Magnetization reversal through soliton flip in biquadratic ferromagnet with varying exchange interactions

CERN Document Server

Daniel, M

2002-01-01

We study the phenomenon of magnetization reversal in the form of a soliton flip in a biquadratic ferromagnetic spin chain induced by varying bilinear and biquadratic exchange interactions. This is carried out by analysing the evolution of the velocity and amplitude of the soliton using a perturbation analysis.

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)

Strong coupling between a permalloy ferromagnetic contact and helical edge channel in a narrow HgTe quantum well

Energy Technology Data Exchange (ETDEWEB)

Kononov, A.; Egorov, S. V. [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation); Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A. [Institute of Semiconductor Physics (Russian Federation); Deviatov, E. V., E-mail: dev@issp.ac.ru [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation)

2016-11-15

We experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band inversion, realized in a narrow, 8 nm wide, HgTe quantum well. In zero magnetic field, we observe strong asymmetry of the edge potential distribution with respect to the ferromagnetic ground lead. This result indicates that the helical edge channel, specific for the structures with band inversion even at the conductive bulk, is strongly coupled to the ferromagnetic side contact, possibly due to the effects of proximity magnetization. This allows selective and spin-sensitive contacting of helical edge states.

Ferromagnetic resonance study of sputtered NiFe/V/NiFe heterostructures

Energy Technology Data Exchange (ETDEWEB)

Alayo, W., E-mail: willian.rodriguez@ufpel.edu.br [Departamento de Física – IFM, Universidade Federal de Pelotas, 96010-900 Rio Grande do Sul (Brazil); Pelegrini, F. [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Baggio-Saitovitch, E. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, RJ, 22290-180 (Brazil)

2015-03-01

The Ni{sub 81}Fe{sub 19}/V/Ni{sub 81}Fe{sub 19} heterostructures has been produced by magnetron sputtering and analyzed by ferromagnetic resonance. Two systems were investigated: the non symmetrical NiFe(50 Å)/V(t)/NiFe(30 Å) trilayers and the symmetrical NiFe(80 Å)/V(t)/NiFe(80 Å) trilayers, with variable ultrathin V thickness t. Ferromagnetic exchange coupling was evidenced for t below 10 Å by the excitation of the optic mode, in the case of the non symmetrical samples, and by the observation of a single resonance mode for the symmetrical trilayers. For larger V thickness, all samples exhibited two modes, which were attributed to the resonance of the individual NiFe layers with different effective magnetizations. The analysis with the equilibrium and resonance conditions provided the exchange coupling constants and effective magnetizations. - Highlights: • We present a study of symmetrical and non symmetrical NiFe/V/NiFe trilayers deposited on Si single crystals by ferromagnetic resonance (FMR) at room temperature. • For the non symmetrical trilayers, the FMR spectra show the optic and acoustic modes for samples with very thin V layer thicknesses, evidencing ferromagnetic exchange coupling, whereas, for larger V thickness, the spectra exhibited two well resolved modes associated to each independent NiFe layer. For the symmetrical trilayers, strong ferromagnetic exchange coupling is evidenced by the observation of a single resonance mode. • The analysis with the equilibrium condition and dispersion relation provides the exchange coupling constants and effective magnetizations.

The effect of disorder and fluctuations on the magnetotransport of a double-exchange ferromagnet (abstract)

International Nuclear Information System (INIS)

Byers, J.M.

1996-01-01

The discovery of colossal magnetoresistance (CMR) in the doped perovskite manganites has reawakened interest in the double-exchange mechanism proposed to Zener. To account for the close relation between ferromagnetism and metallic transport in lanthanum manganites doped with divalent cation (Ca, Sr, Ba) Zener claimed that an electron could delocalize on lattice of spins and still conform to Hund close-quote s Rule if a ferromagnetic coupling between spins were mediated by that same electron. Thus, the onset of metallic behavior (delocalization) is intimately linked to ferromagnetic ordering of the spin lattice. Clearly, the double-exchange mechanism provides some necessary physics but is not sufficient in explaining the key mystery of the CMR materials: What causes the large peak in the resistivity vs. temperature and why is it removed by an applied magnetic field. The effect of disorder and fluctuations on the double-exchange mechanism may provide the answers. Several sources of disorder in these materials act to form a mobility edge via Anderson localization: intrinsic divalent/trivalent cation disorder, off-diagonal disorder caused by the spin lattice and oxygen vacancy disorder. A mean-field calculation reveals that below the Curie temperature those carriers aligned opposite to the magnetization experience a narrowing band as the temperature is reduced. Fermi glass behavior is induced in this minority carrier band by the Fermi level falling below the mobility edge. However, the mean-field result does not contain a peak in resistivity since the majority carrier band does not behave as a Fermi glass and effectively open-quote open-quote shorts out close-quote close-quote the more resistive minority conduction channel. The formation of the resistivity peak requires the inclusion of ferromagnetic fluctuations above the Curie temperature that tend to open-quote open-quote mix close-quote close-quote the two conduction channels. (Abstract Truncated)

Spin spring behavior in exchange coupled soft and high-coercivity hard ferromagnets.

Energy Technology Data Exchange (ETDEWEB)

Shull, R. D.; Shapiro, A. J.; Gornakov, V. S.; Nikitenko, V. I.; Jiang, J. S.; Kaper, H.; Leaf, G.; Bader, S. D.

2000-11-01

The magnetization reversal processes in an epitaxial Fe/Sm{sub 2}Co{sub 7} structure were investigated using the magneto-optical indicator film technique. The dependence of the magnitude and the orientation of the structure average magnetization have been studied on both cycling and rotating the external magnetic field. It was discovered that the magnetization reversal of the soft ferromagnet can proceed by formation of not only one-dimensional, but also two-dimensional, exchange spin springs. Experimental data is compared with a theoretical estimation of the rotational hysteresis loop for a spin system containing a one-dimensional exchange spring.

Gate-Tunable Spin Exchange Interactions and Inversion of Magnetoresistance in Single Ferromagnetic ZnO Nanowires.

Science.gov (United States)

Modepalli, Vijayakumar; Jin, Mi-Jin; Park, Jungmin; Jo, Junhyeon; Kim, Ji-Hyun; Baik, Jeong Min; Seo, Changwon; Kim, Jeongyong; Yoo, Jung-Woo

2016-04-26

Electrical control of ferromagnetism in semiconductor nanostructures offers the promise of nonvolatile functionality in future semiconductor spintronics. Here, we demonstrate a dramatic gate-induced change of ferromagnetism in ZnO nanowire (NW) field-effect transistors (FETs). Ferromagnetism in our ZnO NWs arose from oxygen vacancies, which constitute deep levels hosting unpaired electron spins. The magnetic transition temperature of the studied ZnO NWs was estimated to be well above room temperature. The in situ UV confocal photoluminescence (PL) study confirmed oxygen vacancy mediated ferromagnetism in the studied ZnO NW FET devices. Both the estimated carrier concentration and temperature-dependent conductivity reveal the studied ZnO NWs are at the crossover of the metal-insulator transition. In particular, gate-induced modulation of the carrier concentration in the ZnO NW FET significantly alters carrier-mediated exchange interactions, which causes even inversion of magnetoresistance (MR) from negative to positive values. Upon sweeping the gate bias from -40 to +50 V, the MRs estimated at 2 K and 2 T were changed from -11.3% to +4.1%. Detailed analysis on the gate-dependent MR behavior clearly showed enhanced spin splitting energy with increasing carrier concentration. Gate-voltage-dependent PL spectra of an individual NW device confirmed the localization of oxygen vacancy-induced spins, indicating that gate-tunable indirect exchange coupling between localized magnetic moments played an important role in the remarkable change of the MR.

Switching behaviour of coupled antiferro- and ferromagnetic systems: exchange bias

Energy Technology Data Exchange (ETDEWEB)

Lindgaard, Per-Anker [Materials Research Division, Risoe National Laboratory for Sustainable Energy, Danish Technical University, DK-4000 Roskilde (Denmark)

2009-11-25

The switching behaviour, under reversal of an external field, of a simple, ideal magnetic nanoparticle is studied and the interplay between antiferromagnets and ferromagnets elucidated. It is found that the switching between various multi- q ordering in fcc antiferromagnets (as found theoretically in NiO nanoparticles (Kodama and Berkowitz 1999 Phys. Rev. B 59 6321 and Lindgaard 2003 J. Magn. Magn. Mater. 266 88)) in a field severely limits the exchange biasing potential. The interface between the different magnets is found to be that originally assumed by Meiklejohn and Bean (1956 Phys. Rev. 102 1413).

Ultrathin nanosheets of Mn3O4: A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy

Science.gov (United States)

Wu, Jun-Chi; Peng, Xu; Guo, Yu-Qiao; Zhou, Hao-Dong; Zhao, Ji-Yin; Ruan, Ke-Qin; Chu, Wang-Sheng; Wu, Changzheng

2018-06-01

Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn3O4 nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn3O4 nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.

Exploring the microscopic origin of exchange bias with photoelectron emission microscopy (invited)

International Nuclear Information System (INIS)

Scholl, A.; Nolting, F.; Stohr, J.; Regan, T.; Luning, J.; Seo, J. W.; Locquet, J.-P.; Fompeyrine, J.; Anders, S.; Ohldag, H.

2001-01-01

It is well known that magnetic exchange coupling across the ferromagnet - antiferromagnet interface results in an unidirectional magnetic anisotropy of the ferromagnetic layer, called exchange bias. Despite large experimental and theoretical efforts, the origin of exchange bias is still controversial, mainly because detection of the interfacial magnetic structure is difficult. We have applied photoelectron emission microscopy (PEEM) on several ferromagnet - antiferromagnet thin-film structures and microscopically imaged the ferromagnetic and the antiferromagnetic structure with high spatial resolution. Taking advantage of the surface sensitivity and elemental specificity of PEEM, the magnetic configuration and critical properties such as the Neel temperature were determined on LaFeO 3 and NiO thin films and single crystals. On samples coated with a ferromagnetic layer, we microscopically observe exchange coupling across the interface, causing a clear correspondence of the domain structures in the adjacent ferromagnet and antiferromagnet. Field dependent measurements reveal a strong uniaxial anisotropy in individual ferromagnetic domains. A local exchange bias was observed even in not explicitly field-annealed samples, caused by interfacial uncompensated magnetic spins. These experiments provide highly desired information on the relative orientation of electron spins at the interface between ferromagnets and antiferromagnets. [copyright] 2001 American Institute of Physics

Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

Science.gov (United States)

Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

2016-06-01

High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

Magnetism of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic spin-exchange interaction

International Nuclear Information System (INIS)

Lee, J. Y.; Guan, X. W.; Batchelor, M. T.; Lee, C.

2009-01-01

We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin-exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field H is less than the lower critical field H c1 ; (ii) a ferromagnetic phase of atoms in the hyperfine state |F=1, m F =1> when the external magnetic field exceeds the upper critical field H c2 ; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region H c1 c2 . At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired m F =1 bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.

Modeling and calculation of RKKY exchange coupling to explain Ti-vacancy-induced ferromagnetism in Ta-doped TiO2

Science.gov (United States)

Majidi, Muhammad Aziz; Bupu, Annamaria; Fauzi, Angga Dito

2017-12-01

We present a theoretical study on Ti-vacancy-induced ferromagnetism in anatase TiO2. A recent experimental study has revealed room temperature ferromagnetism in Ta-doped anatase TiO2thin films (Rusydi et al., 2012) [7]. Ta doping assists the formation of Ti vacancies which then induce the formation of localized magnetic moments around the Ti vacancies. As neighboring Ti vacancies are a few unit cells apart, the ferromagnetic order is suspected to be mediated by itinerant electrons. We propose that such an electron-mediated ferromagnetism is driven by Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. To examine our hypothesis, we construct a tight-binding based model Hamiltonian for the anatase TiO2 system. We calculate the RKKY exchange coupling constant of TiO2 as a function of distance between local magnetic moments at various temperatures. We model the system by taking only the layer containing a unit of TiO2, at which the Ti vacancy is believed to form, as our effective two-dimensional unit cell. Our model incorporates the Hubbard repulsive interactions between electrons occupying Ti d orbitals treated within mean-field approximation. The density of states profile resulting from the model captures the relevant electronic properties of TiO2, such as the energy gap of 3.4 eV and the n-type character, which may be a measure of the adequacy of the model. The calculated RKKY coupling constant shows that the ferromagnetic coupling extends up to 3-4 unit cells and enhances slightly as temperature is increased from 0 to 400 K. These results support our hypothesis that the ferromagnetism of this system is driven by RKKY mechanism.

Influence of magnetic dipole and magnetoelastic interactions on the phase states of 2D non-Heisenberg ferromagnetic with complex exchange interactions

International Nuclear Information System (INIS)

Fridman, Yu.A.; Matunin, D.A.; Klevets, Ph.N.; Kosmachev, O.A.

2009-01-01

The phase states of the 2D non-Heisenberg ferromagnetic with anisotropic bilinear and biquadratic exchange interactions are investigated. The limiting cases of the system under consideration are the two-dimensional XY-model with biquadratic exchange interaction and the isotropic Heisenberg ferromagnetic. The account of the magnetic dipole interaction leads to the realization of spatially inhomogeneous quadrupolar phase. The stability regions of various phase transitions for different values of the material parameters are studied. The phase diagram is built. Besides, the temperature phase transitions are investigated. The influence of the magnetoelastic interaction on the formation of the long-range quadrupolar order is determined.

Ferroelectricity with Ferromagnetic Moment in Orthoferrites

Science.gov (United States)

Tokunaga, Yusuke

2010-03-01

Exotic multiferroics with gigantic magnetoelectric (ME) coupling have recently been attracting broad interests from the viewpoints of both fundamental physics and possible technological application to next-generation spintronic devices. To attain a strong ME coupling, it would be preferable that the ferroelectric order is induced by the magnetic order. Nevertheless, the magnetically induced ferroelectric state with the spontaneous ferromagnetic moment is still quite rare apart from a few conical-spin multiferroics. To further explore multiferroic materials with both the strong ME coupling and spontaneous magnetization, we focused on materials with magnetic structures other than conical structure. In this talk we present that the most orthodox perovskite ferrite systems DyFeO3 and GdFeO3 have ``ferromagnetic-ferroelectric,'' i.e., genuinely multiferroic states in which weak ferromagnetic moment is induced by Dzyaloshinskii-Moriya interaction working on Fe spins and electric polarization originates from the striction due to symmetric exchange interaction between Fe and Dy (Gd) spins [1] [2]. Both materials showed large electric polarization (>0.1 μC/cm^2) and strong ME coupling. In addition, we succeeded in mutual control of magnetization and polarization with electric- and magnetic-fields in GdFeO3, and attributed the controllability to novel, composite domain wall structure. [4pt] [1] Y. Tokunaga et al., Phys. Rev. Lett. 101, 097205 (2008). [0pt] [2] Y. Tokunaga et al., Nature Mater. 8, 558 (2009).

Positive magnetoresistance in ferromagnetic Nd-doped In2O3 thin films grown by pulse laser deposition

KAUST Repository

Xing, G. Z.

2014-05-23

We report the magnetic and magnetotransport properties of (In 0.985Nd0.015)2O2.89 thin films grown by pulse laser deposition. The clear magnetization hysteresis loops with the complementary magnetic domain structure reveal the intrinsic room temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (∼29.2%) was observed at 5 K and ascribed to the strong ferromagnetic sp-f exchange interaction in (In0.985Nd0.015)2O 2.89 thin films due to a large Zeeman splitting in an external magnetic field of 50 KOe. © 2014 AIP Publishing LLC.

Tunneling density of states as a function of thickness in superconductor/ strong ferromagnet bilayers

Energy Technology Data Exchange (ETDEWEB)

Reymond, S.

2010-04-29

We have made an experimental study of the tunneling density of states (DOS) in strong ferromagnetic thin films (CoFe) in proximity with a thick superconducting film (Nb) as a function of d{sub F}, the ferromagnetic thickness. Remarkably, we find that as d{sub F} increases, the superconducting DOS exhibits a scaling behavior in which the deviations from the normal-state conductance have a universal shape that decreases exponentially in amplitude with characteristic length d* {approx} 0.4 nm. We do not see oscillations in the DOS as a function of d{sub F}, as expected from predictions based on the Usadel equations, although an oscillation in T{sub c}(d{sub F}) has been seen in the same materials.

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.

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.

Phase states of a 2D easy-plane ferromagnet with strong inclined anisotropy

International Nuclear Information System (INIS)

Fridman, Yu. A.; Klevets, F. N.; Gorelikov, G. A.; Meleshko, A. G.

2012-01-01

We investigate the spin states of a 2D film exhibiting easy-axis anisotropy and a strong single-ion inclined anisotropy whose axis forms a certain angle with the normal to the film surface. Such a system may have an angular ferromagnetic phase, a spatially inhomogeneous state, and a quadrupole phase, whose realization depends substantially on the inclined anisotropy and the orientation of the wavevector in the film plane.

Frequency and temperature dependence of ferromagnetic linewidth in exchange biased Permalloy

International Nuclear Information System (INIS)

Lubitz, P.; Rubinstein, M.; Krebs, J. J.; Cheng, S.-F.

2001-01-01

Ferromagnetic resonance linewidths were measured at 9.5 and 35 GHz and in the temperature range from 77 to 350 K for thin Permalloy (Py) films exchange biased by adjacent layers of NiO, CoO, or IrMn. Compared to unoxidized Py alone, for which the linewidth is nearly temperature independent in this range and scales linearly with frequency, exchange biased Py has broader lines with distinctive temperature dependences for each bias material at 9.5 GHz. Different temperature dependences were observed at 35 GHz. Our results are consistent with relaxation related to thermally driven reversal of the antiferromagnetic grains. Intrinsic damping and inhomogeneities also add to the widths. The qualitative features of the temperature and frequency dependences of the linewidths can be described with the usual expression for the slow relaxation linewidth mechanism. The temperature dependence of the relaxation time is taken from Neel's expression for the reversal time using appropriate rate prefactors and activation energies. [copyright] 2001 American Institute of Physics

Non-quasiparticle states in a half-metallic ferromagnet with antiferromagnetic s-d(f) interaction.

Science.gov (United States)

Irkhin, V Yu

2015-04-22

Non-quasiparticle (incoherent) states which play an important role in the electronic structure of half-metallic ferromagnets (HMF) are investigated consistently in the case of antiferromagnetic s-d(f) exchange interaction. Their appropriate description in the limit of strong correlations requires a rearrangement of perturbation series in comparison with the usual Dyson equation. This consideration provides a solution of the Kondo problem in the HMF case and can be important for first-principle HMF calculations performed earlier for ferromagnetic s-d(f) interaction.

Long-range p-d exchange interaction in a ferromagnet-semiconductor hybrid structure

Science.gov (United States)

Korenev, V. L.; Salewski, M.; Akimov, I. A.; Sapega, V. F.; Langer, L.; Kalitukha, I. V.; Debus, J.; Dzhioev, R. I.; Yakovlev, D. R.; Müller, D.; Schröder, C.; Hövel, H.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Kusrayev, Yu. G.; Bayer, M.

2016-01-01

Hybrid structures synthesized from different materials have attracted considerable attention because they may allow not only combination of the functionalities of the individual constituents but also mutual control of their properties. To obtain such a control an interaction between the components needs to be established. For coupling the magnetic properties, an exchange interaction has to be implemented which typically depends on wavefunction overlap and is therefore short-ranged, so that it may be compromised across the hybrid interface. Here we study a hybrid structure consisting of a ferromagnetic Co layer and a semiconducting CdTe quantum well, separated by a thin (Cd, Mg)Te barrier. In contrast to the expected p-d exchange that decreases exponentially with the wavefunction overlap of quantum well holes and magnetic atoms, we find a long-ranged, robust coupling that does not vary with barrier width up to more than 30 nm. We suggest that the resulting spin polarization of acceptor-bound holes is induced by an effective p-d exchange that is mediated by elliptically polarized phonons.

First-principles study on half-metallic ferromagnetic properties of Zn1- x V x Se ternary alloys

Science.gov (United States)

Khatta, Swati; Tripathi, S. K.; Prakash, Satya

2017-09-01

The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn1- x V x Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction.

Itinerant ferromagnetism in the narrow band limit

CERN Document Server

Liu, S H

2000-01-01

It is shown that in the narrow band, strong interaction limit the paramagnetic state of an itinerant ferromagnet is described by the disordered local moment state. As a result, the Curie temperature is orders of magnitude lower than what is expected from the large exchange splitting of the spin bands. An approximate analysis has also been carried out for the partially ordered state, and the result explains the temperature evolvement of the magnetic contributions to the resistivity and low-energy optical conductivity of CrO sub 2.

Excitation of magnetic inhomogeneities in three-layer ferromagnetic structure with different parameters of the magnetic anisotropy and exchange

Energy Technology Data Exchange (ETDEWEB)

Ekomasov, E.G., E-mail: EkomasovEG@gmail.com [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Murtazin, R.R. [Bashkir State University, 32, Validy Str., Ufa, 450076 (Russian Federation); Nazarov, V.N. [Institute of Molecule and Crystal Physics Ufa Research Centre of Russian Academy of Sciences, Prospekt Oktyabrya 151, Ufa, 450075 (Russian Federation)

2015-07-01

The generation and evolution of magnetic inhomogeneities, emerging in a thin flat layer with the parameters of the magnetic anisotropy and exchange interaction, with the parameters different from other two thick layers of the three-layer ferromagnetic structure, were investigated. The parameters ranges that determine the possibility of their existence were found. The possibility of the external magnetic field influence on the structure and dynamic properties of localized magnetic inhomogeneities was shown. - Highlights: • The generation of magnetic inhomogeneities in the three-layer ferromagnetic. • The influence of an external field on the parameters of magnetic inhomogeneities. • Numerical study of the structure and dynamics of magnetic inhomogeneities.

Exchange bias in finite sized NiO nanoparticles with Ni clusters

International Nuclear Information System (INIS)

Gandhi, Ashish Chhaganlal; Lin, Jauyn Grace

2017-01-01

Structural and magnetic properties of finite sized NiO nanoparticles are investigated with synchrotron X-ray diffraction (XRD), transmission electron microscopy, magnetometer and ferromagnetic resonance (FMR) spectroscopy. A minor Ni phase is detected with synchrotron XRD, attributed to the oxygen defects in the NiO core. A considerable exchange bias of ~100 Oe is observed at 50 K and it drops abruptly and vanishes above 150 K, in association with the reduction of frozen spins. FMR data indicate a strong interaction between ferromagnetic (FM) and antiferromagnetic (AFM) phases below 150 K, consistent with the picture of isolated FM clusters in AFM matrix. - Highlights: • Structural and magnetic properties of finite sized NiO nanoparticles are systematically investigated with several advanced techniques. • A strong interaction between ferromagnetic and antiferromagnetic phases is found below 150 K. • Exchange bias field in finite sized NiO nanoparticles is due to anisotropy energy of Ni clusters over riding the domain wall energy of NiO.

Exchange bias in finite sized NiO nanoparticles with Ni clusters

Energy Technology Data Exchange (ETDEWEB)

Gandhi, Ashish Chhaganlal; Lin, Jauyn Grace, E-mail: jglin@ntu.edu.tw

2017-02-15

Structural and magnetic properties of finite sized NiO nanoparticles are investigated with synchrotron X-ray diffraction (XRD), transmission electron microscopy, magnetometer and ferromagnetic resonance (FMR) spectroscopy. A minor Ni phase is detected with synchrotron XRD, attributed to the oxygen defects in the NiO core. A considerable exchange bias of ~100 Oe is observed at 50 K and it drops abruptly and vanishes above 150 K, in association with the reduction of frozen spins. FMR data indicate a strong interaction between ferromagnetic (FM) and antiferromagnetic (AFM) phases below 150 K, consistent with the picture of isolated FM clusters in AFM matrix. - Highlights: • Structural and magnetic properties of finite sized NiO nanoparticles are systematically investigated with several advanced techniques. • A strong interaction between ferromagnetic and antiferromagnetic phases is found below 150 K. • Exchange bias field in finite sized NiO nanoparticles is due to anisotropy energy of Ni clusters over riding the domain wall energy of NiO.

Positive magnetoresistance in ferromagnetic Nd-doped In2O3 thin films grown by pulse laser deposition

KAUST Repository

Xing, G. Z.; Yi, J. B.; Yan, F.; Wu, Tao; Li, S.

2014-01-01

temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (∼29.2%) was observed at 5 K and ascribed

Competing exchange bias and field-induced ferromagnetism in La-doped BaFe O3

Science.gov (United States)

Fita, I.; Wisniewski, A.; Puzniak, R.; Iwanowski, P.; Markovich, V.; Kolesnik, S.; Dabrowski, B.

2017-04-01

An exchange bias (EB) effect was observed in mixed valent L axB a1 -xFe O3 (x =0.125 , 0.25, 0.33) perovskites exhibiting the antiferromagnetic (AFM) helical order among F e4 + ions coexisting with the ferromagnetic (FM) cluster phase in the ground state. The L a3 + ions for B a2 + site substitution, associated with increase in number of the AFM coupled F e3 + - F e4 + pairs as well as some F e3 + - F e3 + pairs, leads to strengthening of the AFM phase and consequently to the alteration of the EB characteristics, which depend on level of the La doping x . At low doping x ≤0.25 , an abnormal dependence of the EB field, HEB, on the cooling field, Hcool, was found. The HEB increases rapidly with increasing cooling field at low Hcool, but it falls suddenly at cooling fields higher than 20 kOe, reducing by an order of magnitude at 90 kOe. The suppression of EB is caused by the field-induced increased volume of the FM phase, due to the transformation of the AFM helical spin structure into the FM one. Thus, low-doped L axB a1 -xFe O3 demonstrates a competition of two alternate cooling-field-induced effects, one of which leads to the EB anisotropy and another one to the enhanced ferromagnetism. In contrast, the x =0.33 sample, having a strong AFM constituent, shows no field-induced FM and no drop in the EB field. Accordingly, the HEB vs Hcool dependence was found to be well explained in the framework of a model describing phase-separated AFM-FM systems, namely, the model assuming isolated FM clusters of size ˜4 nm embedded in the AFM matrix.

Strong correlation and ferromagnetism in (Ga,Mn)As and (Ga,Mn)N

International Nuclear Information System (INIS)

Filippetti, A.; Spaldin, N.A.; Sanvito, S.

2005-01-01

The band energies of the ferromagnetic diluted magnetic semiconductors (Ga,Mn)As and (Ga,Mn)N are calculated using a self-interaction-free approach which describes covalent and strongly correlated electrons without adjustable parameters. Both materials are half-metallic, although the contribution of Mn-derived d states to the bands around the Fermi energy is very different in the two cases. In (Ga,Mn)As the bands are strongly p-d hybridized, with a dominance of As p states. In contrast in (Ga,Mn)N the Fermi energy lies within three flat bands of mainly d character that are occupied by two electrons. Thus the Mn ion in (Ga,Mn)N behaves as a deep trap acceptor, with the hole at 1.39 eV above the GaN valence band top, and is in excellent agreement with the experimental data

Effect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays

Energy Technology Data Exchange (ETDEWEB)

Gong, W. J.; Liu, W., E-mail: wliu@imr.ac.cn; Feng, J. N.; Zhang, Z. D. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Kim, D. S.; Choi, C. J. [Functional Materials Division, Korea Institute of Materials Science, 531 Changwon- daero, Changwon 631-831 (Korea, Republic of)

2014-04-07

The effect of antiferromagnetic (AFM) layer on exchange bias (EB), training effect, and magnetotransport properties in ferromagnetic (FM) /AFM nanoscale antidot arrays and sheet films Ag(10 nm)/Co(8 nm)/NiO(t{sub NiO})/Ag(5 nm) at 10 K is studied. The AFM layer thickness dependence of the EB field shows a peak at t{sub NiO} = 2 nm that is explained by using the random field model. The misalignment of magnetic moments in the three-dimensional antidot arrays causes smaller decrease of EB field compared with that in the sheet films for training effect. The anomalous magnetotransport properties, in particular positive magnetoresistance (MR) for antidot arrays but negative MR for sheet films are found. The training effect and magnetotransport properties are strongly affected by the three-dimensional spin-alignment effects in the antidot arrays.

Effect of ferromagnetic exchange field on band gap and spin polarisation of graphene on a TMD substrate

Science.gov (United States)

Goswami, Partha

2018-03-01

We calculate the electronic band dispersion of graphene monolayer on a two-dimensional transition metal dichalcogenide substrate (GrTMD) around K and K^' } points by taking into account the interplay of the ferromagnetic impurities and the substrate-induced interactions. The latter are (strongly enhanced) intrinsic spin-orbit interaction (SOI), the extrinsic Rashba spin-orbit interaction (RSOI) and the one related to the transfer of the electronic charge from graphene to substrate. We introduce exchange field ( M) in the Hamiltonian to take into account the deposition of magnetic impurities on the graphene surface. The cavalcade of the perturbations yield particle-hole symmetric band dispersion with an effective Zeeman field due to the interplay of the substrate-induced interactions with RSOI as the prime player. Our graphical analysis with extremely low-lying states strongly suggests the following: The GrTMDs, such as graphene on WY2, exhibit (direct) band-gap narrowing / widening (Moss-Burstein (MB) gap shift) including the increase in spin polarisation ( P) at low temperature due to the increase in the exchange field ( M) at the Dirac points. The polarisation is found to be electric field tunable as well. Finally, there is anticrossing of non-parabolic bands with opposite spins, the gap closing with same spins, etc. around the Dirac points. A direct electric field control of magnetism at the nanoscale is needed here. The magnetic multiferroics, like BiFeO3 (BFO), are useful for this purpose due to the coupling between the magnetic and electric order parameters.

First-principles study on half-metallic ferromagnetic properties of Zn{sub 1-x}V{sub x}Se ternary alloys

Energy Technology Data Exchange (ETDEWEB)

Khatta, Swati; Tripathi, S.K.; Prakash, Satya [Panjab University, Central of Advanced Study in Physics, Department of Physics, Chandigarh (India)

2017-09-15

The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn{sub 1-x}V{sub x}Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction. (orig.)

Direct measurement of the long-range p -d exchange coupling in a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure

Science.gov (United States)

Akimov, I. A.; Salewski, M.; Kalitukha, I. V.; Poltavtsev, S. V.; Debus, J.; Kudlacik, D.; Sapega, V. F.; Kopteva, N. E.; Kirstein, E.; Zhukov, E. A.; Yakovlev, D. R.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Korenev, V. L.; Kusrayev, Yu. G.; Bayer, M.

2017-11-01

The exchange interaction between magnetic ions and charge carriers in semiconductors is considered to be a prime tool for spin control. Here, we solve a long-standing problem by uniquely determining the magnitude of the long-range p -d exchange interaction in a ferromagnet-semiconductor (FM-SC) hybrid structure where a 10-nm-thick CdTe quantum well is separated from the FM Co layer by a CdMgTe barrier with a thickness on the order of 10 nm. The exchange interaction is manifested by the spin splitting of acceptor bound holes in the effective magnetic field induced by the FM. The exchange splitting is directly evaluated using spin-flip Raman scattering by analyzing the dependence of the Stokes shift ΔS on the external magnetic field B . We show that in a strong magnetic field, ΔS is a linear function of B with an offset of Δp d=50 -100 μ eV at zero field from the FM induced effective exchange field. On the other hand, the s -d exchange interaction between conduction band electrons and FM, as well as the p -d contribution for free valence band holes, are negligible. The results are well described by the model of indirect exchange interaction between acceptor bound holes in the CdTe quantum well and the FM layer mediated by elliptically polarized phonons in the hybrid structure.

Influence of the Coulomb interaction on the exchange coupling in granular magnets.

Science.gov (United States)

Udalov, O G; Beloborodov, I S

2017-04-20

We develop a theory of the exchange interaction between ferromagnetic (FM) metallic grains embedded into insulating matrix by taking into account the Coulomb blockade effects. For bulk ferromagnets separated by the insulating layer the exchange interaction strongly depends on the height and thickness of the tunneling barrier created by the insulator. We show that for FM grains embedded into insulating matrix the exchange coupling additionally depends on the dielectric properties of this matrix due to the Coulomb blockade effects. In particular, the FM coupling decreases with decreasing the dielectric permittivity of insulating matrix. We find that the change in the exchange interaction due to the Coulomb blockade effects can be a few tens of percent. Also, we study dependence of the intergrain exchange interaction on the grain size and other parameters of the system.

Ion exchange behaviour of citrate and EDTA anions on strong and weak base organic ion exchangers

International Nuclear Information System (INIS)

Askarieh, M.M.; White, D.A.

1988-01-01

The exchange of citrate and EDTA ions with two strong base and two weak base exchangers is considered. Citrate and EDTA analysis for this work was performed using a colorimetric method developed here. The ions most selectively exchanged on the resins are H 2 cit - and H 2 EDTA 2- , though EDTA is generally less strongly sorbed on strong base resins. In contact with weak base resins, deprotonation of the resin occurs during ion exchange with a noticeable drop in solution pH. Although EDTA sorption can be reversed by nitric acid, citrate ions are significantly held on the resin at low pH. The exchange of citrate can be made reversible if bicarbonate is added to the initial solutions. Alkaline regeneration of exchangers loaded with EDTA proved to be very effective. (author)

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

Science.gov (United States)

Avilés-Félix, L.; Butera, A.; González-Chávez, D. E.; Sommer, R. L.; Gómez, J. E.

2018-03-01

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

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.

A model study of tunneling conductance spectra of ferromagnetically ordered manganites

Science.gov (United States)

Panda, Saswati; Kar, J. K.; Rout, G. C.

2018-02-01

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

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.

Electric-field-controlled spin reversal in a quantum dot with ferromagnetic contacts

Science.gov (United States)

Hauptmann, J. R.; Paaske, J.; Lindelof, P. E.

2008-05-01

Manipulation of the spin states of a quantum dot by purely electrical means is a highly desirable property of fundamental importance for the development of spintronic devices such as spin filters, spin transistors and single spin memories as well as for solid-state qubits. An electrically gated quantum dot in the Coulomb blockade regime can be tuned to hold a single unpaired spin-1/2, which is routinely spin polarized by an applied magnetic field. Using ferromagnetic electrodes, however, the quantum dot becomes spin polarized by the local exchange field. Here, we report on the experimental realization of this tunnelling-induced spin splitting in a carbon-nanotube quantum dot coupled to ferromagnetic nickel electrodes with a strong tunnel coupling ensuring a sizeable exchange field. As charge transport in this regime is dominated by the Kondo effect, we can use this sharp many-body resonance to read off the local spin polarization from the measured bias spectroscopy. We demonstrate that the exchange field can be compensated by an external magnetic field, thus restoring a zero-bias Kondo resonance, and we demonstrate that the exchange field itself, and hence the local spin polarization, can be tuned and reversed merely by tuning the gate voltage.

Enhanced ferromagnetism, metal-insulator transition, and large magnetoresistance in La1-xCaxMn1-xRuxO3 free of eg-orbital double-exchange

Science.gov (United States)

Liu, M. F.; Du, Z. Z.; Liu, H. M.; Li, X.; Yan, Z. B.; Dong, S.; Liu, J.-M.

2014-03-01

The structure, ionic valences, magnetism, and magneto-transport behaviors of mixed valence oxides La1-xCaxMn1-xRuxO3 are systematically investigated. The simultaneous substitutions of La3+ and Mn3+ ions by Ca2+ and Ru4+, respectively, are confirmed by the structural and ionic valence characterizations, excluding the presence of Mn4+ and Ru3+ ions. The enhanced ferromagnetism, induced metal-insulator transition, and remarkable magnetoresistance effect are demonstrated when the substitution level x is lower than ˜0.6, in spite of the absence of the Mn3+-Ru4+ eg-orbital double-exchange. These anomalous magnetotransport effects are discussed based on the competing multifold interactions associated with the Mn3+-Ru4+ super-exchange and strong Ru4+-Ru4+ hopping, while the origins for the metal-insulator transition and magnetoresistance effect remain to be clarified.

Giant spin torque in hybrids with anisotropic p-d exchange interaction

Science.gov (United States)

Korenev, V. L.

2014-03-01

Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here, I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the domain wall motion by current density 104 A/cm2 in ferromagnet/semiconductor hybrids. The experimental observation of the anisotropic torque will facilitate the integration of ferromagnetism into semiconductor electronics.

Giant spin torque in hybrids with anisotropic p-d exchange interaction

International Nuclear Information System (INIS)

Korenev, V. L.

2014-01-01

Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here, I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the domain wall motion by current density 10 4  A/cm 2 in ferromagnet/semiconductor hybrids. The experimental observation of the anisotropic torque will facilitate the integration of ferromagnetism into semiconductor electronics

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)

Standard practice for in situ examination of ferromagnetic Heat-Exchanger tubes using remote field testing

CERN Document Server

American Society for Testing and Materials. Philadelphia

2010-01-01

1.1 This practice describes procedures to be followed during remote field examination of installed ferromagnetic heat-exchanger tubing for baseline and service-induced discontinuities. 1.2 This practice is intended for use on ferromagnetic tubes with outside diameters from 0.500 to 2.000 in. [12.70 to 50.80 mm], with wall thicknesses in the range from 0.028 to 0.134 in. [0.71 to 3.40 mm]. 1.3 This practice does not establish tube acceptance criteria; the tube acceptance criteria must be specified by the using parties. 1.4 Units—The values stated in either inch-pound units or SI units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this practice to establ...

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

Interface currents in topological superconductor–ferromagnet heterostructures

International Nuclear Information System (INIS)

Brydon, P M R; Timm, Carsten; Schnyder, Andreas P

2013-01-01

We propose the existence of a substantial charge current parallel to the interface between a noncentrosymmetric superconductor and a metallic ferromagnet. Our analysis focuses upon two complementary orbital-angular-momentum pairing states of the superconductor, exemplifying topologically nontrivial states which are gapped and gapless in the bulk, respectively. Utilizing a quasiclassical scattering theory, we derive an expression for the interface current in terms of Andreev reflection coefficients. Performing a systematic study of the current, we find stark qualitative differences between the gapped and gapless superconductors, which reflect the very different underlying topological properties. For the fully gapped superconductor, there is a sharp drop in the zero-temperature current as the system is tuned from a topologically nontrivial to a trivial phase. We explain this in terms of the sudden disappearance of the contribution to the current from the subgap edge states at the topological transition. The current in the gapless superconductor is characterized by a dramatic enhancement at low temperatures, and exhibits a singular dependence on the exchange-field strength in the ferromagnetic metal at zero temperature. This is caused by the energy shift of the strongly spin-polarized nondegenerate zero-energy flat bands due to their coupling to the exchange field. We argue that the interface current provides a novel test of the topology of the superconductor, and discuss prospects for the experimental verification of our predictions. (paper)

Spin Transport in Mesoscopic Superconducting-Ferromagnetic Hybrid Conductor

Directory of Open Access Journals (Sweden)

Zein W. A.

2008-01-01

Full Text Available The spin polarization and the corresponding tunneling magnetoresistance (TMR for a hybrid ferromagnetic / superconductor junction are calculated. The results show that these parameters are strongly depends on the exchange field energy and the bias voltage. The dependence of the polarization on the angle of precession is due to the spin flip through tunneling process. Our results could be interpreted as due to spin imbalance of carriers resulting in suppression of gap energy of the superconductor. The present investigation is valuable for manufacturing magnetic recording devices and nonvolatile memories which imply a very high spin coherent transport for such junction.

Spin Transport in Mesoscopic Superconducting-Ferromagnetic Hybrid Conductor

Directory of Open Access Journals (Sweden)

Zein W. A.

2008-01-01

Full Text Available The spin polarization and the corresponding tunneling magnetoresistance (TMR for a hybrid ferromagnetic/superconductor junction are calculated. The results show that these parameters are strongly depends on the exchange field energy and the bias voltage. The dependence of the polarization on the angle of precession is due to the spin flip through tunneling process. Our results could be interpreted as due to spin imbalance of carriers resulting in suppression of gap energy of the superconductor. The present investigation is valuable for manufacturing magnetic recording devices and nonvolatile memories which imply a very high spin coherent transport for such junction.

Strong Interlayer Magnon-Magnon Coupling in Magnetic Metal-Insulator Hybrid Nanostructures

Science.gov (United States)

Chen, Jilei; Liu, Chuanpu; Liu, Tao; Xiao, Yang; Xia, Ke; Bauer, Gerrit E. W.; Wu, Mingzhong; Yu, Haiming

2018-05-01

We observe strong interlayer magnon-magnon coupling in an on-chip nanomagnonic device at room temperature. Ferromagnetic nanowire arrays are integrated on a 20-nm-thick yttrium iron garnet (YIG) thin film strip. Large anticrossing gaps up to 1.58 GHz are observed between the ferromagnetic resonance of the nanowires and the in-plane standing spin waves of the YIG film. Control experiments and simulations reveal that both the interlayer exchange coupling and the dynamical dipolar coupling contribute to the observed anticrossings. The coupling strength is tunable by the magnetic configuration, allowing the coherent control of magnonic devices.

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.

Strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2

Science.gov (United States)

Zhang, Wen; Liu, Yi; Wang, Xiaoying; Zhang, Yun; Xie, Donghua

2018-03-01

The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band-like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons. Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below {T}{{C}}≈ 52 {{K}}, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at {T}X≈ 28 {{K}}, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems. Project supported by the National Natural Science Foundation of China (Grant No. 11404297), the Science Challenge Project (Grant No. TZ2016004), and the Science and Technology Foundation of China Academy of Engineering Physics (Grant Nos. 2013B0301050 and 2014A0301013).

Proximity effect in superconductor/ferromagnet hetero-structures as a function of interface properties

Science.gov (United States)

Sarmiento, Julio; Patino, Edgar J.

2014-03-01

Superconductor/ferromagnet heterostructures are currently a subject of strong research due to novel phenomena resulting from the proximity effect. Among the most investigated ones are the oscillations of the critical temperature as function of the ferromagnet thickness. The oscillatory behavior of Tc is theoretically explained as to be result of the generation of the FFLO (Fulde-Ferrel-Larkin-Ovchinnikov) state of Cooper pairs under the presence of the exchange field of the ferromagnet. With the advancement of experimental techniques for S/F bilayers growth new questions regarding the effect of the interface transparency can to be addressed. For instance the influence of the interface roughness on the proximity effect. For studying this phenomenon Nb/Co and Nb/Cu/Co samples were sputtered on SiO2 substrates with different roughness. Characterization of these samples show a significant variation of Tc with the interface roughness. This results point towards a possible relationship between transparency and roughness of the interface. Proyecto Semilla Facultad de Ciencias Universidad de los Andes.

Giant spin torque in hybrids with anisotropic p-d exchange interaction

Energy Technology Data Exchange (ETDEWEB)

Korenev, V. L., E-mail: korenev@orient.ioffe.ru [A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia and Experimentelle Physik 2, Technische Universitat Dortmund, D-44227 Dortmund (Germany)

2014-03-03

Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here, I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the domain wall motion by current density 10{sup 4} A/cm{sup 2} in ferromagnet/semiconductor hybrids. The experimental observation of the anisotropic torque will facilitate the integration of ferromagnetism into semiconductor electronics.

Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

KAUST Repository

Venkatesh, S.; Franklin, J. B.; Ryan, M. P.; Lee, J.-S.; Ohldag, Hendrik; McLachlan, M. A.; Alford, N. M.; Roqan, Iman S.

2015-01-01

. %) at low oxygen deposition pressure (<25 mTorr) were ferromagnetic at room temperature. Negative magnetoresistance, electric transport properties showed that the ferromagnetic exchange is mediated by a spin-split defect band formed due to oxygen deficiency

Effects of surface exchange anisotropy in Heisenberg ferromagnetic insulators

International Nuclear Information System (INIS)

Selzer, S.; Majlis, N.

1982-03-01

We consider an fcc semi-infinite ferromagnetic insulator displaying an anisotropic exchange interaction between spins on the (111) surface plane of the form Jsub(parallel)[Ssub(i)sup(x)Ssub(j)sup(x)+Ssub(i)sup(y)Ssub(j)sup(y )+etaSsub(i)sup(z)Ssub(j)sup(z)], assuming all other interactions isotropic. A self-consistent RPA calculation is performed, with a Green function method valid for any spin S, up to the bulk transition temperature Tsub(c)sup(b), by imposing that the magnetization of the third layer equals the bulk value. For eta sufficiently large, the surface magnetization is non-zero for T>Tsub(c)sup(b), up to a transition temperature Tsub(c)sup(s)(eta) whenever eta>=etasub(c)>1, where Tsub(c)sup(s)(etasub(c))=Tsub(c)sup(b). For T>Tsub(c)sup(b) the system is equivalent to a film of three layers, where the magnetization of the third one is identically zero as a boundary condition. A discontinuity of the derivative in the curve of the magnetization of the first two layers vs. temperature is found at Tsub(c)sup(b). The results show clearly a cross-over from Heisenberg to Ising behaviour at the surface. (author)

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

Spin- and valley-dependent electronic band structure and electronic heat capacity of ferromagnetic silicene in the presence of strain, exchange field and Rashba spin-orbit coupling

Science.gov (United States)

Hoi, Bui Dinh; Yarmohammadi, Mohsen; Kazzaz, Houshang Araghi

2017-10-01

We studied how the strain, induced exchange field and extrinsic Rashba spin-orbit coupling (RSOC) enhance the electronic band structure (EBS) and electronic heat capacity (EHC) of ferromagnetic silicene in presence of external electric field (EF) by using the Kane-Mele Hamiltonian, Dirac cone approximation and the Green's function approach. Particular attention is paid to investigate the EHC of spin-up and spin-down bands at Dirac K and K‧ points. We have varied the EF, strain, exchange field and RSOC to tune the energy of inter-band transitions and consequently EHC, leading to very promising features for future applications. Evaluation of EF exhibits three phases: Topological insulator (TI), valley-spin polarized metal (VSPM) and band insulator (BI) at given aforementioned parameters. As a new finding, we have found a quantum anomalous Hall phase in BI regime at strong RSOCs. Interestingly, the effective mass of carriers changes with strain, resulting in EHC behaviors. Here, exchange field has the same behavior with EF. Finally, we have confirmed the reported and expected symmetry results for both Dirac points and spins with the study of valley-dependent EHC.

