B film decreased to around 40% of the coercivity of as-deposited Nd-Fe-B film. The Nd-rich phase changed from α-Nd to amorphous Nd(-O), and the interface of Nd 2 Fe 14 B/Nd(-O) became rough. In the Nd-Fe-B films oxidized and subsequent annealed at 350 deg. C, the coercivity decreased to around 20%. In the films, poly crystalline hcp Nd 2 O 3 phase crystallized in Nd-rich phase, and there were some steps at the surface of Nd 2 Fe 14 B phase contacting with hcp Nd 2 O 3 phase. Regardless of crystal orientation of Nd 2 Fe 14 B, the microstructural changes of the interface described above were observed.

Vortex dynamics in ferromagnetic/superconducting bilayers

Energy Technology Data Exchange (ETDEWEB)

Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

2008-07-01

The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

The coercive force of fine particles of monoclinic pyrrhotite (Fe7S8 ...

African Journals Online (AJOL)

The temperature dependence of coercive force (Hc) between 77 K and 600 K has been investigated for fine particles of monoclinic pyrrhotite (Fe7S8) of < 1 mm and 1- 30 mm particle sizes. The study has shown that Hc is strongly dependent on temperature, as temperature rises above room temperature (293 K) to near the ...

Magnetic microstructure of nanocrystalline ferromagnets and nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

Energy Technology Data Exchange (ETDEWEB)

Loeffler, J.; Wagner, W. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Kostorz, G. [Eidgenoessische Technische Hochschule, Zurich (Switzerland); Wiedenmann, A. [HMI Berlin (Germany)

1997-09-01

Magnetic small-angle neutron scattering measurements were performed on nanostructured ferromagnetic materials on the basis of Fe, Ni and Co, produced preferentially by the inert-gas condensation technique, with the aim to determine the magnetic microstructure of mesoscopic small-particle systems. (author) 1 fig., 3 refs.

Critical current enhancement by Lorentz force reduction in superconductor-ferromagnet nanocomposites

International Nuclear Information System (INIS)

Blamire, M G; Dinner, R B; Wimbush, S C; MacManus-Driscoll, J L

2009-01-01

Ferromagnetic pinning centres in superconductors form much deeper potential wells than equivalent insulating or metallic non-superconducting inclusions. However, the resultant pinning forces arising from magnetic inclusions are low because the magnetic interaction takes place over the length scale of the magnetic penetration depth which is large in technological superconductors. Nonetheless, we show that a magnetic inclusion can also reduce the Lorentz force on a vortex, yielding a substantially enhanced critical current density for a given pinning force. We calculate this enhancement for a single vortex pinned by a paramagnetic cylinder as well as a vortex lattice interacting with magnetic inclusions, and find that the inclusion of ferromagnetic particles or rods offers a practical means of enhancing the critical currents in oxide high temperature superconductors.

Temperature dependent magnetic coupling between ferromagnetic FeTaC layers in multilayer thin films

International Nuclear Information System (INIS)

Singh, Akhilesh Kumar; Hsu, Jen-Hwa; Perumal, Alagarsamy

2016-01-01

We report systematic investigations on temperature dependent magnetic coupling between ferromagnetic FeTaC layers and resulting magnetic properties of multilayer structured [FeTaC (~67 nm)/Ta(x nm)] 2 /FeTaC(~67 nm)] thin films, which are fabricated directly on thermally oxidized Si substrate. As-deposited amorphous films are post annealed at different annealing temperatures (T A =200, 300 and 400 °C). Structural analyzes reveal that the films annealed at T A ≤200 °C exhibit amorphous nature, while the films annealed above 200 °C show nucleation of nanocrystals at T A =300 °C and well-defined α-Fe nanocrystals with size of about 9 nm in amorphous matrix for 400 °C annealed films. Room temperature and temperature dependent magnetic hysteresis (M–H) loops reveal that magnetization reversal behaviors and magnetic properties are strongly depending on spacer layer thickness (x), T A and temperature. A large reduction in coercivity (H C ) was observed for the films annealed at 200 °C and correlated to relaxation of stress quenched in during the film deposition. On the other hand, the films annealed at 300 °C exhibit unusual variation of H C (T), i.e., a broad minimum in H C (T) vs T curve. This is caused by change in magnetic coupling between ferromagnetic layers having different microstructure. In addition, the broad minimum in the H C (T) curve shifts from 150 K for x=1 film to 80 K for x=4 film. High-temperature thermomagnetization data show a strong (significant) variation of Curie temperature (T C ) with T A (x). The multilayer films annealed at 200 °C exhibit low value of T C with a minimum of 350 K for x=4 film. But, the films annealed at 400 °C show largest T C with a maximum of 869 K for x=1 film. The observed results are discussed on the basis of variations in magnetic couplings between FeTaC layers, which are majorly driven by temperature, spacer layer thickness, annealing temperature and nature of interfaces. - Highlights: • Preparation and

