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Abstract: Vector hysteresis models are usually used as sub-modules of field computation software tools. When dealing with a massive field computation problem, computational efficiency and practicality of such models become crucial. In this paper, generalization of a recently proposed computationally efficient vector hysteresis model based upon interacting step functions is presented. More specifically, the model is generalized to cover vector hysteresis modeling of both isotropic and anisotropic magnetic media. Model configuration details as well as experimental testing and simulation results are given in the paper. [Copyright &y& Elsevier]

Electrical steel (ES) is the optimal material for magnetic cores of large electrical machines and transformers. This material is graded according to the value of its specific total loss ( P S ). The anisotropy of its magnetic properties is also crucial in the selection for applications. This paper presents a new method of modeling angular properties of P S in Goss oriented ES. Additionally, the proposed method can be combined with the three components P S loss model and the angular behavior can be analyzed in a frequency domain. This approach can limit labor-intensive measurements necessary to describe angular properties of P S of ES with Goss texture. It may be also a useful tool for designers of magnetic cores of electrical devices. [ABSTRACT FROM AUTHOR]

The finite-field methods can be used to intuitively learn about the optical response and find out the atomic contributions to the birefringence and SHG tensors. In this paper, the linear and second-order nonlinear optical properties of ABe 2 BO 3 F 2 family (A = K, Rb, Cs) compounds are investigated using the finite-field methods within different exchange-correlation functionals. The results show that the obtained birefringence and SHG tensors are in good agreement with the experimental values. The atomic contribution to the total birefringence was further investigated using the variation of the atomic charges, and the Born effective charges. The results show that the boron-oxygen groups give main contribution to the anisotropic birefringence. [ABSTRACT FROM AUTHOR]

In this paper a phenomenological approach, based on a generalization in two dimensions of the classical scalar Preisach model, is exploited and identified to reproduce the magnetization curves obtained by accurate micromagnetic simulations of both isotropic and anisotropic polycrystalline Fe–Si films with different values of the anisotropy constants. The identification problem is realized using a suitable set of analytical equations and performing a best fit procedure to the data obtained from micromagnetic simulations of both scalar and rotational loops. The correct reconstruction of all the magnetization processes, as well as of the associated magnetic losses, is achieved through the choice of a small number of either circular or elliptical hysterons, as well as by the implementation of a simple “moving technique” that is necessary to take into account the non-collinearity between the field and the magnetization that occurs in presence of a global uniaxial anisotropy. [ABSTRACT FROM AUTHOR]

This review paper summarizes some of results achieved during last years of our quantum dot (QD) research. We show that the QD shape (aspect ratio and elongation) significantly influences the QD photoluminescence (PL) spectrum. Magnetophotoluminescence can be used for determination of the anisotropy of QDs. While the calculated shifts in magnetic field of the energies of higher radiative transitions are found to be sensitive to the lateral elongation, the shift of the lowest transition is determined mainly by the exciton effective mass. This behavior can be used for determining both the effective mass and the elongation fairly reliably from the magnetophotoluminescence spectra displaying at least two resolved bands. Lateral shape of InAs/GaAs QDs in vertically correlated structures was also studied. We found the ways to control the QD elongation and consequently the energy difference between PL transitions by adjusting properly the spacer layer thickness. The main goal was to redshift QD PL emission towards telecommunication wavelengths of Metal Organic Vapor Phase Epitaxy prepared InAs/GaAs QDs using InGaAs or GaAsSb covering strain reducing layer (SRL). Our results proved that GaAsSb SRL improves the QD PL properties and the type I or type II band alignment can be controlled by both, GaAsSb composition and QD size. Maintaining the type I heterostructure is important for high luminescence efficiency and emission wavelength stability of QD structure. The simulation of electron structure in InAs QDs covered with GaAsSb SRL and experimental results reveal the importance of increasing QD size for obtaining a longer wavelength PL from the type I heterostructure. The type II structure of InAs/GaAs QDs covered by GaAsSb SRL with Sb content near 30% enabled us to achieve extremely long emission wavelength at 1.8 µm. The high amount of antimony in the SRL causes the preservation of QD size, and increased QD size prolongs the PL wavelength. The type II heterostructures with ground state electrons confined in InAs QDs and ground state holes in GaAsSb SRL have a strong potential in detector and solar cell applications as is demonstrated by photocurrent measurement. The dependence of built in electric field on QD PL properties is presented since this knowledge is necessary for application of QDs in different kind of electronic structures. We have experimentally demonstrated that the type I/type II transition of band structure of InAs QD with GaAsSb SRL does not depend only on the composition of the SRL, but also on other structure parameters, like QD size or intensity of electric field. [ABSTRACT FROM AUTHOR]