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.

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

Monte Carlo study of the double and super-exchange model with lattice distortion

Energy Technology Data Exchange (ETDEWEB)

Suarez, J R; Vallejo, E; Navarro, O [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Mexico D. F. (Mexico); Avignon, M, E-mail: jrsuarez@iim.unam.m [Institut Neel, Centre National de la Recherche Scientifique (CNRS) and Universite Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France)

2009-05-01

In this work a magneto-elastic phase transition was obtained in a linear chain due to the interplay between magnetism and lattice distortion in a double and super-exchange model. It is considered a linear chain consisting of localized classical spins interacting with itinerant electrons. Due to the double exchange interaction, localized spins tend to align ferromagnetically. This ferromagnetic tendency is expected to be frustrated by anti-ferromagnetic super-exchange interactions between neighbor localized spins. Additionally, lattice parameter is allowed to have small changes, which contributes harmonically to the energy of the system. Phase diagram is obtained as a function of the electron density and the super-exchange interaction using a Monte Carlo minimization. At low super-exchange interaction energy phase transition between electron-full ferromagnetic distorted and electron-empty anti-ferromagnetic undistorted phases occurs. In this case all electrons and lattice distortions were found within the ferromagnetic domain. For high super-exchange interaction energy, phase transition between two site distorted periodic arrangement of independent magnetic polarons ordered anti-ferromagnetically and the electron-empty anti-ferromagnetic undistorted phase was found. For this high interaction energy, Wigner crystallization, lattice distortion and charge distribution inside two-site polarons were obtained.

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.

Spin-orbit-coupled transport and spin torque in a ferromagnetic heterostructure

KAUST Repository

Wang, Xuhui; Ortiz Pauyac, Christian; Manchon, Aurelien

2014-01-01

Ferromagnetic heterostructures provide an ideal platform to explore the nature of spin-orbit torques arising from the interplay mediated by itinerant electrons between a Rashba-type spin-orbit coupling and a ferromagnetic exchange interaction. For such a prototypic system, we develop a set of coupled diffusion equations to describe the diffusive spin dynamics and spin-orbit torques. We characterize the spin torque and its two prominent—out-of-plane and in-plane—components for a wide range of relative strength between the Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence of the spin torque emerging from our simple Rashba model is in an agreement with experiments. The spin diffusion equation can be generalized to incorporate dynamic effects such as spin pumping and magnetic damping.

Spin-orbit-coupled transport and spin torque in a ferromagnetic heterostructure

KAUST Repository

Wang, Xuhui

2014-02-07

Ferromagnetic heterostructures provide an ideal platform to explore the nature of spin-orbit torques arising from the interplay mediated by itinerant electrons between a Rashba-type spin-orbit coupling and a ferromagnetic exchange interaction. For such a prototypic system, we develop a set of coupled diffusion equations to describe the diffusive spin dynamics and spin-orbit torques. We characterize the spin torque and its two prominent—out-of-plane and in-plane—components for a wide range of relative strength between the Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence of the spin torque emerging from our simple Rashba model is in an agreement with experiments. The spin diffusion equation can be generalized to incorporate dynamic effects such as spin pumping and magnetic damping.

Ferromagnetic-insulators-modulated transport properties on the surface of a topological insulator

International Nuclear Information System (INIS)

Guo Jun-Ji; Liao Wen-Hu

2014-01-01

Transport properties on the surface of a topological insulator (TI) under the modulation of a two-dimensional (2D) ferromagnet/ferromagnet junction are investigated by the method of wave function matching. The single ferromagnetic barrier modulated transmission probability is expected to be a periodic function of the polarization angle and the planar rotation angle, that decreases with the strength of the magnetic proximity exchange increasing. However, the transmission probability for the double ferromagnetic insulators modulated n—n junction and n—p junction is not a periodic function of polarization angle nor planar rotation angle, owing to the combined effects of the double ferromagnetic insulators and the barrier potential. Since the energy gap between the conduction band and the valence band is narrowed and widened respectively in ranges of 0 ≤ θ < π/2 and π/2 < θ ≤ π, the transmission probability of the n—n junction first increases rapidly and then decreases slowly with the increase of the magnetic proximity exchange strength. While the transmission probability for the n—p junction demonstrates an opposite trend on the strength of the magnetic proximity exchange because the band gaps contrarily vary. The obtained results may lead to the possible realization of a magnetic/electric switch based on TIs and be useful in further understanding the surface states of TIs

The origin of room temperature ferromagnetism mediated by Co–VZn complexes in the ZnO grain boundary

KAUST Repository

Devi, Assa Aravindh Sasikala

2016-05-20

Ferromagnetism in polycrystalline ZnO doped with Co has been observed to be sustainable in recent experiments. We use first-principle calculations to show that Co impurities favorably substitute at the grain boundary (GB) rather than in the bulk. We reveal that room-temperature ferromagnetism (RTFM) at the Co-doped ZnO GB in the presence of Zn vacancies is due to ferromagnetic exchange coupling of a pair of closely associated Co atoms in the GB, with a ferromagnetic exchange coupling energy of ∼300 meV, which is in contrast to a previous study that suggested the O vacancy-Co complex induced ferromagnetism. Electronic structure analysis was used to predict the exchange coupling mechanism, showing that the hybridization of O p states with Co and Zn d states enhances the magnetic polarization originating from the GB. Our results indicate that RTFM originates from Co clusters at interfaces or in GBs. © 2016 The Royal Society of Chemistry.

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.

Temperature dependence of exchange bias in (NiFe/IrMn)n multilayer films studied through static and dynamic techniques

Science.gov (United States)

Adams, Daniel J.; Khanal, Shankar; Khan, Mohammad Asif; Maksymov, Artur; Spinu, Leonard

2018-05-01

The in-plane temperature dependence of exchange bias was studied through both dc magnetometry and ferromagnetic resonance spectroscopy in a series of [NiFe/IrMn]n multilayer films, where n is the number of layer repetitions. Major hysteresis loops were recorded in the temperature range of 300 K to 2 K to reveal the effect of temperature on the exchange bias in the static regime while temperature-dependent continuous-wave ferromagnetic resonance for frequencies from 3 to 16 GHz was used to determine the exchange bias dynamically. Strong divergence between the values of exchange bias determined using the two different types of measurements as well as a peak in temperature dependence of the resonance linewidth were observed. These results are explained in terms of the slow-relaxer mechanism.

Half-metallic ferromagnetism in Cu-doped zinc-blende ZnO from first principles study

International Nuclear Information System (INIS)

Li, X.F.; Zhang, J.; Xu, B.; Yao, K.L.

2012-01-01

Electronic structures and magnetism of Cu-doped zinc-blende ZnO have been investigated by the first-principle method based on density functional theory (DFT). The results show that Cu can induce stable ferromagnetic ground state. The magnetic moment of supercell including single Cu atom is 1.0 μ B . Electronic structure shows that Cu-doped zinc-blende ZnO is a p-type half-metallic ferromagnet. The half-metal property is mainly attribute to the crystal field splitting of Cu 3d orbital, and the ferromagnetism is dominated by the hole-mediated double exchange mechanism. Therefore, Cu-doped zinc-blende ZnO should be useful in semiconductor spintronics and other applications. - Highlights: → Magnetism of Cu-doped zinc-blende ZnO. → Cu-doped zinc-blende ZnO shows interesting half-metal character. → Total energies calculations reveal that Cu can induce ferromagnetic ground state. → Ferromagnetism dominated by the hole-mediated double exchange mechanism.

Parallel ferromagnetic resonance and spin-wave excitation in exchange-biased NiFe/IrMn bilayers

Energy Technology Data Exchange (ETDEWEB)

Sousa, Marcos Antonio de, E-mail: marcossharp@gmail.com [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Pelegrini, Fernando [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Alayo, Willian [Departamento de Física, Universidade Federal de Pelotas, Pelotas, 96010-900 (Brazil); Quispe-Marcatoma, Justiniano; Baggio-Saitovitch, Elisa [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, 22290-180 (Brazil)

2014-10-01

Ferromagnetic Resonance study of sputtered Ru(7 nm)/NiFe(t{sub FM})/IrMn(6 nm)/Ru(5 nm) exchange-biased bilayers at X and Q-band microwave frequencies reveals the excitation of spin-wave and NiFe resonance modes. Angular variations of the in-plane resonance fields of spin-wave and NiFe resonance modes show the effect of the unidirectional anisotropy, which is about twice larger for the spin-wave mode due to spin pinning at the NiFe/IrMn interface. At Q-band frequency the angular variations of in-plane resonance fields also reveal the symmetry of a uniaxial anisotropy. A modified theoretical model which also includes the contribution of a rotatable anisotropy provides a good description of the experimental results.

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

Spin current and spin transfer torque in ferromagnet/superconductor spin valves

Science.gov (United States)

Moen, Evan; Valls, Oriol T.

2018-05-01

Using fully self-consistent methods, we study spin transport in fabricable spin valve systems consisting of two magnetic layers, a superconducting layer, and a spacer normal layer between the ferromagnets. Our methods ensure that the proper relations between spin current gradients and spin transfer torques are satisfied. We present results as a function of geometrical parameters, interfacial barrier values, misalignment angle between the ferromagnets, and bias voltage. Our main results are for the spin current and spin accumulation as functions of position within the spin valve structure. We see precession of the spin current about the exchange fields within the ferromagnets, and penetration of the spin current into the superconductor for biases greater than the critical bias, defined in the text. The spin accumulation exhibits oscillating behavior in the normal metal, with a strong dependence on the physical parameters both as to the structure and formation of the peaks. We also study the bias dependence of the spatially averaged spin transfer torque and spin accumulation. We examine the critical-bias effect of these quantities, and their dependence on the physical parameters. Our results are predictive of the outcome of future experiments, as they take into account imperfect interfaces and a realistic geometry.

Domain walls and exchange-interaction in Permalloy/Gd films

International Nuclear Information System (INIS)

Ranchal, R; Aroca, C; Lopez, E

2008-01-01

In this work we study the exchange coupling in Permalloy (Py)/gadolinium (Gd) bilayers. The exchange-coupled Py/Gd system is very temperature dependent and moreover the magnetization process in the Py layer is mainly due to domain wall (DW) displacements which are strongly controlled by pinning effects. We propose that this pinning could be caused by magnetostatic and exchange interactions between Py DWs and the magnetostrictive Gd layer. These effects mask the antiferromagnetic coupling between layers and, depending on temperature and Py thicknesses, apparent ferromagnetic coupling occurs. The study has been performed in the 80-300 K temperature range for different Py layer thicknesses and different Py induced anisotropies

Carrier concentration induced ferromagnetism in semiconductors

International Nuclear Information System (INIS)

Story, T.

2007-01-01

mechanisms and variety of new proposals aiming at proper theoretical description of such features of diluted magnetic semiconductors as magnetic (site) disorder, electronic disorder due to doping, and competition between ferromagnetic and antiferromagnetic exchange interactions. (author)

Magnetic pinning in superconductor-ferromagnet multilayers

International Nuclear Information System (INIS)

Bulaevskii, L. N.; Chudnovsky, E. M.; Maley, M. P.

2000-01-01

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10 6 -10 7 A/cm 2 at high temperatures (but not very close to T c ) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics

Spin waves in two-dimensional ferromagnet with large easy-plane anisotropy

International Nuclear Information System (INIS)

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

2002-01-01

Spin waves in easy-plane two-dimensional ferromagnet when anisotropy is much stronger than exchange are investigated. The spectra of magnons, the spin-spin and quadrupolar correlation functions have been derived. It is shown that in such a system there exist spin waves at low temperatures. Some properties of the quadrupolar ordering in ferromagnets are discussed

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.

Magnetoanisotropic spin-triplet Andreev reflection in ferromagnet-Ising superconductor junctions

Science.gov (United States)

Lv, Peng; Zhou, Yan-Feng; Yang, Ning-Xuan; Sun, Qing-Feng

2018-04-01

We theoretically study the electronic transport through a ferromagnet-Ising superconductor junction. A tight-binding Hamiltonian describing the Ising superconductor is presented. Then by combining the nonequilibrium Green's function method, the expressions of Andreev reflection coefficient and conductance are obtained. A strong magnetoanisotropic spin-triplet Andreev reflection is shown, and the magnetoanisotropic period is π instead of 2 π as in the conventional magnetoanisotropic system. We demonstrate a significant increase of the spin-triplet Andreev reflection for the single-band Ising superconductor. Furthermore, the dependence of the Andreev reflection on the incident energy and incident angle are also investigated. A complete Andreev reflection can occur when the incident energy is equal to the superconducting gap, regardless of the Fermi energy (spin polarization) of the ferromagnet. For the suitable oblique incidence, the spin-triplet Andreev reflection can be strongly enhanced. In addition, the conductance spectroscopies of both zero bias and finite bias are studied, and the influence of gate voltage, exchange energy, and spin-orbit coupling on the conductance spectroscopy are discussed in detail. The conductance exhibits a strong magnetoanisotropy with period π as the Andreev reflection coefficient. When the magnetization direction is parallel to the junction plane, a large conductance peak always emerges at the superconducting gap. This work offers a comprehensive and systematic study of the spin-triplet Andreev reflection and has an underlying application of π -periodic spin valve in spintronics.

Ionized zinc vacancy mediated ferromagnetism in copper doped ZnO thin films

Directory of Open Access Journals (Sweden)

Shi-Yi Zhuo

2012-03-01

Full Text Available This paper reports the origin of ferromagnetism in Cu-doped ZnO thin films. Room-temperature ferromagnetism is obtained in all the thin films when deposited at different oxygen partial pressure. An obviously enhanced peak corresponding to zinc vacancy is observed in the photoluminescence spectra, while the electrical spin resonance measurement implies the zinc vacancy is negative charged. After excluding the possibility of direct exchange mechanisms (via free carriers, we tentatively propose a quasi-indirect exchange model (via ionized zinc vacancy for Cu-doped ZnO system.

Preparation of nuclear grade strongly basic anion exchange resin in hydroxide from

International Nuclear Information System (INIS)

Ke Weiqing

1989-01-01

The two-step transformation method was used to prepare 90 kg nuclear grade strongly basic anion exchange resins by using the industrial grade baking soda and caustic soda manufacutred by mercury-cathode electrolysis. The chloride and biscarbonate fraction on resin is 0.8% and 1.25% respectively, when the baking soda and caustic soda consumption is 8.6 and 13.7 times the total exchange capacity of the strongly basic resin

Angular and linear momentum of excited ferromagnets

NARCIS (Netherlands)

Yan, P.; Kamra, A.; Cao, Y.; Bauer, G.E.W.

2013-01-01

The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist

Exchange anisotropy pinning of a standing spin-wave mode

Science.gov (United States)

Magaraggia, R.; Kennewell, K.; Kostylev, M.; Stamps, R. L.; Ali, M.; Greig, D.; Hickey, B. J.; Marrows, C. H.

2011-02-01

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin-wave thickness mode in Ni80Fe20/Ir25Mn75 exchange-biased bilayers was studied for a range of Ir25Mn75 thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique “fingerprint” of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet-antiferromagnet interface anisotropy. Thermal effects are studied for ultrathin antiferromagnetic Ir25Mn75 thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region.

Tailor-made nano-structured materials for perpendicular recording media and head-precise control of direct/indirect exchange coupling

International Nuclear Information System (INIS)

Takahashi, Migaku; Tsunoda, Masakiyo; Saito, Shin

2009-01-01

Tailor-made nano-structured spin materials obtained by precisely controlled nano-scale fabrication technologies for use in ultra-high density hard disk drives (HDDs), as well as an understanding of their nanomagnetics, are essential from the view point of materials, processes, and physics. Artificial control of the exchange coupling among ferromagnetic layers through the RKKY interaction (indirect) and direct exchange coupling represented as the exchange bias at the ferromagnetic (FM)/antiferromagnetic (AFM) interface are of great interest and have received significant attention to induce new modulated spin structures in conventional simple FM materials. In particular, soft magnetic under layer (SUL) with strong synthetic antiferromagnetic (SAF) coupling between two adjacent soft magnetic layers, exchange coupled stacked media introducing exchange coupling between FM layers and giant exchange anisotropy at the FM/AFM interface have attracted significant attention from the view point of applications. Within the framework of the present paper, we discuss future technical trends for SUL, granular media and the spin-valve head from the viewpoint of direct and/or indirect exchange coupling based on our recent results

Magnetic pinning in superconductor-ferromagnet multilayers

Energy Technology Data Exchange (ETDEWEB)

Bulaevskii, L. N. [Department of Physics and Astronomy, CUNY Lehman College 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Chudnovsky, E. M. [Department of Physics and Astronomy, CUNY Lehman College, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589 (United States); Maley, M. P. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2000-05-01

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10{sup 6}-10{sup 7} A/cm{sup 2} at high temperatures (but not very close to T{sub c}) at least in magnetic fields below 0.1 T. (c) 2000 American Institute of Physics.

The resonance susceptibility of two-layer exchange-coupled ferromagnetic film with a combined uniaxial and cubic anisotropy in the layers

Energy Technology Data Exchange (ETDEWEB)

Shul’ga, N.V., E-mail: shulga@anrb.ru; Doroshenko, R.A.

2016-12-01

A numerical investigation of the resonance dynamic susceptibility of ferromagnetic exchange-coupled two-layer films with a combined cubic and uniaxial magnetic anisotropy of the layers has been performed. It has been found that the presence of cubic anisotropy leads to the fact that much of the off-diagonal components of the dynamic susceptibility are nonzero. The change of the ferromagnetic resonance frequencies and dynamic susceptibility upon the magnetization along the [100], [010], and [011] directions have been calculated. The evolution of the profile of the dynamic susceptibility occurring during the magnetization has been described. The impact of changes in the distribution of equilibrium and dynamic components of the magnetization on the dependences of the components of the dynamic susceptibility and the ferromagnetic resonance frequency on the external magnetic fields has been discussed. - Highlights: • The extremes in the dependences of integrated dynamic susceptibility components are observed at low fields. • Lower extremes can be observed at a shift of the localization of the lower FMR mode toward the interface between the layers. • The features of the distribution of the dynamic susceptibility over the thickness have been discussed. • The cubic anisotropy leads to the fact that the off-diagonal integrated dynamic susceptibility components are essential. • FMR signal can be excited in vicinity of the interlayer boundary.

Thermoelectric effects and spin injection into superconductors with exchange field

Energy Technology Data Exchange (ETDEWEB)

Heikkilae, Tero [Dept. Phys., Univ. Jyvaeskylae (Finland); Silaev, Mihail [O.V. Lounasmaa Lab, Aalto Univ. (Finland); Dept. Theor. Physics, KTH, Stockholm (Sweden); Virtanen, Pauli [O.V. Lounasmaa Lab, Aalto Univ. (Finland); Giazotto, Francesco [NEST CNR-INFM and SNS Pisa (Italy); Ozaeta, Asier; Bergeret, Sebastian [CFM-CSIC and DIPC, San Sebastian (Spain)

2015-07-01

When a thin superconducting film is exposed to a longitudinal magnetic field or is in proximity to a ferromagnet, an exchange field separating the spin bands emerges in it. For low enough exchange fields superconductivity survives, but its response to external driving is strongly modified. In my talk I will show how at linear response such systems exhibit very strong thermoelectric response with an almost ideal efficiency. For strong driving, this effect creates a spin accumulation that can only relax via thermalization, and therefore at low temperatures has a very long range. Therefore our work explains recent observations of the long-range spin accumulation in spin-split superconductors. When injecting spin from injectors with non-collinear magnetization compared to the exchange field, the spins start to rotate around the latter. I will describe how superconductivity modifies this spin Hanle effect so that the resulting nonlocal magnetoresistance depends on the details of spin relaxation, therefore allowing for probing them.

Significant room-temperature ferromagnetism in porous ZnO films: The role of oxygen vacancies

Energy Technology Data Exchange (ETDEWEB)

Hou, Xue; 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); 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 [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China)

2015-10-15

Graphical abstract: - Highlights: • Porous ZnO films were deposited on porous anodic alumina substrates. • Significant ferromagnetism (FM) has been observed in porous ZnO films (110 emu/cm{sup 3}). • The strong magnetic anisotropy was observed in the porous ZnO films. • The origin of FM is attributed to the oxygen vacancy with a local magnetic moment. - Abstract: Pure porous ZnO films were prepared by direct current reactive magnetron sputtering on porous anodic alumina substrates. Remarkably large room-temperature ferromagnetism was observed in the films. The highest saturation moment along the out-of-plane direction was about 110 emu/cm{sup 3}. Experimental and theoretical results suggested that the oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism. There are two modes of coupling between oxygen vacancies in the porous ZnO films: (i) exchange interactions directly between the oxygen vacancies and (ii) with the mediation of conduction electrons. In addition, it was found that the magnetic moment of ZnO films can be changed by tuning the concentration of oxygen vacancies. These observations may be useful in the development of ZnO-based spintronics devices.

Anisotropic exchange interaction induced by a single photon in semiconductor microcavities

Science.gov (United States)

Chiappe, G.; Fernández-Rossier, J.; Louis, E.; Anda, E. V.

2005-12-01

We investigate coupling of localized spins in a semiconductor quantum dot embedded in a microcavity. The lowest cavity mode and the quantum dot exciton are coupled and close in energy, forming a polariton. The fermions forming the exciton interact with localized spins via exchange. Exact diagonalization of a Hamiltonian in which photons, spins, and excitons are treated quantum mechanically shows that a single polariton induces a sizable indirect anisotropic exchange interaction between spins. At sufficiently low temperatures strong ferromagnetic correlations show up without an appreciable increase in exciton population. In the case of a (Cd,Mn)Te quantum dot, Mn-Mn ferromagnetic coupling is still significant at 1 K : spin-spin correlation around 3 for exciton occupation smaller than 0.3. We find that the interaction mediated by photon-polaritons is 10 times stronger than the one induced by a classical field for equal Rabi splitting.

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.

Effect of mechanical boundary conditions on the dynamic and static properties of a strongly anisotropic ferromagnet

International Nuclear Information System (INIS)

Gorelikov, G. A.; Fridman, Yu. A.

2013-01-01

The spectra of coupled magnetoelastic waves in a semi-infinite strongly anisotropic easy-plane ferromagnet with a rigidly fixed face are analyzed for two variants of fixation (in the basal plane and perpendicularly to it). The phase states of the system are determined. Differences in the phase diagrams and elementary excitation spectra depending on the choice of the sample fixation plane are considered. When rotational invariance is taken into account, the nonreciprocity effect for the velocities of sound in a crystal appears. It is shown that the velocity of sound in the sample considerably depends on the symmetry of the imposed mechanical boundary conditions. The phase diagrams of the system under investigation are presented

Ab initio description of the diluted magnetic semiconductor Ga1-xMnxAs: Ferromagnetism, electronic structure, and optical response

Science.gov (United States)

Craco, L.; Laad, M. S.; Müller-Hartmann, E.

2003-12-01

Motivated by a study of various experiments describing the electronic and magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs, we investigate its physical response in detail using a combination of first-principles band structure with methods based on dynamical mean field theory to incorporate strong, dynamical correlations, and intrinsic as well as extrinsic disorder in one single theoretical picture. We show how ferromagnetism is driven by double exchange (DE), in agreement with very recent observations, along with a good quantitative description of the details of the electronic structure, as probed by scanning tunneling microscopy and optical conductivity. Our results show how ferromagnetism can be driven by DE even in diluted magnetic semiconductors with small carrier concentration.

Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

KAUST Repository

Venkatesh, S.

2015-01-07

Gd-doped ZnO thin films prepared by pulsed laser deposition with Gd concentrations varying from 0.02–0.45 atomic percent (at. %) showed deposition oxygen pressure controlled ferromagnetism. Thin films prepared with Gd dopant levels (ferromagnetic at room temperature. Negative magnetoresistance, electric transport properties showed that the ferromagnetic exchange is mediated by a spin-split defect band formed due to oxygen deficiency related defect complexes. Mott\\'s theory of variable range of hopping conduction confirms the formation of the impurity/defect band near the Fermi level.

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.

Phase diagrams of site diluted ferromagnetic thin film

International Nuclear Information System (INIS)

Hamedoun, M.; Bouslykhane, K.; Bakrim, H.; Hourmatallah, A.; Benzakour, N.; Masrour, R.

2006-01-01

The phase transition properties of Ising, classical XY and Heisenberg of diluted ferromagnetic thin film are studied by the method of exact high-temperature series expansions extrapolated with the Pade approximants method. The reduced critical temperature τ c of the diluted ferromagnetic thin films is studied as a function of film thickness L and the exchange interactions in the bulk J b , in the surface J s and between surface and nearest-neighbour layer J - bar . It is found that τ c increases with the exchange interactions of surface and L. The magnetic phase diagram (τ c versus dilution x) is obtained. A critical value of the surface exchange interaction above which the surface magnetism appears is obtained. The dependence of the critical parameter of surface reduced coupling R 2 c as a function of the dilution x and the ratio of the exchange interaction between the surface and nearest-neighbour layer to the bulk one R 1 for the three studied models has been investigated. The percolation threshold is defined as the concentration x p at which τ c =0. The obtained values are x p ∼0.2 in the bulk and x p ∼0.4 at the surface

Competition between superconductivity and magnetism in ferromagnet/superconductor heterostructures

International Nuclear Information System (INIS)

Izyumov, Yurii A; Proshin, Yurii N; Khusainov, Mensur G

2002-01-01

The mutual influence of superconductivity and magnetism in F/S systems, i.e. systems of alternating ferromagnetic (F) and superconducting (S) layers, is comprehensively reviewed. For systems with ferromagnetic metal (FM) layers, a theory of the proximity effect in the dirty limit is constructed based on the Usadel equations. For an FM/S bilayer and an FM/S superlattice, a boundary-value problem involving finite FM/S boundary transparency and the diffusion and wave modes of quasi-particle motion is formulated; and the critical temperature T c is calculated as a function of FM- and S-layer thicknesses. A detailed analysis of a large amount of experimental data amply confirms the proposed theory. It is shown that the superconducting state of an FM/S system is a superposition of two pairing mechanisms, Bardin - Cooper - Schrieffer's in S layers and Larkin - Ovchinnikov - Fulde - Ferrell's in FM ones. The competition between ferromagnetic and antiferromagnetic spontaneous moment orientations in FM layers is explored for the 0- and π-phase superconductivity in FM/S systems. For FI/S structures, where FI is a ferromagnetic insulator, a model for exchange interactions is proposed, which, along with direct exchange inside FI layers, includes indirect Ruderman - Kittel - Kasuya - Yosida exchange between localized spins via S-layer conduction electrons. Within this framework, possible mutual accommodation scenarios for superconducting and magnetic order parameters are found, the corresponding phase diagrams are plotted, and experimental results are explained. The results of the theory of the Josephson effect for S/F/S junctions are presented and the application of the theory of spin-dependent transport to F/S/F junctions is discussed. Application aspects of the subject are examined. (reviews of topical problems)

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.

Magnetic stability in exchange-spring and exchange bias systems after multiple switching cycles.

Energy Technology Data Exchange (ETDEWEB)

Jiang, J. S.; Inomata, A.; You, C.-Y.; Pearson, J. E.; Bader, S. D.

2001-06-01

We have studied the magnetic stability in exchange bias and exchange spring systems prepared via epitaxial sputter deposition. The two interfacial exchange coupled systems, Fe/Cr(211) double superlattices consisting of a ferromagnetic and an antiferromagnetic Fe/Cr superlattice that are exchange coupled through a Cr spacer, and Sin-Co/Fe exchange-spring bilayer structures with ferromagnetically coupled hard Sin-Co layer and soft Fe layer, were epitaxially grown on suitably prepared Cr buffer layers to give rise to different microstructure and magnetic anisotropy. The magnetic stability was investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For uniaxial Fe/Cr exchange biased double superlattices and exchange spring bilayers with uniaxial Sin-Co, small but rapid initial decay in the exchange bias field HE and in the remanent magnetization is observed. However, the exchange spring bilayers with biaxial and random in-plane anisotropy in the Sin-Co layer shows gradual decay in H{sub E} and without large reduction of the magnetization. The different decay behaviors are attributed to the different microstructure and spin configuration of the pinning layers.

Study of switching behavior of exchange-coupled nanomagnets by transverse magnetization metrology

Science.gov (United States)

Dey, Himadri S.; Csaba, Gyorgy; Bernstein, Gary H.; Porod, Wolfgang

2017-05-01

We investigate the static switching modes of nanomagnets patterned from antiferromagnetically exchange-coupled magnetic multilayers, and compare them to nanomagnets having only dipole coupling between the ferromagnetic layers. Vibrating sample magnetometry experiments, supported by micromagnetic simulations, reveal two distinct switching mechanisms between the exchange-coupled and only dipole-coupled nanomagnets. The exchange-coupled nanomagnets exhibit gradual switching of the layers, dictated by the strong antiferromagnetic exchange coupling present between the layers. However, the layers of the only dipole-coupled nanomagnets show abrupt nucleation/growth type switching. A comprehensive understanding of the switching modes of such layered and patterned systems can add new insight into the reversal mechanisms of similar systems employed for spintronic and magneto-logic device applications.

Double and super-exchange model in one-dimensional systems

International Nuclear Information System (INIS)

Vallejo, E.; Navarro, O.; Avignon, M.

2010-01-01

We present an analytical and numerical study of the competition between double and super-exchange interactions in a one-dimensional model. For low super-exchange interaction energy we find phase separation between ferromagnetic and anti-ferromagnetic phases. When the super-exchange interaction energy gets larger, the conduction electrons are self-trapped within separate small magnetic polarons. These magnetic polarons contain a single electron inside two or three sites depending on the conduction electron density and form a Wigner crystallization. A new phase separation is found between these small polarons and the anti-ferromagnetic phase. Spin-glass behavior is obtained consistent with experimental results of the nickelate one-dimensional compound Y 2-x Ca x BaNiO 5 .

Spin-dependent dwell time through ferromagnetic graphene barrier

International Nuclear Information System (INIS)

Sattari, F.

2014-01-01

We investigated the dwell time of electrons tunneling through a ferromagnetic (FM) graphene barrier. The results show that the spin polarization can be efficiently controlled by the barrier width, barrier height, and the incident electron energy. Furthermore, it is found that electrons with different spin orientations will spend different times through the barrier. The difference of the dwell time between spin-up and spin-down electrons arises from the exchange splitting, which is induced by the FM strip. Study results indicate that a ferromagnetic graphene barrier can cause a nature spin filter mechanism in the time domain

Construction of exchange-correlation functionals through interpolation between the non-interacting and the strong-correlation limit

International Nuclear Information System (INIS)

Zhou, Yongxi; Ernzerhof, Matthias; Bahmann, Hilke

2015-01-01

Drawing on the adiabatic connection of density functional theory, exchange-correlation functionals of Kohn-Sham density functional theory are constructed which interpolate between the extreme limits of the electron-electron interaction strength. The first limit is the non-interacting one, where there is only exchange. The second limit is the strong correlated one, characterized as the minimum of the electron-electron repulsion energy. The exchange-correlation energy in the strong-correlation limit is approximated through a model for the exchange-correlation hole that is referred to as nonlocal-radius model [L. O. Wagner and P. Gori-Giorgi, Phys. Rev. A 90, 052512 (2014)]. Using the non-interacting and strong-correlated extremes, various interpolation schemes are presented that yield new approximations to the adiabatic connection and thus to the exchange-correlation energy. Some of them rely on empiricism while others do not. Several of the proposed approximations yield the exact exchange-correlation energy for one-electron systems where local and semi-local approximations often fail badly. Other proposed approximations generalize existing global hybrids by using a fraction of the exchange-correlation energy in the strong-correlation limit to replace an equal fraction of the semi-local approximation to the exchange-correlation energy in the strong-correlation limit. The performance of the proposed approximations is evaluated for molecular atomization energies, total atomic energies, and ionization potentials

Separation of boron isotopes by ion exchange chromatography: studies on regeneration of strong base anion exchange resins

International Nuclear Information System (INIS)

Sharma, B.K.; Subramanian, R.; Mathur, P.K.

1994-01-01

The optimum conditions for the regeneration of strong base anion exchange resins of type-I and type-II were determined for cost-effective separation of isotopes of boron by ion exchange chromatography where the hydroxyl form of an anion exchange resin is equilibrated with boric acid solution containing mannitol as a complexing reagent. The possibility of using unspent alkali content of the effluent was also exploited. Removal of carbonate impurity from Rayon grade caustic lye (used as regenerant after dilution) and recycling of Ba(OH) 2 was studied to avoid waste disposal problems. (author)

Frustration by Multiple Spin Exchange in 2D Solid 3He Films

International Nuclear Information System (INIS)

Siqueira, M.; Nyeki, J.; Cowan, B.; Saunders, J.

1997-01-01

Measurements of the magnetization and heat capacity of the second layer of 3 He films adsorbed on graphite indicate that the evolution of the exchange from antiferromagnetic to ferromagnetic arises from a tuning of the competing exchange processes. At certain coverages the coexistence of an antiferromagnetic heat capacity with a ferromagnetic magnetization is a clear manifestation, predicted by theory, of frustration. At the ferromagnetic anomaly the system is well described by series expansions for a 2D Heisenberg ferromagnet on a triangular lattice. copyright 1997 The American Physical Society

Thickness and bilayer number dependence on exchange bias in ferromagnetic/antiferromagnetic multilayers based on La{sub 1−x}Ca{sub x}MnO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Restrepo-Parra, E., E-mail: erestrepopa@unal.edu.co [Departamento de Física y Química, Universidad Nacional de Colombia-Sede Manizales, A.A. 127 Manizales (Colombia); Agudelo-Giraldo, J.D. [Departamento de Física y Química, Universidad Nacional de Colombia-Sede Manizales, A.A. 127 Manizales (Colombia); Grupo de Investigación y Desarrollo en Informática y Telecomunicaciones, Universidad de Manizales, Manizales (Colombia); Restrepo, J. [Grupo de Magnetismo y Simulación, Instituto de Física, Universidad de Antioquia, A.A. 1226 Medellín (Colombia)

2014-05-01

In this work, simulations of ferromagnetic/antiferromagnetic multilayers of La{sub 1−x}Ca{sub x}MnO{sub 3} have been carried out by using the Monte Carlo method combined with the Metropolis algorithm and the classical Heisenberg model. In the Hamiltonian we have considered three contributions: nearest neighbor exchange interaction, magnetocrystalline anisotropy and Zeeman interaction. Samples were built by including three types of Mn ions depending on their valence state and type of ionic orbital. Both the number of layers and the antiferromagnetic layer thickness influence on the exchange bias phenomenon are analyzed. Hysteresis loops results exhibit not only a shift as evidence of exchange bias but also the formation of plateaus or steps caused by the presence of more than one interface and the low layers thickness. Each layer presents a strong magnetic behavior because the magneto static energy favors formation of multi-domains in contrast with the single-domains of a single layer FM producing one sub-Loop of each domain (each layer). On the other hand, as the number of layers (n) increases, the sub-cycles tend to disappear. As the plateaus disappear, the system is more effective, increasing the coercive and bias fields. Moreover, domain sizes (layers thickness) also affect the shape of the hysteresis loop. On increasing the thickness of the AFM layer, a decrease in the plateaus produced by the uncoupling is generated.

Ion-exchange equilibrium of N-acetyl-D-neuraminic acid on a strong anionic exchanger.

Science.gov (United States)

Wu, Jinglan; Ke, Xu; Zhang, Xudong; Zhuang, Wei; Zhou, Jingwei; Ying, Hanjie

2015-09-15

N-acetyl-D-neuraminic acid (Neu5Ac) is a high value-added product widely applied in the food industry. A suitable equilibrium model is required for purification of Neu5Ac based on ion-exchange chromatography. Hence, the equilibrium uptake of Neu5Ac on a strong anion exchanger, AD-1 was investigated experimentally and theoretically. The uptake of Neu5Ac by the hydroxyl form of the resin occurred primarily by a stoichiometric exchange of Neu5Ac(-) and OH(-). The experimental data showed that the selectivity coefficient for the exchange of Neu5Ac(-) with OH(-) was a non-constant quantity. Subsequently, the Saunders' model, which took into account the dissociation reactions of Neu5Ac and the condition of electroneutrality, was used to correlate the Neu5Ac sorption isotherms at various solution pHs and Neu5Ac concentrations. The model provided an excellent fit to the binary exchange data for Cl(-)/OH(-) and Neu5Ac(-)/OH(-), and an approximate prediction of equilibrium in the ternary system Cl(-)/Neu5Ac(-)/OH(-). This basic information combined with the general mass transfer model could lay the foundation for the prediction of dynamic behavior of fixed bed separation process afterwards. Copyright © 2015 Elsevier Ltd. All rights reserved.

New Trends in Magnetic Exchange Bias

Science.gov (United States)

Mougin, Alexandra; Mangin, Stéphane; Bobo, Jean-Francois; Loidl, Alois

2005-05-01

The study of layered magnetic structures is one of the hottest topics in magnetism due to the growing attraction of applications in magnetic sensors and magnetic storage media, such as random access memory. For almost half a century, new discoveries have driven researchers to re-investigate magnetism in thin film structures. Phenomena such as giant magnetoresistance, tunneling magnetoresistance, exchange bias and interlayer exchange coupling led to new ideas to construct devices, based not only on semiconductors but on a variety of magnetic materials Upon cooling fine cobalt particles in a magnetic field through the Néel temperature of their outer antiferromagnetic oxide layer, Meiklejohn and Bean discovered exchange bias in 1956. The exchange bias effect through which an antiferromagnetic AF layer can cause an adjacent ferromagnetic F layer to develop a preferred direction of magnetization, is widely used in magnetoelectronics technology to pin the magnetization of a device reference layer in a desired direction. However, the origin and effects due to exchange interaction across the interface between antiferromagneic and ferromagnetic layers are still debated after about fifty years of research, due to the extreme difficulty associated with the determination of the magnetic interfacial structure in F/AF bilayers. Indeed, in an AF/F bilayer system, the AF layer acts as “the invisible man” during conventional magnetic measurements and the presence of the exchange coupling is evidenced indirectly through the unusual behavior of the adjacent F layer. Basically, the coercive field of the F layer increases in contact with the AF and, in some cases, its hysteresis loop is shifted by an amount called exchange bias field. Thus, AF/F exchange coupling generates a new source of anisotropy in the F layer. This induced anisotropy strongly depends on basic features such as the magnetocrystalline anisotropy, crystallographic and spin structures, defects, domain patterns etc

Tuning antiferromagnetic exchange interaction for spontaneous exchange bias in MnNiSnSi system

Science.gov (United States)

Jia, Liyun; Shen, Jianlei; Li, Mengmeng; Wang, Xi; Ma, Li; Zhen, Congmian; Hou, Denglu; Liu, Enke; Wang, Wenhong; Wu, Guangheng

2017-12-01

Based on almost all the data from the literature on spontaneous exchange bias (SEB), it is expected that the system will show SEB if it meets two conditions simultaneously: (i) there are the coexistence and competition of antiferromagnetic (AFM) and ferromagnetic (FM) interactions and (ii) AFM interaction should dominate but not be too strong in this competition. In order to verify this view, a systematic study on SEB has been performed in this work. Mn50Ni40Sn10 with strong FM interaction and without SEB is chosen as the mother composition, and the negative chemical pressure is introduced by the substitution of Sn by Si to enhance AFM interaction. It is found that a long-range FM ordering window is closed, and a long-range AFM ordering window is opened. As a result, SEB is triggered and a continuous tuning of the spontaneous exchange bias field (HSEB) from 0 Oe to 1300 Oe has been realized in a Mn50Ni40Sn10-xSix system by the enhanced AFM interaction.

(Anti)-ferromagnetic coupling in Fe/Si multilayers from polarized neutron reflectomy

NARCIS (Netherlands)

Fredrikze, H.; Graaf, van der A; Valkier, M.; Kohlhepp, J.T.; Broeder, den F.J.A.

1997-01-01

Polarized neutron reflectometry data on Fe/Si multilayers are interpreted using strongly depth-dependent magnetization in the Fe layers. This behaviour is ascribed to a depth-dependent mixture of ferromagnetic and anti-ferromagnetic coupled regions in the sample.

Room temperature ferromagnetism in magic-sized Cr-doped CdS diluted magnetic semiconducting quantum dots

International Nuclear Information System (INIS)

Srivastava, Punita; Kumar, Pushpendra; Singh, Kedar

2011-01-01

Manipulation of carrier spins in semiconductors for spintronics applications has received great attention driven by improved functionalities and higher speed operation. Doping of semiconductor nanocrystals by transition-metal ions pronounced as diluted magnetic semiconductors (DMS) has attracted tremendous attention. Such doping is, however, difficult to achieve in low-dimensional strongly quantum-confined nanostructures by conventional growth procedures. In the present case, magic-sized, pure, and Cr-doped CdS DM-QDs have been synthesized by solution phase chemistry (lyothermal method). Structural, optical, and magnetic investigation suggest an intrinsic nature of ferromagnetism with highly quantum-confined system. Optical and magnetic results of pure and doped QDs reveal major physical consequences of dopant localization within the capacity to engineer dopant-carrier exchange interactions introducing magnetic functionalities within the host semiconductor lattice. Unpaired Cr ions in Cd substitutional sites could create spin ordering and ferromagnetic coupling. The results presented herein illustrate some of the remarkable and unexpected complexities that can arise in doped QDs.

Helimagnetism and weak ferromagnetism in edge-shared chain cuprates

International Nuclear Information System (INIS)

Drechsler, S.-L.; Richter, J.; Kuzian, R.; Malek, J.; Tristan, N.; Buechner, B.; Moskvin, A.S.; Gippius, A.A.; Vasiliev, A.; Volkova, O.; Prokofiev, A.; Rakoto, H.; Broto, J.-M.; Schnelle, W.; Schmitt, M.; Ormeci, A.; Loison, C.; Rosner, H.

2007-01-01

The present understanding of a novel growing class of chain cuprates with intriguing magnetic properties is reviewed. Among them, several undoped edge-shared CuO 2 chain compounds show at low temperature a clear tendency to helicoidal magnetical ordering with acute pitch angles and sometimes also to weak ferromagnetism. Our analysis is based on the isotropic 1D frustrated J 1 -J 2 Heisenberg model with ferromagnetic (FM) 1st neighbor and antiferromagnetic 2nd neighbor exchange. The achieved assignment is supported by microscopic calculations of the electronic and magnetic structure. We consider Na(Li)Cu 2 O 2 , LiVCuO 4 as the best studied helimagnets, Li 2 ZrCuO 4 and other systems close to a FM quantum critical point, as well as Li 2 CuO 2 with FM inchain ordering. The interplay of frustrated inchain couplings, anisotropy and interchain exchange is discussed

Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions

International Nuclear Information System (INIS)

Zou Jianfei; Jin Guojun; Ma Yuqiang

2009-01-01

We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.

Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions.

Science.gov (United States)

Zou, Jianfei; Jin, Guojun; Ma, Yu-Qiang

2009-03-25

We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.

Repulsive polarons and itinerant ferromagnetism in strongly polarized Fermi gases

DEFF Research Database (Denmark)

Massignan, Pietro; Bruun, Georg

2011-01-01

We analyze the properties of a single impurity immersed in a Fermi sea. At positive energy and scattering lengths, we show that the system possesses a well-defined but metastable excitation, the repulsive polaron, and we calculate its energy, quasiparticle residue and effective mass. From...... polarized (ferromagnetic) domains are then examined for a binary mixture of atoms with a general mass ratio. Our results indicate that mass imbalance lowers the critical interaction strength for phase-separation, but that very short quasiparticle decay times will complicate the experimental observation...

Phase transitions of a spin-one Ising ferromagnetic superlattice

International Nuclear Information System (INIS)

Saber, A.

2001-09-01

Using the effective field theory with a probability distribution technique, the magnetic properties in an infinite superlattice consisting of two different ferromagnets are studied in a spin-one Ising model. The dependence of the Curie temperatures are calculated as a function of two slabs in one period and as a function of the intra- and interlayer exchange interactions. A critical value of the exchange reduced interaction above which the interface magnetism appears is found. (author)

Influence of the impurity-scattering on zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions

CERN Document Server

Yoshida, N; Itoh, H; Tanaka, Y; Inoue, J I; Kashiwaya, S

2003-01-01

Effects of impurity-scattering on a zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions are theoretically studied. The impurities are introduced through the random potential in ferromagnets near the junction interface. As in the case of normal-metal/insulator/d-wave superconductor junctions, the magnitude of zero-bias conductance peak decreases with increasing the degree of disorder. However, when the magnitude of the exchange potential in ferromagnet is sufficiently large, the random potential can enhance the zero-bias conductance peak in ferromagnetic junctions. (author)

Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

KAUST Repository

Roqan, Iman S.

2015-02-21

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline GdxZn1-xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.

Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes

KAUST Repository

Roqan, Iman S.; Venkatesh, S.; Zhang, Z.; Hussain, S.; Bantounas, Ioannis; Franklin, J. B.; Flemban, Tahani H.; Zou, B.; Lee, J.-S.; Schwingenschlö gl, Udo; Petrov, P. K.; Ryan, M. P.; Alford, N. M.

2015-01-01

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline GdxZn1-xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.

Interplay of dopants and defects in making Cu doped TiO{sub 2} nanoparticle a ferromagnetic semiconductor

Energy Technology Data Exchange (ETDEWEB)

Choudhury, Biswajit, E-mail: biswa.tezu@gmail.com [Department of Physics, Tezpur University, Napaam 784028, Assam (India); Choudhury, Amarjyoti [Department of Physics, Tezpur University, Napaam 784028, Assam (India); Borah, Debajit [Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam (India)

2015-10-15

Here we have studied the role of oxygen defects and Cu dopants on ferromagnetism in Cu doped TiO{sub 2} nanoparticles with nominal Cu concentration of 2%, 4% and 6 mol%. Electron paramagnetic resonance (EPR) spectra analysis reveals the presence of Cu{sup 2+} in the distorted octahedral coordination of TiO{sub 2}. Cu d-states undergo strong p-d coupling with the valence band O 2p state of TiO{sub 2} resulting the extended absorption hump in the visible region. Photoluminescence results reveal the presence of oxygen defect related emission peaks in Cu doped TiO{sub 2}. Room temperature ferromagnetism is observed in all the Cu doped TiO{sub 2} nanoparticles. Saturation magnetization is the highest at 4 mol% and then there is a decrease in magnetization at 6 mol%. Ferromagnetism completely disappears on calcinations of 4% Cu doped TiO{sub 2} in air at 450 °C for 8 h. It is speculated that both oxygen vacancies and Cu d-states are involved in the room temperature ferromagnetism. Spin polarization occurs by the formation of bound magnetic polaron between electrons in Cu{sup 2+}d-states and the unpaired spins in oxygen vacancies. Presence of Cu{sup 2+}-Cu{sup 2+}d-d exchange interaction and Cu{sup 2+}-O{sup 2−}-Cu{sup 2+} antiferromagnetic superexchange interactions might have resulted in the reduction in magnetization at 6 mol% Cu. - Graphical abstract: Ferromagnetism in Cu doped TiO{sub 2} requires presence of both Cu dopant and oxygen vacancies. - Highlights: • Cu doped TiO{sub 2} nanoparticle displays room temperature ferromagnetism. • Ferromagnetism requires presence of both Cu and oxygen vacancies. • Antiferromagnetic interaction persists at high Cu dopant concentration. • Paramagnetism appears on air annealing of the doped system for longer period.

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

Modulational instability and nano-scale energy localization in ferromagnetic spin chain with higher order dispersive interactions

International Nuclear Information System (INIS)

Kavitha, L.; Mohamadou, A.; Parasuraman, E.; Gopi, D.; Akila, N.; Prabhu, A.

2016-01-01

The nonlinear localization phenomena in ferromagnetic spin lattices have attracted a steadily growing interest and their existence has been predicted in a wide range of physical settings. We investigate the onset of modulational instability of a plane wave in a discrete ferromagnetic spin chain with physically significant higher order dispersive octupole–dipole and dipole–dipole interactions. We derive the discrete nonlinear equation of motion with the aid of Holstein–Primakoff (H–P) transformation combined with Glauber's coherent state representation. We show that the discrete ferromagnetic spin dynamics is governed by an entirely new discrete NLS model with complex coefficients not reported so far. We report the study of modulational instability (MI) of the ferromagnetic chain with long range dispersive interactions both analytically in the frame work of linear stability analysis and numerically by means of molecular dynamics (MD) simulations. Our numerical simulations explore that the analytical predictions correctly describe the onset of instability. It is found that the presence of the various exchange and dispersive higher order interactions systematically favors the local gathering of excitations and thus supports the growth of high amplitude, long-lived discrete breather (DB) excitations. We analytically compute the strongly localized odd and even modes. Further, we employ the Jacobi elliptic function method to solve the nonlinear evolution equation and an exact propagating bubble-soliton solution is explored. - Highlights: • Higher order dispersive interactions plays significant role in ferromagnetic spin chain. • The energy localization is studied both analytically and numerically. • The existence of DBs are studied under the effect of higher order dispersive interaction.

Exchange bias and bistable magneto-resistance states in amorphous TbFeCo thin films

Energy Technology Data Exchange (ETDEWEB)

Li, Xiaopu, E-mail: xl6ba@virginia.edu; Ma, Chung T.; Poon, S. Joseph, E-mail: sjp9x@virginia.edu [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Lu, Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Devaraj, Arun [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Spurgeon, Steven R.; Comes, Ryan B. [Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

2016-01-04

Amorphous TbFeCo thin films sputter deposited at room temperature on thermally oxidized Si substrate are found to exhibit strong perpendicular magnetic anisotropy. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb atomic percentages distributed within the amorphous film. Exchange bias accompanied by bistable magneto-resistance states has been uncovered near room temperature by magnetization and magneto-transport measurements. The exchange anisotropy originates from the exchange interaction between the ferrimagnetic and ferromagnetic components corresponding to the two amorphous phases. This study provides a platform for exchange bias and magneto-resistance switching using single-layer amorphous ferrimagnetic thin films that require no epitaxial growth.

Ferromagnetic resonance and spin-wave resonances in GaMnAsP films

Science.gov (United States)

Liu, Xinyu; Li, Xiang; Bac, Seul-Ki; Zhang, Xucheng; Dong, Sining; Lee, Sanghoon; Dobrowolska, Margaret; Furdyna, Jacek K.

2018-05-01

A series of Ga1-xMnxAs1-yPy films grown by MBE on GaAs (100) substrates was systematically studied by ferromagnetic resonance (FMR). Magnetic anisotropy parameters were obtained by analyzing the angular dependence of the FMR data. The results clearly show that the easy axis of the films shifts from the in-plane [100] direction to the out-of-plane [001], indicating the emergence of a strong tensile-strain-induced perpendicular anisotropy when the P content exceeds y ≈ 0.07. Multiple resonances were observed in Ga1-xMnxAs1-yPy films with thicknesses over 48 nm, demonstrating the existence of exchange-dominated non-propagating spin-wave modes governed by surface anisotropy.

Incommensurate Spiral Order from Double-Exchange Interactions

NARCIS (Netherlands)

Azhar, Maria; Mostovoy, Maxim

2017-01-01

The double-exchange model describing interactions of itinerant electrons with localized spins is usually used to explain ferromagnetism in metals. We show that for a variety of crystal lattices of different dimensionalities and for a wide range of model parameters, the ferromagnetic state is

Magnetic decoupling of ferromagnetic metals through a graphene spacer

Energy Technology Data Exchange (ETDEWEB)

Grimaldi, I.; Papagno, M. [Dipartimento di Fisica, Universitá della Calabria, Arcavacata di Rende (CS), 87036 (Italy); Ferrari, L. [Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Roma I-00133 (Italy); Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste (Italy); Sheverdyaeva, P.M.; Mahatha, S.K. [Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste (Italy); Pacilé, D., E-mail: daniela.pacile@fis.unical.it [Dipartimento di Fisica, Universitá della Calabria, Arcavacata di Rende (CS), 87036 (Italy); Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste (Italy); Carbone, C. [Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Trieste (Italy)

2017-03-15

We study the magnetic coupling between different ferromagnetic metals (FMs) across a graphene (G) layer, and the role of graphene as a thin covalent spacer. Starting with G grown on a FM substrate (Ni or Co), we deposited on top at room temperature several FM metals (Fe, Ni, Co). By measuring the dichroic effect of 3p photoemission lines we detect the magnetization of the substrate and the sign of the exchange coupling in FM overlayer at room temperature. We show that the G layer magnetically decouples the FM metals. - Highlights: • The magnetic coupling between ferromagnets mediated by graphene is studied. • To this end, the linear dichroic effect in 3p photoemission lines is employed. • For selected junctions no magnetic coupling is attained through graphene. • Graphene inhibits the magnetic alignment that normally occurs between ferromagnets.

Magnetization study of interlayer exchange in semiconductor EuS-PbS ferromagnetic wedge multilayers

International Nuclear Information System (INIS)

Kowalczyk, L.; Osinniy, V.; Chernyshova, M.; Dziawa, P.; Boratynski, A.; Story, T.; Smits, C.J.P.; Swagten, H.J.M.; Sipatov, A.Yu.; Volobuev, V.V.

2006-01-01

Interlayer coupling was experimentally studied in semiconductor EuS-PbS ferromagnetic superlattice wedge structures grown on KCl (0 0 1) substrates with the wedges covering the semiconductor nonmagnetic PbS spacer layer thickness from 0.3 to 6 nm. Structural parameters of the wedges were examined by X-ray diffraction analysis of EuS-PbS superlattice period. Measurements of magnetic hysteresis loops of EuS-PbS structures were performed by both SQUID (for small terminal parts of the wedge) and MOKE (magneto-optical analysis along the wedge) magnetometry. A strong decrease of magnetic remanence and an increase of saturation field observed for EuS-PbS structures with the PbS spacer thickness decreasing below about 1.5 nm is discussed in terms of the influence of antiferromagnetic interlayer coupling

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...

Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films

Energy Technology Data Exchange (ETDEWEB)

Kim, Ki Yeon; Lee, Jeong Soo

2008-02-15

This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs.

(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.

Strongly reduced band gap in NiMn2O4 due to cation exchange

International Nuclear Information System (INIS)

Huang, Jhih-Rong; Hsu, Han; Cheng, Ching

2014-01-01

NiMn 2 O 4 is extensively used as a basis material for temperature sensors due to its negative temperature coefficient of resistance (NTCR), which is commonly attributed to the hopping mechanism involving coexisting octahedral-site Mn 4+ and Mn 3+ . Using density-functional theory + Hubbard U calculations, we identify a ferrimagnetic inverse spinel phase as the collinear ground state of NiMn 2 O 4 . By a 12.5% cation exchange, a mixed phase with slightly higher energy can be constructed, accompanied by the formation of an impurity-like band in the original 1 eV band gap. This impurity-like band reduces the gap to 0.35 eV, suggesting a possible source of NTCR. - Highlights: • Density functional based calculations were used to study collinear phase of NiMn 2 O 4 . • The ground-state structure is a ferrimagnetic inverse spinel phase. • The tetrahedral and octahedral Mn cations have ferromagnetic interactions. • A 12.5% cation exchange introduces an impurity-like band in the original 1 eV gap. • The 0.35 eV gap suggests a source of negative temperature coefficient of resistance

Influence of voltage on magnetization of ferromagnetic semiconductors with colossal magnetoresistance

International Nuclear Information System (INIS)

Povzner, A.A.; Volkov, A.G.

2017-01-01

Graphical abstract: We investigate nonequilibrium states of strongly correlated electron subsystem of lanthanum manganite, resulting in an external electric field. It is shown that the Joule heat leads to localization of electrons. As result, electric resistance, magnetization and other characteristics of the electronic system are depending on the applied voltage. This leads to the formation of the bistable state of the electronic system in the vicinity of the Curie point in an external electric field. This manifests itself in non-linear current-voltage characteristics of these substances, and should lead to oscillations of the magnetization and current. - Abstract: The nonequilibrium processes of “self-heating” arising during the flow of electric current are studied for ferromagnetic semiconductors with colossal magnetoresistance near the Curie temperature. These processes lead to the emergence of “hot” paramagnons and the destruction of ferromagnetic order. The solution to the heat balance equation takes into account the temperature dependence of the electrical conductivity caused by Anderson localization of electrons due to their scattering on magnetic inhomogeneities. Description of delocalized electrons subsystem takes into account the spin-flip processes leading to the double exchange. At that, the value of the Anderson percolation threshold and the double exchange depends on the amplitude of spin fluctuations. It was found that N-shaped current-voltage characteristics and hysteresis dependencies of magnetization on the voltage arise in a steady state due to the emergence of “hot” (by internal sample temperature) semiconductor paramagnetic phase. It is shown that the occurrence of self-oscillations of current and magnetization there may be.

Influence of voltage on magnetization of ferromagnetic semiconductors with colossal magnetoresistance

Energy Technology Data Exchange (ETDEWEB)

Povzner, A.A., E-mail: a.a.povzner@urfu.ru; Volkov, A.G., E-mail: agvolkov@yandex.ru

2017-06-15

Graphical abstract: We investigate nonequilibrium states of strongly correlated electron subsystem of lanthanum manganite, resulting in an external electric field. It is shown that the Joule heat leads to localization of electrons. As result, electric resistance, magnetization and other characteristics of the electronic system are depending on the applied voltage. This leads to the formation of the bistable state of the electronic system in the vicinity of the Curie point in an external electric field. This manifests itself in non-linear current-voltage characteristics of these substances, and should lead to oscillations of the magnetization and current. - Abstract: The nonequilibrium processes of “self-heating” arising during the flow of electric current are studied for ferromagnetic semiconductors with colossal magnetoresistance near the Curie temperature. These processes lead to the emergence of “hot” paramagnons and the destruction of ferromagnetic order. The solution to the heat balance equation takes into account the temperature dependence of the electrical conductivity caused by Anderson localization of electrons due to their scattering on magnetic inhomogeneities. Description of delocalized electrons subsystem takes into account the spin-flip processes leading to the double exchange. At that, the value of the Anderson percolation threshold and the double exchange depends on the amplitude of spin fluctuations. It was found that N-shaped current-voltage characteristics and hysteresis dependencies of magnetization on the voltage arise in a steady state due to the emergence of “hot” (by internal sample temperature) semiconductor paramagnetic phase. It is shown that the occurrence of self-oscillations of current and magnetization there may be.

Exact time-dependent exchange-correlation potentials for strong-field electron dynamics

International Nuclear Information System (INIS)

Lein, Manfred; Kuemmel, Stephan

2005-01-01

By solving the time-dependent Schroedinger equation and inverting the time-dependent Kohn-Sham scheme we obtain the exact time-dependent exchange-correlation potential of density-functional theory for the strong-field dynamics of a correlated system. We demonstrate that essential features of the exact exchange-correlation potential can be related to derivative discontinuities in stationary density-functional theory. Incorporating the discontinuity in a time-dependent density-functional calculation greatly improves the description of the ionization process

Coexistence of Superconductivity and Ferromagnetism in ...

African Journals Online (AJOL)

KBHEEMA

Ferromagnetic alignment can be expected to be strongly opposed by superconductivity. .... To obtain temperature dependent of energy gap of equation (23), we used the same techniques to solve the integral .... band metal ZrZn2. Nature, 412: ...

Exchange stiffness of Ca-doped YIG

Science.gov (United States)

Avgin, I.; Huber, D. L.

1994-05-01

An effective medium theory for the zero-temperature exchange stiffness of uncompensated Ca-doped YIG is presented. The theory is based on the assumption that the effect of the Ca impurities is to produce strong, random ferromagnetic interactions between spins on the a and d sublattices. In the simplest version of the theory, a fraction, x, of the ad exchange integrals are large and positive, x being related to the Ca concentration. The stiffness is calculated as function of x for arbitrary perturbed ad exchange integral, Jxad. For Jxad≳(1/5)‖8Jaa+3Jdd‖, with Jaa and Jdd denoting the aa and dd exchange integrals, respectively, there is a critical concentration, Xc, such that when x≳Xc, the stiffness is complex. It is suggested that Xc delineates the region where there are significant departures from colinearity in the ground state of the Fe spins. Extension of the theory to a model where the Ca doping is assumed to generate Fe4+ ions on the tetrahedral sites is discussed. Possible experimental tests of the theory are mentioned.

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.

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.

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.

On magnon mediated Cooper pair formation in ferromagnetic superconductors

Directory of Open Access Journals (Sweden)

Rakesh Kar

2014-08-01

Full Text Available Identification of pairing mechanism leading to ferromagnetic superconductivity is one of the most challenging issues in condensed matter physics. Although different models have been proposed to explain this phenomenon, a quantitative understanding about this pairing is yet to be achieved. Using the localized-itinerant model, we find that in ferromagnetic superconducting materials both triplet pairing and singlet pairing of electrons are possible through magnon exchange depending upon whether the Debye cut off frequency of magnons is greater or lesser than the Hund's coupling (J multiplied by average spin (S per site. Taking into account the repulsive interaction due to the existence of paramagnons, we also find an expression for effective interaction potential between a pair of electrons with opposite spins. We apply the developed formalism in case of UGe2 and URhGe. The condition of singlet pairing is found to be fulfilled in these cases, as was previously envisaged by Suhl [Suhl, Phys. Rev. Lett. 87, 167007 (2001]. We compute the critical temperatures of URhGe at ambient pressure and of UGe2 under different pressures for the first time through BCS equation. Thus, this work outlines a very simple way to evaluate critical temperature in case of a superconducting system. A close match with the available experimental results strongly supports our theoretical treatment.

Neutron Scattering from Heisenberg Ferromagnets EuO and EuS

DEFF Research Database (Denmark)

Als-Nielsen, Jens Aage; Dietrich, O. W.; Passell, L.

1976-01-01

Neutron scattering has been used to study the magnetic ordering process in the isotropic exchange coupled ferromagnets EuO and EuS. Quantities investigated include the critical coefficients B and F+ and the critical exponents β, ν, and γ describing respectively the temperature dependence...

Magnetic susceptibility of one-dimensional ferromagnetic CsFeCl3 crystals

International Nuclear Information System (INIS)

Tsuboi, T.; Chiba, M.

1989-01-01

The parallel and perpendicular magnetic susceptibilities of one-dimensional ferromagnetic CsFeCl 3 crystals have been calculated from magnetization measured as a function of temperature in the range 0 to 70 K by means of a superconducting quantum interference device (SQUID). The experimental results have been compared with data from the literature for other Cs-and Rb-containing crystals with ferromagnetic or antiferromagnetic linear chains. Reliable values of the exchange and anisotropy energies can be estimated from experimental susceptibility data using theoretical g-values and the dynamical correlated-effective field approximation

Room temperature ferromagnetism in Co doped ZnO within an optimal doping level of 5%

International Nuclear Information System (INIS)

Mohapatra, J.; Mishra, D.K.; Mishra, Debabrata; Perumal, A.; Medicherla, V.R.R.; Phase, D.M.; Singh, S.K.

2012-01-01

Highlights: ► Zn 1−x Co x O ((0 ≤ x ≤ 0.1)) system synthesized by solid state reaction technique. ► Observation of room temperature ferromagnetism for 3 and 5% Co doped ZnO. ► XPS and EPMA studies predict the occurrence of segregated CoO clusters. ► Suppresses ferromagnetic ordering in higher doping percentage of Co (>5%). -- Abstract: We report on the structural, micro-structural and magnetic properties of Zn 1−x Co x O (0 ≤ x ≤ 0.1) system. Electron probe micro-structural analysis on 5% Co doped ZnO indicates the presence of segregated cobalt oxide which is also confirmed from the Co 2p core level X-ray photoelectron spectrum. The presence of oxygen defects in lower percentage of Co doped ZnO (≤5%) enhances the carrier mediated exchange interaction and thereby enhancing the room-temperature ferromagnetic behaviour. Higher doping percentage of cobalt (>5%) creates weak link between the grains and suppresses the carrier mediated exchange interaction. This is the reason why room temperature ferromagnetism is not observed in 7% and 10% Co doped ZnO.

Theory of Josephson effect in d-wave superconductor/diffusive ferromagnet/d-wave superconductor junctions

NARCIS (Netherlands)

Yokoyama, T.; Tanaka, Y.; Golubov, Alexandre Avraamovitch

2007-01-01

We study Josephson effect in d-wave superconductor/diffusive ferromagnet/d-wave superconductor junctions, changing the exchange field and the angles between the normal to the interfaces and the crystal axes of d-wave superconductors. We find a 0–π transition at a certain value of the exchange field.

Fluoride Thin Films: from Exchange Bias to Multferroicity

Science.gov (United States)

Johnson, Trent A.

This dissertation concerns research into the growth and characterization fluoride thin films by molecular beam epitaxy. After a discussion of relevant background material and experimental procedures in the first two chapters, we study exchange bias in magnetic multilayers incorporating the uniaxial antiferromagnet FeF2, grown to varying thicknesses, sandwiched between ferromagnetic Co layers with fixed thicknesses of 5 and 20 nm. Several bilayers with only the 20 nm thick Co layer were grown for comparative study. The samples were grown on Al2O3 (112¯0) substrates at room temperature. In-situ RHEED and x-ray diffraction indicated the films were polycrystalline. The films were determined to have low surface and interlayer roughness, as determined by AFM and x-ray reflectivity. After field-cooling to below the Neel temperature of FeF2 in a magnetic field of 1 kOe, magnetic hysteresis loops were measured as a function of temperature. We found that both layers had a negative exchange bias, with the exchange bias of the thinner layer larger than that of the thicker layer. In addition, the coercivity below the blocking temperature TB of the thinner layer was significantly larger than that of the thick layer, even though the coercivity of the two layers was the same for T > TB. The exchange bias effect, manifested by a shift in these hysteresis loops, showed a strong dependence on the thickness of the antiferromagnet. Anisotropic magnetoresistance measurements provided additional insight into the magnetization reversal mechanism within the ferromagnets. The thickness dependent exchange anisotropy of trilayer and bilayer samples is explained by adapting a random field model to the antiferromagnet/ferromagnet interface. Finally, We investigate the temperature dependent growth, as well as the magnetic and ferroelectric properties of thin films of the multiferroic compounds BaMF4, where M = Fe, Co, Ni. The films were grown to thicknesses of 50 or 100 nm on single crystal Al2

The load and release characteristics on a strong cationic ion-exchange fiber: kinetics, thermodynamics, and influences.

Science.gov (United States)

Yuan, Jing; Gao, Yanan; Wang, Xinyu; Liu, Hongzhuo; Che, Xin; Xu, Lu; Yang, Yang; Wang, Qifang; Wang, Yan; Li, Sanming

2014-01-01

Ion-exchange fibers were different from conventional ion-exchange resins in their non-cross-linked structure. The exchange was located on the surface of the framework, and the transport resistance reduced significantly, which might mean that the exchange is controlled by an ionic reaction instead of diffusion. Therefore, this work aimed to investigate the load and release characteristics of five model drugs with the strong cationic ion-exchange fiber ZB-1. Drugs were loaded using a batch process and released in United States Pharmacopoeia (USP) dissolution apparatus 2. Opposing exchange kinetics, suitable for the special structure of the fiber, were developed for describing the exchange process with the help of thermodynamics, which illustrated that the load was controlled by an ionic reaction. The molecular weight was the most important factor to influence the drug load and release rate. Strong alkalinity and rings in the molecular structures made the affinity between the drug and fiber strong, while logP did not cause any profound differences. The drug-fiber complexes exhibited sustained release. Different kinds and concentrations of counter ions or different amounts of drug-fiber complexes in the release medium affected the release behavior, while the pH value was independent of it. The groundwork for in-depth exploration and further application of ion-exchange fibers has been laid.

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.

Energy exchange in strongly coupled plasmas with electron drift

International Nuclear Information System (INIS)

Akbari-Moghanjoughi, M.; Ghorbanalilu, M.

2015-01-01

In this paper, the generalized viscoelastic collisional quantum hydrodynamic model is employed in order to investigate the linear dielectric response of a quantum plasma in the presence of strong electron-beam plasma interactions. The generalized Chandrasekhar's relativistic degeneracy pressure together with the electron-exchange and Coulomb interaction effects are taken into account in order to extend current research to a wide range of plasma number density relevant to big planetary cores and astrophysical compact objects. The previously calculated shear viscosity and the electron-ion collision frequencies are used for strongly coupled ion fluid. The effect of the electron-beam velocity on complex linear dielectric function is found to be profound. This effect is clearly interpreted in terms of the wave-particle interactions and their energy-exchange according to the sign of the imaginary dielectric function, which is closely related to the wave attenuation coefficient in plasmas. Such kinetic effect is also shown to be in close connection with the stopping power of a charged-particle beam in a quantum plasma. The effect of many independent plasma parameters, such as the ion charge-state, electron beam-velocity, and relativistic degeneracy, is shown to be significant on the growing/damping of plasma instability or energy loss/gain of the electron-beam

Controllable spin filter composed of ferromagnetic AB-stacking bilayer graphenes

International Nuclear Information System (INIS)

Yu, Yong; Liang, Qifeng; Dong, Jinming

2011-01-01

The electron's tunneling and spin transport in the normal/ferromagnetic/normal (N/FM/N) AB-stacking bilayer graphene (BLG) junction have been studied using Landauer-Buettiker formula. It is found that the resonant conductance peaks could be split well into spin-up and down ones by the exchange field in its FM barrier, leading to a very large spin polarization. More importantly, if a perpendicular electric field is also applied on the FM barrier, a completely spin-polarized flow can be realized by changing its barrier height, making the N/FM/N AB-stacking BLG junction act as a controllable spin filter. -- Highlights: → A study of spin transport in the ferromagnetic bilayer graphene junctions. → A serious of resonant conductance peaks could appear by tuning the barrier height. → The exchange splitting in FM barrier leads to a large spin polarization P. → P=±1 can be realized if a perpendicular electric field is applied to the FM barrier.

Ferromagnetic instabilities in disordered systems in the limit of strong correlations

International Nuclear Information System (INIS)

Magalhaes, A.N.; Troper, A.; Gomes, A.A.

1976-05-01

One derives the criterion for ferromagnetic instabilities in hybridized disordered systems, e.g. transition metal like systems and actinides, within the Coherent Potential Approximation (CPA), the electron-electron correlations being described by Hubbard' approximation. In the case of actinides, one treats approximately the motion of d electrons while the diagonal disorder within the f band is fully taken into account. In the case of a trnsition metal like system, except for Hubbard's approximation in dealing with d-d electron correlations, our procedure is exact within the spirit of CPA

A triple-bridged azido-Cu(II) chain compound fine-tuned by mixed carboxylate/ethanol linkers displays slow-relaxation and ferromagnetic order: synthesis, crystal structure, magnetic properties and DFT calculations.

Science.gov (United States)

Liu, Xiangyu; Chen, Sanping; Grancha, Thais; Pardo, Emilio; Ke, Hongshan; Yin, Bing; Wei, Qing; Xie, Gang; Gao, Shengli

2014-11-07

A new azido-Cu(II) compound, [Cu(4-fba)(N3)(C2H5OH)] (4-fba = 4-fluorobenzoic acid) (1), has been synthesized and characterized. The X-ray crystal structure analysis demonstrates that only one crystallographically independent Cu(II) ion in the asymmetric unit of 1 exhibits a stretched octahedral geometry in which two azido N atoms and two carboxylic O atoms locate in the equatorial square, while two ethanol O atoms occupy the apical positions, forming a 1D Cu(II) chain with an alternating triple-bridge of EO-azido, syn,syn-carboxylate, and μ2-ethanol. The title compound consists of ferromagnetically interacting ferromagnetic chains, which exhibit ferromagnetic order (T(c) = 7.0 K). The strong ferromagnetic coupling between adjacent Cu(II) ions within each chain is due to the countercomplementarity of the super-exchange pathways, whereas the ferromagnetic interchain interactions--responsible for the long-range magnetic ordering--are most likely due to the presence of coordinated ethanol molecules establishing hydrogen bonds with neighboring chains. DFT calculations have been performed on compound 1 to offer a qualitative theoretical explanation of the magnetic behavior.

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.

Spin-dependent Goos–Hänchen shift and spin beam splitter in gate-controllable ferromagnetic graphene

Energy Technology Data Exchange (ETDEWEB)

Wang, Y. [School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Liu, Y., E-mail: stslyl@mail.sysu.edu.cn [School of Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Wang, B., E-mail: wangbiao@mail.sysu.edu.cn [School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China)

2014-03-15

The transmission and Goos–Hänchen (GH) shift for charge carriers in gate-controllable ferromagnetic graphene induced by ferromagnetic insulator are investigated theoretically. Numerical results demonstrate that spin-up and spin-down electrons exhibit remarkably different transmission and GH shifts. The spin-dependent GH shifts directly demonstrate the spin beam splitting effect, which can be controlled by the voltage of gate. We attribute the spin beam splitting effect to the combination of tunneling through potential barrier and Zeeman interaction from the magnetic field and the exchange proximity interaction between the ferromagnetic insulator and graphene. In view of the spin beam splitting effect and the spin-dependent GH shifts, the gate-controllable ferromagnetic graphene might be utilized to design spin beam splitter.

Spin-dependent Goos–Hänchen shift and spin beam splitter in gate-controllable ferromagnetic graphene

International Nuclear Information System (INIS)

Wang, Y.; Liu, Y.; Wang, B.

2014-01-01

The transmission and Goos–Hänchen (GH) shift for charge carriers in gate-controllable ferromagnetic graphene induced by ferromagnetic insulator are investigated theoretically. Numerical results demonstrate that spin-up and spin-down electrons exhibit remarkably different transmission and GH shifts. The spin-dependent GH shifts directly demonstrate the spin beam splitting effect, which can be controlled by the voltage of gate. We attribute the spin beam splitting effect to the combination of tunneling through potential barrier and Zeeman interaction from the magnetic field and the exchange proximity interaction between the ferromagnetic insulator and graphene. In view of the spin beam splitting effect and the spin-dependent GH shifts, the gate-controllable ferromagnetic graphene might be utilized to design spin beam splitter

Valley and spin thermoelectric transport in ferromagnetic silicene junctions

International Nuclear Information System (INIS)

Ping Niu, Zhi; Dong, Shihao

2014-01-01

We have investigated the valley and spin resolved thermoelectric transport in a normal/ferromagnetic/normal silicene junction. Due to the coupling between the valley and spin degrees of freedom, thermally induced pure valley and spin currents can be demonstrated. The magnitude and sign of these currents can be manipulated by adjusting the ferromagnetic exchange field and local external electric field, thus the currents are controllable. We also find fully valley and/or spin polarized currents. Similar to the currents, owing to the band structure symmetry, tunable pure spin and/or valley thermopowers with zero charge counterpart are generated. The results obtained here suggest a feasible way of generating a pure valley (spin) current and thermopower in silicene

Ab initio calculations of half-metallic ferromagnetism in Cr-doped MgSe and MgTe semiconductors

Energy Technology Data Exchange (ETDEWEB)

Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Sohaib, M.U. [Lahore Development Authority, 54590 Lahore (Pakistan); Ghulam Abbas, S.M. [Department of Chemistry, University of Agriculture, Faisalabad 38040 (Pakistan); Shaukat, A., E-mail: schaukat@gmail.com [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan)

2015-01-15

The full-potential linear-augmented-plane-waves plus local-orbitals (FP-LAPW+lo) method has been employed for investigation of half-metallic ferromagnetism in Cr-doped ordered zinc-blende MgSe and MgTe semiconductors. Calculations of exchange and correlation (XC) effects have been carried out using generalized gradient approximation (GGA) and orbital independent modified Becke–Johnson potential coupled with local (spin) density approximation (mBJLDA). The thermodynamic stability of the compounds and their preferred magnetic orders have been analyzed in terms of the heat of formation and minimum total energy difference in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering, respectively. Calculated electronic properties reveal that the Cr-doping induces ferromagnetism in MgSe and MgTe which gives rise to a half-metallic (HM) gap at Fermi level (E{sub F}). Further, the electronic band structure is discussed in terms of s (p)–d exchange constants that are consistent with typical magneto-optical experiment and the behavior of charge spin densities is presented for understanding the bonding nature. Our results demonstrate that the higher effective potential for the spin-down case is responsible for p–d exchange splitting. Total magnetic moment (mainly due to Cr-d states) of these compounds is 4µ{sub B}. Importantly, the electronic properties and HM gap obtained using mBJLDA show remarkable improvement as compared to the results obtained using standard GGA functional. - Highlights: • Spin effect theoretical study on Cr-doped MgSe and MgTe is performed. • Half-metallic ferromagnetism in Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te is established. • Results of WC-GGA and mBJLDA are compared for performance. • HM gaps for Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te show nonlinear variation with x. • Important values of exchange splitting/constants and moments are reported.

Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study

Energy Technology Data Exchange (ETDEWEB)

Zighem, F; Roussigne, Y; Cherif, S-M; Moch, P [Laboratoire des Proprietes Mecaniques et Thermodynamiques des Materiaux, CNRS UPR 9001, Universite Paris Nord, 93430 Villetaneuse (France); Ben Youssef, J [Laboratoire de Magnetisme de Bretagne, CNRS, Universite de Bretagne Occidentale, 29285 Brest (France); Paumier, F, E-mail: fatih.zighem@cea.f [Institut Pprime, CNRS UPR 3346, Universite de Poitiers, ENSMA, 86962 Futuroscope (France)

2010-10-13

Microstrip ferromagnetic resonance and Brillouin scattering are used to provide a comparative determination of the magnetic parameters of thin permalloy layers interfaced with a non-magnetic (Al{sub 2}O{sub 3}) or with an antiferromagnetic oxide (NiO). It results from our microstructural study that no preferential texture is favoured in the observed polycrystalline sublayers. It is shown that the perpendicular anisotropy can be monitored using an interfacial surface energy term which is practically independent of the nature of the interface. In the interval of thicknesses investigated (5-25 nm) the saturation magnetization does not significantly differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy and exchange bias anisotropy are also derived from the study of the dynamic magnetic excitations and compared with our independent evaluations using conventional magnetometry.

Ferromagnetic resonance features of degenerate GdN semiconductor

Energy Technology Data Exchange (ETDEWEB)

Vidyasagar, Reddithota, E-mail: dr.vidyasagar1979@gmail.com [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Sakurai, Takahiro; Shimokawa, Tokuro [Centre for Support to Research and Education Activities, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Ohta, Hitoshi [Molecular Photoscience Research Center and Graduate School of Science, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan)

2017-06-15

Using X-band Ferromagnetic Resonance (FMR) Spectroscopy, we demonstrate the microscopic ferromagnetic resonance features of degenerated GdN semiconductor. The FMR spectrum suggests a single resonance mode below 10 K; interestingly, this particular structure is found to exhibit a peculiar magnetic resonance (PMR) on the top of the uniform FMR while temperature increases from 12–36 K. The low-field PMR mode attributed to the differently magnetized part of the film with an easy in-plane axis. The narrow-field gap between PMR and uniform FMR suggests the strong coupling owning to the differently magnetized part with easy in-plane axis and the magnetized part with an out-of-plane axis. The saturation magnetization, cubic magnetocrystalline anisotropy, and uniaxial anisotropy of GdN epitaxial film have been evaluated by the angular-dependence FMR. - Highlights: • Observation of peculiar magnetic resonance (PMR) on the top of ferromagnetic resonance (FMR). • Newly evolving PMR manifests differently magnetized part of the film with an easy in-plane axis. • Narrow gap between PMR and FMR owing to the strong interaction between two spin–wave resonances. • Uniaxial anisotropy increases with GdN thickness decreases.

Long-range ferromagnetic order induced by a donor impurity band exchange in SnO{sub 2}:Er{sup 3+} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Aragón, F. H.; Coaquira, J. A. H. [Núcleo de Física Aplicada, Institute of Physics, University of Brasília, Brasília DF 70910-900 (Brazil); Chitta, V. A. [Instituto de Física, Universidade de São Paulo, São Paulo, SP 05508-000 (Brazil); Hidalgo, P. [Faculdade Gama-FGA, Sector Central Gama, Universidade de Brasília, Brasília, DF72405-610 (Brazil); Brito, H. F. [Instituto de Química, Universidade de São Paulo, São Paulo, SP 05508-000 (Brazil)

2013-11-28

In this work, the structural and magnetic properties of Er-doped SnO{sub 2} (SnO{sub 2}:Er) nanoparticles are reported. The SnO{sub 2}:Er nanoparticles have been synthesized by a polymer precursor method with Er content from 1.0% to 10.0%. X-ray diffraction results indicate the formation of only the rutile-type structure in all samples. The estimated mean crystallite size shows a decrease from ∼10 to ∼4 nm when the Er content is increased from 1.0% to 10.0%. The particle size values have been corroborated by transmission electron microscopy technique. The thermal dependence of the magnetization is consistent with the 3+ oxidation state of erbium ions for all samples. A strong paramagnetic-like behavior coexisting with a ferromagnetic phase has been determined for samples with Er content below 5.0%. Above this concentration, only a paramagnetic behavior has been determined. Isothermal magnetization curves are consistent with the occurrence of long-range ferromagnetic order mediated by donor electrons forming bound magnetic polarons which overlap to produce a spin-split impurity band.

The electronic structures and ferromagnetism of Fe-doped GaSb: The first-principle calculation study

Science.gov (United States)

Lin, Xue-ling; Niu, Cao-ping; Pan, Feng-chun; Chen, Huan-ming; Wang, Xu-ming

2017-09-01

The electronic structures and the magnetic properties of Fe doped GaSb have been investigated by the first-principles calculation based on the framework of the generalized gradient approximation (GGA) and GGA+U schemes. The calculated results indicated that Fe atoms tend to form the anti-ferromagnetic (AFM) coupling with the nearest-neighbor positions preferentially. Compared with the anti-ferromagnetic coupling, the ferromagnetic interactions occurred at the second nearest-neighbor and third nearest-neighbor sites have a bigger superiority energetically. The effect of strong electron correlation at Fe-d orbit taking on the magnetic properties predicted by GGA+U approach demonstrated that the ferromagnetic (FM) coupling between the Fe ions is even stronger in consideration of the strong electron correlation effect. The ferromagnetism in Fe doped GaSb system predicted by our investigation implied that the doping of Fe into GaSb can be as a vital routine for manufacturing the FM semiconductors with higher Curie temperature.

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.

The ferromagnet spin-1/2 Ising superlattice in a transverse field

International Nuclear Information System (INIS)

Bouziane, T.; Saber, M.; Belaaraj, A.; Ainane, A.

1998-09-01

The phase transitions of a ferromagnet spin-1/2 Ising superlattice consisting of two different materials in a transverse field is examined with the use of effective field theory that accounts for the self-spin function correlation. The critical temperature of the system is studied as a function of the thickness of the constituents in a unit cell and of exchange interactions in each material. A critical interface exchange interaction above which the interface magnetism appears is found. The effects of a uniform transverse field and the interface exchange interaction on the parameters of the system are also investigated. (author)

Free energy distribution function of a random Ising ferromagnet

International Nuclear Information System (INIS)

Dotsenko, Victor; Klumov, Boris

2012-01-01

We study the free energy distribution function of a weakly disordered Ising ferromagnet in terms of the D-dimensional random temperature Ginzburg–Landau Hamiltonian. It is shown that besides the usual Gaussian 'body' this distribution function exhibits non-Gaussian tails both in the paramagnetic and in the ferromagnetic phases. Explicit asymptotic expressions for these tails are derived. It is demonstrated that the tails are strongly asymmetric: the left tail (for large negative values of the free energy) is much slower than the right one (for large positive values of the free energy). It is argued that at the critical point the free energy of the random Ising ferromagnet in dimensions D < 4 is described by a non-trivial universal distribution function which is non-self-averaging

Diclofenac removal in urine using strong-base anion exchange polymer resins.

Science.gov (United States)

Landry, Kelly A; Boyer, Treavor H

2013-11-01

One of the major sources of pharmaceuticals in the environment is wastewater effluent of which human urine contributes the majority of pharmaceuticals. Urine source separation has the potential to isolate pharmaceuticals at a higher concentration for efficient removal as well as produce a nutrient byproduct. This research investigated the efficacy of using strong-base anion exchange polymer resins to remove the widely detected and abundant pharmaceutical, diclofenac, from synthetic human urine under fresh and ureolyzed conditions. The majority of experiments were conducted using a strong-base, macroporous, polystyrene resin (Purolite A520E). Ion-exchange followed a two-step removal rate with rapid removal in 1 h and equilibrium removal in 24 h. Diclofenac removal was >90% at a resin dose of 8 mL/L in both fresh and ureolyzed urine. Sorption of diclofenac onto A520E resin was concurrent with desorption of an equivalent amount of chloride, which indicates the ion-exchange mechanism is occurring. The presence of competing ions such as phosphate and citrate did not significantly impact diclofenac removal. Comparisons of three polystyrene resins (A520E, Dowex 22, Dowex Marathon 11) as well as one polyacrylic resin (IRA958) were conducted to determine the major interactions between anion exchange resin and diclofenac. The results showed that polystyrene resins provide the highest level of diclofenac removal due to electrostatic interactions between quaternary ammonium functional groups of resin and carboxylic acid of diclofenac and non-electrostatic interactions between resin matrix and benzene rings of diclofenac. Diclofenac was effectively desorbed from A520E resin using a regeneration solution that contained 4.5% (m/m) NaCl in an equal-volume mixture of methanol and water. The greater regeneration efficiency of the NaCl/methanol-water mixture over the aqueous NaCl solution supports the importance of non-electrostatic interactions between resin matrix and benzene rings

Defect-impurity complex induced long-range ferromagnetism in GaN nanowires

KAUST Repository

Assa Aravindh, S

2015-12-14

Present work investigates the structural, electronic and magnetic properties of Gd doped wurtzite GaN nanowires (NWs) oriented along the [0001] direction in presence of intrinsic defects by employing the GGA + U approximation. We find that Ga vacancy (VGa) exhibits lower formation energy compared to N vacancy. Further stabilization of point defects occurs due to the presence of Gd. The strength of ferromagnetism (FM) increases by additional positive charge induced by the VGa. Electronic structure analysis shows that VGa introduces defect levels in the band gap leading to ferromagnetic coupling due to the hybridization of the p states of the Ga and N atoms with the Gd d and f states. Ferromagnetic exchange coupling energy of 76.4 meV is obtained in presence of Gd-VGa complex; hence, the FM is largely determined by the cation vacancy-rare earth complex defects in GaN NWs.

Defect-impurity complex induced long-range ferromagnetism in GaN nanowires

KAUST Repository

Assa Aravindh, S; Roqan, Iman S.

2015-01-01

Present work investigates the structural, electronic and magnetic properties of Gd doped wurtzite GaN nanowires (NWs) oriented along the [0001] direction in presence of intrinsic defects by employing the GGA + U approximation. We find that Ga vacancy (VGa) exhibits lower formation energy compared to N vacancy. Further stabilization of point defects occurs due to the presence of Gd. The strength of ferromagnetism (FM) increases by additional positive charge induced by the VGa. Electronic structure analysis shows that VGa introduces defect levels in the band gap leading to ferromagnetic coupling due to the hybridization of the p states of the Ga and N atoms with the Gd d and f states. Ferromagnetic exchange coupling energy of 76.4 meV is obtained in presence of Gd-VGa complex; hence, the FM is largely determined by the cation vacancy-rare earth complex defects in GaN NWs.

Ferromagnetic Spin Coupling as the Origin of 0.7 Anomaly in Quantum Point Contacts

OpenAIRE

Aryanpour, K.; Han, J. E.

2008-01-01

We study one-dimensional itinerant electron models with ferromagnetic coupling to investigate the origin of 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 incohe...

Charge order suppression, emergence of ferromagnetism and absence of exchange bias effect in Bi0.25Ca0.75MnO3 nanoparticles: Electron paramagnetic resonance and magnetization studies

Science.gov (United States)

Singh, Geetanjali; Bhat, S. V.

2012-06-01

We report the results of magnetization and electron paramagnetic resonance (EPR) studies on nanoparticles (average diameter ˜ 30 nm) of Bi0.25Ca0.75MnO3 (BCMO) and compare them with the results on bulk BCMO. The nanoparticles were prepared using the nonaqueous sol-gel technique and characterized by XRD and TEM analysis. Magnetization measurements were carried out with a commercial physical property measurement system (PPMS). While the bulk BCMO exhibits a charge ordering transition at ˜230 K and an antiferromagnetic (AFM) transition at ˜130 K, in the nanoparticles, the CO phase is seen to have disappeared and a transition to a ferromagnetic (FM) state is observed at Tc ˜ 120 K. However, interestingly, the exchange bias effect observed in other nanomanganite ferromagnets is absent in BCMO nanoparticles. EPR measurements were carried out in the X-band between 8 and 300 K. Lineshape fitting to a Lorentzian with two terms (accounting for both the clockwise and anticlockwise rotations of the microwave field) was employed to obtain the relevant EPR parameters as functions of temperature. The results confirm the occurrence of ferromagnetism in the nanoparticles of BCMO.

Ferromagnetic resonance study of structure and relaxation of magnetization in NiFe/Ru superlattices

Energy Technology Data Exchange (ETDEWEB)

Alayo, W., E-mail: willian.rodriguez@ufpel.edu.br [Depto. de Física, Univ. Federal de Pelotas, Campus Universitário, 96010-900, Pelotas, RS (Brazil); Landi Jr, S. [Instituto Federal Goiano, Rio Verde 75901-970 (Brazil); Pelegrini, F. [Instituto de Física, Universidade Federal de Goiás, Goiânia 74001-970 (Brazil); Baggio-Saitovitch, E. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro 22290-180 (Brazil)

2014-01-15

The structural properties and relaxation processes of magnetization in [Ni{sub 81}Fe{sub 19}(t{sub 1})/Ru(t{sub 2})]{sub N} superlattices (N=number of bilayers) were analyzed by ferromagnetic resonance (FMR) with a fixed microwave frequency. One series of samples was deposited with constant NiFe layer thickness (t{sub 1}) and variable Ru layer thickness (t{sub 2}); the other series, with constant t{sub 2} and variable t{sub 1}. A single FMR mode was observed for t{sub 2}<15 Å and t{sub 1}>75 Å and it has been attributed to the resonance of the exchange-coupled NiFe layers across the Ru interlayers. For the other values of t{sub 1} and t{sub 2}, several FMR modes appeared and they were associated to non-coupled magnetic phases with different effective magnetization formed during the multilayer growth. The FMR linewidths were analyzed as a function of the magnetic layer thickness and a strong dependence on t{sub 1}{sup −2} was observed. It was attributed to the contribution of the two-magnon scattering mechanism for the linewidth. - Highlights: • We present a study of magnetic properties of NiFe/Ru superlattices by ferromagnetic resonance (FMR). • The FMR spectra show several modes for large Ru thicknesses and for low NiFe thicknesses. • The above behavior is correlated with the interlayer exchange coupling. • The two-magnon scattering mechanism is revealed by the dependence of the FMR linewidth on the NiFe thickness.