Electromagnetic-acoustic coupling in ferromagnetic metals at liquid-helium temperatures

DEFF Research Database (Denmark)

Gordon, R A

1981-01-01

Electromagnetic-acoustic coupling at the surface and in the bulk of ferromagnetic metals at liquid-helium temperatures has been studied using electromagnetically excited acoustic standing-wave resonances at MHz frequencies in a number of ferromagnetic metals and alloys of commercial interest...

Growth and giant coercive field of spinel-structured Co3- x Mn x O4 thin films

Science.gov (United States)

Kwak, Yongsu; Song, Jonghyun; Koo, Taeyeong

2016-08-01

We grew epitaxial thin films of CoMn2O4 and Co2MnO4 on Nb-doped SrTiO3(011) and SrTiO3(001) single crystal substrates using pulsed laser deposition. The magnetic Curie temperature ( T c ) of the Co2MnO4 thin films was ~176 K, which is higher than that of the bulk whereas CoMn2O4 thin films exhibited a value of T c (~151 K) lower than that of the bulk. For the Co2MnO4 thin films, the M - H loop showed a coercive field of ~0.7 T at 10 K, similar to the value for the bulk. However, the M -H loop of the CoMn2O4(0 ll) thin film grown on a Nb-doped SrTiO3(011) substrate exhibited a coercive field of ~4.5 T at 30 K, which is significantly higher than those of the Co2MnO4 thin film and bulk. This giant coercive field, only observed for the CoMn2O4(0 ll) thin film, can be attributed to the shape anisotropy and strong spin-orbit coupling.

Defect-induced ferromagnetism in semiconductors: A controllable approach by particle irradiation

International Nuclear Information System (INIS)

Zhou, Shengqiang

2014-01-01

Making semiconductors ferromagnetic has been a long dream. One approach is to dope semiconductors with transition metals (TM). TM ions act as local moments and they couple with free carriers to develop collective magnetism. However, there are no fundamental reasons against the possibility of local moment formation from localized sp states. Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators including ZnO and TiO 2 . This kind of observation challenges the conventional understanding of ferromagnetism. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accident or by mistake. Therefore, in this field theory goes much ahead of experimental investigation. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in ZnO, TiO 2 and SiC. In this short review, we also summarize some results by other groups using energetic ions to introduce defects, and thereby magnetism in various materials. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism

Coercive Tactics and Web Advertising Performance

Directory of Open Access Journals (Sweden)

Jiwon Lee

2017-07-01

Full Text Available By questioning contemporary coercive or intrusive web advertising activities, this study sheds light on the recent conditions of web advertising by focusing on a comprehensive process that leads to web ad performance. A total of 400 questionnaires were distributed by the principal investigators of this study. 170 were returned from 200 distributed questionnaires given in South Korea and 100 were returned from 200 distributed questionnaires in China. The responses total 248 out of 400 distributed questionnaires. The relationships among the measured factors are analyzed by the structural equation modeling method. Results show that the use of web ad tactics often leads to negative consequences, creating a user present avoidance behavior condition towards both the ad and ad-hosting website. In terms of the performance of the ad-hosting website, website retention was strongly influenced by content blocking. In addition, the results of the comparative test suggest that the influence of avoidance on advertising performance is stronger among users of newspaper websites than e-commerce websites.

Analysis of ferromagnetic shielding of the ITER NBI

International Nuclear Information System (INIS)

Roccella, M.; Lucca, F.; Roccella, R.; Cocilovo, V.; Ramogida, G.; Portone, A.; Tanga, A.; Formisano, A.; Martone, R.