The anisotropy compensated Tb0.3Dy0.7Fe1.95 serves as an ideal alloy system to study the effect of microstructural refinement influencing coercivity. The cast alloy was melt spun and ball milled (with and without magnetic field) to impart microstructural refinement and correlated with the development of coercivity. Coercivity as high as 6500Oe obtained during magnetic field assisted ball milling due to fine particle size, alignment of particles and strain. Coercivity of 1000Oe obtained during melt spinning due to fine grain size and attacking faults on account of fast cooling. A comparative study highlighting coercivity mechanisms in the samples prepared by different routes has been highlighted in this paper. [ABSTRACT FROM AUTHOR]

-Abstract: This paper describes a method for determining the anisotropy parameter of thermoelectromotive force of electron–phonon drag (M) by deformation of n-Si in direction [001]; the experimental data on measuring of temperature dependence of the Hall effect, charge carrier lifetime, tensoresistance and tenso-thermoelectromotive force of transmutation doped n-Si crystals, which subjected to high-temperature annealing at during 2 and 72h, and cooled from the annealing temperature to the room one with 1, 15, 1000K/min rates, were presented. It is shown that the anisotropy of drag thermoelectromotive force is greatly increased in the experiments with the transmutation doped silicon at 85K, due to the action of high-temperature annealing. [ABSTRACT FROM AUTHOR]

Abstract: Heisenberg antiferromagnetic chains based on Ni2+ ions with integer spin S=1 exhibit intriguing behavior, e.g. the Haldane gap phase and the large-D phase. The predicted transitions between the two phases and the Neel phase has generated search for real candidate systems. Crucial to this search is the interplay between the ‘in-plane anisotropy’, i.e. the rhombic zero-field splitting (ZFS) E-term, and the ‘planar anisotropy’, i.e. the axial ZFS D-term. This paper clarifies intricate properties of orthorhombic ZFS Hamiltonians (H ZFS ) and inconsistencies revealed by critical survey of pertinent studies. Reporting the non-standard (D, E) sets with λ=E/D out of the standard range (0, 1/3) alongside the standard sets with λ∝(0, 1/3) indicates that these properties are not recognized. We show that direct comparisons of the non-standard and standard sets are meaningless and lead to incorrect conclusions on the strength of the ‘in-plane anisotropy’ (E) as compared with the ‘planar anisotropy’ (D). To remedy such problems, the ZFSP sets reported for the large-D phase candidate systems are reanalyzed using orthorhombic standardization. The six physically equivalent ZFSP sets are determined in the conventional (D, E) and Stevens ( , ) notation. These considerations help understanding intricacies inherent in orthorhombic H ZFS and provide consistent data for future modeling of ZFS parameters in the large-D phase and Haldane gap systems. [Copyright &y& Elsevier]