Coupling of microwave magnetic dynamics in thin ferromagnetic films to stripline transducers in the geometry of the broadband stripline ferromagnetic resonance

Energy Technology Data Exchange (ETDEWEB)

Kostylev, M., E-mail: mikhail.kostylev@uwa.edu.au [School of Physics, The University of Western Australia, Crawley 6009 (Australia)

2016-01-07

We constructed a quasi-analytical self-consistent model of the stripline-based broadband ferromagnetic resonance (FMR) measurements of ferromagnetic films. Exchange-free description of magnetization dynamics in the films allowed us to obtain simple analytical expressions. They enable quick and efficient numerical simulations of the dynamics. With this model, we studied the contribution of radiation losses to the ferromagnetic resonance linewidth, as measured with the stripline FMR. We found that for films with large conductivity of metals the radiation losses are significantly smaller than for magneto-insulating films. Excitation of microwave eddy currents in these materials contributes to the total microwave impedance of the system. This leads to impedance mismatch with the film environment resulting in decoupling of the film from the environment and, ultimately, to smaller radiation losses. We also show that the radiation losses drop with an increase in the stripline width and when the sample is lifted up from the stripline surface. Hence, in order to eliminate this measurement artefact, one needs to use wide striplines and introduce a spacer between the film and the sample surface. The radiation losses contribution is larger for thicker films.

All-optical measurement of interlayer exchange coupling in Fe/Pt/FePt thin films

Science.gov (United States)

Berk, C.; Ganss, F.; Jaris, M.; Albrecht, M.; Schmidt, H.

2018-01-01

Time Resolved Magneto Optic Kerr Effect spectroscopy was used to all-optically study the dynamics in exchange coupled Fe(10 nm)/Pt(x = 0-5 nm)/FePt (10 nm) thin films. As the Pt spacer decreases, the effective magnetization of the layers is seen to evolve towards the strong coupling limit where the two films can be described by a single effective magnetization. The coupling begins at x = 1.5 nm and reaches a maximum exchange coupling constant of 2.89 erg/cm2 at x = 0 nm. The films are ferromagnetically coupled at all Pt thicknesses in the exchange coupled regime (x ≤ 1.5 nm). A procedure for extracting the interlayer exchange constant by measuring the magnetic precession frequencies at multiple applied fields and angles is outlined. The dynamics are well reproduced using micromagnetic simulations.

The Kondo effect in ferromagnetic atomic contacts.

Science.gov (United States)

Calvo, M Reyes; Fernández-Rossier, Joaquín; Palacios, Juan José; Jacob, David; Natelson, Douglas; Untiedt, Carlos

2009-04-30

Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system; this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent log-normal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.

Ferromagnetic properties of manganese doped iron silicide

Science.gov (United States)

Ruiz-Reyes, Angel; Fonseca, Luis F.; Sabirianov, Renat

We report the synthesis of high quality Iron silicide (FeSi) nanowires via Chemical Vapor Deposition (CVD). The materials exhibits excellent magnetic response at room temperature, especially when doped with manganese showing values of 2.0 X 10-04 emu for the FexMnySi nanowires. SEM and TEM characterization indicates that the synthesized nanowires have a diameter of approximately 80nm. MFM measurements present a clear description of the magnetic domains when the nanowires are doped with manganese. Electron Diffraction and XRD measurements confirms that the nanowires are single crystal forming a simple cubic structure with space group P213. First-principle calculations were performed on (111) FeSi surface using the Vienna ab initio simulation package (VASP). The exchange correlations were treated under the Ceperley-Alder (CA) local density approximation (LDA). The Brillouin Zone was sampled with 8x8x1 k-point grid. A total magnetic moment of about 10 μB was obtained for three different surface configuration in which the Iron atom nearest to the surface present the higher magnetization. To study the effect of Mn doping, Fe atom was replaced for a Mn. Stronger magnetization is presented when the Mn atom is close to the surface. The exchange coupling constant have been evaluated calculating the energy difference between the ferromagnetic and anti-ferromagnetic configurations.

Origin of spin-dependent asymmetries in electron transmission through ultrathin ferromagnetic films

International Nuclear Information System (INIS)

Gokhale, M.P.; Mills, D.L.

1991-01-01

We present theoretical calculations of exchange asymmetries in the transmission of electrons through ultrathin films of ferromagnetic Fe. The results account nicely for the magnitude of the asymmetries observed by Pappas et al. in photoemission studies of Cu covered by an ultrathin film of Fe. We argue that exchange asymmetry in the transmissivity of the Fe film, rather than the spin dependence of the electron mean free path, is responsible for the effects reported by these authors

Elucidation of the enhanced ferromagnetic origin in Mn-doped ZnO nanocrystals embedded into a SiO₂ matrix

Energy Technology Data Exchange (ETDEWEB)

Lee, Sejoon; Lee, Youngmin; Kim, Deukyoung [Dongguk University, Seoul (Korea, Republic of)

2013-01-01

The origin of the enhanced room temperature ferromagnetism in Mn-doped ZnO (ZnO:Mn) nanocrystals is investigated. ZnO:Mn nanocrystals, which were fabricated by using a laser irradiation method with a 248-nm KrF excimer laser, exhibited two-times increase in the spontaneous magnetization (∼0.4 emu/cm³ at 300 K) compared to the ZnO:Mn thin film (∼0.2 emu/cm³ at 300 K). The increased exchange integral of J₁/k{sub B} = 51.6 K in ZnO:Mn nanocrystals, in comparison with the ZnO:Mn thin film (J₁/k{sub B} = 46.9 K), is indicative of the enhanced ferromagnetic exchange interaction. This is attributed to the large number of acceptor defects in the SiO₂-capped ZnO:Mn nanocrystals. Namely, the holes bound to the acceptor defects form microscopic bound-magnetic-polarons with Mn ions; hence, long-range ferromagnetic coupling is enhanced. The results suggest that ferromagnetism in ZnO-based dilute magnetic semiconductors can be controlled by modulating the density of native point defects, which can be chemically and thermodynamically modified during the material synthesis or preparation.

Room temperature ferromagnetism in liquid-phase pulsed laser ablation synthesized nanoparticles of nonmagnetic oxides

International Nuclear Information System (INIS)

Singh, S. C.; Gopal, R.; Kotnala, R. K.

2015-01-01

Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects

Novel room temperature ferromagnetic semiconductors

Energy Technology Data Exchange (ETDEWEB)

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

2004-06-01

distribution of Mn substituting for Zn a 2⁺ state in the ZnO lattice. Ferromagnetic Resonance (FMR) technique is used to confirm the existence of ferromagnetic ordering at temperatures as high as 425K. The ab initio calculations were found to be consistent with the observation of ferromagnetism arising from fully polarized Mn 2⁺ state. The key to observed room temperature ferromagnetism in this system is the low temperature processing, which prevents formation of clusters, secondary phases and the host ZnO from becoming n-type. The electronic structure of the same Mn doped ZnO thin films studied using XAS, XES and RIXS, revealed a strong hybridization between Mn 3d and O 2p states, which is an important characteristic of a Dilute magnetic Semiconductor (DMS). It is shown that the various processing conditions like sintering temperature, dopant concentration and the properties of precursors used for making of DMS have a great influence on the final properties. Use of various experimental techniques to verify the physical properties, and to understand the mechanism involved to give rise to ferromagnetism is presented. Methods to improve the magnetic moment in Mn doped ZnO are also described. New promising DMS materials (such as Cu doped ZnO are explored). The demonstrated new capability to fabricate powder, pellets, and thin films of room temperature ferromagnetic semiconductors thus makes possible the realization of a wide range of complex elements for a variety of new multifunctional phenomena related to Spintronic devices as well as magneto-optic components.

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.

Effects of surface and bulk transverse fields on critical behaviour of ferromagnetic films

International Nuclear Information System (INIS)

Saber, A.; Lo Russo, S.; Mattei, G.

2002-02-01

The influence of surface and bulk transverse fields on the critical behaviour of a ferromagnetic Ising film is studied using the effective field theory based on a single-site cluster method. Surface exchange enhancement is considered and a critical value is obtained. The dependence of the critical uniform transverse field on film thickness, phase diagrams in the fields, critical surface transverse field versus the bulk one, and exchange coupling ratio are presented. (author)

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.

Magnetic exchange interactions in Mn doped ZnSnAs{sub 2} chalcopyrite

Energy Technology Data Exchange (ETDEWEB)

Bouhani-Benziane, H.; Sahnoun, O. [Laboratoire de Physique Quantique de la Matière et Modélisation Mathématique (LPQ3M), University of Mascara (Algeria); Sahnoun, M., E-mail: sahnoun_cum@yahoo.fr [Laboratoire de Physique Quantique de la Matière et Modélisation Mathématique (LPQ3M), University of Mascara (Algeria); Department of Chemistry, University of Fribourg (Switzerland); Driz, M. [Laboratoire de Sciences des Matériaux (LSM), University of Sidi Bel Abbes (Algeria); Daul, C. [Department of Chemistry, University of Fribourg (Switzerland)

2015-12-15

Accurate ab initio full-potential augmented plane wave (FP-LAPW) electronic calculations within generalized gradient approximation have been performed for Mn doped ZnSnAs{sub 2} chalcopyrites, focusing on their electronic and magnetic properties as a function of the geometry related to low Mn-impurity concentration and the spin magnetic alignment (i.e., ferromagnetic vs antiferromagnetic). As expected, Mn is found to be a source of holes and localized magnetic moments of about 4 µ{sub B} per Mn atom are calculated which are sufficiently large. The defect calculations are firstly performed by replacing a single cation (namely Zn and Sn) with a single Mn atom in the pure chalcopyrite ZnSnAs{sub 2} supercell, and their corresponding formation energies show that the substitution of a Sn atom (rather than Zn) by Mn is strongly favored. Thereafter, a comparison of total energy differences between ferromagnetic (FM) and antiferromagnetic (AFM) are given. Surprisingly, the exchange interaction between a Mn pairs is found to oscillate with the distance between them. Consequently, the AFM alignment is energetically favored in Mn-doped ZnSnAs{sub 2} compounds, except for low impurity concentration associated with lower distances between neighboring Mn impurities, in this case the stabilization of FM increases. Moreover, the ferromagnetic alignment in the Mn-doped ZnSnAs{sub 2} systems behaves half-metallic; the valence band for majority spin orientation is partially filled while there is a gap in the density of states for the minority spin orientation. This semiconducting gap of ~1 eV opened up in the minority channel and is due to the large bonding–antibonding splitting from the p–d hybridization. Our findings suggest that the Mn-doped ZnSnAs{sub 2} chalcopyrites could be a different class of ferromagnetic semiconductors. - Highlights: • ab initio calculations were performed on Mn doped ZnSnAs{sub 2} chalcopyrite. • Substitution of a Sn atom (rather than Zn) by Mn

Transport through hybrid superconducting/ferromagnetic double-path junction

Energy Technology Data Exchange (ETDEWEB)

Facio, T.J.S. [Departamento de Física e Química, Universidade Estadual Paulista – UNESP, 15385-000, Ilha Solteira, SP (Brazil); Orellana, P.A. [Departamento de Física, Universidad Técnica Federico Santa Maria, Av. Vicuña Mackenna, 3939, Santiago (Chile); Jurelo, A.R. [Departamento de Física, Universidade Estadual de Ponta Grossa – UEPG, 84030-000, Ponta Grossa, PR (Brazil); Figueira, M.S. [Instituto de Física, Universidade Federal Fluminense, 24210-340, Niterói, RJ (Brazil); Cabrera, G.G. [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas – UNICAMP, 13083-859, Campinas, SP (Brazil); Siqueira, E.C., E-mail: ecosta@utfpr.edu.br [Departamento de Física, Universidade Tecnológica Federal do Paraná – UTFPR, 84016-210, Ponta Grossa, PR (Brazil)

2017-02-05

In this paper we study a double-path junction formed by a ferromagnetic and a superconductor lead. The first path connects the superconductor and ferromagnet directly while the second path connects these metals through a quantum dot. The whole system works as an Aharonov–Bohm interferometer allowing the study of the interference between these two paths under the presence of spin imbalance and Andreev bound states. We considered the effect of Fano interference on the electronic transmittance through the quantum dot and observed two regimes of conduction depending on the strength of the direct coupling. For the weak coupling regime, the transmittance presented the usual four resonances due to the Andreev bound states whereas for the strong coupling regime the profile was inverted and resonances became anti-resonances. However, even in the strong coupling regime it was possible to observe a central resonance due to the interference between the Andreev bound states. We have also studied the signatures of Fano interference on the average occupation within the quantum dot. The spin accumulation was analyzed and how it depends on the direct coupling and an external magnetic field applied to the system. The results obtained may be used in a possible experimental implementation of this system in order to probe spin related effects in ferromagnetic superconductor nanostructures. - Highlights: • An Aharonov–Bohm interferometer composed by a quantum-dot coupled to a superconductor and ferromagnetic lead is studied. • The transmittance through the QD is determined by the interplay between Andreev and Fano interference. • Spin accumulation within the quantum dot is studied as a function of bias/gate voltages and an external magnetic flux.

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.

Influence of strong single-ion anisotropy on phase states of 3D and 2D frustrated magnets

International Nuclear Information System (INIS)

Fridman, Yu.A.; Kosmachev, O.A.; Matunin, D.A.; Gorelikov, G.A.; Klevets, Ph.N.

2010-01-01

We investigated the influence of strong single-ion anisotropy, exceeding exchange interaction, and frustrated exchange interaction on spin-wave excitation spectra and phase states using the Hubbard operators' technique, allowing the exact account of single-ion anisotropy. The results show that both the homogeneous phases (ferromagnetic and quadrupolar) and the spatially inhomogeneous phase (spiral structure) are possible in the 3D magnetic crystal. The region of existence of the spiral structure is considerably smaller than that in the analogues system, but with weak single-ion anisotropy. The situation is more complex in the 2D system; another spatially inhomogeneous state (the domain structure) can be realized in addition to the spiral magnetic structure. The phase diagrams for both the 3D and 2D systems were plotted.

Room temperature ferromagnetism and half metallicity in nickel doped ZnS: Experimental and DFT studies

Energy Technology Data Exchange (ETDEWEB)

Akhtar, Muhammad Saeed [School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Centre of Excellence in Solid State Physics, University of the Punjab, Lahore 54590 (Pakistan); Malik, Mohammad Azad, E-mail: Azad.malik@manchester.ac.uk [School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Riaz, Saira; Naseem, Shahzad [Centre of Excellence in Solid State Physics, University of the Punjab, Lahore 54590 (Pakistan)

2015-06-15

The nickel doped nanocrystalline ZnS thin films were deposited onto glass substrates by chemical bath deposition (CBD). Also ZnS:Ni nanoparticles were synthesized by CBD/co-precipitation method. Powder X-ray diffraction (p-XRD) studies demonstrate that both thin films and nanoparticles correspond to sphalerite (cubic) phase of ZnS with slight shift towards higher 2θ values due to incorporation of nickel in the ZnS lattice. The crystallite sizes estimated by Scherrer equation were 4 and 2.6 nm for ZnNiS thin films and nanoparticles, respectively. Scanning Electron Microscopy (SEM) images reveal that the morphology of thin films is based on quasi-spherical particles with nano scale dimensions. Energy Dispersive X-ray (EDX) spectroscopy confirms that the as-deposited thin films have a stoichiometry consistent with the nickel doped ZnS. Full-potential linearized augmented plane wave (FP-L/APW) method based on spin-polarized density functional theory (DFT) was employed to investigate the electronic and magnetic properties of ZnNiS for the doping concentration. Exchange-correlation functional was studied using generalized gradient approximation (GGA + U) method. Electronic band structures and density of states (DOS) demonstrate 100% spin polarization (half metallicity) with ferromagnetic exchange interactions. Superconducting quantum interference device (SQUID) analysis confirms the theoretical observation of ferromagnetism in nickel doped ZnS. These ZnS based half metallic ferromagnets seem to have virtuous applications in future spintronic devices. - Highlights: • ZnS.Ni thin films and nanoparticles were deposited onto glass substrates by CBD. • p-XRD correspond to sphalerite (cubic) phase of ZnS with slight shift in peaks. • DFT was employed to investigate the properties of ZnS.Ni. • DOS demonstrate 100% spin polarization with ferromagnetic exchange interactions. • SQUID analysis confirms the theoretical observations of nickel doped ZnS.

Elucidation of the enhanced ferromagnetic origin in Mn-doped ZnO nanocrystals embedded into a SiO2 matrix

International Nuclear Information System (INIS)

Lee, Sejoon; Lee, Youngmin; Kim, Deukyoung

2013-01-01

The origin of the enhanced room temperature ferromagnetism in Mn-doped ZnO (ZnO:Mn) nanocrystals is investigated. ZnO:Mn nanocrystals, which were fabricated by using a laser irradiation method with a 248-nm KrF excimer laser, exhibited two-times increase in the spontaneous magnetization (∼0.4 emu/cm 3 at 300 K) compared to the ZnO:Mn thin film (∼0.2 emu/cm 3 at 300 K). The increased exchange integral of J 1 /k B = 51.6 K in ZnO:Mn nanocrystals, in comparison with the ZnO:Mn thin film (J 1 /k B = 46.9 K), is indicative of the enhanced ferromagnetic exchange interaction. This is attributed to the large number of acceptor defects in the SiO 2 -capped ZnO:Mn nanocrystals. Namely, the holes bound to the acceptor defects form microscopic bound-magnetic-polarons with Mn ions; hence, long-range ferromagnetic coupling is enhanced. The results suggest that ferromagnetism in ZnO-based dilute magnetic semiconductors can be controlled by modulating the density of native point defects, which can be chemically and thermodynamically modified during the material synthesis or preparation.

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.

Polarized-photon frequency filter in double-ferromagnetic barrier silicene junction

Energy Technology Data Exchange (ETDEWEB)

Chantngarm, Peerasak; Yamada, Kou [Domain of Mechanical Science and Technology, Graduate School of Science and Technology, Gunma University, Gunma (Japan); Soodchomshom, Bumned, E-mail: Bumned@hotmail.com [Department of Physics, Faculty of Science, Kasetsart University Bangkok 10900 (Thailand)

2017-05-01

We present an analytical study of effects from circularly polarized light illumination on controlling spin-valley currents in a dual ferromagnetic-gated silicene. Two different perpendicular electric fields are applied into the ferromagnetic (FM) gates and the photo-irradiated normal (NM) area between the gates. One parallel (P) and two anti-parallel (AP) configurations of exchange fields applied along with chemical potential to the gates are used in this investigation. Interestingly, the studied junction might give rise to polarized-photon frequency filter. Spin-valley filtering can be achieved at the off-resonant frequency region with appropriate direction of electric fields and the configuration of exchange fields (AP-1 or AP-2). Under the photo irradiation, this study found that tunneling magnetoresistance (TMR) is controllable to achieve giant magnetoresistance (GMR) by adjusting electric fields or chemical potentials. Our study suggests the potential of photo-sensing devices in spin-valleytronics realm. - Highlights: • Photon-frequency control of spin-valley currents in silicene is investigated. • Complete photon frequency filtering effect is predicted. • Giant magnetoresistance induced by polarized photon is also found. • The junction is applicable for photo-sensing devices in spin-valleytronics realm.

Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots.

Science.gov (United States)

Ward, T Z; Gai, Z; Xu, X Y; Guo, H W; Yin, L F; Shen, J

2011-04-15

In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.

Competing interactions in ferromagnetic/antiferromagnetic perovskite superlattices

Energy Technology Data Exchange (ETDEWEB)

Takamura, Y.; Biegalski, M.B.; Christen, H.M.

2009-10-22

Soft x-ray magnetic dichroism, magnetization, and magnetotransport measurements demonstrate that the competition between different magnetic interactions (exchange coupling, electronic reconstruction, and long-range interactions) in La{sub 0.7}Sr{sub 0.3}FeO{sub 3}(LSFO)/La{sub 0.7}Sr{sub 0.3}MnO{sub 3}(LSMO) perovskite oxide superlattices leads to unexpected functional properties. The antiferromagnetic order parameter in LSFO and ferromagnetic order parameter in LSMO show a dissimilar dependence on sublayer thickness and temperature, illustrating the high degree of tunability in these artificially layered materials.

Mechanism of carrier-induced ferromagnetism in diluted magnetic semiconductors

International Nuclear Information System (INIS)

Takahashi, M.; Furukawa, N.; Kubo, K.

2004-01-01

Using the spin-polarized band obtained by applying the dynamical coherent potential approximation to a simple model, we have calculated the magnetization of Ga x Mn 1-x As as a function of the temperature for various values of carrier density. The result is consistent with the experimental observation, supporting the view previously proposed by us that the ferromagnetism is induced by the carriers in the bandtail through double-exchange-like mechanism

Phase transitions of ferromagnetic Ising films with amorphous surfaces

International Nuclear Information System (INIS)

Saber, M.; Ainane, A.; Dujardin, F.; Stebe, B.

1997-08-01

The critical behavior of a ferromagnetic Ising film with amorphous surfaces is studied within the framework of the effective field theory. The dependence of the critical temperature on exchange interaction strength ratio, film thickness, and structural fluctuation parameter is presented. It is found that an order-disorder magnetic transition occurs by varying the thickness of the film. Such a result is in agreement with experiments performed recently on Fe-films. (author). 39 refs, 4 figs

Quantitative determination of spin-dependent quasiparticle renormalization in ferromagnetic 3d metals

Energy Technology Data Exchange (ETDEWEB)

Sanchez-Barriga, Jaime; Varykhalov, Andrei; Fink, Joerg; Rader, Oliver; Duerr, Hermann; Eberhardt, Wolfgang [Bessy GmbH, Berlin (Germany)

2008-07-01

Spin dependent low-energy electronic excitations in 3d ferromagnets are of special interest due to the need of a microscopic understanding of the electronic structure of solids. Low-energy electrons (or holes) become dressed by a cloud of excitations resulting in quasiparticles of a finite lifetime and a different effective mass. These type of excitations have been studied by many theoretical methods, and it has been found that because of many body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV. Interestingly, it has been shown that strong correlation effects could particularly affect majority spin electrons, leading to a pronounced damping of quasiparticles at binding energies around 2 eV and above. In order to give an experimental corroboration to these findings, we have performed a systematic study of the spin-dependent quasiparticle lifetime and band structure of ferromagnetic 3d transition metal surfaces by means of spin and angle-resolved photoemission spectroscopy. On hcp Co(0001), fcc Ni(111) and bcc Fe(110), we have found a more pronounced renormalization of the majority spin quasiparticle spectral weight going from Ni to Co which are both strong ferromagnets. For Fe, a weak ferromagnet, such a process becomes more prominent in the minority channel.

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

Dynamics of magnetization in ferromagnet with spin-transfer torque

Science.gov (United States)

Li, Zai-Dong; He, Peng-Bin; Liu, Wu-Ming

2014-11-01

We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out

Solid-phase extraction sorbent consisting of alkyltrimethylammonium surfactants immobilized onto strong cation-exchange polystyrene resin.

Science.gov (United States)

Reid, Kendra R; Kennedy, Lonnie J; Crick, Eric W; Conte, Eric D

2002-10-25

Presented is a solid-phase extraction sorbent material composed of cationic alkyltrimethylammonium surfactants attached to a strong cation-exchange resin via ion-exchange. The original hydrophilic cation-exchange resin is made hydrophobic by covering the surface with alkyl chains from the hydrophobic portion of the surfactant. The sorbent material now has a better ability to extract hydrophobic molecules from aqueous samples. The entire stationary phase (alkyltrimethylammonium surfactant) is removed along with the analyte during the elution step. The elution step requires a mild elution solvent consisting of 0.25 M Mg2+ in a 50% 2-propanol solution. The main advantage of using a removable stationary phase is that traditionally utilized toxic elution solvents such as methylene chloride, which are necessary to efficiently release strongly hydrophobic species from SPE stationary phases, may now be avoided. Also, the final extract is directly compatible with reversed-phase liquid chromatography. The performance of this procedure is presented using pyrene as a test molecule.

Role of the antiferromagnetic bulk spins in exchange bias

Energy Technology Data Exchange (ETDEWEB)

Schuller, Ivan K. [Center for Advanced Nanoscience and Physics Department, University of California San Diego, La Jolla, CA 92093 (United States); Morales, Rafael, E-mail: rafael.morales@ehu.es [Department of Chemical-Physics & BCMaterials, University of the Basque Country UPV/EHU (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Batlle, Xavier [Departament Física Fonamental and Institut de Nanociència i Nanotecnologia, Universitat de Barcelona, c/ Martí i Franqués s/n, 08028 Barcelona, Catalonia (Spain); Nowak, Ulrich [Department of Physics, University of Konstanz, 78464 Konstanz (Germany); Güntherodt, Gernot [Physics Institute (IIA), RWTH Aachen University, Campus RWTH-Melaten, 52074 Aachen (Germany)

2016-10-15

This “Critical Focused Issue” presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice. - Highlights: • We address the role of bulk antiferromagnetic spins in the exchange bias phenomenon. • Significant experiments on how bulk AFM spins determine exchange bias are highlighted. • We explain the model that accounts for experimental results.

Role of the antiferromagnetic bulk spins in exchange bias

International Nuclear Information System (INIS)

Schuller, Ivan K.; Morales, Rafael; Batlle, Xavier; Nowak, Ulrich; Güntherodt, Gernot

2016-01-01

This “Critical Focused Issue” presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice. - Highlights: • We address the role of bulk antiferromagnetic spins in the exchange bias phenomenon. • Significant experiments on how bulk AFM spins determine exchange bias are highlighted. • We explain the model that accounts for experimental results.

Larmor diffraction in the ferromagnetic superconductor UGe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Ritz, Robert; Pfleiderer, Christian [Physik Department E21, TU Muenchen, D-85748 Garching (Germany); Sokolov, Dmitry; Huxley, Andrew [School of Physics and Astronomy, Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Keller, Thomas [MPI fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart (Germany)

2010-07-01

Larmor Diffaction (LD) is a neutron resonance spin-echo technique which allows the study of the lattice constant as well the distribution of lattice constants. It was traditionally thought that neutron spin-echo measurements cannot be used in materials such as superconductors or ferromagnets, because they strongly depolarize a polarized neutron beam. In UGe{sub 2} we are able to demonstrate that this technique may be applied in ferromagnetic superconductors with a magnetic Ising anisotropy. UGe{sub 2} exhibits two ferromagnetic phases which are separated by a transition at temperature T{sub x}. With increasing hydrostatic pressure superconductivity emerges at the pressure for which T{sub x} is suppressed. Using LD we studied the temperature dependence of the lattice constant as well as the distribution of lattice constants for all three axis of UGe{sub 2} down to 0.5 K and at pressures up to 12 kbar.

45° sign switching of effective exchange bias due to competing anisotropies in fully epitaxial Co3FeN/MnN bilayers

Science.gov (United States)

Hajiri, T.; Yoshida, T.; Filianina, M.; Jaiswal, S.; Borie, B.; Asano, H.; Zabel, H.; Kläui, M.

2018-01-01

We report an unusual angular-dependent exchange bias effect in ferromagnet/antiferromagnet bilayers, where both ferromagnet and antiferromagnet are epitaxially grown. Numerical model calculations predict an approximately 45° period for the sign switching of the exchange-bias field, depending on the ratio between magnetocrystalline anisotropy and exchange-coupling constant. The switching of the sign is indicative of a competition between a fourfold magnetocrystalline anisotropy of the ferromagnet and a unidirectional anisotropy field of the exchange coupling. This predicted unusual angular-dependent exchange bias and its magnetization switching process are confirmed by measurements on fully epitaxial Co3FeN/MnN bilayers by longitudinal and transverse magneto-optic Kerr effect magnetometry. These results provide a deeper understanding of the exchange coupling phenomena in fully epitaxial bilayers with tailored materials and open up a complex switching energy landscape engineering by anisotropies.

A computational study of magnetic exchange interactions of 3d and 4f electrons in Ti-Ce co-doped AlN

Energy Technology Data Exchange (ETDEWEB)

Majid, Abdul, E-mail: abdulmajid40@yahoo.com [Department of Physics, University of Gujrat, Gujrat (Pakistan); Department of Adaptive Machine Systems, Osaka University, Osaka (Japan); Azmat, Mian [Department of Physics, University of Gujrat, Gujrat (Pakistan); Rana, Usman Ali; Khan, Salah Ud-Din [Sustainable Energy Technologies Center, College of Engineering, King Saud University, PO-Box 800, Riyadh 11421 (Saudi Arabia); Alzahrani, Eman [Department of Chemistry, Faculty of Science, Taif University, 888 Taif (Saudi Arabia)

2016-08-15

To investigate the nature of 3d-4f exchange interactions in III-Nitride semiconductors, Ti-Ce co-doped AlN were studied using first principles calculations. The calculations were performed using supercell approach with varying dopant concentration and different inter-dopant separation. The configuration with dopant located as nearest neighbor distance and diluted concentration of 3.125% was found most stable. The results exhibited prominent evidence of 3d-4f-5d strong hybridization suggesting 3d-4f direct exchange interactions which may play valuable role to exploit the system as high Curie temperature ferromagnetic semiconductors for use in spintronics. Moreover, metal to metal charge transfer was also observed in the materials which may be exploited for their use in electrochemical applications. The 4f-5d and 3d-5d hybridizations were observed that predicts excellent luminescence phenomena in the materials. The presence of impurity related deep intermediate bands suggest applications of the materials in opto-electronic and spintronics devices. - Highlights: • Double exchange interaction in Ti:AlN. • Impurity induced narrowing of band gap. • Superexchange interaction in Ce:AlN. • 3d-4f exchange interaction between Ti-3d and Ce-4f states. • High Curie temperature n-type ferromagnetic semiconductors.

A computational study of magnetic exchange interactions of 3d and 4f electrons in Ti-Ce co-doped AlN

International Nuclear Information System (INIS)

Majid, Abdul; Azmat, Mian; Rana, Usman Ali; Khan, Salah Ud-Din; Alzahrani, Eman

2016-01-01

To investigate the nature of 3d-4f exchange interactions in III-Nitride semiconductors, Ti-Ce co-doped AlN were studied using first principles calculations. The calculations were performed using supercell approach with varying dopant concentration and different inter-dopant separation. The configuration with dopant located as nearest neighbor distance and diluted concentration of 3.125% was found most stable. The results exhibited prominent evidence of 3d-4f-5d strong hybridization suggesting 3d-4f direct exchange interactions which may play valuable role to exploit the system as high Curie temperature ferromagnetic semiconductors for use in spintronics. Moreover, metal to metal charge transfer was also observed in the materials which may be exploited for their use in electrochemical applications. The 4f-5d and 3d-5d hybridizations were observed that predicts excellent luminescence phenomena in the materials. The presence of impurity related deep intermediate bands suggest applications of the materials in opto-electronic and spintronics devices. - Highlights: • Double exchange interaction in Ti:AlN. • Impurity induced narrowing of band gap. • Superexchange interaction in Ce:AlN. • 3d-4f exchange interaction between Ti-3d and Ce-4f states. • High Curie temperature n-type ferromagnetic semiconductors.

Room-temperature ferromagnetism observed in C-/N-/O-implanted MgO single crystals

Science.gov (United States)

Li, Qiang; Ye, Bonian; Hao, Yingping; Liu, Jiandang; Zhang, Jie; Zhang, Lijuan; Kong, Wei; Weng, Huimin; Ye, Bangjiao

2013-01-01

MgO single crystals were implanted with 70 keV C/N/O ions at room temperature with respective doses of 2 × 1016 and 2 × 1017 ions/cm2. All samples with high-dose implantation showed room temperature hysteresis in magnetization loops. Magnetization and slow positron annihilation measurements confirmed that room temperature ferromagnetism in O-implanted samples was attributed to the presence of Mg vacancies. Furthermore, the introduction of C or N played more effective role in ferromagnetic performance than Mg vacancies. Moreover, the magnetic moment possibly occurred from the localized wave function of unpaired electrons and the exchange interaction formed a long-range magnetic order.

Ferromagnetic resonance in coupled permalloy double films separated by a Cu interlayer

Science.gov (United States)

Maksymowicz, A. Z.; Whiting, J. S. S.; Watson, M. L.; Chambers, A.

1991-03-01

Ferromagnetic resonance (FMR) at 16 GHz was used to study the magnetic coupling between two-layers of permalloy separated by a nonmagnetic Cu layer. Samples with the same thickness (600 Å) of both permalloy layers were deposited from e-gun sources onto glass substrates in UHV. The thickness d of the Cu interlayer was varied from 5 to 37 Å. The exchange coupling energy ( E = - KM1· M2) model was used to describe the interaction between the two magnetic layers. It was found from the ferromagnetic resonance data in the perpendicular configuration that K( d) follows an exponential law, K = K0e - d/ q, where q = 9.3 Å.

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

Electric Field Controlled Magnetism in BiFeO3/Ferromagnet Films

Science.gov (United States)

Holcomb, M. B.; Chu, Y. H.; Martin, L. W.; Gajek, M.; Seidel, J.; Ramesh, R.; Scholl, A.; Fraile-Rodriguez, A.

2008-03-01

Electric field control of magnetism is a hot technological topic at the moment due to its potential to revolutionize today's devices. Magnetoelectric materials, those having both electric and magnetic order and the potential for coupling between the two, are a promising avenue to approach electric control. BiFeO3, both a ferroelectric and an antiferromagnet, is the only single phase room temperature magnetoelectric that is currently known. In addition to other possibilities, its multiferroic nature has potential in the very active field of exchange bias, where an antiferromagnetic thin film pins the magnetic direction of an adjoining ferromagnetic layer. Since this antiferromagnet is electrically tunable, this coupling could allow electric-field control of the ferromagnetic magnetization. Direction determination of antiferromagnetic domains in BFO has recently been shown using linear and circular dichroism studies. Recently, this technique has been extended to look at the magnetic domains of a ferromagnetic grown on top of BFO. The clear magnetic changes induced by application of electric fields reveal the possibility of electric control.

Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

Directory of Open Access Journals (Sweden)

P. A. Bhobe

2015-10-01

Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

Interface exchange parameters in La{sub 2/3}Ca{sub 1/3}Mn{sub 3}O/La{sub 1/3}Ca{sub 2/3}Mn{sub 3}O bilayers: a Monte Carlo approach

Energy Technology Data Exchange (ETDEWEB)

Restrepo-Parra, E., E-mail: erestrepopa@unal.edu.co [Universidad Nacional de Colombia-Sede Manizales, PCM Computational Applications, Manizales (Colombia); Londoño-Navarro, J. [Universidad Nacional de Colombia-Sede Manizales, PCM Computational Applications, Manizales (Colombia); Restrepo, J. [Grupo de Magnetismo y Simulación. Instituto de Física. Universidad de Antioquia. A.A. 1226, Medellín (Colombia)

2013-10-15

Ferromagnetic/antiferromagnetic (FM/AF) bilayers have been widely studied because they exhibit special phenomena, such as exchange bias and magnetoresistance. These effects are strongly influenced by interface behavior. In this work, a study of hysteresis loops in La{sub 2/3}Ca{sub 1/3}MnO{sub 3}/La{sub 1/3}Ca{sub 2/3}MnO{sub 3} bilayers is presented. Simulations were carried out using the Monte Carlo method combined with the Metropolis algorithm and Heisenberg model. The study was focused on determining the most suitable exchange parameters at the interface by applying the model proposed by Kiwi. This model considers the use of two interface exchange parameters to represent the anisotropy that occurs at the interface because of the contact between two phases (ferromagnetic and antiferromagnetic). These two interface exchange parameters were named J{sub I1} and J{sub I2}. Initially, we assumed J{sub I1} to be equal to J{sub I2} without presenting exchange bias. Then, J{sub I1} and J{sub I2} were assumed to be different. In this configuration, the exchange phenomenon appeared in the hysteresis loops. It was also observed that the exchange bias is strongly dependent on the ratio of J{sub I1} to J{sub I2}. As J{sub I1} increases, the exchange bias decreases slowly and becomes comparable to the effective exchange bias field, assuming that it only depends on ΔJ{sub I}=J{sub I1}−J{sub I2}. - Highlights: • Exchange bias is influenced by the type of interaction ions and exchange parameters. • An interface asymmetric is required for observing the exchange bias phenomenon. • Monte Carlo method allows simulating the exchange bias phenomenon in FM/AF systems.

Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

Science.gov (United States)

Stamopoulos, D; Aristomenopoulou, E

2015-08-26

Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

Influence of the structural properties on the pseudocritical magnetic behavior of single-wall ferromagnetic nanotubes

Energy Technology Data Exchange (ETDEWEB)

Salazar-Enriquez, C.D. [PCM Computational Applications, Universidad Nacional de Colombia - Sede Manizales, A.A. 127 Manizales (Colombia); Restrepo-Parra, E., E-mail: erestrepopa@unal.edu.co [PCM Computational Applications, Universidad Nacional de Colombia - Sede Manizales, A.A. 127 Manizales (Colombia); Restrepo, J. [Grupo de Magnetismo y Simulacion Gplus, Instituto de Fisica, Universidad de Antioquia, A.A. 1226 Medellin (Colombia)

2012-04-15

In this work we address the influence of the crystalline structure, concretely when the system under study is formed by square or hexagonal unit cells, upon the magnetic properties and pseudocritical behavior of single-wall ferromagnetic nanotubes. We focus not only on the effect of the geometrical shape of the unit cell but also on their dimensions. The model employed is based on the Monte Carlo method, the Metropolis dynamics and a nearest neighbors classical Heisenberg Hamiltonian. Magnetization per magnetic site, magnetic susceptibility, specific heat and magnetic energy were computed. These properties were computed varying the system size, unit cell dimension and temperature. The dependence of the nearest neighbor exchange integral on the nanotubes geometrical characteristics is also discussed. Results revealed a strong influence of the system topology on the magnetic properties caused by the difference in the coordination number between square and hexagonal unit cell. Moreover, the nanotubes diameter influence on magnetic properties is only observed at very low values, when the distance between atoms is less than it, presented by the 2D sheet. On the other hand, it was concluded that the surface-related finite-size effects do not influence the magnetic nanotubes properties, contrary to the case of other nano-systems as thin films and nanoparticles among others. - Highlights: Black-Right-Pointing-Pointer Unit cell geometry has strong influence on the magnetic properties in ferromagnetic nanotubes. Black-Right-Pointing-Pointer The nanotube diameter increase produces a decrease of interaction between nearest neighbor. Black-Right-Pointing-Pointer Surface-related finite-size effects do not influence the magnetic nanotubes properties.

Influence of the structural properties on the pseudocritical magnetic behavior of single-wall ferromagnetic nanotubes

International Nuclear Information System (INIS)

Salazar-Enríquez, C.D.; Restrepo-Parra, E.; Restrepo, J.

2012-01-01

In this work we address the influence of the crystalline structure, concretely when the system under study is formed by square or hexagonal unit cells, upon the magnetic properties and pseudocritical behavior of single-wall ferromagnetic nanotubes. We focus not only on the effect of the geometrical shape of the unit cell but also on their dimensions. The model employed is based on the Monte Carlo method, the Metropolis dynamics and a nearest neighbors classical Heisenberg Hamiltonian. Magnetization per magnetic site, magnetic susceptibility, specific heat and magnetic energy were computed. These properties were computed varying the system size, unit cell dimension and temperature. The dependence of the nearest neighbor exchange integral on the nanotubes geometrical characteristics is also discussed. Results revealed a strong influence of the system topology on the magnetic properties caused by the difference in the coordination number between square and hexagonal unit cell. Moreover, the nanotubes diameter influence on magnetic properties is only observed at very low values, when the distance between atoms is less than it, presented by the 2D sheet. On the other hand, it was concluded that the surface-related finite-size effects do not influence the magnetic nanotubes properties, contrary to the case of other nano-systems as thin films and nanoparticles among others. - Highlights: ► Unit cell geometry has strong influence on the magnetic properties in ferromagnetic nanotubes. ► The nanotube diameter increase produces a decrease of interaction between nearest neighbor. ► Surface-related finite-size effects do not influence the magnetic nanotubes properties.

Exchange bias of patterned systems: Model and numerical simulation

International Nuclear Information System (INIS)

Garcia, Griselda; Kiwi, Miguel; Mejia-Lopez, Jose; Ramirez, Ricardo

2010-01-01

The magnitude of the exchange bias field of patterned systems exhibits a notable increase in relation to the usual bilayer systems, where a continuous ferromagnetic film is deposited on an antiferromagnet insulator. Here we develop a model, and implement a Monte Carlo calculation, to interpret the experimental observations which is consistent with experimental results, on the basis of assuming a small fraction of spins pinned ferromagnetically in the antiferromagnetic interface layer.

45○ sign switching of effective exchange bias due to competing anisotropies in fully epitaxial Co3FeN/MnN bilayers.

Science.gov (United States)

Hajiri, Tetsuya; Yoshida, Takuya; Filianina, Mariia; Jaiswal, Samridh; Borie, Benjamin; Asano, H; Zabel, Hartmut; Klaui, Mathias

2017-11-20

We report an unusual angular-dependent exchange bias effect in ferromagnet/antiferromagnet bilayers, where both ferromagnet and antiferromagnet are epitaxially grown. Numerical model calculations predict an approximately 45$^\\circ$ period for the sign switching of the exchange-bias field, depending on the ratio between magnetocrystalline anisotropy and exchange-coupling constant. The switching of the sign is indicative of a competition between a fourfold magnetocrystalline anisotropy of the ferromagnet and a unidirectional anisotropy field of the exchange coupling. This predicted unusual angular-dependent exchange bias and its magnetization switching process are confirmed by measurements on fully epitaxial Co$_3$FeN/MnN bilayers by longitudinal and transverse magneto-optic Kerr effect magnetometry. These results provide a deeper understanding of the exchange coupling phenomena in fully epitaxial bilayers with tailored materials and open up a complex switching energy landscape engineering by anisotropies. © 2017 IOP Publishing Ltd.

Anisotropy of the Faraday effect in the weak ferromagnetic YFeO3

International Nuclear Information System (INIS)

Zenkov, A.V.; Krichevtsov, B.B.; Moskvin, A.S.; Mukimov, K.M.; Pisarev, R.V.; Ruvinshtejn, M.M.

1989-01-01

The field strength dependence of the Faraday effect in the weak ferromagnetic YFeO 3 at the wavelength λ=0.63 μm are investigated experimentally for various directions of propagation of the light k-vector and magnetic field H-vector. It is shown that the variation of the Faraday effect for k-vector parallel c-vector and H-vector parallel a-vector is not proportional to the change of the magnetic moment component m z . The ferro-, antiferro- and diamagnetic contributions to the Faraday effect are separated on the basis of a phenomenological description of the Faraday effect in YFeO 3 . It is found that the antiferromagnetic contribution which determines the Faraday effect is strongly anisotropic. The microscopic mechanisms of the Faraday effect in YFeO 3 are considered theoretically for the case of the dipole-allowed 6 A 1g → 6 T 1u transition. It is shown that the mechanisms proposed earlier cannot explain the strong anisotropy of the antiferromagnetic contribution. In order to explain the anisotropy the spin-foreign orbit exchange-relativistic interaction should be taken into account

Quantum chemical analysis of binary and ternary ferromagnetic alloys; Quantenchemische Untersuchungen binaerer und ternaerer ferromagnetischer Legierungen

Energy Technology Data Exchange (ETDEWEB)

Jacobs, Yasemin Erika Charlotte

2007-02-23

In this work the electronic structures, densities of states, chemical bonding, magnetic exchange Parameters and Curie temperatures of binary and ternary ferromagnetic alloys are analyzed. The electronic structure of ferromagnetic MnAl has been calculated using density-functional techniques (TB-LMTO-ASA, FPLAPW) and quantum chemically analyzed by means of the crystal orbital Hamilton population analysis. The crystal structure of the ferromagnetic tetragonal MnAl may be understood to originate from the structure of nonmagnetic cubic MnAl with a CsCl motif through a two-step process. While the nonmagnetic cubic structure is stable against a structural deformation, antibonding Mn-Mn interactions at the Fermi level lead to spin polarization and the onset of magnetism, i.e., a symmetry reduction taking place solely in the electronic degrees of freedom, by that emptying antibonding Mn-Mn states. Residual antibonding Al--Al states can only be removed by a subsequent, energetically smaller structural deformation towards the tetragonal system. As a final result, homonuclear bonding is strengthened and heteronuclear bonding is weakened. Corresponding DFT calculations of the electronic structure as well as the calculation of the chemical bonding and the magnetic exchange interactions have been performed on the basis of LDA and GGA for a series of ferromagnetic full Heusler alloys of general formula Co2MnZ (Z=Ga,Si,Ge,Sn), Rh2MnZ (Z=Ge,Sn,Pb), Ni2MnZ (Z=Ga,In,Sn), Pd2MnZ (Z=Sn,Sb) and Cu2MnZ (Z=Al,In,Sn). The connection between the electronic spectra and the magnetic interactions have been studied. Correlations between the chemical bondings in Heusler alloys derived from COHP analysis and magnetic phenomena are obvious, and different mechanisms leading to spin polarization and ferromagnetism are derived. The band dependence of the exchange parameters, their dependence on volume and valence electron concentration have been thoroughly analyzed within the Green function technique

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.