2006-01-01

In ITER two heating and one diagnostic Neutral Beam Injectors (NBIs) are foreseen [P. L. Mondino et al., ''ITER neutral beam system '', Nucl. Fus., vol. 40, p. 501 (2000)]. Inside these components there are very stringent limits on the magnetic field (the flux density must be below some Gauss (G) along the ion path and below 20 G in the neutralizing region). To achieve these performances in an environment with high stray field due to the plasma and the poloidal field coils, both passive and active shielding systems are foreseen. The present design of the Magnetic Field Reduction System (MFRS) is made of seven active coils and of a box surrounding the NBI region, consisting of ferromagnetic plates 15 cm thick. The electromagnetic analysis of the effectiveness of these shields has been performed by a full 3D FEM model using the ANSYS code. To perform the FEM modeling of the component special care has been used to face the particular geometrical features of the component (a box of about 15 x 5 x 5 m vs. a ferromagnetic layer of only 15 cm thick). To insert an adequate number of FEM elements (at least 5) in the thickness of the ferromagnetic layer, without a prohibitive increase in the total FEM elements number, a particular modeling approach (a sort of '' Chinese boxes '' technique) has been developed. Due to this technique the FEM model enclosing the ferromagnetic box results completely independent on the fine FEM structure inside the shielding layer. It has been even possible, using this technique, introducing a thin (below 1 cm thick) slot all through the shielding plates, without perturbing the rest of the model. This slot has been used to analyze the effects of possible manufacturing lacks on the residual magnetic field inside the component. This technique has allowed the use of only structured meshes made by brick elements, much more accurate than the tetra elements, needed in the usual free meshing techniques. To have the possibility of changing the shielding

Anomalous Hall effect and Nernst effect in itinerant ferromagnets

International Nuclear Information System (INIS)

Asamitsu, A.; Miyasato, T.; Abe, N.; Fujii, T.; Onose, Y.; Onoda, S.; Nagaosa, N.; Tokura, Y.

2007-01-01

Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in many ferromagnetic metals including pure metals, oxides, and calcogenides, are studied to obtain unified understandings of their origins. We show the universal behavior of anomalous Hall conductivity σ xy as a function of longitudinal conductivity σ xx over six orders of magnitude, which is well reproduced by rigorous unified theory assuming both intrinsic and extrinsic contributions to the AHE. ANE is closely related with AHE and gives us further information about the electronic state in the ground state of ferromagnets. The temperature dependence of transverse Peltier coefficient α xy shows almost similar behavior among various ferromagnets and this behavior is expected from a conventional Boltzmann transport theory

Anomalous Hall effect and Nernst effect in itinerant ferromagnets

International Nuclear Information System (INIS)

Miyasato, T.; Abe, N.; Fujii, T.; Asamitsu, A.; Onose, Y.; Onoda, S.; Nagaosa, N.; Tokura, Y.

2007-01-01

Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in many ferromagnetic metals including pure metals, oxides, and chalcogenides, are studied to obtain unified understandings of their origins. We show the universal behavior of anomalous Hall conductivity σ xy as a function of longitudinal conductivity σ xx over six orders of magnitude, which is well reproduced by a recent theory assuming both the intrinsic and extrinsic contributions to the AHE. ANE is closely related with AHE and gives us further information about the electronic state in the ground state of ferromagnets. The temperature dependence of transverse Peltier coefficient α xy shows almost similar behavior among various ferromagnets, and this behavior is expected from a conventional Boltzmann transport theory

Ferromagnetism in the two-dimensional periodic Anderson model

International Nuclear Information System (INIS)

Batista, C. D.; Bonca, J.; Gubernatis, J. E.

2001-01-01

Using the constrained-path Monte Carlo method, we studied the magnetic properties of the two-dimensional periodic Anderson model for electron fillings between 1/4 and 1/2. We also derived two effective low-energy theories to assist in interpreting the numerical results. For 1/4 filling, we found that the system can be a Mott or a charge-transfer insulator, depending on the relative values of the Coulomb interaction and the charge-transfer gap between the two noninteracting bands. The insulator may be a paramagnet or antiferromagnet. We concentrated on the effect of electron doping on these insulating phases. Upon doping we obtained a partially saturated ferromagnetic phase for low concentrations of conduction electrons. If the system were a charge-transfer insulator, we would find that the ferromagnetism is induced by the well-known Ruderman-Kittel-Kasuya-Yosida interaction. However, we found a novel correlated hopping mechanism inducing the ferromagnetism in the region where the nondoped system is a Mott insulator. Our regions of ferromagnetism spanned a much smaller doping range than suggested by recent slave boson and dynamical mean-field theory calculations, but they were consistent with that obtained by density-matrix renormalization group calculations of the one-dimensional periodic Anderson model

Which patients are in highest risk of coercive measures after admission to a general psychiatric ward?