The angular dependence of the exchange bias (ADEB) has been investigated in detail for ferromagnetic/antiferromagnetic bilayers with noncollinear uniaxial and unidirectional anisotropies. Two different types of the jump phenomenon, complete and incomplete jump phenomena, have been proved to occur at the orientations of the intrinsic easy and hard axes. A special position for the intrinsic easy and hard axes, which makes an angular deviation of 58.2826° from the uniaixal anisotropy axis, has been deduced by analyzing the magnetization reversal processes based on the principle of minimal energy. When the angular deviation of the intrinsic easy or hard axis from the uniaxial anisotropy axis is above the critical value of 58.2826°, the complete jump phenomenon will be shown in the ADEB. On the contrary, once this angular deviation is not more than 58.2826°, the incomplete jump phenomenon occurs, and the critical angle will be observed in the ADEB. The determined formula of the critical angle is also obtained by analyzing the magnetization reversal processes. Additionally, the extreme value problem of the exchange bias is studied in this paper. The coercivity always reaches its maximum value when the external field points along the intrinsic easy axis. The minimal coercivity occurs at the orientation of the critical angle. However, there are two orientations of the applied field to gain the maximal exchange bias field. One is the direction of the intrinsic hard axis when the complete jump phenomenon occurs at this orientation. The other one is the orientation of the critical angle under the condition that the incomplete jump phenomenon takes place at the intrinsic hard axis. The numerical calculations are consistent with the involved experimental observations, indicating that our method is valid to study the ADEB and it is an effective method to achieve the maximal exchange bias field as well as the maximal or minimal coercivity by adjusting the orientation of the external field. [ABSTRACT FROM AUTHOR]

Abstract: BC5 is a newly synthesized superhard material. We present a systematic investigation of optical properties of BC5 in P3m1 and I-4m2 phases at ambient and high pressure in the framework of density functional theory with the generalized gradient approximation (GGA) in this paper. Optical properties such as dielectric function, refractive index, absorption, reflectivity and electron energy-loss spectrum are obtained successfully. The feature in the spectra of the optical parameters is discussed. Through calculation, we find BC5 is optically anisotropic. Moreover, the dielectric function exhibits a large change at 70GPa pressure for P3m1 BC5 phase, but I-4m2 phase not, indicating the stable electronic structure that the I-4m2 phase possesses. [Copyright &y& Elsevier]

Abstract: Diffuse polarized neutron scattering studies have been carried out on single crystals of pyrochlore spin ice Ho2−x Y x Ti2O7 (x=0, 0.3, and 1) to investigate the effects of doping and anisotropy on spin correlations in the system. The crystals were aligned with the (1−10) orientation coincident with the direction of neutron polarization. For all the samples studied the spin flip (SF) diffuse scattering (i.e. the in-plane component) reveals that the spin correlations can be described using a nearest-neighbour spin ice model (NNSM) at higher temperatures (T=3.6K) and a dipolar spin ice model (DSM) as the temperature is reduced (T=30mK). In the non-spin flip (NSF) channel (i.e. the out-of-plane component), the signature of strong antiferromagnetic correlations is observed for all the samples at the same temperature as the dipolar spin ice behaviour appears in the SF channel. Our studies show that the non-magnetic dopant Y does not significantly alter SF or NSF scattering for the spin ice state, even when Y doping is as high as 50%. In this paper, we focus on the experimental results of the highly doped spin ice HoYTi2O7 and compare our results with pure spin ice Ho2Ti2O7. The crossover from a dipolar to a nearest-neighbour spin ice behaviour and the doping insensitivity in spin ices are briefly discussed. [Copyright &y& Elsevier]

Abstract: The paper deals with the analysis of clusters'' size in diverse magnetization states of a system of ferromagnetic particles organized in a perfect 2D array with all the anisotropy axes perpendicular to the plane (perpendicular medium) following the evolution of the clusters in correlation with various parameters like applied field or interaction strength. We present numerical simulations for a two-level Ising-type model each magnetic entity being characterized by a Stoner–Wohlfarth nonlinear energy barrier and a rectangular hysteresis loop (Ising–Preisach hysteron). In the simulations we took into account, the long-range inter-particle magnetostatic interactions in an attempt to mimic as accurately as possible with a still simple model, materials like Bit-Patterned media that are now considered as good candidates for the magnetic memories of the future. [Copyright &y& Elsevier]