Room temperature ferromagnetism in (In{sub 1-x}Ni{sub x}){sub 2}O{sub 3} thin films

Energy Technology Data Exchange (ETDEWEB)

Sai Krishna, N. [Thin Films Laboratory, School of Advanced Sciences, VIT University, Vellore 632014, Tamilnadu (India); Kaleemulla, S., E-mail: skaleemulla@gmail.com [Thin Films Laboratory, School of Advanced Sciences, VIT University, Vellore 632014, Tamilnadu (India); Amarendra, G. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu (India); UGC-DAE-CSR, Kalpakkam Node, Kokilamedu 603104,Tamilnadu (India); Madhusudhana Rao, N.; Krishnamoorthi, C.; Rigana Begam, M. [Thin Films Laboratory, School of Advanced Sciences, VIT University, Vellore 632014, Tamilnadu (India); Omkaram, I. [Department of Electronics and Radio Engineering, Kyung Hee University, Yongin-si, Gyeonggi-do 446-701 (Korea, Republic of); Sreekantha Reddy, D. [Department of Physics and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2015-06-15

Polycrystalline (In{sub 1−x}Ni{sub x}){sub 2}O{sub 3} thin films (x=0.00, 0.03, 0.05 and 0.07) were deposited on glass substrates by electron beam evaporation technique. The effect of Ni concentration on composition, structural and magnetic properties of (In{sub 1−x}Ni{sub x}){sub 2}O{sub 3} thin films was studied. Increment in the Ni concentration does increase the oxygen vacancies and ferromagnetic strength in (In{sub 1−x}Ni{sub x}){sub 2}O{sub 3} thin films. X-ray photoelectron spectroscopy (XPS) studies indicate the dopant Ni exists in Ni (II) state in In{sub 2}O{sub 3} host. Ferromagnetism was attributed to intrinsic nature of the sample rather than any secondary magnetic phases exist in the films. The observed ferromagnetism in (In{sub 1−x}Ni{sub x}){sub 2}O{sub 3} was attributed to ferromagnetic exchange interaction between Ni{sup 2+} ions via single free electron trapped in oxygen vacancy. Increase in oxygen vacancies with Ni concentration lead to increase in such an oxygen vacancy mediated ferromagnetic pairs resulting in increase in ferromagnetic strength with Ni concentration.

Half-metallicity and ferromagnetism of TcX (X=C, Si and Ge) in zinc blende structure

Energy Technology Data Exchange (ETDEWEB)

Liu, Yong [College of Science, Yanshan University, Qinhuangdao 066004 (China); Physics Department, Brock University, St. Catharines, ON, Canada L2S 3A1 (Canada); Xing, Yue [College of Science, Yanshan University, Qinhuangdao 066004 (China); Bose, S.K., E-mail: sbose@brocku.ca [Physics Department, Brock University, St. Catharines, ON, Canada L2S 3A1 (Canada); Zhao, Yong-Hong [Department of Physics, Sichuan Normal University, Chengdu 610068 (China)

2013-02-15

We report results of a first-principles density-functional study of three binary transition-metal compounds TcX (X=C, Si and Ge) in the hypothetical cubic zinc blende (ZB) structure. Our calculations are based on the full potential linear augmented plane wave (FP-LAPW) plus local orbitals method, together with generalized gradient approximation for the exchange-correlation potential. Half-metallic (HM) ferromagnetism is observed in these binary compounds for their optimized cell volumes. In the HM state, these compounds possess an integer magnetic moment (1.000{mu}{sub B}) per formula unit, which is one of the important characteristics of half-metallic ferromagnets (HMFs). The ferromagnetic (FM) state is found to be stable for ZB TcC, TcSi and TcGe against the nonmagnetic (NM) and antiferromagnetic (AFM) states. Calculations show that half-metallicity can be maintained for a wide range of lattice constants in these binary compounds. Density functional calculations of exchange interactions and the Curie temperatures reveal similar trends for the three compounds with respect to the lattice parameter. These compounds are compatible with the traditional semiconductors, and could be useful in spin-electronics and other applications. The most important aspect of this work is to explore the possibility of not only magnetism, but HM ferromagnetism in compounds involving NM elements and 4d transition element Tc. - Highlights: Black-Right-Pointing-Pointer We study magnetism of the compounds TcSi, TcC, and TcGe. Black-Right-Pointing-Pointer These compounds, with nonmagnetic constituents, are found to be ferromagnetic. Black-Right-Pointing-Pointer They show robust half-metallicity in zinc blende structure. Black-Right-Pointing-Pointer Estimated Curie temperatures suggest that synthesis of these compounds is worth pursuing.

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.

Superconducting Properties of Lead-Bismuth Films Controlled by Ferromagnetic Nanowire Arrays

Science.gov (United States)

Ye, Zuxin; Lyuksyutov, Igor F.; Wu, Wenhao; Naugle, Donald G.

2011-03-01

Superconducting properties of lead-bismuth (82% Pb and 18% Bi) alloy films deposited on ferromagnetic nanowire arrays have been investigated. Ferromagnetic Co or Ni nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb 82 Bi 18 films are then quench-condensed onto the polished surface of the AAO membranes filled with magnetic nanowires. A strong dependence of the Pb 82 Bi 18 superconducting properties on the ratio of the superconducting film thickness to the magnetic nanowire diameter and the material variety was observed.

Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles

Directory of Open Access Journals (Sweden)

S. K. Giri

2011-09-01

Full Text Available In this letter, we report that the charge/orbital order state of bulk antiferromagnetic Sm0.5Ca0.5MnO3 is suppressed and confirms the appearance of weak ferromagnetism below 65 K followed by a low temperature spin glass like transition at 41 K in its nano metric counterpart. Exchange anisotropy effect has been observed in the nano manganites and can be tuned by the strength of the cooling magnetic field (Hcool. The values of exchange fields (HE, coercivity (HC, remanence asymmetry (ME and magnetic coercivity (MC are found to strongly depend on cooling magnetic field and temperature. HE increases with increasing Hcool but for larger Hcool, HE tends to decrease due to the growth of ferromagnetic cluster size. Magnetic training effect has also been observed and it has been analyzed thoroughly using spin relaxation model. A proposed phenomenological core-shell type model is attributed to an exchange coupling between the spin-glass like shell (surrounding and antiferromagnetic core of Sm0.5Ca0.5MnO3 nano manganites mainly on the basis of uncompensated surface spins. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructured manganites may cause exchange anisotropy, which is of special interests for potential application in multifunctional spintronic devices.

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.

Magnons coherent transmission and its heat transport at ultrathin insulating ferromagnetic nanojunctions

Directory of Open Access Journals (Sweden)

Ghantous M. Abou

2012-06-01

Full Text Available A model calculation is presented for the magnons coherent transmission and corresponding heat transport at magnetic insulating nanojunctions. The system consists of a ferromagnetically ordered ultrathin insulating junction between two semi-infinite ferromagnetically ordered leads. Spin dynamics are analyzed using the equations of motion for the spin precession displacements, valid for the range of temperatures of interest. Coherent scattering cross-sections at the junction boundary are calculated using the phase field matching theory, for all the incidence angles on the boundary from the lead bands, for arbitrary angles of incidence, at variable temperatures, and for different nano thicknesses of the ultrathin junction. The model is general; it is applied in particular to the Fe/Gd/Fe system with a sandwiched ferromagnetic Gd junction. It yields also the thermal conductivity due to the magnons coherent transmission between the two leads when these are maintained at slightly different temperatures. The calculation is carried out for state of the art values of the exchange constants, and elucidates the relation between the coherent scattering transmission of magnons and their thermal conductivity, for different thicknesses.

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

Theoretical interpretation of the nuclear magnetic properties of solid 3He in the context of a four-spin exchange model

International Nuclear Information System (INIS)

Roger, Michel.

1980-06-01

The model presented in this thesis, with only two adjustable parameters, is alone able to account quantitatively for all the results described in chapter I and interpreted in chapter II. The development of this model was based originally on two essential ideas: - the simple model given in introduction suggests that in a hard-sphere quantum solid, three- and four-particle exchanges may be as important and even more favourable than two-atom exchanges. - By accounting for four-spin exchange terms in the Hamiltonian of the system, fourth power terms of the order parameter (polarisation) liable to give first-order transitions are introduced into the equation of free energy in a molecular field. On the basis of these two ideas the thesis is arranged in two parts: 1) Part one (ch. III to VIII) analyses the consequences, from the viewpoint of magnetic and thermodynamic properties, of a phenomenological Hamiltonian including four-spin exchanges. 2) The aim of part two is to estimate from microscopic equations the hierarchy amongst 2, 3 and 4-particle exchanges. A new approach, due to J.M. Delrieu, is proposed for a realistic wave function approximation accounting for the geometric correlations between hard cores. Reasons are given to justify the existence of a strong four-particle exchange in body-centred cubic 3 He. In a compact hexagonal lattice on the other hand the three-particle exchange is shown to be predominant. However three-particle exchanges promote ferromagnetism, so an ordered ferromagnetic phase is foreseen for compact hexagonal 3 He. A crucial test for our model would be to measure the sign of the Curie-Weiss constant in c.h. 3 He [fr

Spin-wave dynamics and exchange interactions in multiferroic NdFe3(BO3)4 explored by inelastic neutron scattering

Science.gov (United States)

Golosovsky, I. V.; Ovsyanikov, A. K.; Aristov, D. N.; Matveeva, P. G.; Mukhin, A. A.; Boehm, M.; Regnault, L.-P.; Bezmaternykh, L. N.

2018-04-01

Magnetic excitations and exchange interactions in multiferroic NdFe3(BO3)4 were studied by inelastic neutron scattering in the phase with commensurate antiferromagnetic structure. The observed spectra were analyzed in the frame of the linear spin-wave theory. It was shown that only the model, which includes the exchange interactions within eight coordination spheres, describes satisfactorily all observed dispersion curves. The calculation showed that the spin-wave dynamics is governed by the strongest antiferromagnetic intra-chain interaction and three almost the same inter-chain interactions. Other interactions, including ferromagnetic exchange, appeared to be insignificant. The overall energy balance of the antiferromagnetic inter-chain exchange interactions, which couple the moments from the adjacent ferromagnetic layers as well as within a layer, stabilizes ferromagnetic arrangement in the latter. It demonstrates that the pathway geometry plays a crucial role in forming of the magnetic structure.

Effects of interfacial frustration in ferromagnet/antiferromagnet bilayers

Science.gov (United States)

Urazhdin, Sergei; Ma, Tianyu

While the ferromagnet (F)/antiferromagnet (AF) bilayers have been extensively studied in the context of exchange bias, and more recently in the context of antiferromagnetic spintronics, the fundamental understanding of the nature of the magnetic state in this system is still a subject a debate. We will present measurements of magnetization aging in several F/AF systems based on AF=FeMn, CoO, and NiO, universally observed in all of these systems when AF layers are sufficiently thin. Quite generally, the aging curves are well-described by the power law with a small exponent. We show that the aging characteristics such as the dependence on temperature and the magnetic history are inconsistent with the Arrhenius activation, disproving the granular models of exchange bias. Furthermore, we show that the aging characteristics qualitatively change across the exchange bias blocking temperature, demonstrating that the latter is similar to the glass transition temperature, and is not simply of a characteristic activation temperature of the AF domains. We discuss the our findings in the context of frustration due to the random effective exchange field at the F/AF interface. supported by NSF DMR.

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.

Strongly suppressed proximity effect and ferromagnetism in topological insulator/ferromagnet/superconductor thin film trilayers of Bi2Se3/SrRuO3/underdoped YBa2Cu3O x : a possible new platform for Majorana nano-electronics

Science.gov (United States)

Koren, Gad

2018-07-01

We report properties of a topological insulator–ferromagnet–superconductor trilayers comprised of thin films of 20 nm thick {Bi}}2{Se}}3 on 10 nm SrRuO3 on 30 nm {YBa}}2{Cu}}3{{{O}}}x. As deposited trilayers are underdoped and have a superconductive transition with {{T}}{{c}} onset at 75 K, zero resistance at 65 K, {{T}}Cueri} at 150 K and {{T}}* of about 200 K. Further reannealing under vacuum yields the 60 K phase of {YBa}}2{Cu}}3{{{O}}}x which still has zero resistance below about 40 K. Only when 10 × 100 microbridges were patterned in the trilayer, some of the bridges showed resistive behavior all the way down to low temperatures. Magnetoresistance versus temperature of the superconductive ones showed the typical peak due to flux flow against pinning below {{T}}{{c}}, while the resistive ones showed only the broad leading edge of such a peak. All this indicates clearly weak-link superconductivity in the resistive bridges between superconductive {YBa}}2{Cu}}3{{{O}}}x grains via the topological and ferromagnetic cap layers. Comparing our results to those of a reference trilayer (RTL) with the topological {Bi}}2{Se}}3 layer substituted by a non-superconducting highly overdoped {La}}1.65{Sr}}0.35{CuO}}4, indicates that the superconductive proximity effect as well as ferromagnetism in the topological trilayer are actually strongly suppressed compared to the non-topological RTL. This strong suppression could originate in lattice and Fermi levels mismatch as well as in short coherence length and unfavorable effects of strong spin–orbit coupling in {Bi}}2{Se}}3 on the d-wave pairing of {YBa}}2{Cu}}3{{{O}}}x. Proximity induced edge currents in the SRO/YBCO layer could lead to Majorana bound states, a possible signature of which is observed in the present study as zero bias conductance peaks.

An orthogonal ferromagnetically coupled tetracopper(II) 2 x 2 homoleptic grid supported by micro-O4 bridges and its DFT study.

Science.gov (United States)

Roy, Somnath; Mandal, Tarak Nath; Barik, Anil Kumar; Pal, Sachindranath; Butcher, Ray J; El Fallah, Mohamed Salah; Tercero, Javier; Kar, Susanta Kumar

2007-03-28

A pyrazole based ditopic ligand (PzOAP), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and methyl ester of imino picolinic acid, reacts with Cu(NO3)2.6H2O to form a self-assembled, ferromagnetically coupled, alkoxide bridged tetranuclear homoleptic Cu(II) square grid-complex [Cu4(PzOAP)4(NO3)2] (NO3)2.4H2O (1) with a central Cu4[micro-O4] core, involving four ligand molecules. In the Cu4[micro-O4] core, out of four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by the nitrate ion. The complex 1 has been characterized structurally and magnetically. Although Cu-O-Cu bridge angles are too large (138-141 degrees) and Cu-Cu distances are short (4.043-4.131 A), suitable for propagation of expected antiferromagnetic exchange interactions within the grid, yet intramolecular ferromagnetic exchange (J = 5.38 cm(-1)) is present with S = 4/2 magnetic ground state. This ferromagnetic interaction is quite obvious from the bridging connections (d(x2-y2)) lying almost orthogonally between the metal centers. The exchange pathways parameters have been evaluated from density functional calculations.

Local density of states and order parameter configurations in layered ferromagnet-superconductor structures

Energy Technology Data Exchange (ETDEWEB)

Halterman, Klaus [Physics and Computational Sciences, Research and Engineering Sciences Department, Naval Air Warfare Center, China Lake, CA 93555 (United States)]. E-mail: klaus.halterman@navy.mil; Valls, Oriol T. [School of Physics and Astronomy and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455 (United States)]. E-mail: otvalls@umn.edu

2005-04-01

We analyze the local density of states (LDOS) of heterostructures consisting of alternating ferromagnet, F, and superconductor, S, layers. We consider structures of the SFS and SFSFSFS type, with thin nanometer scale F and S layers, within the ballistic regime. The spin-splitting effects of the ferromagnet and the mutual coupling between the S regions, yield several nontrivial stable and metastable pair amplitude configurations, and we find that the details of the spatial behavior of the pair amplitude govern the calculated electronic spectra. These are reflected in discernible signatures of the LDOS. The roles that the magnetic exchange energy, interface scattering strength, and the Fermi wavevector mismatch each have on the LDOS for the different allowed junction configurations, are systematically investigated.

Local density of states and order parameter configurations in layered ferromagnet-superconductor structures

International Nuclear Information System (INIS)

Halterman, Klaus; Valls, Oriol T.

2005-01-01

We analyze the local density of states (LDOS) of heterostructures consisting of alternating ferromagnet, F, and superconductor, S, layers. We consider structures of the SFS and SFSFSFS type, with thin nanometer scale F and S layers, within the ballistic regime. The spin-splitting effects of the ferromagnet and the mutual coupling between the S regions, yield several nontrivial stable and metastable pair amplitude configurations, and we find that the details of the spatial behavior of the pair amplitude govern the calculated electronic spectra. These are reflected in discernible signatures of the LDOS. The roles that the magnetic exchange energy, interface scattering strength, and the Fermi wavevector mismatch each have on the LDOS for the different allowed junction configurations, are systematically investigated

Exchange bias studied with polarized neutron reflectivity

International Nuclear Information System (INIS)

Velthuis, S. G. E. te

2000-01-01

The role of Polarized Neutron Reflectivity (PNR) for studying natural and synthetic exchange biased systems is illustrated. For a partially oxidized thin film of Co, cycling of the magnetic field causes a considerable reduction of the bias, which the onset of diffuse neutron scattering shows to be due to the loosening of the ferromagnetic domains. On the other hand, PNR measurements of a model exchange bias junction consisting of an n-layered Fe/Cr antiferromagnetic (AF) superlattice coupled with an m-layered Fe/Cr ferromagnetic (F) superlattice confirm the predicted collinear magnetization in the two superlattices. The two magnetized states of the F (along or opposite to the bias field) differ only in the relative orientation of the F and adjacent AF layer. The possibility of reading clearly the magnetic state at the interface pinpoints the commanding role that PNR is having in solving this intriguing problem

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.

Spiral correlations in frustrated one-dimensional spin-1/2 Heisenberg J1-J2-J3 ferromagnets

International Nuclear Information System (INIS)

Zinke, R; Richter, J; Drechsler, S-L

2010-01-01

We use the coupled cluster method for infinite chains complemented by exact diagonalization of finite periodic chains to discuss the influence of a third-neighbor exchange J 3 on the ground state of the spin- 1/2 Heisenberg chain with ferromagnetic nearest-neighbor interaction J 1 and frustrating antiferromagnetic next-nearest-neighbor interaction J 2 . A third-neighbor exchange J 3 might be relevant to describe the magnetic properties of the quasi-one-dimensional edge-shared cuprates, such as LiVCuO 4 or LiCu 2 O 2 . In particular, we calculate the critical point J 2 c as a function of J 3 , where the ferromagnetic ground state gives way for a ground state with incommensurate spiral correlations. For antiferromagnetic J 3 the ferro-spiral transition is always continuous and the critical values J 2 c of the classical and the quantum model coincide. On the other hand, for ferromagnetic J 3 ∼ 1 | the critical value J 2 c of the quantum model is smaller than that of the classical model. Moreover, the transition becomes discontinuous, i.e. the model exhibits a quantum tricritical point. We also calculate the height of the jump of the spiral pitch angle at the discontinuous ferro-spiral transition.

Capillary trap column with strong cation-exchange monolith for automated shotgun proteome analysis.

Science.gov (United States)

Wang, Fangjun; Dong, Jing; Jiang, Xiaogang; Ye, Mingliang; Zou, Hanfa

2007-09-01

A 150 microm internal diameter capillary monolithic column with a strong cation-exchange stationary phase was prepared by direct in situ polymerization of ethylene glycol methacrylate phosphate and bisacrylamide in a trinary porogenic solvent consisting dimethylsulfoxide, dodecanol, and N,N'-dimethylformamide. This phosphate monolithic column exhibits higher dynamic binding capacity, faster kinetic adsorption of peptides, and more than 10 times higher permeability than the column packed with commercially available strong cation-exchange particles. It was applied as a trap column in a nanoflow liquid chromatography-tandem mass spectrometry system for automated sample injection and online multidimensional separation. It was observed that the sample could be loaded at a flow rate as high as 40 microL/min with a back pressure of approximately 1300 psi and without compromising the separation efficiency. Because of its good orthogonality to the reversed phase separation mechanism, the phosphate monolithic trap column was coupled with a reversed-phase column for online multidimensional separation of 19 microg of the tryptic digest of yeast proteins. A total of 1522 distinct proteins were identified from 5608 unique peptides (total of 54,780 peptides) at the false positive rate only 0.46%.

Magnetic helices as metastable states of finite XY ferromagnetic chains: An analytical study

Science.gov (United States)

Popov, Alexander P.; Pini, Maria Gloria

2018-04-01

We investigated a simple but non trivial model, consisting of a chain of N classical XY spins with nearest neighbor ferromagnetic interaction, where each of the two end-point spins is assumed to be exchange-coupled to a fully-pinned fictitious spin. In the mean field approximation, the system might be representative of a soft ferromagnetic film sandwiched between two magnetically hard layers. We show that, while the ground state is ferromagnetic and collinear, the system can attain non-collinear metastable states in the form of magnetic helices. The helical solutions and their stability were studied analytically in the absence of an external magnetic field. There are four possible classes of solutions. Only one class is metastable, and its helical states contain an integer number of turns. Among the remaining unstable classes, there is a class of helices which contain an integer number of turns. Therefore, an integer number of turns in a helical configuration is a necessary, but not a sufficient, condition for metastability. These results may be useful to devise future applications of metastable magnetic helices as energy-storing elements.

Inhomogeneous superconductivity in a ferromagnet

International Nuclear Information System (INIS)

Kontos, T.; Aprili, M.; Lesueur, J.; Genet, F.; Boursier, R.; Grison, X.

2003-01-01

We have studied a new superconducting state where the condensate wave function resulting from conventional pairing, is modified by an exchange field. Superconductivity is induced into a ferromagnetic thin film (F) by the proximity effect with a superconducting reservoir (S). We observed oscillations of the superconducting order parameter induced in F as a function of the distance from the S/F interface. They originate from the finite momentum transfer provided to Cooper pairs by the splitting of the spin up and down bands. We measured the superconducting density of states in F by tunneling spectroscopy and the Josephson critical current when F is coupled with a superconducting counter-electrode. Negative values of the superconducting order parameter are revealed by capsized tunneling spectra in F and a negative Josephson coupling (π-junction)

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

Synergy of exchange bias with superconductivity in ferromagnetic-superconducting layered hybrids: the influence of in-plane and out-of-plane magnetic order on superconductivity

International Nuclear Information System (INIS)

Stamopoulos, D; Manios, E; Pissas, M

2007-01-01

It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as was preliminarily highlighted in Stamopoulos et al (2007 Phys. Rev. B 75 014501), and extensively studied in this work, under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure. Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni 80 Fe 20 and low-T c superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in Stamopoulos et al (2007 Phys. Rev. B 75 184504) enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire. The relative in-plane magnetization configuration of the outer FM layers exerts a secondary contribution on the SC interlayer. Since the exchange bias directly controls the in-plane magnetic order it also controls the out-of-plane rotation of

Ferromagnetic resonance response of electron-beam patterned arrays of ferromagnetic nanoparticles

Science.gov (United States)

Jung, Sukkoo; Watkins, Byron; Feller, Jeffrey; Ketterson, John; Chandrasekhar, Venkat

2001-03-01

We report on the fabrication and the dynamic magnetic properties of periodic permalloy dot arrays. Electron-beam lithography and e-gun evaporation have been used to make the arrays with the aspect ratio of 2 (dot diameter : 40 nm, height : 80 nm) and periods of 100 - 200 nm. The magnetic properties of the arrays and their interactions have been investigated by ferromagnetic resonance (FMR), magnetic force microscopy (MFM), and SQUID magnetometry. The measured FMR data show that the position and magnitude of resonant absorption peaks strongly depend on the angle between magnetic field and the lattice structure. The results of dot arrays with various kinds of structural parameters will be presented. Supported by Army Research Office, DAAD19-99-1-0334/P001

Superconducting properties of Pb82Bi18 films controlled by ferromagnetic nanowire arrays

International Nuclear Information System (INIS)

Ye Zuxin; Lyuksyutov, Igor F; Wu Wenhao; Naugle, Donald G

2011-01-01

The superconducting properties of Pb 82 Bi 18 alloy films deposited on ferromagnetic nanowire arrays have been investigated. Ferromagnetic Co or Ni nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb 82 Bi 18 films are then quench condensed onto the polished surface of the AAO membranes filled with magnetic nanowires. A strong dependence of the Pb 82 Bi 18 superconducting properties on the ratio of the superconducting film thickness to the magnetic nanowire diameter and material variety was observed.

Superconducting properties of Pb82Bi18 films controlled by ferromagnetic nanowire arrays

Science.gov (United States)

Ye, Zuxin; Lyuksyutov, Igor F.; Wu, Wenhao; Naugle, Donald G.

2011-02-01

The superconducting properties of Pb82Bi18 alloy films deposited on ferromagnetic nanowire arrays have been investigated. Ferromagnetic Co or Ni nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb82Bi18 films are then quench condensed onto the polished surface of the AAO membranes filled with magnetic nanowires. A strong dependence of the Pb82Bi18 superconducting properties on the ratio of the superconducting film thickness to the magnetic nanowire diameter and material variety was observed.

Proximity effects and Josephson currents in ferromagnet. Spin-triplet superconductors junctions

International Nuclear Information System (INIS)

Terrade, Damien

2015-01-01

Spin-triplet superconductivity, first attached to the description of 3 He, is now generally considered to also occur in heavy-fermions compounds and in perovskite ruthenium oxide Sr 2 RuO 4 . The latter material is especially interesting since many experiments show strong evidences for a unitary chiral spin-triplet state. Moreover, the recent fabrication of thin heterostructures made of ferromagnetic SrRuO 3 on the top of Sr 2 RuO 4 strongly encourages new theoretical studies on the interplay between spin-triplet superconductor and ferromagnet in similar fashion to spin-singlet superconductors. Using an extended tight-binding Hamiltonian to model the superconductor, we discuss in this thesis the specific proximity effects of such interface by solving self-consistently the Bogoliubov-De Gennes equations on two- and three-dimensional lattices in the ballistic limit. We obtain the spatial profile of the superconducting order parameters at the interface as well as the spin-polarisation and the current across the Josephson junctions. In contrast to heterostructures made of spin-singlet superconductor, we show that the physical properties at the interface are not only controlled by the strength of the magnetization inside the ferromagnet but also by its orientation due to the existence of a finite pair spin projection of the spin-triplet Cooper pairs. We analyse in the first part the spin-polarisation and the Gibbs free energy at the three-dimensional ferromagnet-chiral spin-triplet superconductor interface. Then, the second part of the thesis is dedicated to the study of the Josephson junctions made of a chiral spin-triplet superconductor and a ferromagnetic barrier. More precisely, we analyse the existence of 0-π state transitions in two- and three-dimensional junctions with respect to the strength and the orientation of the magnetization. Finally, we study the proximity effects at the interface of helical spin-triplet superconductors. They differ from the chiral

Magnus force and inertia properties of magnetic vortices in weak ferromagnets

International Nuclear Information System (INIS)

Zvezdin, A.K.; Zvezdin, K.A.

2010-01-01

The question of the Magnus force in weak ferromagnets acting on magnetic vortices (Bloch lines), within domain boundary has been investigated and the general formula of the Magnus force has been derived. It is shown that the Magnus force is non-zero in most types domain boundaries and determined by the average sublattice magnetization, Dzyaloshinskii coupling constants and exchange interaction between the sublattices. Generalized expressions have been obtained for the effective Langrangian and Rayleigh functions in weak ferromagnets allowing for their vortex structure. The mass of a vortex was considered and the value m * ∼ 10 -14 g/cm was obtained for YFeO 3 . The dynamic bending of the domain boundary in the presence of a moving vortex has been analyzed. A formula has been obtained, which describes the dependence of the vortex velocity in a motionless domain boundary upon the magnetic-field.

Blue shift of the plasma edge of a ferromagnetic semimetal

International Nuclear Information System (INIS)

Wachter, P.; Bommeli, F.; Degiorgi, L.; Burlet, P.; Bourdarot, F.

1998-01-01

Full text: In general rare earth pnictides are semimetals and antiferromagnets. Only some nitrides are quoted as ferri or ferromagnetic. However, it has been shown when prepared stoichiometrically and in single crystalline form the free carrier concentration is only in the percent per cation range, thus they are typical low carrier systems. Under these conditions the nitrides are all canted antiferromagnets and metamagnets, i.e. they show Abstract only. The full magnetic moment only with an applied magnetic field. However, when prepared as single crystals but with excess of the rare earths they become spontaneously ferromagnets due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in addition to the superexchange mechanisms. On such ferromagnetic compositions of TbN and GdN and also in EuB 6 a new magneto-optic effect has been discovered, a spontaneous blue shift of the plasma edge upon magnetic order. The plasma edge is measured with optical reflectivity and it depends on the free carrier concentration. In other words the free carrier concentration increases upon ferromagnetic order. This effect can be understood with the spontaneous exchange splitting of mainly the 5d conduction band, lowering the bottom of the spin up 5d band, thus increasing the indirect overlap with the valence p band of the anions and thus enhancing the carrier concentration. This blue shift of the plasma edge follows a spin correlation function. An external magnetic field applied near TC enhances the blue shift since the magnetization is not yet saturated. For T→0 a magnetic field has no effect since the magnetization is spontaneously saturated

Ferromagnetic Behaviors in Fe-Doped NiO Nanofibers Synthesized by Electrospinning Method

Directory of Open Access Journals (Sweden)

Yi-Dong Luo

2013-01-01

Full Text Available Ni1−xFexO nanofibers with different Fe doping concentration have been synthesized by electrospinning method. An analysis of the phase composition and microstructure shows that Fe doping has no influence on the crystal structure and morphology of NiO nanofibers, which reveals that the doped Fe ions have been incorporated into the NiO host lattice. Pure NiO without Fe doping is antiferromagnetic, yet all the Fe-doped NiO nanofiber samples show obvious room-temperature ferromagnetic properties. The saturation magnetization of the nanofibers can be enhanced with increasing Fe doping concentration, which can be ascribed to the double exchange mechanism through the doped Fe ions and free charge carriers. In addition, it was found that the diameter of nanofibers has significant impact on the ferromagnetic properties, which was discussed in detail.

Skyrmion burst and multiple quantum walk in thin ferromagnetic films

International Nuclear Information System (INIS)

Ezawa, Motohiko

2011-01-01

We propose a new type of quantum walk in thin ferromagnetic films. A giant Skyrmion collapses to a singular point in a thin ferromagnetic film, emitting spin waves, when external magnetic field is increased beyond the critical one. After the collapse the remnant is a quantum walker carrying spin S. We determine its time evolution and show the diffusion process is a continuous-time quantum walk. We also analyze an interference of two quantum walkers after two Skyrmion bursts. The system presents a new type of quantum walk for S>1/2, where a quantum walker breaks into 2S quantum walkers. -- Highlights: → A giant Skyrmion collapses to a singular point by applying strong magnetic field. → Quantum walk is realized in thin ferromagnetic films by Skyrmion collapsing. → Quantum walks for S=1/2 and 1 are exact solvable, where S represents the spin. → Quantum walks for >1/2 presents a new type of quantum walks, i.e., 'multiple quantum walks'. → Skyrmion bursts which occur simultaneously exhibit an interference as a manifestation of quantum walk.

Room-temperature ferromagnetism in pure and Co doped CeO2 powders

International Nuclear Information System (INIS)

Wen Qiye; Zhang Huaiwu; Song Yuanqiang; Yang Qinghui; Zhu Hao; Xiao, John Q

2007-01-01

We report the room-temperature (RT) ferromagnetism (FM) observed in pure and Co doped CeO 2 powder. An insulating nonmagnetic CeO 2 single crystal, after grinding into fine powder, shows an RT-FM with a small magnetization of 0.0045 emu g -1 . However, the CeO 2 powder became paramagnetic after oxygen annealing, which strongly suggests an oxygen vacancy meditated FM ordering. Furthermore, by doping Co into CeO 2 powder the FM can significantly enhance through a F-centre exchange (FCE) coupling mechanism, in which both oxygen vacancies and magnetic ions are involved. As the Co content increases, the FM of Co doped CeO 2 initially increases to a maximum 0.47 emu g -1 , and then degrades very quickly. The complex correlation between the Co content and saturation magnetization was well interpreted by supposing the coexistence of three subsets of Co ions in CeO 2 . Our results reveal that the large RT-FM observed in Co doped CeO 2 powder originates from a combination effect of oxygen vacancies and transition metal doping

Defect types and room temperature ferromagnetism in N-doped rutile TiO2 single crystals

Science.gov (United States)

Qin, Xiu-Bo; Li, Dong-Xiang; Li, Rui-Qin; Zhang, Peng; Li, Yu-Xiao; Wang, Bao-Yi

2014-06-01

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), and positron annihilation analysis (PAS). Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3+, arising from titanium vacancies and the replacement of O with N atoms in the rutile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism (RTFM), and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.

Muon spin relaxation in ferromagnets. Pt. 1

International Nuclear Information System (INIS)

Lovesey, S.W.; Karlsson, E.B.

1991-04-01

Expressions for the dipolar and hyperfine contributions to the relaxation rate of muons implanted in a ferromagnet are presented and analysed using the Heisenberg model of spin-waves including dipolar and Zeeman energies. Calculations for EuO indicate that relaxation is likely to be dominated by the hyperfine mechanism, even if the ratio of the hyperfine and dipolar coupling constants is small. The hyperfine mechanism is sensitive to the dipolar energy of the atomic spins, whereas the dipolar mechanisms depend essentially on the exchange energy. For both mechanisms there is an almost quadratic dependence on temperature, throughout much of the ordered magnetic phase, which reflects two-spin-wave difference events from the Raman-type relaxation processes. (author)

Magnetic and thermal behaviour of the amorphous ferromagnet Fe79B16Si5

International Nuclear Information System (INIS)

Shaisha, E.E.; Bahgat, A.A.

1985-01-01

Spin waves in the amorphous ferromagnet Fe 79 B 16 Si 5 are studied by Moessbauer effect spectroscopy. The magnetic hyperfine field (MHF) is measured at the Fe sites of such a ferromagnet, which exhibits a temperature dependence of the form, H(T)/H(0) = (1 - BT/sup 3/2/ - CT/sup 5/2/), indicative of spin wave excitations in amorphous ferromagnets. The T/sup 3/2/ behaviour and the distribution of the exchange interactions are studied in detail as a function of the MHF. The spin wave excitations constant B/sub 3/2/ = BT/sub C//sup 3/2/ = 0.3 +- 0.05 and C/sub 5/2/ = CT/sub C//sup 5/2/ = 0.3 +- 0.05,Are obtained by fitting the experimental data, and where T/sub C/ = 670 K. The results sh=ow that the contribution of C/sub 5/2/ is extremely effective above 124 K, while the ratio C/sub 5/2//C/sub 3/2/ = 1.0 indicates that the present magnetic interaction is of long range order character. On the other hand, fluctuations of the exchange interaction constant are found to decrease with increasing temperature. Some information regarding the directions of the magnetic moments are obtained during the study of the magnetic anisotropy course. The values of the Einstein and Debye temperatures as measured from the thermal shift results are theta/sub E/ = 250 K and theta/sub D/ = 350 K,And from the Moessbauer factor measurements theta/sub E/ = 165 K and theta/sub D/ = 285 K. (autho=r)

Ion exchange removal of chromium (iii) from tannery wastes by using a strong acid cation exchange resin amberlite ir-120 h+ and its hybrids

International Nuclear Information System (INIS)

Ahmad, T.

2014-01-01

A strong acid cation exchange resin Amberlite IR-120 H+ and its hybrids with Mn(OH)/sub 2/, Cu(OH)/sub 2/ and Fe(OH)/sub 3/ are used for the removal of chromium (III) from spent tannery bath. The experimental data give good fits with the Langmuir sorption model. The thermodynamic parameters entropy (delta S), enthalpy (delta H) and free energy (delta G) changes are computed, which reveal that the chromium removal from tannery wastes by ion exchangers is an endothermic, physical sorption and entropically driven process. The rate of sorption is found to increase with the increase of resin dosage, stirring speed and temperature. Different kinetic models such as film diffusion, particle diffusion and Lagergren pseudo first order are used to evaluate the mechanism of the process. It is found that the hybrid ion exchange resins have better removal capacity as compared to the parent ion exchanger. The increase in the removal capacity is found to be in the order of the corresponding PZC values of the hybrid ion exchangers. Further, it is suggested that the higher exchange capacity is the result of Donnan effect and specific adsorption of chromium by the oxides / hydroxides present inside the matrix of the organic cation exchanger. (author)

Spin-glass-like dynamics of ferromagnetic clusters in La0.75Ba0.25CoO3

International Nuclear Information System (INIS)

Kumar, Devendra

2014-01-01

We report a magnetization study of the compound La 0.75 Ba 0.25 CoO 3 where the Ba 2+ doping is just above the critical limit for percolation of ferromagnetic clusters. The field cooled and zero-field cooled (ZFC) magnetization exhibit thermomagnetic irreversibility and the ac susceptibility shows a frequency dependent peak at the ferromagnetic ordering temperature (T C  ≈ 203 K) of the clusters. These features indicate the presence of a non-equilibrium state below T C . For the non-equilibrium state, the dynamic scaling of the imaginary part of the ac susceptibility and the static scaling of the nonlinear susceptibility clearly establish a spin-glass-like cooperative freezing of ferromagnetic clusters at 200.9(2) K. The assertion of the occurrence of spin-glass-like freezing of ferromagnetic clusters is further substantiated by ZFC ageing and memory experiments. We also observe certain dynamical features which are not present in a typical spin glass, such as: the initial magnetization after ZFC ageing first increases and then decreases with the waiting time; and there is an imperfect recovery of relaxation in negative temperature cycling experiments. This imperfect recovery transforms to perfect recovery for concurrent field cycling. Our analysis suggests that these additional dynamical features have their origin in the inter-cluster exchange interaction and cluster size distribution. The inter-cluster exchange interaction above the magnetic percolation level gives a superferromagnetic state in some granular thin films, but our results show the absence of a typical superferromagnetic-like state in La 0.75 Ba 0.25 CoO 3 . (paper)

The half-metallic ferromagnetism character in Be1-xVxY (Y=Se and Te) alloys: An ab-initio study

Science.gov (United States)

Sajjad, M.; Manzoor, Sadia; Zhang, H. X.; Noor, N. A.; Alay-e-Abbas, S. M.; Shaukat, A.; Khenata, R.

2015-04-01

Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p-d hybridization which yields small magnetic moments on the Be, Se and Te sites.

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)

Ferromagnetic material inspection for feedwater heater and condenser tubes

International Nuclear Information System (INIS)

Anon.

1987-01-01

In recent years, special ferritic stainless steels, such as AL29-4C/sup TM/, Sea-Cure/sup TM/, E-Brite/sup TM/, 439, and similar alloys have been introduced as tube material in condensers, feedwater heaters, moisture separator/reheaters, and other heat exchangers. In addition, carbon steel tubes are widely used in feedwater heaters and heat exchangers in chemical plants. The main problem with the in-service inspection of these ferritic alloys and carbon steel tubes lies in their highly ferromagnetic properties. These properties severely limit the application of the standard eddy current techniques. The effort was undertaken under EPRI sponsorship to develop a reliable technique for in-service inspection of ferromagnetic tubes. The new method combines the measurement of magnetic flux leakage generated around the defects with measurement of total flux in the tube wall. The heart of the inspection system is a special ID probe that magnetizes the tube and generates signals for any tube defect. A permanent record of inspection is provided with a strip-chart or magnetic tape recorder. The laboratory and field evaluation of this new system demonstrated its very good sensitivity to small defects, its reliability, and its ruggedness. Defects as small as 10% external wall loss in heavy wall carbon steel tube were detected. Tubes in the power plant were inspected at a rate of 300-500 tubes per eight-hour shift. The other advantages of this newly developed technique are its simplicity, low cost of instrumentation, easy data interpretation, and full portability

Exchange interactions and the state of iron atoms in Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ}

Energy Technology Data Exchange (ETDEWEB)

Chezhina, N.V., E-mail: chezhina@nc2490.spb.edu [St. Petersburg State University, 7/9 Universitetskaya Nab., 199034 (Russian Federation); Korolev, D.A. [St. Petersburg State University, 7/9 Universitetskaya Nab., 199034 (Russian Federation); Zhuk, N.A. [Syktyvkar State University (Russian Federation); Lutoev, V.P.; Makeev, B.A. [Institute of Geology Komi Scientific Center of Ural branch of Russian Academy of Sciences, Syktyvkar (Russian Federation)

2017-03-15

On the basis of the results of magnetic susceptibility and ESR studies of the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions iron atoms in the solid solutions of cubic modification of bismuth niobate were found to exist as Fe(III) monomers and exchange bound Fe(III)-O-Fe(III) dimers with antiferro- and ferromagnetic type of superexchange. The exchange parameters and the distribution of monomers and dimers in the solid solutions were calculated as a function of paramagnetic atom content. - Graphical abstract: The study of the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions showed that the introduction of iron atoms into the structure of Bi{sub 3}NbO{sub 7} stabilizes the cubic structure of bismuth niobate making the phase transition tetragonal ↔ cubic structure irreversible. In the Bi{sub 3}Nb{sub 1−x}Fe{sub x}O{sub 7−δ} solid solutions we observe the formation of dimers with antiferro- and ferromagnetic exchange. Such clusters are partially retained even at the infinite dilution of the solid solution, which testifies for their rigidity. A sufficiently high parameter of ferromagnetic exchange in a dimer (+53 cm{sup −1}) seems to result from iron atoms being located in the vicinity of oxygen vacancy. - Highlights: • The reversible transition cubic – tetragonal modifications in Bi{sub 3}NbO{sub 7} becomes irreversible. • Only cubic modification of Bi{sub 3}Nb{sub 1-x}Fe{sub x}O{sub 7-δ} is stable due to clusters of Fe atoms. • These clusters are sufficiently strong and retained even at the infinite dilution. • The calculations of magnetic susceptibility give the distribution of the clusters and single atoms.

Observation of giant exchange bias in bulk Mn50Ni42Sn8 Heusler alloy

Science.gov (United States)

Sharma, Jyoti; Suresh, K. G.

2015-02-01

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn50Ni42Sn8 Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (Tf) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

Effect of fractons and magnons in dilute ferromagnets on resistivity

International Nuclear Information System (INIS)

Li Jianxin; Jiang Qing; Tian Decheng

1993-01-01

Based on the s - d exchange model, we investigate the temperature-dependent resistivity arising from the scattering of electrons off fractons and magnons in dilute Heisenberg ferromagnets on three-dimensional bond percolation network. The results indicate that the contribution of fracton scatterings to the resistivity varies from T 3 / 2 to T 2 dependence as the concentration of bonds approaches the percolation threshold, while the magnon scattering contributes a resistivity varying as T 3 / 2 regardless of the changes in concentration of bonds. (author). 21 refs, 4 figs

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.

The importance of Fe interface states for ferromagnet-semiconductor based spintronic devices

Science.gov (United States)

Chantis, Athanasios

2009-03-01

I present our recent theoretical studies of the bias-controlled spin injection, detection sensitivity and tunneling anisotropic magnetoresistance in ferromagnetic-semiconductor tunnel junctions. Using first-principles electron transport methods we have shown that Fe 3d minority-spin surface (interface) states are responsible for at least two important effects for spin electronics. First, they can produce a sizable Tunneling Anisotropic Magnetoresistance in magnetic tunnel junctions with a single Fe electrode. The effect is driven by a Rashba shift of the resonant surface band when the magnetization changes direction. This can introduce a new class of spintronic devices, namely, Tunneling Magnetoresistance junctions with a single ferromagnetic electrode that can function at room temperatures. Second, in Fe/GaAs(001) magnetic tunnel junctions they produce a strong dependence of the tunneling current spin-polarization on applied electrical bias. A dramatic sign reversal within a voltage range of just a few tenths of an eV is found. This explains the observed sign reversal of spin-polarization in recent experiments of electrical spin injection in Fe/GaAs(001) and related reversal of tunneling magnetoresistcance through vertical Fe/GaAs/Fe trilayers. We also present a theoretical description of electrical spin-detection at a ferromagnet/semiconductor interface. We show that the sensitivity of the spin detector has strong bias dependence which, in the general case, is dramatically different from that of the tunneling current spin-polarization. We show that in realistic ferromagnet/semiconductor junctions this bias dependence can originate from two distinct physical mechanisms: 1) the bias dependence of tunneling current spin-polarization, which is of microscopic origin and depends on the specific properties of the interface, and 2) the macroscopic electron spin transport properties in the semiconductor. Our numerical results show that the magnitude of the voltage signal

Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction

International Nuclear Information System (INIS)

Tian Hong-Yu; Wang Jun

2012-01-01

We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions. The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon. It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived, the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG, while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect, in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations. Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

The semi-infinite anisotropic spin-1/2 Heisenberg ferromagnet

International Nuclear Information System (INIS)

Benyoussef, A.; Boubekri, A.; Ez-Zahraouy, H.; Saber, M.

1998-08-01

Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions, the phase transitions in the semi-infinite anisotropic spin-1/2 Heisenberg ferromagnet on a simple cubic lattice are examined. For fixed values of the reduced exchange anisotropic parameter, the critical temperature of the system is studied as a function of the ratio R of the surface exchange couplings to the bulk ones. It was found that if R ≤ R c , the system orders at the bulk critical temperature T B c /J and if R ≥ R c , the system exhibits two successive transitions. The surface orders at the surface critical temperature T S c /J which is higher than T B c /J and as the temperature is lowered, in the presence of ordered surface, the bulk orders at T B c /J. (author)

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.