DEFF Research Database (Denmark)

Højlund, Mikkel; Høgh, Lene; Nørregaard, Anne-Mette

2017-01-01

Background Coercive measures, especially mechanical restraint, are more frequently applied to some patients in general psychiatry. In order to tailor an intervention to reduce mechanical restraint we sought to create an evidence base speci c to our population in general psychiatry. Aims To identi...... is currently being tested at the Department of Psychiatry in Aabenraa, Denmark and has until now lead to a decrease in episodes with mechanical restraint from 18 in 2015 to 9 in 2016, and only 1 episode in the rst half of 2017.......Background Coercive measures, especially mechanical restraint, are more frequently applied to some patients in general psychiatry. In order to tailor an intervention to reduce mechanical restraint we sought to create an evidence base speci c to our population in general psychiatry. Aims To identify...

Spin Funneling for Enhanced Spin Injection into Ferromagnets

Science.gov (United States)

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-07-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.

Carbon Nanotubes Filled with Ferromagnetic Materials

Directory of Open Access Journals (Sweden)

Albrecht Leonhardt

2010-08-01

Full Text Available Carbon nanotubes (CNT filled with ferromagnetic metals like iron, cobalt or nickel are new and very interesting nanostructured materials with a number of unique properties. In this paper we give an overview about different chemical vapor deposition (CVD methods for their synthesis and discuss the influence of selected growth parameters. In addition we evaluate possible growth mechanisms involved in their formation. Moreover we show their identified structural and magnetic properties. On the basis of these properties we present different application possibilities. Some selected examples reveal the high potential of these materials in the field of medicine and nanotechnology.

Carbon Nanotubes Filled with Ferromagnetic Materials

Science.gov (United States)

Weissker, Uhland; Hampel, Silke; Leonhardt, Albrecht; Büchner, Bernd

2010-01-01

Carbon nanotubes (CNT) filled with ferromagnetic metals like iron, cobalt or nickel are new and very interesting nanostructured materials with a number of unique properties. In this paper we give an overview about different chemical vapor deposition (CVD) methods for their synthesis and discuss the influence of selected growth parameters. In addition we evaluate possible growth mechanisms involved in their formation. Moreover we show their identified structural and magnetic properties. On the basis of these properties we present different application possibilities. Some selected examples reveal the high potential of these materials in the field of medicine and nanotechnology. PMID:28883334

Magnetoresistance at artificial interfaces in epitaxial ferromagnetic thin films

International Nuclear Information System (INIS)

Fontcuberta, J.; Bibes, M.; Martinez, B.; Trtik, V.; Ferrater, C.; Sanchez, F.; Varela, M.

2000-01-01

Epitaxial La 2/3 Sr 1/3 MnO 3 and SrRuO 3 thin films have been grown by laser ablation on single-crystalline SrTiO 3 substrates. Prior to manganite or ruthenate deposition tracks have been patterned on the SrTiO 3 substrate by using an appropriately focused laser beam. In the experiments here reported linear tracks have been formed. The magnetotransport properties of the films, particularly the magnetoresistance, along paths parallel and perpendicular to the track have been extensively investigated and compared to similar data recorded on films grown on bicrystalline STO substrates. Whereas in LSMO a significant low-field tunnel magnetoresistance develops across the artificial interface, in SRO this tunnel contribution is absent. However, a significant high-field magnetoresistance is observed for both metallic and ferromagnetic systems. The results are analysed and discussed within the framework of the current understanding of double exchange and itinerant ferromagnets. Magnetoresistance data for various configurations of the track array are presented

Room-temperature ferromagnetic transitions and the temperature dependence of magnetic behaviors in FeCoNiCr-based high-entropy alloys

Science.gov (United States)

Na, Suok-Min; Yoo, Jin-Hyeong; Lambert, Paul K.; Jones, Nicholas J.