The phase diagrams of a ferromagnetic thin film in a random magnetic field

Energy Technology Data Exchange (ETDEWEB)

Zaim, N.; Zaim, A., E-mail: ah_zaim@yahoo.fr; Kerouad, M., E-mail: m.kerouad@fs-umi.ac.ma

2016-10-07

In this paper, the magnetic properties and the phase diagrams of a ferromagnetic thin film with a thickness N in a random magnetic field (RMF) are investigated by using the Monte Carlo simulation technique based on the Metropolis algorithm. The effects of the RMF and the surface exchange interaction on the critical behavior are studied. A variety of multicritical points such as tricritical points, isolated critical points, and triple points are obtained. It is also found that the double reentrant phenomenon can appear for appropriate values of the system parameters. - Highlights: • Phase diagrams of a ferromagnetic thin film are examined by the Monte Carlo simulation. • The effect of the random magnetic field on the magnetic properties is studied. • Different types of the phase diagrams are obtained. • The dependence of the magnetization and susceptibility on the temperature are investigated.

Effect of anisotropy on the magnon energy gap in a two-layer ferromagnetic superlattice

International Nuclear Information System (INIS)

Qiu Rongke; Liang Jing; Li Qingfeng; Zhang Zhidong; Song Panpan; Hong Xiaomin

2009-01-01

The magnon energy bands or spectra in a two-layer ferromagnetic superlattice are studied. It is found that a modulated energy gap exists in the magnon energy band along K x direction perpendicular to the superlattice plane, which is different from the optical magnon gap at K x =0. The anisotropy, the spin quantum numbers and the interlayer exchange couplings all affect the magnon energy gap. If the anisotropy exists, there will be no acoustic energy branch in the system. There is a competition effect of the anisotropy and the spin quantum number on the magnon energy gap. The competition achieves a balance at the zero energy gap, at which the symmetry of the system is higher. The two energy spectra of the two-layer ferromagnetic superlattice are lowered with increasing temperature.

A non-magnetic spacer layer effect on spin layers (7/2,3) in a bi-layer ferromagnetic dendrimer structure: Monte Carlo study

Science.gov (United States)

Jabar, A.; Tahiri, N.; Bahmad, L.; Benyoussef, A.

2016-11-01

A bi-layer system consisting of layers of spins (7/2, 3) in a ferromagnetic dendrimer structure, separated by a non-magnetic spacer, is studied by Monte Carlo simulations. The effect of the RKKY interactions is investigated and discussed for such system. It is shown that the magnetic properties in the two magnetic layers depend strongly on the thickness of the magnetic and non-magnetic layers. The total magnetizations and susceptibilities are studied as a function of the reduced temperature. The effect of the reduced exchange interactions as well as the reduced crystal field is outlined. On other hand, the critical temperature is discussed as a function of the magnetic layer values. To complete this study we presented and discussed the magnetic hysteresis cycles.

Green function theory of random ferromagnets with large exchange anisotropy

International Nuclear Information System (INIS)

Patterson, J.D.

1977-01-01

Spin 1/2 systems which are coupled with an Ising-like Hamiltonian with fluctuating exchange are discussed by the use of thermodynamic Green functions in four different approximations. The first is equivalent to a local mean field approximation and the second is an approximation to the first in which the local mean field is assumed to be proportional to the overall magnetization and to the sum of the neighboring exchange 'bonds'. The third is also a special case of the first, but the local mean field is approximated in such a way as to be appropriate for the discussion of spin glasses. The fourth is a coherent potential-like approximation (CPA). The second approximation can be shown to imply no reduction of the Curie temperature (T sub(c)) due to exchange fluctuations, while the CPA does result in a lowering of T sub(c) (assuming small fluctuations about an average positive exchange in both cases). However, the CPA that was used is also an approximation to the second method. Hence, even though the CPA does result in a lowering of T sub(c) (which is generally conceded to be correct for the original model), this fact cannot be used as an argument for the validity of the CPA. This calculation thus emphasizes the necessity of critically examining any CPA-like calculation before accepting its predictions as valid [pt

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

Why Seemingly Trivial Events Sometimes Evoke Strong Emotional Reactions: The Role of Social Exchange Rule Violations.

Science.gov (United States)

Leary, Mark R; Diebels, Kate J; Jongman-Sereno, Katrina P; Fernandez, Xuan Duong

2015-01-01

People sometimes display strong emotional reactions to events that appear disproportionate to the tangible magnitude of the event. Although previous work has addressed the role that perceived disrespect and unfairness have on such reactions, this study examined the role of perceived social exchange rule violations more broadly. Participants (N = 179) rated the effects of another person's behavior on important personal outcomes, the degree to which the other person had violated fundamental rules of social exchange, and their reactions to the event. Results showed that perceptions of social exchange rule violations accounted for more variance in participants' reactions than the tangible consequences of the event. The findings support the hypothesis that responses that appear disproportionate to the seriousness of the eliciting event are often fueled by perceived rule violations that may not be obvious to others.

Spontaneous exchange bias formation driven by a structural phase transition in the antiferromagnetic material.

Science.gov (United States)

Migliorini, A; Kuerbanjiang, B; Huminiuc, T; Kepaptsoglou, D; Muñoz, M; Cuñado, J L F; Camarero, J; Aroca, C; Vallejo-Fernández, G; Lazarov, V K; Prieto, J L

2018-01-01

Most of the magnetic devices in advanced electronics rely on the exchange bias effect, a magnetic interaction that couples a ferromagnetic and an antiferromagnetic material, resulting in a unidirectional displacement of the ferromagnetic hysteresis loop by an amount called the 'exchange bias field'. Setting and optimizing exchange bias involves cooling through the Néel temperature of the antiferromagnetic material in the presence of a magnetic field. Here we demonstrate an alternative process for the generation of exchange bias. In IrMn/FeCo bilayers, a structural phase transition in the IrMn layer develops at room temperature, exchange biasing the FeCo layer as it propagates. Once the process is completed, the IrMn layer contains very large single-crystal grains, with a large density of structural defects within each grain, which are promoted by the FeCo layer. The magnetic characterization indicates that these structural defects in the antiferromagnetic layer are behind the resulting large value of the exchange bias field and its good thermal stability. This mechanism for establishing the exchange bias in such a system can contribute towards the clarification of fundamental aspects of this exchange interaction.

Vortex Flipping in Superconductor-Ferromagnet Spin Valve Structures

Science.gov (United States)

Patino, Edgar J.; Aprili, Marco; Blamire, Mark; Maeno, Yoshiteru

2014-03-01

We report in plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni, below the superconducting transition Tc, our results show strong evidence of vortex flipping driven by the ferromagnets magnetization. This is a direct consequence of proximity effect that leads to vortex supercurrents leakage into the ferromagnets. Here the polarized electron spins are subject to vortices magnetic field occasioning vortex flipping. Such novel mechanism has been made possible for the first time by fabrication of the F/S/F/AF multilayered spin valves with a thin-enough S layer to barely confine vortices inside as well as thin-enough F layers to align and control the magnetization within the plane. When Co is used there is no observation of vortex flipping effect. This is attributed to Co shorter coherence length. Interestingly instead a reduction in pinning field of about 400 Oe is observed when the Nb layer is in superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts any explanation must be directly related to proximity effect and thus a remarkable phenomenon that deserves further investigation. Programa Nacional de Ciencias Basicas COLCIENCIAS (No. 120452128168).

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.

Defect mediated ferromagnetism in Ni-doped ZnO nanocrystals evidenced by positron annihilation spectroscopy

Science.gov (United States)

Chen, Zhi-Yuan; Chen, Z. Q.; Zou, B.; Zhao, X. G.; Tang, Z.; Wang, S. J.

2012-10-01

NiO/ZnO nanocomposites with NiO content of 4 at. % and 20 at. % were annealed up to 1200 °C to get Ni doped ZnO nanocrystals. Raman scattering spectra illustrate a broad and strong band at 500-600cm-1 in all nanocomposites after annealing above 700 °C, which suggests incorporation of Ni in the ZnO lattice. However, x-ray diffraction measurements show that NiO phase can be still observed in all nanocomposites after annealing, which indicates that Ni is partially doped into the ZnO structure. Positron annihilation measurements reveal large number of vacancy defects in the interface region of all nanocomposites, and they are gradually recovered with increasing annealing temperature up to 1000 °C. Room temperature ferromagnetism can be observed in the NiO/ZnO nanocomposites, which is stronger in the 20 at. % NiO/ZnO nanocomposites, and the magnetization decreases continuously with increasing annealing temperature. This indicates that the ferromagnetism at low annealing temperatures originates from the NiO nanograins, and they become antiferromanetic after subsequent higher temperature annealing which leads to the weakening of ferromagnetism. After annealing up to 1000 °C, the ferromagnetism in both the two samples becomes nearly invisible. The disappearance of ferromagnetism shows good coincidence with the recovery of vacancy defects in NiO/ZnO nanocomposites. It can be inferred that the ferromagnetism is mediated by vacancy defects which are distributed in the interface region.

Modeling and simulation of protein elution in linear pH and salt gradients on weak, strong and mixed cation exchange resins applying an extended Donnan ion exchange model.

Science.gov (United States)

Wittkopp, Felix; Peeck, Lars; Hafner, Mathias; Frech, Christian

2018-04-13

Process development and characterization based on mathematic modeling provides several advantages and has been applied more frequently over the last few years. In this work, a Donnan equilibrium ion exchange (DIX) model is applied for modelling and simulation of ion exchange chromatography of a monoclonal antibody in linear chromatography. Four different cation exchange resin prototypes consisting of weak, strong and mixed ligands are characterized using pH and salt gradient elution experiments applying the extended DIX model. The modelling results are compared with the results using a classic stoichiometric displacement model. The Donnan equilibrium model is able to describe all four prototype resins while the stoichiometric displacement model fails for the weak and mixed weak/strong ligands. Finally, in silico chromatogram simulations of pH and pH/salt dual gradients are performed to verify the results and to show the consistency of the developed model. Copyright © 2018 Elsevier B.V. All rights reserved.

Spin transfer in an open ferromagnetic layer: from negative damping to effective temperature

Energy Technology Data Exchange (ETDEWEB)

Wegrowe, J-E; Ciornei, M C; Drouhin, H-J [Laboratoire des Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642 and CEA/DSM/DRECAM, 91128 Palaiseau Cedex (France)

2007-04-23

Spin transfer is a typical spintronics effect that allows a ferromagnetic layer to be switched by spin injection. All experimental results concerning spin transfer (quasi-static hysteresis loops or AC resonance measurements) are described on the basis of the Landau-Lifshitz-Gilbert equation of the magnetization, in which additional current dependent terms are added, like current dependent effective fields and current dependent damping factors, that can be positive or negative. The origin of these terms can be investigated further by performing stochastic experiments, like one-shot relaxation experiments under spin injection in the activation regime of the magnetization. In this regime, the Neel-Brown activation law is observed which leads to the introduction of a current dependent effective temperature. In order to define these counterintuitive parameters (effective temperature and negative damping), a detailed thermokinetic analysis of the different sub-systems involved is performed. This report presents a thermokinetic description of the different forms of energy exchanged between the electric and the ferromagnetic sub-systems at a normal/ferromagnetic junction. The derivation of the Fokker-Planck equation in the framework of the thermokinetic theory allows the transport parameters to be defined from the entropy variation and refined with the Onsager reciprocity relations and symmetry properties of the magnetic system. The contribution of the spin polarized current is introduced as an external source term in the conservation laws of the ferromagnetic layer. Due to the relaxation time separation, this contribution can be reduced to an effective damping. The flux of energy transferred between the ferromagnet and the spin polarized current can be positive or negative, depending on the spin accumulation configuration. The effective temperature is deduced in the activation (stationary) regime, provided that the relaxation time that couples the magnetization to the

Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires

OpenAIRE

Butschkow, Christian H.; Reiger, Elisabeth; Geißler, Stefan; Rudolph, Andreas; Soda, Marcello; Schuh, Dieter; Woltersdorf, Georg; Wegscheider, Werner; Weiss, Dieter

2011-01-01

We investigate, angle dependent, the magnetoresistance (MR) of individual self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic temperatures. The shape of the MR traces and the observed strong anisotropies in transport can be ascribed to the interplay of the negative magnetoresistance effect and a strong uniaxial anisotropy with the magnetic easy direction pointing along the wire axis. The magnetoresistance can be well described by a quantitative analysis based on the ...

Semi-strong informational efficiency in the Polish foreign exchange market

OpenAIRE

Luksz Goczek

2015-01-01

During the financial crisis a notion that the Polish exchange rate is not determined effectively was very dominant, because of a contagion effect of the global financial crisis on the Polish economy. In addition, many foreign exchange market analysts explained developments in the Polish exchange market trough a hypothesis that the Polish zloty exchange rate follows other exchange rates. This contradicts market efficiency as this would lead to profitable arbitrage possibility based on past inf...

Exchange coupling interactions in a Fe6 complex: A theoretical study using density functional theory

International Nuclear Information System (INIS)

Cauchy, Thomas; Ruiz, Eliseo; Alvarez, Santiago

2006-01-01

Theoretical methods based on density functional theory have been employed to analyze the exchange interactions in an Fe 6 complex. The calculated exchange coupling constants are consistent with an S=5 ground state and agree well with those reported previously for other Fe III polynuclear complexes. Ferromagnetic interactions may appear through exchange pathways formed by two bridging hydroxo or oxo ligands

Creation and Annihilation of Skyrmions in the Frustrated Magnets with Competing Exchange Interactions.

Science.gov (United States)

Hu, Yong; Chi, Xiaodan; Li, Xuesi; Liu, Yan; Du, An

2017-11-22

In triangular-lattice magnets, the coexistence of third-neighbor antiferromagnetic and nearest-neighbor ferromagnetic exchange interactions can induce rich magnetic phases including noncoplanar skyrmion crystals. Based on Monte Carlo simulation, we studied the dependence of magnetic phase transition on exchange interaction strength. Under the consideration of uniaxial anisotropy and magnetic field both perpendicular to the film plane, a large antiferromagnetic exchange interaction induces a high frustration. When the value of antiferromagnetic exchange interaction is one and a half times larger than the ferromagnetic one, a magnetic phase composed of canting spin stripes, never observed in the chiral magnets, forms. Interestingly, different canting spin stripes along three 120 degree propagation directions may coexist randomly in a magnetic phase, attesting that the canting spin stripes are three-fold degenerate states akin to helices and the multiple state of canting spin stripes is a circular configuration with zero skyrmion charge number. Moreover, skyrmions and antiskyrmions can be observed simultaneously in the configuration at the low temperature nearly close to 0 K, and their configuration and diameter properties are discussed. Finally, the mechanisms of skyrmion creation and annihilation are properly interpreted by comparing exchange and Zeeman energy terms.

Dynamical corrections to density-functional theory for quasiparticles in ferromagnetic 4f systems. I. T = 0 results for EuO

International Nuclear Information System (INIS)

Nolting, W.; Borstel, G.; Borgiel, W.

1987-01-01

A theory for the electronic quasiparticle spectrum of ferromagnetic 4f systems is presented and applied to the semiconductor EuO. The starting point is a d-f exchange model, which we solve exactly for T = 0. One of the results is a simple relationship between the spin-up quasiparticle energies and the ''free'' Bloch energies epsilon-c/sub m/(k), which we use to fix the epsilon-c/sub m/(k) in a highly realistic manner by performing a new self-consistent spin-polarized band-structure calculation based on density-functional theory. With the so-determined Bloch energies we investigate the spin-down quasiparticle spectrum, which exhibits even at T = 0 strong many-body effects as a consequence of spin-exchange processes between localized magnetic 4f moments and itinerant conduction electrons. We discuss in detail the spin-down quasiparticle spectral density for the ΓL direction, which should be observable in an inverse photoemission experiment. The shape of this function is strongly k dependent, revealing different types of quasiparticles. The prominent quasiparticle peaks in the spin-down quasiparticle spectral density are used to construct a quasiparticle band structure, which shows some striking deviations from the one-particle solution of the density-functional theory. Furthermore, results for the electronic self-energy and the quasiparticle density of states are presented

Anisotropic ferromagnetic behaviors in highly orientated epitaxial NiO-based thin films

Directory of Open Access Journals (Sweden)

Yu-Jun Zhang

2015-07-01

Full Text Available Antiferromagnetic materials attract a great amount of attention recently for promising antiferromagnet-based spintronics applications. NiO is a conventional antiferromagnetic semiconductor material and can show ferromagnetism by doping other magnetic elements. In this work, we synthesized epitaxial Fe-doped NiO thin films on SrTiO3 substrates with various crystal orientations by pulsed laser deposition. The room-temperature ferromagnetism of these films is anisotropic, including the saturated magnetization and the coercive field. The anisotropic magnetic behaviors of Fe-doped NiO diluted magnetic oxide system should be closely correlated to the magnetic structure of antiferromagnetic NiO base. Within the easy plane of NiO, the coercive field of the films becomes smaller, and larger coercive field while tested out of the easy plane of NiO. The saturated magnetization anisotropy is due to different strain applied by different substrates. These results lead us to more abundant knowledge of the exchange interactions in this conventional antiferromagnetic system.

Skyrmion clusters from Bloch lines in ferromagnetic films

KAUST Repository

Garanin, Dmitry A.

2017-12-29

Conditions under which various skyrmion objects emerge in experiments on thin magnetic films remain largely unexplained. We investigate numerically centrosymmetric spin lattices in films of finite thickness with ferromagnetic exchange, magnetic anisotropy, and dipole-dipole interaction. Evolution of labyrinth domains into compact topological structures on application of the magnetic field is found to be governed by the configuration of Bloch lines inside domain walls. Depending on the combination of Bloch lines, the magnetic domains evolve into individual skyrmions, biskyrmions, or more complex topological objects. While the geometry of such objects is sensitive to the parameters, their topological charge is uniquely determined by the topological charge of Bloch lines inside the magnetic domain from which the object emerges.

Ferromagnetic transitions of a spin-one Ising film in a surface and bulk transverse fields

International Nuclear Information System (INIS)

Saber, A.; Lo Russo, S.; Mattei, G.; Mattoni, A.

2002-01-01

Using the effective field theory method, we have calculated the Curie temperature of a spin-one Ising ferromagnetic film in a surface and bulk transverse fields. Numerical calculations give phase diagrams under various parameters. Surface exchange enhancement is considered. The dependence of the critical transverse field on film thickness, and phase diagrams in the fields, critical surface transverse field versus the bulk one are presented

A novel magnetoresistance induced by charge ordering in ferromagnetic/charge-ordered/ferromagnetic trilayers

Science.gov (United States)

Wang, Haiou; Li, Jinwei; Su, Kunpeng; Huo, Dexuan; Tan, Weishi

2015-10-01

Microstructure, magnetoresistance (MR) and magnetic properties of Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3/Pr0.7Sr0.3MnO3 trilayers, which are shown to be tunable with different La0.5Ca0.5MnO3 spacer thickness, are investigated. The trilayer with 6 nm thick La0.5Ca0.5MnO3 spacer show \\text{MR}∼37{%} at 195 K in 1 T and \\text{MR}∼80{%} at 220 K in 9 T, which is realized through the double-exchange mechanism. In contrast, trilayers with the thicker La0.5Ca0.5MnO3 spacer show enhanced MR at a wide low-temperature range. The obtained \\text{MR}∼52{%} at 50 K in 1 T in the trilayer with 18 nm thick La0.5Ca0.5MnO3 spacer is superior to that of other magnetic nanoscales. We surmise that this MR originates in the ferromagnetic/antiferromagnetic competition accompanied with the formation of a charge-ordered antiferromagnetic state and the collapse of the charge-ordered state at the applied magnetic field, rather than in the double-exchange mechanism. Large and tunable MR can be realized by controlling the strain state (the thickness of the La0.5Ca0.5MnO3 spacer), which can be applied in the used devices.

Strong exchange and magnetic blocking in N₂³⁻-radical-bridged lanthanide complexes.

Science.gov (United States)

Rinehart, Jeffrey D; Fang, Ming; Evans, William J; Long, Jeffrey R

2011-05-22

Single-molecule magnets approach the ultimate size limit for spin-based devices. These complexes can retain spin information over long periods of time at low temperature, suggesting possible applications in high-density information storage, quantum computing and spintronics. Notably, the success of most such applications hinges upon raising the inherent molecular spin-inversion barrier. Although recent advances have shown the viability of lanthanide-containing complexes in generating large barriers, weak or non-existent magnetic exchange coupling allows fast relaxation pathways that mitigate the full potential of these species. Here, we show that the diffuse spin of an N(2)(3-) radical bridge can lead to exceptionally strong magnetic exchange in dinuclear Ln(III) (Ln = Gd, Dy) complexes. The Gd(III) congener exhibits the strongest magnetic coupling yet observed for that ion, while incorporation of the high-anisotropy Dy(III) ion gives rise to a molecule with a record magnetic blocking temperature of 8.3 K at a sweep rate of 0.08 T s(-1).

Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2

Science.gov (United States)

Yamasaki, Yuji; Moriya, Rai; Arai, Miho; Masubuchi, Satoru; Pyon, Sunseng; Tamegai, Tsuyoshi; Ueno, Keiji; Machida, Tomoki

2017-12-01

Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature T C ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.

Modelization of nanospace interaction involving a ferromagnetic atom: a spin polarization effect study by thermogravimetric analysis.

Science.gov (United States)

Santhanam, K S V; Chen, Xu; Gupta, S

2014-04-01

Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.

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.)

Theory of weak localization in ferromagnetic (Ga,Mn)As

Czech Academy of Sciences Publication Activity Database

Garate, I.; Sinova, J.; Jungwirth, Tomáš; MacDonald, A.

2009-01-01

Roč. 79, č. 15 (2009), 155702/1-155702/13 ISSN 1098-0121 R&D Projects: GA MŠk LC510; GA AV ČR KAN400100652; GA ČR GEFON/06/E002 EU Projects: European Commission(XE) 214499 - NAMASTE; European Commission(XE) 015728 - NANOSPIN Grant - others:AV ČR(CZ) AP0801 Program:Akademická prémie - Praemium Academiae Institutional research plan: CEZ:AV0Z10100521 Keywords : electrical conductivity * exchange interactions (electron) * ferromagnetic materials * gallium arsenide * magnetic semiconductors * magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009 http://link.aps.org/doi/10.1103/PhysRevB.79.155207

Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron

Directory of Open Access Journals (Sweden)

C. P. Chui

2014-03-01

Full Text Available Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

Monte Carlo simulations of a ferromagnetic-FeF2 system

International Nuclear Information System (INIS)

Billoni, Orlando V.; Tamarit, Francisco A.; Cannas, Sergio A.

2006-01-01

In this work, we perform Monte Carlo simulations to study the magnetization reversal mechanism in ferromagnetic thin films on FeF 2 . In particular, we emulate a bilayer AFM/FM structure, where the AFM interface corresponds to an uncompensated (100) plane. The magnetic moments are modeled by classical Heisenberg spin variables. Our analysis focus on the role of the exchange interaction J AF between the FM spins and the spins belonging to the AFM interface on the reversal mechanisms of the magnetization. By simulating hysteresis loops we study the effect of temperature on the bias field

Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts

DEFF Research Database (Denmark)

Hu, C.-M.; Nitta, Junsaku; Jensen, Ane

2001-01-01

Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spi...

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

Thermal and particle size distribution effects on the ferromagnetic resonance in magnetic fluids

International Nuclear Information System (INIS)

Marin, C.N.

2006-01-01

Thermal and particle size distribution effects on the ferromagnetic resonance of magnetic fluids were theoretically investigated, assuming negligible interparticle interactions and neglecting the viscosity of the carrier liquid. The model is based on the usual approach for the ferromagnetic resonance description of single-domain magnetic particle systems, which was amended in order to take into account the finite particle size effect, the particle size distribution and the orientation mobility of the particles within the magnetic fluid. Under these circumstances the shape of the resonance line, the resonance field and the line width are found to be strongly affected by the temperature and by the particle size distribution of magnetic fluids

Characterization of Low-Molecular-Weight Heparins by Strong Anion-Exchange Chromatography.

Science.gov (United States)

Sadowski, Radosław; Gadzała-Kopciuch, Renata; Kowalkowski, Tomasz; Widomski, Paweł; Jujeczka, Ludwik; Buszewski, Bogusław

2017-11-01

Currently, detailed structural characterization of low-molecular-weight heparin (LMWH) products is an analytical subject of great interest. In this work, we carried out a comprehensive structural analysis of LMWHs and applied a modified pharmacopeial method, as well as methods developed by other researchers, to the analysis of novel biosimilar LMWH products; and, for the first time, compared the qualitative and quantitative composition of commercially available drugs (enoxaparin, nadroparin, and dalteparin). For this purpose, we used strong anion-exchange (SAX) chromatography with spectrophotometric detection because this method is more helpful, easier, and faster than other separation techniques for the detailed disaccharide analysis of new LMWH drugs. In addition, we subjected the obtained results to statistical analysis (factor analysis, t-test, and Newman-Keuls post hoc test).

Domain wall engineering through exchange bias

International Nuclear Information System (INIS)

Albisetti, E.; Petti, D.

2016-01-01

The control of the structure and position of magnetic domain walls is at the basis of the development of different magnetic devices and architectures. Several nanofabrication techniques have been proposed to geometrically confine and shape domain wall structures; however, a fine tuning of the position and micromagnetic configuration is hardly achieved, especially in continuous films. This work shows that, by controlling the unidirectional anisotropy of a continuous ferromagnetic film through exchange bias, domain walls whose spin arrangement is generally not favored by dipolar and exchange interactions can be created. Micromagnetic simulations reveal that the domain wall width, position and profile can be tuned by establishing an abrupt change in the direction and magnitude of the exchange bias field set in the system. - Highlights: • Micromagnetic simulations study domain walls in exchange biased thin films. • Novel domain wall configurations can be stabilized via exchange bias. • Domain walls nucleate at the boundary of regions with different exchange bias. • Domain wall width and spin profile are controlled by tuning the exchange bias.

Nonlinear localized excitations in magnets with a weak exchange interaction as a soliton problem

International Nuclear Information System (INIS)

Gvozdikova, M.V.; Kovalev, A.S.

1998-01-01

The spin dynamics of soliton-like localized excitations in a discrete ferromagnet chain with an easy axis anisotropy and a weak exchange interaction is studied. The connection of these excitations with longwave magnetic solitons is discussed. The localized excitation frequency dependence on exchange interaction is found for a fixed number of spin deviation. It is shown that this dependence modifies essentially when the exchange interaction becomes comparable with an anisotropy value

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

Defect induced d0 ferromagnetism in a ZnO grain boundary

KAUST Repository

Devi, Assa Aravindh Sasikala

2015-12-08

Several experimental studies have referred to the grain boundary(GB) defect as the origin of ferromagnetism in zinc oxide (ZnO). However, the mechanism of this hypothesis has never been confirmed. Present study investigates the atomic structure and the effect of point defects in a ZnOGB using the generalized gradient approximation+U approximation. The relaxed GB possesses large periodicity and channels with 8 and 10 numbered atoms having 4 and 3 fold coordination. The Znvacancy (VZn) shows a tendency to be attracted to the GB, relative to the bulk-like region. Although no magnetization is obtained from point defect-free GB, VZn induces spin polarization as large as 0.68 μB/atom to the O sites at the GB.Ferromagnetic exchange energy >150 eV is obtained by increasing the concentration of VZn and by the injection of holes into the system. Electronic structure analysis indicates that the spin polarization without external dopants originates from the O 2p orbitals, a common feature of d0semiconductors.

Defect induced d0 ferromagnetism in a ZnO grain boundary

KAUST Repository

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

2015-01-01

Several experimental studies have referred to the grain boundary(GB) defect as the origin of ferromagnetism in zinc oxide (ZnO). However, the mechanism of this hypothesis has never been confirmed. Present study investigates the atomic structure and the effect of point defects in a ZnOGB using the generalized gradient approximation+U approximation. The relaxed GB possesses large periodicity and channels with 8 and 10 numbered atoms having 4 and 3 fold coordination. The Znvacancy (VZn) shows a tendency to be attracted to the GB, relative to the bulk-like region. Although no magnetization is obtained from point defect-free GB, VZn induces spin polarization as large as 0.68 μB/atom to the O sites at the GB.Ferromagnetic exchange energy >150 eV is obtained by increasing the concentration of VZn and by the injection of holes into the system. Electronic structure analysis indicates that the spin polarization without external dopants originates from the O 2p orbitals, a common feature of d0semiconductors.

Strong Cation Exchange Chromatography in Analysis of Posttranslational Modifications: Innovations and Perspectives

Science.gov (United States)

Edelmann, Mariola J.

2011-01-01

Strong cation exchange (SCX) chromatography has been utilized as an excellent separation technique that can be combined with reversed-phase (RP) chromatography, which is frequently used in peptide mass spectrometry. Although SCX is valuable as the second component of such two-dimensional separation methods, its application goes far beyond efficient fractionation of complex peptide mixtures. Here I describe how SCX facilitates mapping of the protein posttranslational modifications (PTMs), specifically phosphorylation and N-terminal acetylation. The SCX chromatography has been mainly used for enrichment of these two PTMs, but it might also be beneficial for high-throughput analysis of other modifications that alter the net charge of a peptide. PMID:22174558

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

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.

High Br- Content CsPb(Cl yBr1- y)3 Perovskite Nanocrystals with Strong Mn2+ Emission through Diverse Cation/Anion Exchange Engineering.

Science.gov (United States)

Li, Fei; Xia, Zhiguo; Pan, Caofeng; Gong, Yue; Gu, Lin; Liu, Quanlin; Zhang, Jin Z

2018-04-11

The unification of tunable band edge (BE) emission and strong Mn 2+ doping luminescence in all-inorganic cesium lead halide perovskite nanocrystals (NCs) CsPbX 3 (X = Cl and Br) is of fundamental importance in fine tuning their optical properties. Herein, we demonstrate that benefiting from the differentiation of the cation/anion exchange rate, ZnBr 2 and preformed CsPb 1- x Cl 3 : xMn 2+ NCs can be used to obtain high Br - content Cs(Pb 1- x- z Zn z )(Cl y Br 1- y ) 3 : xMn 2+ perovskite NCs with strong Mn 2+ emission, and the Mn 2+ substitution ratio can reach about 22%. More specifically, the fast anion exchange could be realized by the soluble halide precursors, leading to anion exchange within a few seconds as observed from the strong BE emission evolution, whereas the cation exchange instead generally required at least a few hours; moreover, their exchange mechanism and dynamics process have been evaluated. The Mn 2+ emission intensity could be further varied by controlling the replacement of Mn 2+ by Zn 2+ with prolonged ion exchange reaction time. White light emission of the doped perovskite NCs via this cation/anion synergistic exchange strategy has been realized, which was also successfully demonstrated in a prototype white light-emitting diode (LED) device based on a commercially available 365 nm LED chip.

Ferromagnetism and temperature-dependent electronic structure in metallic films

International Nuclear Information System (INIS)

Herrmann, T.

1999-01-01

In this work the influence of the reduced translational symmetry on the magnetic properties of thin itinerant-electron films and surfaces is investigated within the strongly correlated Hubbard model. Firstly, the possibility of spontaneous ferromagnetism in the Hubbard model is discussed for the case of systems with full translational symmetry. Different approximation schemes for the solution of the many-body problem of the Hubbard model are introduced and discussed in detail. It is found that it is vital for a reasonable description of spontaneous ferromagnetism to be consistent with exact results concerning the general shape of the single-electron spectral density in the limit of strong Coulomb interaction between the electrons. The temperature dependence of the ferromagnetic solutions is discussed in detail by use of the magnetization curves as well as the spin-dependent quasi particle spectrum. For the investigation of thin films and surfaces the approximation schemes for the bulk system have to be generalized to deal with the reduced translational symmetry. The magnetic behavior of thin Hubbard films is investigated by use of the layer dependent magnetization as a function of temperature as well as the thickness of the film. The Curie-temperature is calculated as a function of the film thickness. Further, the magnetic stability at the surface is discussed in detail. Here it is found that for strong Coulomb interaction the magnetic stability at finite temperatures is reduced at the surface compared to the inner layers. This observation clearly contradicts the well-known Stoner picture of band magnetism and can be explained in terms of general arguments which are based on exact results in the limit of strong Coulomb interaction. The magnetic behavior of the Hubbard films can be analyzed in detail by inspecting the local quasi particle density of states as well as the wave vector dependent spectral density. The electronic structure is found to be strongly spin

Bacterial growth on ion exchange resin - investigations with a strong cationic exchanger. Pt. 3. Disinfection with peracetic acid

Energy Technology Data Exchange (ETDEWEB)

Flemming, H.C.

1984-12-01

The suitability of peracetic acid (PAA) for the disinfection of ion exchangers was investigated. 0.02% PAA is suitable for satisfactory disinfection. In this way corrosive effects are strongly reduced. Ca/sup 2+/-ions seem to protect the bacteria, therefore the disinfection should be done with the Na/sup +/-form. The disinfection has no remanent effect and therefore is not suitable for preventing bacterial aftergrowth during off-periods. A combination of silver and disinfectant can accomplish this, until a new, silver-tolerant microflora has evolved. In this case the use of 0.02% PAA is imperative, because higher concentrations will dissolve the silver. As a principle the effectiveness of disinfection procedure should be monitored bacteriologically.

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 )

Ferromagnetic nanorings

International Nuclear Information System (INIS)

Vaz, C A F; Hayward, T J; Llandro, J; Schackert, F; Morecroft, D; Bland, J A C; Klaeui, M; Laufenberg, M; Backes, D; Ruediger, U; Castano, F J; Ross, C A; Heyderman, L J; Nolting, F; Locatelli, A; Faini, G; Cherifi, S; Wernsdorfer, W

2007-01-01

Ferromagnetic metal rings of nanometre range widths and thicknesses exhibit fundamentally new spin states, switching behaviour and spin dynamics, which can be precisely controlled via geometry, material composition and applied field. Following the discovery of the 'onion state', which mediates the switching to and between vortex states, a range of fascinating phenomena has been found in these structures. In this overview of our work on ring elements, we first show how the geometric parameters of ring elements determine the exact equilibrium spin configuration of the domain walls of rings in the onion state, and we show how such behaviour can be understood as the result of the competition between the exchange and magnetostatic energy terms. Electron transport provides an extremely sensitive probe of the presence, spatial location and motion of domain walls, which determine the magnetic state in individual rings, while magneto-optical measurements with high spatial resolution can be used to probe the switching behaviour of ring structures with very high sensitivity. We illustrate how the ring geometry has been used for the study of a wide variety of magnetic phenomena, including the displacement of domain walls by electric currents, magnetoresistance, the strength of the pinning potential introduced by nanometre size constrictions, the effect of thermal excitations on the equilibrium state and the stochastic nature of switching events

Ferromagnetism and nonmetallic transport of thin-film α-FeSi(2): a stabilized metastable material.

Science.gov (United States)

Cao, Guixin; Singh, D J; Zhang, X-G; Samolyuk, German; Qiao, Liang; Parish, Chad; Jin, Ke; Zhang, Yanwen; Guo, Hangwen; Tang, Siwei; Wang, Wenbin; Yi, Jieyu; Cantoni, Claudia; Siemons, Wolter; Payzant, E Andrew; Biegalski, Michael; Ward, T Z; Mandrus, David; Stocks, G M; Gai, Zheng

2015-04-10

A metastable phase α-FeSi_{2} was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on α-FeSi_{2} (111) thin films, while the bulk material of α-FeSi_{2} is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi_{2} obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.

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.

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

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.

Magnetoelastic bending and snapping of ferromagnetic plates in oblique magnetic fields

International Nuclear Information System (INIS)

Zhou Youhe

1995-01-01

Ferritic stainless steel has been considered for structural components such as first walls and blankets of fusion power reactors because the material shows low rates of irradiation swelling. Since it is magnetizable, the magnetoelastic interaction between magnetic field and deformation of the structures in a fusion reactor is so strong that their safety is of concern due to the magnetoelastic bending, buckling and magnetic damping, etc. Basic research of the magnetoelastic characteristics of ferromagnetic plate has been paid special attention by researchers. In this paper, the magnetoelastic bending and snapping are studied for a ferromagnetic plate in an oblique magnetic field. The theoretical model is based on the variational principle where the functional is employed as real total energy in the system including external work. The obtained expression of magnetic force on the plate is the same as that derived from the dipole model when the total magnetic field in the ferromagnetic medium is considered. In order to effectively solve the nonlinearly coupled interaction problem between magnetic field and mechanical deformation, a numerical program combining the finite element method for analyzing the magnetic field with the finite difference technique for finding out the bending deformation of the plate is employed to obtain the solution of magnetoelastic bending of a soft ferromagnetic plate. The numerical calculations are carried out for the typical example of a ferromagnetic cantilevered beam-plate in an oblique magnetic field. From the bending curves, that is the tip deflection versus applied magnetic fields, the critical magnetic field for the magnetoelastic snapping is predicted by the Southwell plot. The theoretical predictions show that the critical magnetic field decreases with the increase in incident angle of the oblique magnetic field. By the effect of incident angle on the magnetic buckling, the discrepancy between theoretical and experimental data can

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.

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.

Removal of tartrazine from aqueous solutions by strongly basic polystyrene anion exchange resins.

Science.gov (United States)

Wawrzkiewicz, Monika; Hubicki, Zbigniew

2009-05-30

The removal of tartrazine from aqueous solutions onto the strongly basic polystyrene anion exchangers of type 1 (Amberlite IRA-900) and type 2 (Amberlite IRA-910) was investigated. The experimental data obtained at 100, 200, 300 and 500 mg/dm(3) initial concentrations at 20 degrees C were applied to the pseudo-first order, pseudo-second order and Weber-Morris kinetic models. The calculated sorption capacities (q(e,cal)) and the rate constant of the first order adsorption (k(1)) were determined. The pseudo-second order kinetic constants (k(2)) and capacities were calculated from the plots of t/q(t) vs. t, 1/q(t) vs. 1/t, 1/t vs. 1/q(t) and q(t)/t vs. q(t) for type 1, type 2, type 3 and type 4 of the pseudo-second order expression, respectively. The influence of phase contact time, solution pH and temperature on tartrazine removal was also discussed. The FTIR spectra of pure anion exchangers and those loaded with tartrazine were recorded, too.

Observation of ferromagnetic resonance in a microscopic sample using magnetic resonance force microscopy

International Nuclear Information System (INIS)

Zhang, Z.; Hammel, P.C.; Wigen, P.E.

1996-01-01

We report the observation of a ferromagnetic resonance signal arising from a microscopic (∼20μmx40μm) particle of thin (3μm) yttrium iron garnet film using magnetic resonance force microscopy (MRFM). The large signal intensity in the resonance spectra suggests that MRFM could become a powerful microscopic ferromagnetic resonance technique with a micron or sub-micron resolution. We also observe a very strong nonresonance signal which occurs in the field regime where the sample magnetization readily reorients in response to the modulation of the magnetic field. This signal will be the main noise source in applications where a magnet is mounted on the cantilever. copyright 1996 American Institute of Physics

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.

Mathematical simulation and calculation of the continuous countercurrent process of ion-exchange extraction of strontium from strongly mineralized solutions

International Nuclear Information System (INIS)

Nikashina, V.A.; Guryanova, L.N.; Baturova, L.L.; Venetsianov, E.V.; Ivanov, V.A.; Nikolaev, N.P.

1993-01-01

The program open-quotes Countercurrentclose quotes is developed for the simulation of a continuous ion-exchange extraction of strontium from strongly mineralized NaCl and CaCl 2 solutions using a KB-4 carboxylic cation-exchanger in the countercurrent columns. The program allows one to Calculate the conditions of Ca and Sr separation depending on the mode of operation at the sorption and regeneration stages, the residual Sr content on the overloaded sorbent, and the Sr separation on incompletely regenerated KB-4. It also makes it possible to find the optimal separation conditions. The program open-quotes Countercurrentclose quotes can be also used to simulate other ion-exchange processes

The field-induced laws of thermodynamic properties in the two-dimensional spin-1 ferromagnetic Heisenberg model with the exchange and single-ion anisotropies

International Nuclear Information System (INIS)

Pu Qiurong; Chen Yuan

2013-01-01

Green's function method is applied to investigate the two-dimensional spin-1 ferromagnetic Heisenberg model with the exchange and single-ion anisotropies. In the presence of the magnetic field, the effects of the anisotropies and field on the thermodynamic properties are obtained within the random phase approximation combining with Anderson-Callen approximation. The field-induced laws are found for the thermodynamic properties. Field dependences of heights of the susceptibility maximum and specific heat maximum fit well to power laws. The linear increase at high fields is shown for positions of the susceptibility maximum and specific heat maximum. A power law at low fields occurs for the position of the susceptibility maximum. At the positions of the maxima, the magnetization and internal energy display the power-law increase and linear decrease with the field, respectively. The exponents of the power laws are dependent of the anisotropies, as well as the slopes of the linear laws. Our results do not support the 2/3 power law which was obtained by the Landau theory.

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.

Bombarding energy dependence of nucleon exchange and energy dissipation in the strongly damped reaction 209Bi + 136Xe

International Nuclear Information System (INIS)

Wilcke, W.W.; Schroeder, W.U.; Huizenga, J.R.; Birkelund, J.R.; Randrup, J.

1980-01-01

Although considerable progress has been achieved in the understanding of strongly damped reactions at energies several MeV/u above the Coulomb barrier, some important experimental results are not yet clearly understood. Among these is the degree of correlation between the nucleon exchange and the large energy losses observed. Experimental evidence suggesting nucleon exchange as described by a one-body model to be the major component of the dissipation mechanism is discussed. It is concluded that the previously unexplained bombarding energy dependence between energy loss and fragment charge dispersion can be understood on the basis of a nucleon exchange model, provided the Pauli exclusion principle is taken into account. No necessity is seen to invoke further energy dissipation mechanisms. 7 figures

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)

Mathematical simulation and calculation of continuous countercurrent process of ion-exchange extraction of strontium from strongly mineralized solutions

International Nuclear Information System (INIS)

Nikashina, V.A.; Venitsianov, E.V.; Ivanov, V.A.; Gur'yanova, L.N.; Nikolaev, N.P.; Baturova, L.L.; Moskovskij Gosudarstvennyj Univ., Moscow

1993-01-01

A program 'Countercurrent' is developed for the simulation of a continuous ion-exchange extraction of strontium from the strongly mineralized solutions containing NaCl and CaCl 2 using carboxylic cation exchanger KB-4 in countercurrent columns. The use of the program allows one to calculate the consitions of Ca and Sr separation depending on the modes of operation at the stage of sorption as well as regeneration, to calculate a residual Sr content on an overloaded sorbent and Sr separation on an incompletely regenerated KB-4, and to find the optimal separation conditions

A variational study of the self-trapped magnetic polaron formation in double-exchange model

International Nuclear Information System (INIS)

Liu Tao; Feng Mang; Wang Kelin

2005-01-01

We study the formation of self-trapped magnetic polaron (STMP) in an antiferro/ferromagnetic double-exchange model semi-analytically by variational solutions. It is shown that the Jahn-Teller effect is not essential to the STMP formation and the STMP forms in the antiferromagnetic material within the region of the order of the lattice constant. We also confirm that no ground state STMP exists in the ferromagnetic background, but the ground state bound MP could appear due to the impurity potential

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.

Defect induced d{sup 0} ferromagnetism in a ZnO grain boundary

Energy Technology Data Exchange (ETDEWEB)

Assa Aravindh, Sasikala Devi; Schwingenschloegl, Udo; Roqan, Iman S, E-mail: iman.roqan@kaust.edu.sa [Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 2955-6900 (Saudi Arabia)

2015-12-14

Several experimental studies have referred to the grain boundary (GB) defect as the origin of ferromagnetism in zinc oxide (ZnO). However, the mechanism of this hypothesis has never been confirmed. Present study investigates the atomic structure and the effect of point defects in a ZnO GB using the generalized gradient approximation+U approximation. The relaxed GB possesses large periodicity and channels with 8 and 10 numbered atoms having 4 and 3 fold coordination. The Zn vacancy (V{sub Zn}) shows a tendency to be attracted to the GB, relative to the bulk-like region. Although no magnetization is obtained from point defect-free GB, V{sub Zn} induces spin polarization as large as 0.68 μ{sub B}/atom to the O sites at the GB. Ferromagnetic exchange energy >150 eV is obtained by increasing the concentration of V{sub Zn} and by the injection of holes into the system. Electronic structure analysis indicates that the spin polarization without external dopants originates from the O 2p orbitals, a common feature of d{sup 0} semiconductors.

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.)

Suppression of Magnetic Quantum Tunneling in a Chiral Single-Molecule Magnet by Ferromagnetic Interactions.

Science.gov (United States)

Lippert, Kai-Alexander; Mukherjee, Chandan; Broschinski, Jan-Philipp; Lippert, Yvonne; Walleck, Stephan; Stammler, Anja; Bögge, Hartmut; Schnack, Jürgen; Glaser, Thorsten

2017-12-18

Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn III -Mn III exchange from antiferromagnetic in the achiral SMM [Mn III 6 Cr III ] 3+ to ferromagnetic in the new chiral SMM RR [Mn III 6 Cr III ] 3+ . Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR [Mn III 6 Cr III ] 3+ enforce a well-defined S t = 21/2 ground state with substantially less mixing of M S substates in contrast to [Mn III 6 Cr III ] 3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U eff is smaller than the calculated energy barrier U in [Mn III 6 Cr III ] 3+ due to tunneling pathways, whereas U eff equals U in RR [Mn III 6 Cr III ] 3+ demonstrating the absence of quantum tunneling.

Surface Spin Glass Ordering and Exchange Bias in Nanometric Sm0.09Ca0.91MnO3 Manganites

Science.gov (United States)

Giri, S. K.; Nath, T. K.

2011-07-01

We have thoroughly investigated the entire magnetic state of under doped ferromagnetic insulating manganite Sm0.09Ca0.91MnO3 through temperature dependent linear and non-linear ac magnetic susceptibility and magnetization measurements. This ferromagnetic insulating manganite is found to have frequency dependent ferromagnetic to paramagnetic transition temperature at around 108 K. Exchange- bias effect are observed in field -cooled magnetic hysteresis loops for this nanoparticle. We have attributed our observation to the formation of ferromagnetic cluster which are formed as a consequence of intrinsic phase separation below certain temperature in this under doped manganites. We have carried out electronic- and magneto-transport measurements to support these observed results.

Fabry-Perot magnonic ballistic coherent transport across ultrathin ferromagnetic lamellar bcc Ni nanostructures between Fe leads

Science.gov (United States)

Khater, A.; Saim, L.; Tigrine, R.; Ghader, D.

2018-06-01

We propose thermodynamically stable systems of ultrathin lamellar bcc Ni nanostructures between bcc Fe leads, sbnd Fe[Ni(n)]Fesbnd , based on the available literature for bcc Ni overlayers on Fe(001) surfaces, and establish the necessary criteria for their structural and ferromagnetic order, for thicknesses n ≤ 6 bcc Ni monatomic layers. The system is globally ferromagnetic. A theoretical model is presented to investigate and understand the ballistic coherent scattering of Fe spin-waves, incident from the leads, at the ferromagnetic bcc Ni nanostructure. The Nisbnd Ni and Nisbnd Fe exchange are computed using the Ising effective field theory (EFT), and the magnetic ground state of the system is constructed in the Heisenberg representation. We compute the spin-wave eigenmodes localized on the bcc Ni nanostructure, using the phase field matching theory (PFMT), illustrating the effects of symmetry breaking on the confinement of localized spin excitations. The reflection and transmission scattering properties of spin-waves incident from the Fe leads, across the embedded Ni nanostructures are investigated within the framework of the same PFMT methodology. A highly refined Fabry-Perot magnonic ballistic coherent transmission spectra is observed for these sbnd Fe[Ni(n)]Fesbnd systems.

Magnetic properties of a ferromagnet spin-S, Ising, XY and Heisenberg models semi-infinites systems

International Nuclear Information System (INIS)

Masrour, R.; Hamedoun, M.; Hourmatallah, A.; Bouslykhane, K.; Benzakour, N.

2008-01-01

The magnetic properties of a ferromagnet spin-S a disordered semi-infinite system with a face-centered cubic lattice are investigated using the high-temperature series expansions technique extrapolated with Pade approximants method for Heisenberg, XY and Ising models. The reduced critical temperature of the system τ c =(k B T c )/(2S(S+1)J b ) is studied as function of the thickness of the film and the exchange interactions in the bulk, and within the surfaces J b ,J s and J perpendicular , respectively. It is found that τ c increases with the exchange interactions of surface. The magnetic phase diagrams (τ c versus the dilution x) and the percolation threshold are obtained

Ferromagnetic ordering in ThSi{sub 2} type CeAu{sub 0.28}Ge{sub 1.72}

Energy Technology Data Exchange (ETDEWEB)

Sebastian, C. Peter, E-mail: s-peter@northwestern.ed [Department of Chemistry, Northwestern University, 2145 N. Sheridan Road, Evanston, IL 60208-3113 (United States); Kanatzidis, Mercouri G., E-mail: m-kanatzidis@northwestern.ed [Department of Chemistry, Northwestern University, 2145 N. Sheridan Road, Evanston, IL 60208-3113 (United States)

2010-04-15

The compound CeAu{sub 0.28}Ge{sub 1.72} crystallizes in the ThSi{sub 2} structure type in the tetragonal space group I4{sub 1}/amd with lattice parameters a=b=4.2415(6) A c=14.640(3) A. CeAu{sub 0.28}Ge{sub 1.72} is a polar intermetallic compound having a three-dimensional Ge/Au polyanion sub-network filled with Ce atoms. The magnetic susceptibility data show Curie-Weiss law behavior above 50 K. The compound orders ferromagnetically at {approx}8 K with estimated magnetic moment of 2.48 mu{sub B}/Ce. The ferromagnetic ordering is confirmed by the heat capacity data which show a rise at {approx}8 K. The electronic specific heat coefficient (gamma) value obtained from the paramagnetic temperature range 15-25 K is {approx}124(5) mJ/ mol K{sup 2}. The entropy change due to the ferromagnetic transition is {approx}4.2 J/mol K which is appreciably reduced compared to the value of R ln(2) expected for a crystal-field-split doublet ground state and/or Kondo exchange interactions. - Graphical abstract: CeAu{sub 0.28}Ge{sub 1.72} crystallizes in the ThSi{sub 2} structure type in the tetragonal space group I4{sub 1}/amd and orders ferromagnetically at {approx}8 K.

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

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.

Experimental evidence of spin glass and exchange bias behavior in sputtered grown α-MnO{sub 2} nanorods

Energy Technology Data Exchange (ETDEWEB)

Kumar, Ashwani; Sanger, Amit; Singh, Amit Kumar; Kumar, Arvind [Nanoscience Laboratory, Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Kumar, Mohit [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Chandra, Ramesh [Nanoscience Laboratory, Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee 247667 (India)

2017-07-01

Highlights: • We have synthesized the α-MnO{sub 2} nanorods by using DC reactive sputtering. • We observed Spin glass and exchange bias behavior at low temperature in sputtered grown α-MnO{sub 2} nanorods. • Exchange bias arises due to exchange coupling of uncompensated FM spins and AFM spins at FM/AFM interface. - Abstract: Here, we present a single-step process to synthesize the α-MnO{sub 2} nanorods forest using reactive DC magnetron sputtering for the application of magnetic memories. The structural and morphological properties of the α-MnO{sub 2} nanorods were systematically studied using numerous analytical techniques, including X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy and transmission electron microscopy. The magnetic measurements suggest that the α-MnO{sub 2} nanorods exhibit spin glass and exchange bias behaviour at low temperature. Such low temperature behaviour is explained by the core-shell type structure of nanorods. Antiferromagnetic core and shell of uncompensated ferromagnetic spins leads to the formation of antiferromagnetic/ferromagnetic (AFM/FM) interfaces, which originates exchange bias in the sample.

Ferromagnetic domain structures and spin configurations measured in doped manganite

DEFF Research Database (Denmark)

He, J.Q.; Volkov, V.V.; Beleggia, Marco

2010-01-01

We report on measurements of the spin configuration across ferromagnetic domains in La0.325Pr0.3Ca0.375MnO3 films obtained by means of low-temperature Lorentz electron microscopy with in situ magnetizing capabilities. Due to the particular crystal symmetry of the material, we observe two sets of ...... and the crystal symmetry might affect the magnetoresistivity under an applied magnetic field in a strongly correlated electron system....

Correlation between charge transfer and exchange coupling in carbon-based magnetic materials

Energy Technology Data Exchange (ETDEWEB)

Nguyen, Anh Tuan, E-mail: tuanna@hus.edu.vn [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Science and Technology Department, Vietnam National University, Hanoi, 144 Xuan Thuy, Cau Giay, Hanoi (Viet Nam); Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Nomi, Ishikawa, 923-1292 Japan (Japan); Nguyen, Van Thanh; Nguyen, Huy Sinh [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Pham, Thi Tuan Anh [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Faculty of Science, College of Hai Duong, Nguyen Thi Due, Hai Duong (Viet Nam); Do, Viet Thang [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Faculty of Science, Haiphong University, 171 Phan Dang Luu, Kien An, Hai Phong (Viet Nam); Dam, Hieu Chi [Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Nomi, Ishikawa, 923-1292 Japan (Japan)

2015-10-15

Several forms of carbon-based magnetic materials, i.e. single radicals, radical dimers, and alternating stacks of radicals and diamagnetic molecules, have been investigated using density-functional theory with dispersion correction and full geometry optimization. Our calculated results demonstrate that the C{sub 31}H{sub 15} (R{sub 4}) radical has a spin of ½. However, in its [R{sub 4}]{sub 2} dimer structure, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, eight alternating stacks, R{sub 4}/D{sub 2m}/R{sub 4} (with m = 3-10), were designed. Our calculated results show that charge transfer (Δn) between R{sub 4} radicals and the diamagnetic molecule D{sub 2m} occurs with a mechanism of spin exchange (J) in stacks. The more electrons that transfer from R{sub 4} to D{sub 2m}, the stronger the ferromagnetic spin-exchange in stacks. In addition, our calculated results show that Δn can be tailored by adjusting the electron affinity (E{sub a}) of D{sub 2m}. The correlation between Δn, E{sub a}, m, and J is discussed. These results give some hints for the design of new ferromagnetic carbon-based materials.

Electric field-controlled magnetization in exchange biased IrMn/Co/PZT multilayers

International Nuclear Information System (INIS)

Huong Giang, D T; Duc, N H; Agnus, G; Maroutian, T; Lecoeur, P

2013-01-01

Electric-field modulating exchange bias and near 180° deterministic magnetization switching at room temperature are demonstrated in simple antiferromagnetic/ferromagnetic/ferroelectric (AFM/FM/FE) exchange-coupled multiferroic multilayers of IrMn/Co/PZT. A rather large exchange bias field shift up to ΔH ex /H ex = 500% was obtained. This change governs mainly the electric-field strength rather than the applied current. It is explained as being realized through the competition between the electric-field induced uniaxial and unidirectional anisotropies. These results show good prospects for low-power spintronic devices. (paper)

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.

Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

Energy Technology Data Exchange (ETDEWEB)

Sharma, Jyoti; Suresh, K. G., E-mail: suresh@iitb.ac.in [Magnetic Materials Laboratory, Department of Physics, Indian institute of Technology Bombay, Mumbai, Maharashtra 400076 (India)

2015-02-16

We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

Fault diagnosis for the heat exchanger of the aircraft environmental control system based on the strong tracking filter.

Science.gov (United States)

Ma, Jian; Lu, Chen; Liu, Hongmei

2015-01-01

The aircraft environmental control system (ECS) is a critical aircraft system, which provides the appropriate environmental conditions to ensure the safe transport of air passengers and equipment. The functionality and reliability of ECS have received increasing attention in recent years. The heat exchanger is a particularly significant component of the ECS, because its failure decreases the system's efficiency, which can lead to catastrophic consequences. Fault diagnosis of the heat exchanger is necessary to prevent risks. However, two problems hinder the implementation of the heat exchanger fault diagnosis in practice. First, the actual measured parameter of the heat exchanger cannot effectively reflect the fault occurrence, whereas the heat exchanger faults are usually depicted by utilizing the corresponding fault-related state parameters that cannot be measured directly. Second, both the traditional Extended Kalman Filter (EKF) and the EKF-based Double Model Filter have certain disadvantages, such as sensitivity to modeling errors and difficulties in selection of initialization values. To solve the aforementioned problems, this paper presents a fault-related parameter adaptive estimation method based on strong tracking filter (STF) and Modified Bayes classification algorithm for fault detection and failure mode classification of the heat exchanger, respectively. Heat exchanger fault simulation is conducted to generate fault data, through which the proposed methods are validated. The results demonstrate that the proposed methods are capable of providing accurate, stable, and rapid fault diagnosis of the heat exchanger.

Fault diagnosis for the heat exchanger of the aircraft environmental control system based on the strong tracking filter.

Directory of Open Access Journals (Sweden)

Jian Ma

Full Text Available The aircraft environmental control system (ECS is a critical aircraft system, which provides the appropriate environmental conditions to ensure the safe transport of air passengers and equipment. The functionality and reliability of ECS have received increasing attention in recent years. The heat exchanger is a particularly significant component of the ECS, because its failure decreases the system's efficiency, which can lead to catastrophic consequences. Fault diagnosis of the heat exchanger is necessary to prevent risks. However, two problems hinder the implementation of the heat exchanger fault diagnosis in practice. First, the actual measured parameter of the heat exchanger cannot effectively reflect the fault occurrence, whereas the heat exchanger faults are usually depicted by utilizing the corresponding fault-related state parameters that cannot be measured directly. Second, both the traditional Extended Kalman Filter (EKF and the EKF-based Double Model Filter have certain disadvantages, such as sensitivity to modeling errors and difficulties in selection of initialization values. To solve the aforementioned problems, this paper presents a fault-related parameter adaptive estimation method based on strong tracking filter (STF and Modified Bayes classification algorithm for fault detection and failure mode classification of the heat exchanger, respectively. Heat exchanger fault simulation is conducted to generate fault data, through which the proposed methods are validated. The results demonstrate that the proposed methods are capable of providing accurate, stable, and rapid fault diagnosis of the heat exchanger.

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.

Abnormal room temperature ferromagnetism in CuO/ZnO nanocomposites via hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Lu, Ping; Zhou, Wei; Li, Ying; Wang, Jianchun; Wu, Ping, E-mail: pingwu@tju.edu.cn

2017-03-31

Highlights: • CuO/ZnO nanocomposites have been synthesized by a one-step hydrothermal method. • The interaction between ZnO and CuO causes a modification of electronic structure. • The abnormal RTFM is discovered at the interface of CuO/ZnO. • The M{sub S} can be tuned by changing the phase ratios of the CuO and ZnO. • The indirect double-exchange model was employed to explain the origin of magnetism. - Abstract: CuO/ZnO nanocomposites have been successfully synthesized by a one-step hydrothermal method with different phase ratios. Field emission scanning electron microscopy and transmission electron microscopy results show that the obtained products of nanosheets are composed of small primary particles with an average size of about 20 nm. With the increasing proportion of CuO phase, nanosheets have significant collapse and the amount of small sheets increases obviously. The abnormal room temperature ferromagnetism was discovered at the interface between diamagnetic ZnO and antiferromagnetic CuO, which can be tuned by changing the phase ratios. Optical spectra indicate that the interaction between ZnO and CuO modifies the electronic structure of nanocomposites. XPS results verify the valence change of Cu ions and the presence of oxygen vacancies, which are ultimately responsible for the observed ferromagnetism. The indirect double-exchange model was employed to explain the origin of magnetism. Our study suggests that magnetically functional interfaces exhibit very appealing properties for novel devices.

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.

Synthesis, structure and magnetic properties of La3Co2SbO9: A double perovskite with competing antiferromagnetic and ferromagnetic interactions

International Nuclear Information System (INIS)

Franco, D.G.; Fuertes, V.C.; Blanco, M.C.; Fernández-Díaz, M.T.; Sánchez, R.D.; Carbonio, R.E.

2012-01-01

The synthesis, structural characterization, and magnetic properties of La 3 Co 2 SbO 9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2 1 /n. Co 2+ and Sb 5+ have the maximum order allowed for the La 3 Co 2 SbO 9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) Å, b=5.6842(2) Å, c=7.9748(2) Å and β=89.999(3)°. Magnetization measurements indicate the presence of ferromagnetic correlations with T C =55 K attributed to the exchange interactions for non-linear Co 2+ –O–Sb 5+ –O–Co 2+ paths. The effective magnetic moment obtained experimentally is μ exp =4.38 μ B (per mol Co 2+ ), between the theoretical one for spin only (3.87 μ B ) and spin-orbit value (6.63 μ B ), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 μ B /f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration. - Graphical abstract: Co–O–Co (Yellow octahedra only) rich zones (antiferromagnetic) are in contact with Co–O–Sb–O–Co (Red and yellow octahedra) rich zones (Ferromagnetic) to give the peculiar magnetic properties, as a consequence, a complex hysteresis loop can be observed composed by a main and irreversible curve in all the measured range, superimposed with a ferromagnetic component at low fields. Highlights: ► La 3 Co 2 SbO 9 has small Goldschmidt Tolerance Factor (t) due to the small size of La 3+ . ► Small t determines an angle for the path Co 2+ –O–Sb 5+ –O–Co 2+ of 153°. ► Ferromagnetism is attributed to exchange interactions for Co 2+ –O–Sb 5+ –O–Co 2+ paths. ► Ferromagnetic nanoclusters are embedded in an antiferromagnetic

Magnetocaloric effect (MCE): Microscopic approach within Tyablikov approximation for anisotropic ferromagnets

Energy Technology Data Exchange (ETDEWEB)

Kotelnikova, O.A.; Prudnikov, V.N. [Physical Faculty, Lomonosov State University, Department of Magnetism, Moscow (Russian Federation); Rudoy, Yu.G., E-mail: rudikar@mail.ru [People' s Friendship University of Russia, Department of Theoretical Physics, Moscow (Russian Federation)

2015-06-01

The aim of this paper is to generalize the microscopic approach to the description of the magnetocaloric effect (MCE) started by Kokorina and Medvedev (E.E. Kokorina, M.V. Medvedev, Physica B 416 (2013) 29.) by applying it to the anisotropic ferromagnet of the “easy axis” type in two settings—with external magnetic field parallel and perpendicular to the axis of easy magnetization. In the last case there appears the field induced (or spin-reorientation) phase transition which occurs at the critical value of the external magnetic field. This value is proportional to the exchange anisotropy constant at low temperatures, but with the rise of temperature it may be renormalized (as a rule, proportional to the magnetization). We use the explicit form of the Hamiltonian of the anisotropic ferromagnet and apply widely used random phase approximation (RPA) (known also as Tyablikov approximation in the Green function method) which is more accurate than the well known molecular field approximation (MFA). It is shown that in the first case the magnitude of MCE is raised whereas in the second one the MCE disappears due to compensation of the critical field renormalized with the magnetization.

Establishing exchange bias below T-N with polycrystalline Ni0.52Co0.48O/Co bilayers

DEFF Research Database (Denmark)

Berkowitz, A.E.; Hansen, Mikkel Fougt; Tang, Y.J.

2005-01-01

Exchange-coupled bilayers of polycrystalline ferromagnetic (FM) Co on antiferromagnetic (AFM) Ni0.52Co0.48O were investigated with emphasis on the issue of establishing an exchange-bias field, H-E, below the AFM ordering temperature, T-N. It was found that field-cooling the bilayers through T-N p...

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.

Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

Science.gov (United States)

Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration

The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.

Thermodynamics of the frustrated ferromagnetic spin-1/2 Heisenberg chain

International Nuclear Information System (INIS)

Richter, J; Haertel, M; Ihle, D; Drechsler, S-L

2009-01-01

We studied the thermodynamics of the one-dimensional J 1 -J 2 spin-1/2 Heisenberg chain for ferromagnetic nearest-neighbor bonds J 1 2 > 0 using full diagonalization of finite rings and a second-order Green-function formalism. Thereby we focus on J 2 1 |/4 where the ground state is still ferromagnetic, but the frustration influences the thermodynamic properties. We found that their critical indices are not changed by J 2 . The analysis of the low-temperature behavior of the susceptibility χ leads to the conclusion that this behavior changes from χ ∝ T -2 at J 2 1 |/4 to χ ∝ T -3/2 at the quantum-critical point J 2 = |J 1 |/4. Another effect of the frustration is the appearance of an extra low-T maximum in the specific heat C v (T) for J 2 and |J 1 |/8, indicating its strong influence on the low-energy spectrum.

The half-metallic ferromagnetism character in Be1−xVxY (Y=Se and Te) alloys: An ab-initio study

International Nuclear Information System (INIS)

Sajjad, M.; Manzoor, Sadia; Zhang, H.X.; Noor, N.A.; Alay-e-Abbas, S.M.; Shaukat, A.; Khenata, R.

2015-01-01

Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites. - Highlights: • Density functional calculations for V-doped BeSe and BeTe are performed. • V-doped BeSe and BeTe are found to be stable half-metallic ferromagnetism. • Improved electronic properties are achieved using mBJLDA which confirm HMF. • The half-metallic gaps show non-linear variation with increasing dopant concentration

Interfacial spin cluster effects in exchange bias systems

Energy Technology Data Exchange (ETDEWEB)

Carpenter, R., E-mail: rc548@york.ac.uk; Vallejo-Fernandez, G.; O' Grady, K. [Department of Physics, The University of York, York YO10 5DD (United Kingdom)

2014-05-07

In this work, the effect of exchange bias on the hysteresis loop of CoFe is observed. The evolution of the coercivities and the shift of the hysteresis loop during the annealing process has been measured for films deposited on NiCr and Cu seed layers. Through comparison of the as deposited and field annealed loops, it is clear that for an exchange biased material, the two coercivities are due to different reversal processes. This behaviour is attributed to spin clusters at the ferromagnet/antiferromagnet interface, which behave in a similar manner to a fine particle system.

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

Thickness dependent ferromagnetism in thermally decomposed NiO thin films

Energy Technology Data Exchange (ETDEWEB)

Ravikumar, Patta; Kisan, Bhagaban; Perumal, Alagarsamy, E-mail: perumal@iitg.ernet.in

2016-11-15

We report the effects of film thickness, annealing temperature and annealing environments on thermal decomposition behavior and resulting magnetic properties of NiO (t=50–300 nm) thin films. All the NiO films were prepared directly on thermally oxidized Si at ambient temperature using magnetron sputtering technique and post annealed at different temperatures (T{sub A}) under vacuum and oxygen atmospheres. As-deposited films exhibit face centered cubic structure with large lattice constant due to strain induced during sputtering process. With increasing T{sub A}, the lattice constant decreases due to the release of strain and thickness dependent thermal decomposition reaction of NiO into Ni has been observed for the NiO films annealed at 500 °C under vacuum condition. As a result, the antiferromagnetic nature of the as-deposited NiO films transforms into ferromagnetic one with dominant thickness dependent ferromagnetic behavior at room temperature. In addition, the existence of both Ni and NiO phases in the annealed NiO films shows noticeable exchange bias under field cooling condition. The behavior of thermal decomposition was not observed for the NiO films annealed under oxygen condition which results in no detectable change in the magnetic properties. The observed results are discussed on the basis of thickness dependent thermal decomposition in NiO films with increasing T{sub A} and changing annealing conditions. - Highlights: • Preparation of highly strained single layer NiO films with different thicknesses. • Study the effects of annealing under different environments on crystal structure. • Understanding the origin of thickness dependent thermal decomposition reaction. • Investigate the role of thermal decomposition reaction on the magnetic properties. • Study the interaction between NiO and Ni phases on the exchange bias mechanism.

Transition from weak ferromagnetism to metamagnetism in the itinerant-electron system Y{sub 1-x}La{sub x}Co{sub 9}Si{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Nishiyama, M; Kohara, T [Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297 (Japan); Nakamura, H [Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501 (Japan)

2010-01-15

The magnetism of solid solution Yi{sub 1-x}La{sub x}Co{sub 9}Si{sub 4} between strongly enhanced Pauli paramagnetic LaCo{sub 9}Si{sub 4} and weakly ferromagnetic YCo{sub 9}Si{sub 4} has been investigated. The Curie temperature T{sub C} in the ferromagnetic region and the metamagnetic transition field H{sub M} in the paramagnetic region change continuously against x and approach zero at the same composition x {approx_equal} 0.15, suggesting the presence of a critical point from spontaneous to field-induced ferromagnetism.

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.

Phenomenological description of anisotropy effects in some ferromagnetic superconductors

Energy Technology Data Exchange (ETDEWEB)

Shopova, Diana V., E-mail: sho@issp.bas.bg [TCCM Research Group, Institute of Solid State Physics, Bulgarian Academy of Sciences, BG-1784 Sofia (Bulgaria); Todorov, Michail D. [Department of Applied Mathematics and Computer Science, Technical University of Sofia, 1000 Sofia (Bulgaria)

2015-07-03

We study phenomenologically the role of anisotropy in ferromagnetic superconductors UGe{sub 2}, URhGe, and UCoGe for the description of their phase diagrams. We use the Ginzburg–Landau free energy in its uniform form as we will consider only spatially independent solutions. This is an expansion of previously derived results where the effect of Cooper-pair and crystal anisotropies is not taken into account. The three compounds are separately discussed with the special stress on UGe{sub 2}. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed. - Highlights: • Anisotropic Landau energy for description of ferromagnetic superconductors is proposed. • Meissner phases are described with their existence and stability conditions. • The application of the model to UGe{sub 2} is discussed. • The limitations to apply the model for description of experimental data are explained.

Transport coefficients of Dirac ferromagnet: Effects of vertex corrections

Science.gov (United States)

Fujimoto, Junji

2018-03-01

As a strongly spin-orbit-coupled metallic model with ferromagnetism, we have considered an extended Stoner model to the relativistic regime, named Dirac ferromagnet in three dimensions. In a previous paper [J. Fujimoto and H. Kohno, Phys. Rev. B 90, 214418 (2014), 10.1103/PhysRevB.90.214418], we studied the transport properties giving rise to the anisotropic magnetoresistance (AMR) and the anomalous Hall effect (AHE) with the impurity potential being taken into account only as the self-energy. The effects of the vertex corrections (VCs) to AMR and AHE are reported in this paper. AMR is found not to change quantitatively when the VCs are considered, although the transport lifetime is different from the one-electron lifetime and the charge current includes additional contributions from the correlation with spin currents. The side-jump and the skew-scattering contributions to AHE are also calculated. The skew-scattering contribution is dominant in the clean case as can be seen in the spin Hall effect in the nonmagnetic Dirac electron system.

SOLVENT EFFECTS IN THE LIQUID-PHASE HYDRATION OF CYCLOHEXENE CATALYZED BY A MACROPOROUS STRONG ACID ION-EXCHANGE RESIN

NARCIS (Netherlands)

PANNEMAN, HJ; BEENACKERS, AACM

1992-01-01

The liquid-phase hydration of cyclohexene, a pseudo first order reversible reaction catalyzed by a strong acid ion exchange resin, macroporous Amberlite XE 307, was investigated in solvent mixtures of water and sulfolane. A decrease by a factor of 3 and 6 is observed in the experimentally measured

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

CONAN—The cruncher of local exchange coefficients for strongly interacting confined systems in one dimension

DEFF Research Database (Denmark)

Loft, Niels Jakob Søe; Kristensen, Lasse Bjørn; Thomsen, Anders

2016-01-01

We consider a one-dimensional system of particles with strong zero-range interactions. This system can be mapped onto a spin chain of the Heisenberg type with exchange coefficients that depend on the external trap. In this paper, we present an algorithm that can be used to compute these exchange...... coefficients. We introduce an open source code CONAN (Coefficients of One-dimensional N-Atom Networks) which is based on this algorithm. CONAN works with arbitrary external potentials and we have tested its reliability for system sizes up to around 35 particles. As illustrative examples, we consider a harmonic...... trap and a box trap with a superimposed asymmetric tilted potential. For these examples, the computation time typically scales with the number of particles as O(N3.5±0.4). Computation times are around 10 s for N=10 particles and less than 10 min for N=20 particles....

Theoretical study on the perpendicular anisotropic magnetoresistance using Rashba-type ferromagnetic model

Science.gov (United States)

Yahagi, Y.; Miura, D.; Sakuma, A.

2018-05-01

We investigated the anisotropic magnetoresistance (AMR) effects in ferromagnetic-metal multi-layers stacked on non-magnetic insulators in the context of microscopic theory. We represented this situation with tight-binding models that included the exchange and Rashba fields, where the Rashba field was assumed to originate from spin-orbit interactions as junction effects with the insulator. To describe the AMR ratios, the DC conductivity was calculated based on the Kubo formula. As a result, we showed that the Rashba field induced both perpendicular and in-plane AMR effects and that the perpendicular AMR effect rapidly decayed with increasing film thickness.

Anisotropic sensor and memory device with a ferromagnetic tunnel barrier as the only magnetic element.

Science.gov (United States)

Lόpez-Mir, L; Frontera, C; Aramberri, H; Bouzehouane, K; Cisneros-Fernández, J; Bozzo, B; Balcells, L; Martínez, B

2018-01-16

Multiple spin functionalities are probed on Pt/La 2 Co 0.8 Mn 1.2 O 6 /Nb:SrTiO 3 , a device composed by a ferromagnetic insulating barrier sandwiched between non-magnetic electrodes. Uniquely, La 2 Co 0.8 Mn 1.2 O 6 thin films present strong perpendicular magnetic anisotropy of magnetocrystalline origin, property of major interest for spintronics. The junction has an estimated spin-filtering efficiency of 99.7% and tunneling anisotropic magnetoresistance (TAMR) values up to 30% at low temperatures. This remarkable angular dependence of the magnetoresistance is associated with the magnetic anisotropy whose origin lies in the large spin-orbit interaction of Co 2+ which is additionally tuned by the strain of the crystal lattice. Furthermore, we found that the junction can operate as an electrically readable magnetic memory device. The findings of this work demonstrate that a single ferromagnetic insulating barrier with strong magnetocrystalline anisotropy is sufficient for realizing sensor and memory functionalities in a tunneling device based on TAMR.

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.

Inhomogeneity in the spin channel of ferromagnetic CMR manganites

Energy Technology Data Exchange (ETDEWEB)

Heffner, R.H.; Sonier, J.E.; MacLaughlin, D.E.; Nieuwenhuys, G.J.; Mezei, F.; Ehlers, G.; Mitchell, J.F.; Cheong, S.-W

2003-02-01

Colossal magnetoresistance manganites are archetypes in which to study the strong coupling between spin, charge and lattice degrees of freedom in materials. We present muon spin-lattice relaxation data in ferromagnetic (FM) ground state materials from the manganite series La{sub 1-x}Ca{sub x}MnO{sub 3} and La{sub 1-x-y}Pr{sub y}Ca{sub x}MnO{sub 3}. These measurements reveal several characteristic relaxation modes arising from the strong spin-charge-lattice interactions. We also present results from neutron-spin-echo spectroscopy, which directly measures the spin-spin correlation function in a time domain comparable to {mu}SR. A qualitative model for the FM transition in the manganites involving microscopic phase separation is suggested by these data.

Laser-induced ultrafast demagnetization time and spin moment in ferromagnets: First-principles calculation

Energy Technology Data Exchange (ETDEWEB)

Zhang, G. P., E-mail: gpzhang@indstate.edu [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States); Si, M. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); George, Thomas F. [Office of the Chancellor and Center for Nanoscience, Departments of Chemistry and Biochemistry and Physics and Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121 (United States)

2015-05-07

When a laser pulse excites a ferromagnet, its spin undergoes a dramatic change. The initial demagnetization process is very fast. Experimentally, it is found that the demagnetization time is related to the spin moment in the sample. In this study, we employ the first-principles method to directly simulate such a process. We use the fixed spin moment method to change the spin moment in ferromagnetic nickel, and then we employ the Liouville equation to couple the laser pulse to the system. We find that in general the dependence of demagnetization time on the spin moment is nonlinear: It decreases with the spin moment up to a point, after which an increase with the spin moment is observed, followed by a second decrease. To understand this, we employ an extended Heisenberg model, which includes both the exchange interaction and spin-orbit coupling. The model directly links the demagnetization rate to the spin moment itself and demonstrates analytically that the spin relaxes more slowly with a small spin moment. A future experimental test of our predictions is needed.

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...

In silico CrNF, a half-metallic ferromagnetic nitride–fluoride mimicking CrO2

International Nuclear Information System (INIS)

Matar, Samir F.

2014-01-01

Isoelectronic with CrO 2 , CrNF is proposed in silico based on rutile derived structures with DFT computations. The ground state structure defined from cohesive energies is of MgUO 4 -type, characterized by short covalent Cr–N and long ionic Cr–F distances. Like CrO 2 it is a half-metallic ferromagnet with M=2 μ B /FU integer magnetization with reduced band gap at minority spins. Major difference of magnetic response to pressure characterizes CrNF as a soft ferromagnet versus hard magnetic CrO 2 . The chemical bonding properties point to prevailing covalent Cr–N versus ionic Cr–F bonding. Different synthesis routes are examined. - Highlights: • DFT identification of CrNF is based on isoelectronicity and rutile derivatives. • Similarly to CrO 2 , CrNF is a half-metallic ferromagnet with reduced band gap. • Strong pressure dependence of magnetization of CrNF oppositely to CrO 2 . • Covalent Cr–N bonding prevails in spite of the presence of ionic Cr–F. • Cohesive energies favor the synthesis for which protocols are proposed

Exchange and spin-fluctuation superconducting pairing in the strong correlation limit of the Hubbard model

International Nuclear Information System (INIS)

Plakida, N. M.; Anton, L.; Adam, S. . Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, PO Box MG-6, RO-76900 Bucharest - Magurele; RO); Adam, Gh. . Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, PO Box MG-6, RO-76900 Bucharest - Magurele; RO)

2001-01-01

A microscopical theory of superconductivity in the two-band singlet-hole Hubbard model, in the strong coupling limit in a paramagnetic state, is developed. The model Hamiltonian is obtained by projecting the p-d model to an asymmetric Hubbard model with the lower Hubbard subband occupied by one-hole Cu d-like states and the upper Hubbard subband occupied by two-hole p-d singlet states. The model requires two microscopical parameters only, the p-d hybridization parameter t and the charge-transfer gap Δ. It was previously shown to secure an appropriate description of the normal state properties of the high -T c cuprates. To treat rigorously the strong correlations, the Hubbard operator technique within the projection method for the Green function is used. The Dyson equation is derived. In the molecular field approximation, d-wave superconducting pairing of conventional hole (electron) pairs in one Hubbard subband is found, which is mediated by the exchange interaction given by the interband hopping, J ij = 4 (t ij ) 2 / Δ. The normal and anomalous components of the self-energy matrix are calculated in the self-consistent Born approximation for the electron-spin-fluctuation scattering mediated by kinematic interaction of the second order of the intraband hopping. The derived numerical and analytical solutions predict the occurrence of singlet d x 2 -y 2 -wave pairing both in the d-hole and singlet Hubbard subbands. The gap functions and T c are calculated for different hole concentrations. The exchange interaction is shown to be the most important pairing interaction in the Hubbard model in the strong correlation limit, while the spin-fluctuation coupling results only in a moderate enhancement of T c . The smaller weight of the latter comes from two specific features: its vanishing inside the Brillouin zone (BZ) along the lines, |k x | + |k y |=π pointing towards the hot spots and the existence of a small energy shell within which the pairing is effective. By

Coupled magnetoelastic waves in ferromagnetic shape-memory alloys

Science.gov (United States)

Bar'Yakhtar, V. G.; Danilevich, A. G.; L'Vov, V. A.

2011-10-01

The theory of the spectra of coupled magnetoelastic waves in ferromagnetic shape-memory alloys (FSMA) is developed. The possibility of an abnormally strong coupling of spin waves with the soft elastic mode at approaching the martensitic transformation (MT) temperature is disclosed. In particular the magnetoelastic waves in Ni-Mn-Ga single crystals are considered. A considerable (by an order of magnitude) reduction of the shear elastic modulus and an appropriate lowering of the transversal velocity of sound in the applied magnetic field are predicted. Optimum conditions for the experimental observation of the predicted effects are specified.

Anisotropy of the Faraday effect in the weak ferromagnet YFeO3

International Nuclear Information System (INIS)

Zenkov, A.V.; Krichevtsov, B.B.; Moskvin, A.S.; Mukimov, K.M.; Pisarev, R.V.; Ruvinshtein, M.M.

1989-01-01

An experimental investigation was made of the magnetic-field dependence of the Faraday effect in a weak ferromagnet YFeO 3 at the wavelength λ = 0.63 μm. Measurements were made for different orientations of the direction of light propagation k and of the magnetic field H. Changes in the Faraday effect in the k parallel c, H parallel a case were not proportional to changes in the component of the magnetic moment m z . A phenomenological description of the Faraday effect in YFeO 3 was used to separate the ferromagnetic, antiferromagnetic, and diamagnetic contributions to the effect. The antiferromagnetic contribution dominating the Faraday effect was strongly anisotropic. A theoretical analysis was made of the microscopic Faraday effect mechanisms in YFeO 3 using the example of a dipole-allowed transition 6 A 1g → 6 T 1u

Enhanced exchange anisotropy in IrMn/CoFeB systems and its correlation with uncompensated interfacial spins

DEFF Research Database (Denmark)

Du, Yuqing; Pan, Genhua; Moate, Roy

2010-01-01

Bottom pinned exchange bias systems of IrMn/CoFe and IrMn/CoFeB on CoFe seed layers were studied. Enhanced exchange anisotropy has been observed for IrMn/CoFeB samples annealed at 350 °C. The ferromagnetic and antiferromagnetic layers of both samples are polycrystalline and textured {110} for the...

Magnetization reversal and domain correlation for a non-collinear and out-of-plane exchange-coupled system

International Nuclear Information System (INIS)

Paul, Amitesh; Paul, N; Mattauch, Stefan

2011-01-01

We have investigated the impact of out-of-plane ferromagnetic (FM) anisotropy (which can be coincident with the direction of unidirectional anisotropy), where antiferromagnetic (AF) anisotropy is along the film plane. This provides a platform for non-collinear exchange coupling in an archetypal exchange coupled system in an unconventional way. We probe the in-plane magnetization by the depth-sensitive vector magnetometry technique. The experimental findings reveal a magnetization reversal (i) that is symmetric for both the branches of the hysteresis loop, (ii) that is characterized by vertically correlated domains associated with a strong transverse component of magnetization and (iii) that remains untrained (suppression of trained state) with field cycling. This scenario has been compared with in-plane magnetization reversal for a conventional in-plane unidirectional anisotropic case in the same system that shows usual asymmetric reversal and training for vertically uncorrelated domains. We explain the above observations for the out-of-plane case in terms of inhomogeneous magnetic states due to competing perpendicular anisotropies that result in non-collinear FM-AF coupling. This study provides direct evidence for the vertical correlation of domains mediated by out-of-plane exchange coupling.

Asymmetrically shaped hysteresis loop in exchange-biased FeNi/FeMn film

International Nuclear Information System (INIS)

Gnatchenko, S.L.; Merenkov, D.N.; Bludov, A.N.; Pishko, V.V.; Shakhayeva, Yu.A.; Baran, M.; Szymczak, R.; Novosad, V.A.

2006-01-01

The magnetization reversal of the bilayer polycrystalline FeNi(50 A)/FeMn(50 A) film sputtered in a magnetic field has been studied by magnetic and magneto-optical techniques. The external magnetic fields were applied along the easy or hard magnetization axis of the ferromagnetic permalloy layer. The asymmetry of hysteresis loop has been found. Appreciable asymmetry and the exchange bias were observed only in the field applied along the easy axis. The specific features of magnetization reversal were explained within the phenomenological model that involves high-order exchange anisotropy and misalignment of the easy axes of the antiferromagnetic and ferromagnetic layers. It has been shown that the film can exist in one of three equilibrium magnetic states in the field applied along the easy axis. The transitions between these states occur as first-order phase transitions. The observed hysteresis loop asymmetry is related to the existence of the metastable state

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)

Proximity induced ferromagnetism, superconductivity, and finite-size effects on the surface states of topological insulator nanostructures

Science.gov (United States)

Sengupta, Parijat; Kubis, Tillmann; Tan, Yaohua; Klimeck, Gerhard

2015-01-01

Bi2Te3 and Bi2Se3 are well known 3D-topological insulators (TI). Films made of these materials exhibit metal-like surface states with a Dirac dispersion and possess high mobility. The high mobility metal-like surface states can serve as building blocks for a variety of applications that involve tuning their dispersion relationship and opening a band gap. A band gap can be opened either by breaking time reversal symmetry, the proximity effect of a superconductor or ferromagnet or adjusting the dimensionality of the TI material. In this work, methods that can be employed to easily open a band gap for the TI surface states are assessed. Two approaches are described: (1) Coating the surface states with a ferromagnet which has a controllable magnetization axis. The magnetization strength of the ferromagnet is incorporated as an exchange interaction term in the Hamiltonian. (2) An s-wave superconductor, because of the proximity effect, when coupled to a 3D-TI opens a band gap on the surface. Finally, the hybridization of the surface Dirac cones can be controlled by reducing the thickness of the topological insulator film. It is shown that this alters the band gap significantly.

Transport and pairing properties of helical edges with proximity induced superconductivity and ferromagnetism

Energy Technology Data Exchange (ETDEWEB)

Keidel, Felix; Burset, Pablo; Trauzettel, Bjoern [Institute of Theoretical Physics and Astrophysics, University of Wuerzburg, 97074 Wuerzburg (Germany); Crepin, Francois [Laboratoire de Physique Theorique de la Matiere Condensee, UPMC, Sorbonne Universites, 75252 Paris (France)

2016-07-01

The scientific interest in Quantum Spin Hall systems is far from declining. While these certainly are fascinating by themselves, there is plenty of new and exciting physics to arise when superconductivity and ferromagnetism are brought into the game. The strong constraint of helicity in the edge states of a two-dimensional topological insulator is responsible for an intimate relation between the allowed scattering processes in a hybrid junction and the parameters of the system, namely the superconducting order parameter and the magnetic field. In our work, we study a helical liquid in proximity to a conventional s-wave superconductor and ferromagnetic insulators by means of a Green's function analysis. The ferromagnet gives rise to sub-gap Andreev/Majorana bound states and non-local crossed Andreev reflection (CAR), both of which decisively affect the pairing and transport properties of the junction. As a result, the simple s-wave symmetry of the superconductor is enriched and unconventional odd-frequency triplet superconductivity emerges. Strikingly, we have identified a setup that favors CAR over electron co-tunneling and may allow for the indirect measurement of the symmetries of the superconducting order parameter.

Unusual metal-insulator transition in disordered ferromagnetic films

International Nuclear Information System (INIS)

Muttalib, K.A.; Wölfle, P.; Misra, R.; Hebard, A.F.

2012-01-01

We present a theoretical interpretation of recent data on the conductance near and farther away from the metal-insulator transition in thin ferromagnetic Gd films of thickness b≈2-10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d=3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L φ ≲b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal-insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.

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.

Anomalous magnetic viscosity in α-Fe(Co)/(Nd,Pr)2Fe14B exchange-spring magnet

International Nuclear Information System (INIS)

Hai, Nguyen Hoang; Chau, Nguyen; Ngo, Duc-The; Gam, Duong Thi Hong

2011-01-01

This article presents an anomalous magnetic viscosity in α-Fe(Co)/(Nd,Pr) 2 Fe 14 B exchange-spring magnet. A similar effect has been observed in non-interacting or weakly interacting systems but not in a strong interacting magnetic systems. We reported a new procedure to measure magnetic relaxation under various magnetic fields. Changing the applied magnetic field by different field protocols during the reversal process, we found that a memory effect of the magnetization appeared if the field change is large enough. The mechanism of the phenomenon can be explained in the model of conventional magnetic reversal in strong ferromagnetic systems with an energy barrier distribution. The study of such magnetic relaxations can provide some information related to the energy barrier distribution function. - Highlights: → The memory effect was observed in a strong magnetically interacting system. → The memory effect on hard magnets can be explained by conventional reversal mechanism. → And it provides some information of the energy barrier for the reversal of magnetic moments.

Ferromagnetism in CVT grown tungsten diselenide single crystals with nickel doping

Science.gov (United States)

Habib, Muhammad; Muhammad, Zahir; Khan, Rashid; Wu, Chuanqiang; Rehman, Zia ur; Zhou, Yu; Liu, Hengjie; Song, Li

2018-03-01

Two dimensional (2D) single crystal layered transition materials have had extensive consideration owing to their interesting magnetic properties, originating from their lattices and strong spin-orbit coupling, which make them of vital importance for spintronic applications. Herein, we present synthesis of a highly crystalline tungsten diselenide layered single crystal grown by chemical vapor transport technique and doped with nickel (Ni) to tailor its magnetic properties. The pristine WSe2 single crystal and Ni-doped crystal were characterized and analyzed for magnetic properties using both experimental and computational aspects. It was found that the magnetic behavior of the 2D layered WSe2 crystal changed from diamagnetic to ferromagnetic after Ni-doping at all tested temperatures. Moreover, first principle density functional theory (DFT) calculations further confirmed the origin of room temperature ferromagnetism of Ni-doped WSe2, where the d-orbitals of the doped Ni atom promoted the spin moment and thus largely contributed to the magnetism change in the 2D layered material.

Electric-field-induced extremely large change in resistance in graphene ferromagnets

Science.gov (United States)

Song, Yu

2018-01-01

A colossal magnetoresistance (˜100×10^3% ) and an extremely large magnetoresistance (˜1×10^6% ) have been previously explored in manganite perovskites and Dirac materials, respectively. However, the requirement of an extremely strong magnetic field (and an extremely low temperature) makes them not applicable for realistic devices. In this work, we propose a device that can generate even larger changes in resistance in a zero-magnetic field and at a high temperature. The device is composed of graphene under two strips of yttrium iron garnet (YIG), where two gate voltages are applied to cancel the heavy charge doping in the YIG-induced half-metallic ferromagnets. By calculations using the Landauer-Büttiker formalism, we demonstrate that, when a proper gate voltage is applied on the free ferromagnet, changes in resistance up to 305×10^6% (16×10^3% ) can be achieved at the liquid helium (nitrogen) temperature and in a zero magnetic field. We attribute such a remarkable effect to a gate-induced full-polarization reversal in the free ferromagnet, which results in a metal-state to insulator-state transition in the device. We also find that the proposed effect can be realized in devices using other magnetic insulators, such as EuO and EuS. Our work should be helpful for developing a realistic switching device that is energy saving and CMOS-technology compatible.