2018-05-01

High-entropy alloys (HEAs) containing multiple principle alloying elements exhibit unique properties so they are currently receiving great attention for developing innovative alloy designs. In FeCoNi-based HEAs, magnetic behaviors strongly depend on the addition of alloying elements, usually accompanied by structural changes. In this work, the effect of non-magnetic components on the ferromagnetic transition and magnetic behaviors in equiatomic FeCoNiCrX (X=Al, Ga, Mn and Sn) HEAs was investigated. Alloy ingots of nominal compositions of HEAs were prepared by arc melting and the button ingots were cut into discs for magnetic measurements as functions of magnetic field and temperature. The HEAs of FeCoNiCrMn and FeCoNiCrSn show typical paramagnetic behaviors, composed of solid solution FCC matrix, while the additions of Ga and Al in FeCoNiCr exhibit ferromagnetic behaviors, along with the coexistence of FCC and BCC phases due to spinodal decomposition. The partial phase transition in both HEAs with the additions of Ga and Al would enhance ferromagnetic properties due to the addition of the BCC phase. The saturation magnetization for the base alloy FeCoNiCr is 0.5 emu/g at the applied field of 20 kOe (TC = 104 K). For the HEAs of FeCoNiCrGa and FeCoNiCrAl, the saturation magnetization significantly increased to 38 emu/g (TC = 703 K) and 25 emu/g (TC = 277 K), respectively. To evaluate the possibility of solid solution FCC and BCC phases in FeCoNiCr-type HEAs, we introduced a parameter of valence electron concentration (VEC). The proposed rule for solid solution formation by the VEC was matched with FeCoNiCr-type HEAs.

Superconducting Ferromagnetic Nanodiamond

Czech Academy of Sciences Publication Activity Database

Zhang, G.; Samuely, T.; Xu, Z.; Jochum, J. K.; Volodin, A.; Zhou, S. Q.; May, P. W.; Onufriienko, O.; Kacmarik, J.; Steele, J. A.; Li, J.; Vanacken, J.; Vacík, Jiří; Szabo, P.; Yuan, H. F.; Roeffaers, M. B. J.; Cerbu, D.; Samuely, P.; Hofkens, J.; Moshchalkov, V.V.

2017-01-01

Roč. 11, č. 6 (2017), s. 5358-5366 ISSN 1936-0851 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA MŠk LM2015056 Institutional support: RVO:61389005 Keywords : nanodiamond * superconductivity and ferromagnetism * spin fluctuations * giant positive magnetoresistance * anamalous Hall effect Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders OBOR OECD: Nano-materials (production and properties ) Impact factor: 13.942, year: 2016

Active and passive kink mode studies in a tokamak with a movable ferromagnetic wall

Energy Technology Data Exchange (ETDEWEB)

Levesque, J. P.; Hughes, P. E.; Bialek, J.; Byrne, P. J.; Mauel, M. E.; Navratil, G. A.; Peng, Q.; Rhodes, D. J.; Stoafer, C. C. [Department of Applied Physics and Applied Mathematics, Columbia University, 500 W. 120th Street, New York, New York 10027 (United States)

2015-05-15

High-resolution active and passive kink mode studies are conducted in a tokamak with an adjustable ferromagnetic wall near the plasma surface. Ferritic tiles made from 5.6 mm thick Hiperco{sup ®} 50 alloy have been mounted on the plasma-facing side of half of the in-vessel movable wall segments in the High Beta Tokamak-Extended Pulse device [D. A. Maurer et al., Plasma Phys. Controlled Fusion 53, 074016 (2011)] in order to explore ferritic resistive wall mode stability. Low-activation ferritic steels are a candidate for structural components of a fusion reactor, and these experiments examine MHD stability of plasmas with nearby ferromagnetic material. Plasma-wall separation for alternating ferritic and non-ferritic wall segments is adjusted between discharges without opening the vacuum vessel. Amplification of applied resonant magnetic perturbations and plasma disruptivity are observed to increase when the ferromagnetic wall is close to plasma surface instead of the standard stainless steel wall. Rapidly rotating m/n=3/1 external kink modes have higher growth rates with the nearby ferritic wall. Feedback suppression of kinks is still as effective as before the installation of ferritic material in vessel, in spite of increased mode growth rates.

Topological Aspects of Solitons in Ferromagnets

International Nuclear Information System (INIS)

Ren Jirong; Wang Jibiao; Li Ran; Xu Donghui; Duan Yishi

2008-01-01

Two kinds of topological soliton (skyrmion and magnetic vortex ring) in ferromagnets are studied. They have the common topological origin, a tensor H αβ = n-vector · (∂ α n-vector x ∂ β n-vector ), which describes the non-trivial distribution of local orientation of magnetization n-vector at large distances in space. The topological stability of skyrmion is protected by the winding number. Knot-like topological defect as magnetic vortex rings is also studied. On the assumption that magnetic vortex rings are geometric lines, we present their δ-function distribution in ferromagnetic materials. Furthermore, it is briefly shown that Hopf invariant is a proper topological invariant to describe the topology of magnetic vortex rings

Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores.

Science.gov (United States)

Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

2016-10-07

The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ[over ¯] of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.

High-frequency permeability of electroplated CoNiFe and CoNiFe-C alloys