Switching behaviour of coupled antiferro- and ferromagnetic systems: exchange bias

DEFF Research Database (Denmark)

Lindgård, Per-Anker

2009-01-01

in NiO nanoparticles (Kodama and Berkowitz 1999 Phys. Rev. B 59 6321 and Lindgård 2003 J. Magn. Magn. Mater. 266 88)) in a field severely limits the exchange biasing potential. The interface between the different magnets is found to be that originally assumed by Meiklejohn and Bean (1956 Phys. Rev. 102...

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory.

Science.gov (United States)

Gómez-Coca, Silvia; Ruiz, Eliseo

2012-03-07

The magnetic properties of a new family of single-molecule magnet Ni(3)Mn(2) complexes were studied using theoretical methods based on Density Functional Theory (DFT). The first part of this study is devoted to analysing the exchange coupling constants, focusing on the intramolecular as well as the intermolecular interactions. The calculated intramolecular J values were in excellent agreement with the experimental data, which show that all the couplings are ferromagnetic, leading to an S = 7 ground state. The intermolecular interactions were investigated because the two complexes studied do not show tunnelling at zero magnetic field. Usually, this exchange-biased quantum tunnelling is attributed to the presence of intermolecular interactions calculated with the help of theoretical methods. The results indicate the presence of weak intermolecular antiferromagnetic couplings that cannot explain the ferromagnetic value found experimentally for one of the systems. In the second part, the goal is to analyse magnetic anisotropy through the calculation of the zero-field splitting parameters (D and E), using DFT methods including the spin-orbit effect.

Exchange bias and asymmetric hysteresis loops from a microscopic model of core/shell nanoparticles

International Nuclear Information System (INIS)

Iglesias, Oscar; Batlle, Xavier; Labarta, Amilcar

2007-01-01

We present Monte Carlo simulations of hysteresis loops of a model of a magnetic nanoparticle with a ferromagnetic core and an antiferromagnetic shell with varying values of the core/shell interface exchange coupling which aim to clarify the microscopic origin of exchange bias observed experimentally. We have found loop shifts in the field direction as well as displacements along the magnetization axis that increase in magnitude when increasing the interfacial exchange coupling. Overlap functions computed from the spin configurations along the loops have been obtained to explain the origin and magnitude of these features microscopically

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.

Enhanced room temperature ferromagnetism in electrodeposited Co-doped ZnO nanostructured thin films by controlling the oxygen vacancy defects

Energy Technology Data Exchange (ETDEWEB)

Simimol, A. [Nanomaterials Research Lab, Surface Engineering Division, CSIR-National Aerospace Laboratories, Post Bag No. 1779, Bangalore 560017 (India); Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Anappara, Aji A. [Department of Physics, National Institute of Technology Calicut, Calicut 673601 (India); Greulich-Weber, S. [Department of Physics, Nanophotonic Materials, Faculty of Science, University of Paderborn, 33095 Paderborn (Germany); Chowdhury, Prasanta [Nanomaterials Research Lab, Surface Engineering Division, CSIR-National Aerospace Laboratories, Post Bag No. 1779, Bangalore 560017 (India); Barshilia, Harish C., E-mail: harish@nal.res.in

2015-06-07

We report the growth of un-doped and cobalt doped ZnO nanostructures fabricated on FTO coated glass substrates using electrodeposition method. A detailed study on the effects of dopant concentration on morphology, structural, optical, and magnetic properties of the ZnO nanostructures has been carried out systematically by varying the Co concentration (c.{sub Co}) from 0.01 to 1 mM. For c.{sub Co }≤ 0.2 mM, h-wurtzite phase with no secondary phases of Co were present in the ZnO nanostructures. For c.{sub Co} ≤ 0.2 mM, the photoluminescence spectra exhibited a decrease in the intensity of ultraviolet emission as well as band-gap narrowing with an increase in dopant concentration. All the doped samples displayed a broad emission in the visible range and its intensity increased with an increase in Co concentration. It was found that the defect centers such as oxygen vacancies and zinc interstitials were the source of the visible emission. The X-ray photoelectron spectroscopy studies revealed, Co was primarily in the divalent state, replacing the Zn ion inside the tetrahedral crystal site of ZnO without forming any cluster or secondary phases of Co. The un-doped ZnO nanorods exhibited diamagnetic behavior and it remained up to a c.{sub Co} of 0.05 mM, while for c.{sub Co }> 0.05 mM, the ZnO nanostructures exhibited ferromagnetic behavior at room temperature. The coercivity increased to 695 G for 0.2 mM Co-doped sample and then it decreased for c.{sub Co }> 0.2 mM. Our results illustrate that up to a threshold concentration of 0.2 mM, the strong ferromagnetism is due to the oxygen vacancy defects centers, which exist in the Co-doped ZnO nanostructures. The origin of strong ferromagnetism at room temperature in Co-doped ZnO nanostructures is attributed to the s-d exchange interaction between the localized spin moments resulting from the oxygen vacancies and d electrons of Co{sup 2+} ions. Our findings provide a new insight for tuning the

Magnetic behavior of Van Vleck ions and an electron gas interacting by exchange

International Nuclear Information System (INIS)

Palermo, L.; Silva, X.A. da.

1980-01-01

The magnetic behavior of a model in which Van Vleck ions, under the action of a crystal field, interacting by exchange with an electron gas is investigated. The condition of onset of ferromagnetism and the behavior of the critical temperature, band and ionic magnetizations (and susceptibilities) versus temperature, as a function of the band width, exchange interaction and the crystal field splitting energy parameters are obtained within an approximation equivalent to a molecular field formulation. (Author) [pt

Spin-polarized carrier injection effect in ferromagnetic semiconductor/diffusive semiconductor/superconductor junctions

Energy Technology Data Exchange (ETDEWEB)

Akazaki, T [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198 Japan (Japan); Sawa, Y; Yokoyama, T; Tanaka, Y [Department of Applied Physics, Nagoya University, Nagoya, 464-8603 Japan (Japan); Golubov, A A [Faculty of Science and Technology, University of Twente, Enschede (Netherlands); Munekata, H [Image Science and Engineering Lab., Tokyo Institute of Technology, Yokohama, Kanagawa, 226-8503 Japan (Japan); Nishizawa, N; Takayanagi, H [International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 3-13 Sakura, Tsukuba, 305-0003 Japan (Japan)], E-mail: h-taka@rs.kagu.tus.ac.jp

2009-02-01

We study the transport properties of a p-InMnAs/n-InAs/Nb junction where a p-InMnAs can be regarded as a spin injector. Differential conductance of the n-InAs channel is measured as a function of injection current from p-InMnAs or from Nb at 20 mK. A conductance minimum appears at zero-bias voltage with no current injection. As the injection current from p-InMnAs increases, the minimum gradually disappears. This conductance behaviour is very different from that of the injection case from Nb. We also calculate the conductance in the n-InAs channel by taking account of the exchange field in the InAs channel that is induced by InMnAs ferromagnet. The difference between the conductance behaviours on injection current direction can be explained by the inverse proximity effect that the exchange field is also induced in the superconducting electrode.

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...

Comparative study on bromide and iodide ion-isotopic exchange reactions using strongly basic anion exchange resin Duolite A-113

International Nuclear Information System (INIS)

Lokhande, R.S.; Dole, M.H.; Singare, P.U.

2006-01-01

Kinetics of ion-isotopic exchange reaction was studied using industrial grade ion exchange resin Duolite A-113. The radioactive isotopes 131 I and 82 Br were used to trace the ion-isotopic exchange reaction. The experiments were performed in the temperature range of 26.0degC to 43.0degC and the concentration of external ionic solution varying from 0.005 M to 0.100 M. For bromide ion-isotopic exchange reaction, the calculated values of specific reaction rate, initial rate of bromide ion exchange, and amount of bromide ions exchanged were obtained higher than that for iodide ion-isotopic exchange reaction under identical experimental conditions. The observed variation in the results for two ion-isotopic exchange reactions was due to the difference in the ionic size of bromide and iodide ions. (author)

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

Spin supercurrent in Josephson contacts with noncollinear ferromagnets

International Nuclear Information System (INIS)

Shomali, Zahra; Zareyan, Malek; Belzig, Wolfgang

2011-01-01

We present a theoretical study of the Josephson coupling of two superconductors that are connected through a diffusive contact consisting of noncollinear ferromagnetic domains. The leads are conventional s-wave superconductors with a phase difference of ψ. Firstly, we consider a contact with two domains with magnetization vectors misoriented by an angle θ. Using the quantum circuit theory, we found that in addition to the charge supercurrent, which shows a 0-π transition relative to the angle θ, a spin supercurrent with a spin polarization normal to the magnetization vectors flows between the domains. While the charge supercurrent is odd in ψ and even in θ, the spin supercurrent is even in ψ and odd in θ. Furthermore, with asymmetric insulating barriers at the interfaces of the junction, the system may experience an antiferromagnetic-ferromagnetic phase transition for ψ=π. Secondly, we discuss the spin supercurrent in an extended magnetic texture with multiple domain walls. We find the position-dependent spin supercurrent. While the direction of the spin supercurrent is always perpendicular to the plane of the magnetization vectors, the magnitude of the spin supercurrent strongly depends on the phase difference between the superconductors and the number of domain walls. In particular, our results reveal the high sensitivity of spin- and charge-transport in the junction to the number of domain walls in the ferromagnet. We show that superconductivity in coexistence with noncollinear magnetism can be used in a Josephson nanodevice to create a controllable spin supercurrent acting as a spin transfer torque on a system. Our results demonstrate the possibility of coupling the superconducting phase to the magnetization dynamics and, hence, constituting a quantum interface, for example between the magnetization and a superconducting qubit.

Spin-orbit torque in 3D topological insulator-ferromagnet heterostructure: crossover between bulk and surface transport

KAUST Repository

Ghosh, Sumit; Manchon, Aurelien

2017-01-01

Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our model accounts for spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large damping torque reported recently is more likely attributed to interfacial magnetoelectric effect, while spin Hall torque remains small even in the bulk-dominated regime.

Spin-orbit torque in 3D topological insulator-ferromagnet heterostructure: crossover between bulk and surface transport

KAUST Repository

Ghosh, Sumit

2017-11-29

Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our model accounts for spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large damping torque reported recently is more likely attributed to interfacial magnetoelectric effect, while spin Hall torque remains small even in the bulk-dominated regime.

Thermal expansion of two-dimensional itinerant nearly ferromagnetic metal

International Nuclear Information System (INIS)

Konno, R; Hatayama, N; Takahashi, Y; Nakano, H

2009-01-01

Thermal expansion of two-dimensional itinerant nearly ferromagnetic metal is investigated according to the recent theoretical development of magneto-volume effect for the three-dimensional weak ferromagnets. We particularly focus on the T 2 -linear thermal expansion of magnetic origin at low temperatures, so far disregarded by conventional theories. As the effect of thermal spin fluctuations we have found that the T-linear thermal expansion coefficient shows strong enhancement by assuming the double Lorentzian form of the non-interacting dynamical susceptibility justified in the small wave-number and low frequency region. It grows faster in proportional to y -1/2 as we approach the magnetic instability point than two-dimensional nearly antiferromagnetic metals with ln(1/y s ) dependence, where y and y s are the inverses of the reduced uniform and staggered magnetic susceptibilities, respectively. Our result is consistent with the Grueneisen's relation between the thermal expansion coefficient and the specific heat at low temperatures. In 2-dimensional electron gas we find that the thermal expansion coefficient is divergent with a finite y when the higher order term of non-interacting dynamical susceptibility is taken into account.

Surface ferromagnetism and superconducting properties of nanocrystalline niobium nitride

International Nuclear Information System (INIS)

Shipra, R.; Kumar, Nitesh; Sundaresan, A.

2013-01-01

Nanocrystalline δ-NbN x samples have been synthesized by reacting NbCl 5 and urea at three different temperatures. A comparison of their structural, magnetic, transport and thermal properties is reported in the present study. The size of the particles and their agglomeration extent increase with increasing reaction temperature. The sample prepared at 900 °C showed the highest superconducting transition temperature (T c ) of 16.2 K with a transition width, ∼1.8 K, as obtained from the resistivity measurement on cold-pressed bars. Above T c , magnetization measurements revealed the presence of surface ferromagnetism which coexists with superconductivity below T c . Heat capacity measurements confirm superconductivity with strong electron–phonon coupling constant. The sample prepared at 800 °C shows a lower T c (10 K) while that prepared at 700 °C exhibit no superconductivity down to the lowest temperature (3 K) measured. - Highlights: ► Synthesis of δ-NbN nanoparticles by urea nitridation of NbCl 5 . ► Superconducting transition temperature (T c ) is 16.2 K. ► Superconductivity and surface ferromagnetism coexist in the nanoparticles. ► Effect of size and agglomeration on the physical properties of nanoparticles

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.

Chemical disorder and charge transport in ferromagnetic manganites

International Nuclear Information System (INIS)

Pickett, W.E.; Singh, D.J.

1997-01-01

Disorder broadening due to randomly distributed La 3+ and A 2+ (A=Ca,Sr,Ba) cations is combined with a virtual-crystal treatment of the average system to evaluate the effects on both majority and minority transport in the ferromagnetic La 2/3 A 1/3 MnO 3 system. The low-density minority carriers which lie in the band tail are localized by disorder, while the majority carriers retain long mean free paths reflected in the observed strongly metallic conductivity. In addition to obtaining transport parameters, we provide evidence that local distortions are due to nearby ionic charges rather than to ion size considerations. copyright 1997 The American Physical Society

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

Double perovskites with strong spin-orbit coupling

Science.gov (United States)

Cook, Ashley M.

We first present theoretical analysis of powder inelastic neutron scattering experiments in Ba2FeReO6 performed by our experimental collaborators. Ba2FeReO6, a member of the double perovskite family of materials, exhibits half-metallic behavior and high Curie temperatures Tc, making it of interest for spintronics applications. To interpret the experimental data, we develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures the experimental observations. We then develop a tight-binding model of the double perovskite Ba 2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. The uncovered interplay of strong correlations and spin-orbit coupling lends partial support to our previous work, which used a local moment description to capture the spin wave dispersion found in neutron scattering measurements. We then adapt this tight-binding model to study {111}-grown bilayers of half-metallic double perovskites such as Sr2FeMoO6. The combination of spin-orbit coupling, inter-orbital hybridization and symmetry-allowed trigonal distortion leads to a rich phase diagram with tunable ferromagnetic order, topological C= +/-1, +/-2 Chern bands, and a C = +/-2 quantum anomalous Hall insulator regime. We have also performed theoretical analysis of inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO 6 and La2MgIrO6. Models with dominant Kitaev exchange seem to most naturally

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

The half-metallic ferromagnetism character in Be{sub 1−x}V{sub x}Y (Y=Se and Te) alloys: An ab-initio study

Energy Technology Data Exchange (ETDEWEB)

Sajjad, M. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Manzoor, Sadia [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Zhang, H.X. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing Key Laboratory of Work Safety Intelligent Monitoring, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Shaukat, A. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria)

2015-04-01

Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites. - Highlights: • Density functional calculations for V-doped BeSe and BeTe are performed. • V-doped BeSe and BeTe are found to be stable half-metallic ferromagnetism. • Improved electronic properties are achieved using mBJLDA which confirm HMF. • The half-metallic gaps show non-linear variation with increasing dopant concentration.

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.

Kerr microscopy study of exchange-coupled FePt/Fe exchange spring magnets

Energy Technology Data Exchange (ETDEWEB)

Hussain, Zaineb; Kumar, Dileep [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India); Reddy, V. Raghavendra, E-mail: varimalla@yahoo.com [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India); Gupta, Ajay [Amity Center for Spintronic Materials, Amity University, Noida 201303 (India)

2017-05-15

Magnetization reversal and magnetic microstructure of top soft magnetic layer (Fe) in exchange spring coupled L1{sub 0} FePt/Fe is studied using high resolution Kerr microscopy. With remnant state of the hard magnetic layer (L1{sub 0} FePt) as initial condition, magnetization loops along with magnetic domains are recorded for the top soft magnetic layer (Fe) using Kerr microscopy. Considerable shifting of Fe layer hysteresis loop from center which is similar to exchange bias phenomena is observed. It is also observed that one can tune the magnitude of hysteresis shift by reaching the remanent state from different saturating fields (H{sub SAT}) and also by varying the angle between measuring field and H{sub SAT}. The hysteresis loops and magnetic domains of top soft Fe layer demonstrate unambiguously that soft magnetic layer at remanent state in such exchange coupled system is having unidirectional anisotropy. An analogy is drawn and the observations are explained in terms of established model of exchange bias phenomena framed for field-cooled ferromagnetic - antiferromagnetic bilayer systems. - Highlights: • Kerr microscopy of top soft magnetic Fe layer in exchange spring coupled L1{sub 0} FePt (30 nm)/Fe (22 nm) is reported. • Considerable shifting of Fe layer hysteresis loop from center which is similar to exchange bias phenomena is observed. • Tuneable nature of magnitude of hysteresis shift is shown. • It is unambiguously shown that the top soft Fe magnetic layer at remanent state is having unidirectional anisotropy.

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.

Exchange Interactions on the Highest-Spin Reported Molecule: the Mixed-Valence Fe42 Complex

Science.gov (United States)

Aravena, Daniel; Venegas-Yazigi, Diego; Ruiz, Eliseo

2016-04-01

The finding of high-spin molecules that could behave as conventional magnets has been one of the main challenges in Molecular Magnetism. Here, the exchange interactions, present in the highest-spin molecule published in the literature, Fe42, have been analysed using theoretical methods based on Density Functional Theory. The system with a total spin value S = 45 is formed by 42 iron centres containing 18 high-spin FeIII ferromagnetically coupled and 24 diamagnetic low-spin FeII ions. The bridging ligands between the two paramagnetic centres are two cyanide ligands coordinated to the diamagnetic FeII cations. Calculations were performed using either small Fe4 or Fe3 models or the whole Fe42 complex, showing the presence of two different ferromagnetic couplings between the paramagnetic FeIII centres. Finally, Quantum Monte Carlo simulations for the whole system were carried out in order to compare the experimental and simulated magnetic susceptibility curves from the calculated exchange coupling constants with the experimental one. This comparison allows for the evaluation of the accuracy of different exchange-correlation functionals to reproduce such magnetic properties.

Exchange bias in Fe/Cr double superlattices

International Nuclear Information System (INIS)

Jiang, J. S.; Felcher, G. P.; Inomata, A.; Goyette, R.; Nelson, C.; Bader, S. D.

1999-01-01

Utilizing the oscillatory interlayer exchange coupling in Fe/Cr superlattices, we have constructed ''double superlattice'' structures where a ferromagnetic (F) and an antiferromagnetic (AF) Fe/Cr superlattice are coupled through a Cr spacer. The minor hysteresis loops in the magnetization are shifted from zero field, i.e., the F superlattice is exchange biased by the AF one. The double superlattices are sputter-deposited with (211) epitaxy and possess uniaxial in-plane magnetic anisotropy. The magnitude of the bias field is satisfactorily described by the classic formula for collinear spin structures. The coherent structure and insensitivity to atomic-scale roughness makes it possible to determine the spin distribution by polarized neutron reflectivity, which confirms that the spin structure is collinear. The magnetic reversal behavior of the double superlattices suggests that a realistic model of exchange bias needs to address the process of nucleating local reverse domains

Exchange bias in Fe/Cr double superlattices

International Nuclear Information System (INIS)

Jiang, J. S.; Felcher, G. P.; Inomata, A.; Goyette, R.; Nelson, C. S.; Bader, S. D.

2000-01-01

Utilizing the oscillatory interlayer exchange coupling in Fe/Cr superlattices, we have constructed ''double superlattice'' structures where a ferromagnetic (F) and an antiferromagnetic (AF) Fe/Cr superlattice are coupled through a Cr spacer. The minor hysteresis loops in the magnetization are shifted from zero field, i.e., the F superlattice is exchange biased by the AF one. The double superlattices are sputter deposited with (211) epitaxy and possess uniaxial in-plane magnetic anisotropy. The magnitude of the bias field is satisfactorily described by the classic formula for collinear spin structures. The coherent structure and insensitivity to atomic-scale roughness makes it possible to determine the spin distribution by polarized neutron reflectivity, which confirms that the spin structure is collinear. The magnetic reversal behavior of the double superlattices suggests that a realistic model of exchange bias needs to address the process of nucleating local reverse domains. (c) 2000 American Vacuum Society

Magnetic Circular X-ray Dichroism Study of Paramagnetic and Anti-Ferromagnetic States in SrFeO3 Using a 10-T Superconducting Magnet

International Nuclear Information System (INIS)

Okamoto, J.; Mamiya, K.; Fujimori, S.-I.; Okane, T.; Saitoh, Y.; Muramatsu, Y.; Fujimori, A.; Ishiwata, S.; Takano, M.

2004-01-01

Magnetic circular x-ray dichroism (MCXD) measurements in Fe 2p absorption have been done on SrFeO3, which shows a spiral anti-ferromagnetism, by using a 10-T superconducting magnet. Finite MCXD structures have been observed under magnetic field of 8 T even in the paramagnetic and anti-ferromagnetic states. The intensity of the MCXD structure at hv ∼ 710 eV increases linearly as magnetic field increases linearly and the total magnetic moments estimated by MCXD sum rules roughly corresponds to the magnetization measured by SQUID measurements. MCXD study of paramagnetic and/or anti-ferromagnetic samples can be done by using a superconducting magnet that generates a strong magnetic field enough to induce finite magnetization

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.

Strong cation exchange-type chiral stationary phase for enantioseparation of chiral amines in subcritical fluid chromatography.

Science.gov (United States)

Wolrab, Denise; Kohout, Michal; Boras, Mario; Lindner, Wolfgang

2013-05-10

A new strong cation exchange type chiral stationary phase (SCX CSP) based on a syringic acid amide derivative of trans-(R, R)-2-aminocyclohexanesulfonic acid was applied to subcritical fluid chromatography (SFC) for separation of various chiral basic drugs and their analogues. Mobile phase systems consisting of aliphatic alcohols as polar modifiers and a broad range of amines with different substitution patterns and lipophilicity were employed to evaluate the impact on the SFC retention and selectivity characteristics. The observed results point to the existence of carbonic and carbamic acid salts formed as a consequence of reactions occurring between carbon dioxide, the alcoholic modifiers and the amine species present in the sub/supercritical fluid medium, respectively. Evidence is provided that these species are essential for affecting ion exchange between the strongly acidic chiral selector units and the basic analytes, following the well-established stoichiometric displacement mechanisms. Specific trends were observed when different types of amines were used as basic additives. While ammonia gave rise to the formation of the most strongly eluting carbonic and carbamic salt species, simple tertiary amines consistently provided superior levels of enantioselectivity. Furthermore, trends in the chiral SFC separation characteristics were investigated by the systematic variation of the modifier content and temperature. Different effects of additives are interpreted in terms of changes in the relative concentration of the transient ionic species contributing to analyte elution, with ammonia-derived carbamic salts being depleted at elevated temperatures by decomposition. Additionally, in an effort to optimize SFC enantiomer separation conditions for selected analytes, the impact of the type of the organic modifier, temperature, flow rate and active back pressure were also investigated. Copyright © 2013 Elsevier B.V. All rights reserved.

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 ...

Phase separation and exchange bias effect in Ca doped EuCrO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Deng, Dongmei, E-mail: dmdeng@shu.edu.cn [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Wang, Xingyu; Zheng, Jiashun; Qian, Xiaolong [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Yu, Dehong; Sun, Dehui [Bragg Institute, Australian Nuclear Science and Technology Organization, Kirrawee DC, NSW 2232 (Australia); Jing, Chao [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Lu, Bo [Analysis and Measurement Center and Laboratory for Microstructures of Shanghai University, Shanghai 200444 (China); Kang, Baojuan; Cao, Shixun; Zhang, Jincang [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China)

2015-12-01

The rare-earth chromites have attracted increasing interests in recent years, as a member of a few single-phase multiferroic materials. We studied the structure and magnetic property of a series of Ca-doped EuCrO{sub 3} samples by using X-ray powder diffraction and Physical Property Measurement System. Phase separation, rotation of magnetization in M(T) curve and exchange bias effect have been identified. The Eu{sub 0.7}Ca{sub 0.3}CrO{sub 3} polycrystalline sample may be intrinsically phase-separated, with Cr{sup 3+}-rich, Cr{sup 4+}-rich canted antiferromagnetic regions surrounded by spin glass-like frustrated phase, resulting in several magnetic features including: (1) a broad and slow increase of M(T) curve with the decrease of temperature; (2) rotation of magnetization with increasing cooling field; (3) exchange bias and glassy magnetism. The rotation of magnetization is ascribed to the rotation of the moment of Cr{sup 4+}-rich regions, arising from the competition between exchange coupling energy and magnetostatic energy. The exchange bias effect suggests the formation of weak ferromagnetic unidirectional anisotropy during field cooling, due to the exchange coupling among weak ferromagnetic domains and surrounding spin glass-like regions. This result helps understanding the interaction among different magnetic domains and phases in a complex system. - Highlights: • Exchange bias effect and glassy magnetism were observed in Eu{sub 0.7}Ca{sub 0.3}CrO{sub 3}. • Rotation of the moments of Cr{sup 4+}-rich regions result in the rotation of magnetization in M(T) curve. • Spin glass-like regions contribute to the observed exchange bias effect.

Magnetotransport properties of Cr1−δTe thin films with strong perpendicular magnetic anisotropy

Directory of Open Access Journals (Sweden)

L. Zhou

2017-12-01

Full Text Available P-type ferromagnetic Cr1-δTe thin films with the Curie temperature of 170K were epitaxially grown on GaAs substrate. Low-temperature magnetotransport study reveals that the film has a strong perpendicular magnetic anisotropy (PMA and an anisotropic magnetoresistance (AMR ratio up to 8.1%. Furthermore, reduced anomalous Hall effect is observed at low temperatures in Cr1-δTe, suggesting the possible crossover of the contribution to AHE from the intrinsic mechanism to extrinsic skew scattering. Distinctive from conventional transition metal ferromagnets, the AMR ratio is also greatly suppressed at low temperatures. Our work demonstrates that epitaxial Cr1-δTe films are interesting platforms for studying the physics underlying the strong PMA and large AMR.

Six-state, three-level, six-fold ferromagnetic wire system

International Nuclear Information System (INIS)

Blachowicz, T.; Ehrmann, A.

2013-01-01

Six stable states at remanence were identified in iron wire samples of 6-fold spatial symmetry using micromagnetic simulations and the finite element method. Onion and domain-wall magnetic states were tailored by sample shape and guided by an applied magnetic field with a fixed in-plane direction. Different directions of externally applied magnetic fields revealed a tendency for stability or nonstability of the considered states. -- Highlights: ► In a ferromagnetic wire sample six stable states at remanence were discovered. ► Presented wires provide new effects not met in classical thin-layered solutions. ► The mechanism of working results from competing demagnetizing and exchange fields. ► For different physical conditions onion and domain-wall states were observed. ► Wire samples of 6-fold symmetry can lead to many-level information storage devices

Six-state, three-level, six-fold ferromagnetic wire system

Energy Technology Data Exchange (ETDEWEB)

Blachowicz, T., E-mail: tomasz.blachowicz@polsl.pl [Institute of Physics, Silesian University of Technology, 44-100 Gliwice (Poland); Ehrmann, A. [Faculty of Textile and Clothing Technology, Niederrhein University of Applied Sciences, 41065 Mönchengladbach (Germany)

2013-04-15

Six stable states at remanence were identified in iron wire samples of 6-fold spatial symmetry using micromagnetic simulations and the finite element method. Onion and domain-wall magnetic states were tailored by sample shape and guided by an applied magnetic field with a fixed in-plane direction. Different directions of externally applied magnetic fields revealed a tendency for stability or nonstability of the considered states. -- Highlights: ► In a ferromagnetic wire sample six stable states at remanence were discovered. ► Presented wires provide new effects not met in classical thin-layered solutions. ► The mechanism of working results from competing demagnetizing and exchange fields. ► For different physical conditions onion and domain-wall states were observed. ► Wire samples of 6-fold symmetry can lead to many-level information storage devices.

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.

Antisite-disorder driven large exchange bias effect in phase separated La{sub 1.5}Ca{sub 0.5}CoMnO{sub 6} double perovskite

Energy Technology Data Exchange (ETDEWEB)

Sahoo, R.C.; Paladhi, D. [Department of Physics, Indian Institute of Technology Kharagpur, West Bengal 721302 (India); Dasgupta, Papri; Poddar, A. [Experimental Condensed Matter Physics Division, Saha Institute of Nuclear Physics, West Bengal (India); Singh, Ripandeep; Das, A. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Nath, T.K., E-mail: tnath@phy.iitkgp.ernet.in [Department of Physics, Indian Institute of Technology Kharagpur, West Bengal 721302 (India)

2017-04-15

Investigations of structural and magnetic properties of polycrystalline hole doped double perovskite La{sub 1.5}Ca{sub 0.5}CoMnO{sub 6} has clearly revealed the existence of structural antisite-disorder (either, Co–O–Co or Mn–O–Mn) in the system. The ordering of Co{sup 2+} and Mn{sup 4+} gives rise to a ferromagnetic transition around 157 K. A spin-canted antiferromagnetic transition is found in this material at T{sub CAFM} ~9 K. The effect of antisite-disorder in the double perovskite structure is most likely the prime reason for antiferromagnetic interaction. The temperature dependent inverse susceptibility exhibits Curie-Weiss like behaviour and it yields an effective paramagnetic moment of 6.49 μ{sub B}. At very low temperature (Tstrong hysteresis loop shift with large exchange bias (EB) field of H{sub EB} ~5.5 kOe and can be tuned by the cooling field. The presence of zero-field cooled spontaneous EB effect (P-type and N-type) is confirmed to be not an experimental artefact - an inherent property of this double perovskite material. A phenomenological model has been proposed to explain the exchange coupling between the ferromagnetic and canted-antiferromagnetic interfaces of antisite-disordered La{sub 1.5}Ca{sub 0.5}CoMnO{sub 6} mainly on the basis of uncompensated interface spins. - Highlights: • Large exchange bias (EB) effect has been observed in 25% Ca doped La{sub 2}CoMnO{sub 6} antisite-disordered system. • Neutron powder diffraction analysis clearly suggested canted antiferromagnetic spin ordering at low temperature in our phase separated system. • A phenomenological model has been proposed for experimental results. • The results may be useful to acquire enough information about exchange biased interfaces for various magnetic device applications.

Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

KAUST Repository

Železný , J.; Gao, H.; Manchon, Aurelien; Freimuth, Frank; Mokrousov, Yuriy; Zemen, J.; Mašek, J.; Sinova, Jairo; Jungwirth, T.

2017-01-01

One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

KAUST Repository

Železný, J.

2017-01-10

One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

Half-metallic ferromagnetism in full-Heusler compounds ACaX2 (A = K and Rb; X = N and O)

International Nuclear Information System (INIS)

Umamaheswari, R.; Vijayalakshmi, D.; Yogeswari, M.; Kalpana, G.

2014-01-01

Electronic structure and magnetic properties of hypothetical ACaX 2 (A = K and Rb; X= N and O) compounds in full-Heusler phase have been investigated based on density functional theory (DFT) within the local density approximation (LDA). The electronic band structures and density of states of these compounds show that the spin-down electrons have metallic, and the spin-up electrons have a semi conducting gap resulting in stable half-metallic ferromagnetic behaviour. The strong spin polarization of 2p states of N and O atoms is found to be the origin of ferromagnetism which results in a total magnetic moment of 3 μB and 1 μB respectively

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

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.

Magnetic coupling at rare earth ferromagnet/transition metal ferromagnet interfaces: A comprehensive study of Gd/Ni

Science.gov (United States)

Higgs, T. D. C.; Bonetti, S.; Ohldag, H.; Banerjee, N.; Wang, X. L.; Rosenberg, A. J.; Cai, Z.; Zhao, J. H.; Moler, K. A.; Robinson, J. W. A.

2016-07-01

Thin film magnetic heterostructures with competing interfacial coupling and Zeeman energy provide a fertile ground to study phase transition between different equilibrium states as a function of external magnetic field and temperature. A rare-earth (RE)/transition metal (TM) ferromagnetic multilayer is a classic example where the magnetic state is determined by a competition between the Zeeman energy and antiferromagnetic interfacial exchange coupling energy. Technologically, such structures offer the possibility to engineer the macroscopic magnetic response by tuning the microscopic interactions between the layers. We have performed an exhaustive study of nickel/gadolinium as a model system for understanding RE/TM multilayers using the element-specific measurement technique x-ray magnetic circular dichroism, and determined the full magnetic state diagrams as a function of temperature and magnetic layer thickness. We compare our results to a modified Stoner-Wohlfarth-based model and provide evidence of a thickness-dependent transition to a magnetic fan state which is critical in understanding magnetoresistance effects in RE/TM systems. The results provide important insight for spintronics and superconducting spintronics where engineering tunable magnetic inhomogeneity is key for certain applications.

Coexistence of ferromagnetism and spin glass behavior in antiferromagnetic Y2BaCuO5

International Nuclear Information System (INIS)

Zhu, Zhonghua; Gao, Daqiang; Zhang, Jing; Shi, Zhenhua; Gao, Hua; Yang, Zhaolong; Zhang, Zhipeng; Xue, Desheng

2013-01-01

Highlights: • Room temperature ferromagnetism is observed in ultrafine Y 2 BaCuO 5 particles. • The observed ferromagnetism originates from the oxygen defects. • A very interesting spin glass transition located at about 110 K is found. -- Abstract: We report the synthesis of a series of Y 2 BaCuO 5 samples by varying the annealing temperature with a citrate pyrolysis technique. X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy observation show the formation of a columnar Y 2 BaCuO 5 phase and these samples are composed of many irregular particles with different particle size. Magnetic measurements show that these samples exhibit room temperature ferromagnetism and the saturation magnetization decreases with increasing sintering temperature. Post-heating treatment under argon atmosphere can enhance the ferromagnetism greatly, suggesting that the magnetism is attributed to the surface oxygen defects. By measuring magnetization versus temperature curves after zero field cooling with various applied magnetic fields, two magnetic phase transitions located at about 11 and 110 K are revealed. The position of the peak at about 11 K is independent of the magnetic field; the other peak, however, becomes rounder and shifts to lower temperatures with increasing the magnetic field, showing a strong field dependence. In addition, the virgin magnetization curves with the measured temperature below 110 K display an S-type. These features are suggestive of an antiferromagnetic phase transition at about 11 K and a spin glass transition at about 110 K

Positron annihilation studies of vacancy-type defects and room temperature ferromagnetism in chemically synthesized Li-doped ZnO nanocrystals

International Nuclear Information System (INIS)

Ghosh, S.; Khan, Gobinda Gopal; Mandal, K.; Thapa, Samudrajit; Nambissan, P.M.G.

2014-01-01

Highlights: • Evidence of zinc vacancy-induced intrinsic ferromagnetism in Li-doped ZnO. • Modification of defects and properties through alkali metal substitution. • Study of defect-modification using positron annihilation spectroscopy. • New way to prepare ZnO-based magnetic semiconductor for spintronic applications. -- Abstract: In this article, we have investigated the effects of Li incorporation on the lattice defects and room-temperature d 0 ferromagnetic behaviour in ZnO nanocrystals by correlating X-ray photoelectron, photoluminescence and positron annihilation spectroscopic study in details. It is found that at low doping level ( 1+ is an effective substituent of Zn site, but it prefers to occupy the interstitial positions when Li-doping exceeds 7 at.% resulting in lattice expansion and increase of particle sizes. The pristine ZnO nanocrystals exhibit ferromagnetic behaviour which is further enhanced significantly after few percentage of Li-doping in ZnO. The magnitude of both saturation magnetizations (M S ) as well as the Curie temperature (T C ) are found to increase considerably up to Li concentration of 10 at.% and then started to decrease on further Li-doping. The gradual enhancement of Zn vacancy (V Zn ) defects in ZnO nanocrystals due to Li substitution as confirmed from photoluminescence and positron annihilation spectroscopy measurements might be responsible to induce paramagnetic moments within ZnO host. The ferromagnetic exchange interaction between the localised moments of V Zn defects can be mediated though the holes arising due to Li-substitutional (Li Zn ) acceptor defects within ZnO. Hence, Li doping in ZnO favours in stabilizing considerable V Zn defects and thus helps to sustain long-range high-T C ferromagnetism in ZnO which can be a promising material in future spintronics

Positron annihilation studies of vacancy-type defects and room temperature ferromagnetism in chemically synthesized Li-doped ZnO nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Ghosh, S., E-mail: sghoshphysics@gmail.com [S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098 (India); Khan, Gobinda Gopal [Centre for Research in Nanoscience and Nanotechnology, University of Calcutta, Technology Campus, Block JD2, Sector III, Salt Lake City, Kolkata 700098 (India); Mandal, K. [S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098 (India); Thapa, Samudrajit; Nambissan, P.M.G. [Centre for Research in Nanoscience and Nanotechnology, University of Calcutta, Technology Campus, Block JD2, Sector III, Salt Lake City, Kolkata 700098 (India); Saha Institute of Nuclear Physics, Sector 1, Block AF, Bidhannagar, Kolkata 700064 (India)

2014-03-25

Highlights: • Evidence of zinc vacancy-induced intrinsic ferromagnetism in Li-doped ZnO. • Modification of defects and properties through alkali metal substitution. • Study of defect-modification using positron annihilation spectroscopy. • New way to prepare ZnO-based magnetic semiconductor for spintronic applications. -- Abstract: In this article, we have investigated the effects of Li incorporation on the lattice defects and room-temperature d{sup 0} ferromagnetic behaviour in ZnO nanocrystals by correlating X-ray photoelectron, photoluminescence and positron annihilation spectroscopic study in details. It is found that at low doping level (<7 at.%), Li{sup 1+} is an effective substituent of Zn site, but it prefers to occupy the interstitial positions when Li-doping exceeds 7 at.% resulting in lattice expansion and increase of particle sizes. The pristine ZnO nanocrystals exhibit ferromagnetic behaviour which is further enhanced significantly after few percentage of Li-doping in ZnO. The magnitude of both saturation magnetizations (M{sub S}) as well as the Curie temperature (T{sub C}) are found to increase considerably up to Li concentration of 10 at.% and then started to decrease on further Li-doping. The gradual enhancement of Zn vacancy (V{sub Zn}) defects in ZnO nanocrystals due to Li substitution as confirmed from photoluminescence and positron annihilation spectroscopy measurements might be responsible to induce paramagnetic moments within ZnO host. The ferromagnetic exchange interaction between the localised moments of V{sub Zn} defects can be mediated though the holes arising due to Li-substitutional (Li{sub Zn}) acceptor defects within ZnO. Hence, Li doping in ZnO favours in stabilizing considerable V{sub Zn} defects and thus helps to sustain long-range high-T{sub C} ferromagnetism in ZnO which can be a promising material in future spintronics.

The role of Co impurities and oxygen vacancies in the ferromagnetism of Co-doped SnO2: GGA and GGA+U studies

International Nuclear Information System (INIS)

Wang Hongxia; Yan Yu; Mohammed, Y. Sh.; Du Xiaobo; Li Kai; Jin Hanmin

2009-01-01

The electronic structure and ferromagnetic stability of Co-doped SnO 2 are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective U Co transforms the ground state of Co-doped SnO 2 to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+U Co calculations show that the pure substitutional Co defects in SnO 2 cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+U Co show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of U Co enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb U O on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+U Co calculations are not changed by the correction of band gap.

Manipulating molecule-substrate exchange interactions via graphene

Science.gov (United States)

Bhandary, Sumanta; Eriksson, Olle; Sanyal, Biplab

2013-03-01

Organometallic molecules with a 3d metal center carrying a spin offers many interesting properties, e.g., existence of multiple spin states. A recent interest has been in understanding the magnetic exchange interaction between these organometallic molecules and magnetic substrates both from experiments and theory. In this work, we will show by calculations based on density functional theory how the exchange interaction is mediated via graphene in a geometry containing iron porphyrin(FeP)/graphene/Ni(111). The exchange interaction varies from a ferromagnetic to an antiferromagnetic one depending on the lattice site and type of defect in the graphene lattice along with the switching of spin state of Fe in FeP between S=1 and S=2, which should be detectable by x-ray magnetic circular dichroism experiments. This scenario of complex magnetic couplings with large magnetic moments may offer a unique spintronic logic device. We acknowledge financial support from the Swedish Research Council, KAW foundation and the ERC(project 247062 - ASD).

Exchange rate rebounds after foreign exchange market interventions

Science.gov (United States)

Hoshikawa, Takeshi

2017-03-01

This study examined the rebounds in the exchange rate after foreign exchange intervention. When intervention is strongly effective, the exchange rate rebounds at next day. The effect of intervention is reduced slightly by the rebound after the intervention. The exchange rate might have been 67.12-77.47 yen to a US dollar without yen-selling/dollar-purchasing intervention of 74,691,100 million yen implemented by the Japanese government since 1991, in comparison to the actual exchange rate was 103.19 yen to the US dollar at the end of March 2014.

Localized magnetic excitations for a line of magnetic impurities in a transverse Ising thin film ferromagnet

International Nuclear Information System (INIS)

Leite, R.V.; Oliveira Filho, L.O. de; Milton Pereira, J.; Cottam, M.G.; Costa Filho, R.N.

2009-01-01

A Green's function method is used to obtain the spectrum of spin excitations associated with a linear array of magnetic impurities implanted in a ferromagnetic thin film. The equations of motion for the Green's functions of the anisotropic film are written in the framework of the Ising model in a transverse field. The frequencies of localized modes are calculated as a function of the interaction parameters for the exchange coupling between impurity-spin pairs, host-spin pairs, and impurity-host neighbors, as well as the effective field parameter at the impurity sites.

Experimental study of mixed ferromagnetic spin glass systems

International Nuclear Information System (INIS)

Mirebeau, I.

1987-01-01

The mixed ferromagnetic spin glass systems are characterized by a distribution of positive and negative exchange interactions whose maximum occurs at a positive value. We have undertaken an experimental study of amorphous (Fe 1-x Mn x ) .75 PBA1, polycrystalline and monocrystalline Ni 1-x Mn x and Au 1-x Fe x alloys. By Moessbauer effect, magnetization and neutron scattering, we show that below a ''canting'' temperature T K , spin components transverse to the mean magnetization become frozen. Small angle neutron scattering studies with an applied field show a magnetic ''structure'' i.e. the intensity exhibits a maximum at a finite q value for temperatures below T K . This structure has been studied as a function of temperature, applied field and concentration using both small angle neutron scattering and 3 axis spectrometry where we separate the elastic from the inelastic components. Possible interpretations of this new structure will be given [fr

Investigations of mechanical, electronic, and magnetic properties of non-magnetic MgTe and ferro-magnetic Mg0.75TM0.25Te (TM = Fe, Co, Ni): An ab-initio calculation

International Nuclear Information System (INIS)

Mahmood, Q; Alay-e-Abbas, S M; Mahmood, I; Noor, N A; Asif, Mahmood

2016-01-01

The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic (FM) Mg 0.75 TM 0.25 Te (TM = Fe, Co, Ni) in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local (spin) density approximation (mBJLDA) is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mg 0.75 TM 0.25 Te alloys in the FM phase are also presented. For electronic properties, the spin-polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the (110) plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites (Fe, Co, Ni), as well as at the non-magnetic sites (Mg, Te). It is found that the p–d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites. (paper)

Characterization of a strongly textured non-ferromagnetic Cu-33 at%Ni substrate coated with a CeO₂ buffer layer

DEFF Research Database (Denmark)

Tian, Hui; Suo, H.L.; Yue, Zhao

2013-01-01

the fraction of the cube {001}〈100〉 texture is 99.8% and the fraction of boundary misorientations with angles greater than 10 is only 5%. The material is shown to be non-ferromagnetic at typical operating temperatures for coated conductors. Furthermore, it is shown that a CeO2 buffer layer can be successfully...

Preparation and characterization of flexible ferromagnetic nanocomposites for microwave applications

International Nuclear Information System (INIS)

Thomas, Teena; Kanoth, Bipinbal P.; Nijas, C.M.; Joy, P.A.; Joseph, Joseph M.; Kuthirummal, Narayanan; Thachil, Eby T.

2015-01-01

Highlights: • Fe 3 O 4 nanoparticles (∼20 nm) were synthesised by co-precipitation method. • Nanoparticles were homogeneously distributed in natural rubber through latex stage processing. • Mechanical properties and magnetic properties of composites improved with loading Fe 3 O 4 nanoparticles. • Imaginary part of permeability increases with nanoparticle loading improving the microwave absorption characteristics. • Infrared spectra reveal strong interaction between NR and iron oxide nanoparticles. - Abstract: Magnetic Fe 3 O 4 nanoparticles (∼20 nm) were synthesized using the chemical co-precipitation method with a view of developing flexible and easily processable ferromagnetic materials with high mouldability to be used as microwave absorbers. The nanoparticles prepared were incorporated into natural rubber through latex stage processing. This novel processing method gives better dispersion of particles in the rubber matrix. The composites were characterized using XRD, SEM, vibrating sample magnetometer, dynamic mechanical analyzer, cavity perturbation, thermogravimetry (TGA), and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). A notable improvement in the mechanical properties of composites was observed upon adding Fe 3 O 4 particles. Magnetic and microwave characteristics of the composites indicate the formation of a flexible ferromagnetic material with good microwave absorption characteristics

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.