Abstract: In this paper, the critical behavior of the general XY spin chain with the Dzyaloshinsky–Moriya (DM) interaction is studied by means of a Loschmidt Echo (LE) calculation. LE presents a Gauss decay in the region of magnetic field intensity |λ|<1 and an exponential decay in the region of |λ|>1. There exists a critical spin chain size N C. When spin chain size is larger than N C, the value of λ corresponding to the minimum value of LE (λ m) is independent of the spin chain size and keeps a stable value. In the region of λ<0, the stable value is same for different DM interactions. In the region of λ>0, the stable value varies with changing DM interaction. [Copyright &y& Elsevier]

Abstract: The change in the specific heat by the application of magnetic field up to 16T for high temperature superconductor system for DyBa2Cu3O7−x by Revaz et al. is examined through the phenomenological Ginzburg–Landau(G–L) theory of anisotropic Type-II superconductors. The observed specific heat anomaly near T c with magnetic field is explained qualitatively through the expression 〈ΔC〉=(B a /T c ) t/(1−t)(αΘ(γ)/λ 2 m (0)), which is the anisotropic formulation of the G–L theory in the London limit developed by Kogan and coworkers; relating to the change in specific heat ΔC for the variation of applied magnetic field for different orientations with c-axis. The analysis of this equation explains satisfactorily the specific heat anomaly near T c and determines the anisotropic ratio γ as 5.608, which is close to the experimental value 5.3±0.5 given in the paper of Revaz et al. for this system. [Copyright &y& Elsevier]

Abstract: Perpendicular-magnetized pseudo-spin-valves (PSV) boast the advantages of lower aspect ratio, greater magnetic stability and thermal stability; and hence constitute a promising candidate for achieving higher integration area density. In this paper, we investigate the spin transport and spin transfer torque in a Co/Cu(111)/Co perpendicular PSV structure where the magnetization of the Co layers are oriented in the out-of-plane direction, in the presence of a spin-polarized current in the perpendicular-to-plane (CPP) geometry. Both ballistic spin-dependent transmission/reflection at the two Co–Cu interfaces and diffusive spin relaxation within the Co and Cu layers are considered in our model. The ballistic calculations predict an absorbed spin current component at the Cu-free Co interface, which constitutes the main source (∼90%) of the total spin transfer torque in the free Co layer. The remaining torque arises from the spin relaxation of transmitted spin current within the free Co layer. Our model predicts a lower range of the critical current density of less than 107 A/cm2 for perpendicularly magnetized PSVs, while that for in-plane magnetized PSVs is of the order of several 107 A/cm2. Additionally, perpendicularly magnetized PSVs also possess other practical advantages which make them promising candidates for future MRAM applications. [Copyright &y& Elsevier]

Abstract: In this paper, we analyze the behaviour of Fe-rich wires that have been submitted to a current annealing, with and without an applied torsional stress. The structural relaxation and induced anisotropies achieved in the samples produce different effects in the magneto-impedance and torsion impedance response, in comparison with the as-quenched wire, due to the different domain structure and magnetization processes involved. [Copyright &y& Elsevier]

Abstract: This paper discusses the change in the ellipticity of two-dimensional magnetization trajectories as the applied field rotates from the easy axis to the hard axis of a material. Furthermore, the impact that the reversible magnetization has on the ellipticity is discussed, including the relationship between the magnetization squareness and the reversible component of the magnetization. [Copyright &y& Elsevier]

We have constructed a model for studying the hysteresis of an assembly of magnetic moments by zero-temperature Monte Carlo simulation. The magnetic particles are arranged in a close packed face centered cubic lattice with variable number of coordination shells around a central particle. The expression of the magnetic interaction contains an anisotropic pseudodipolar term besides the usual isotropic exchange. The novelty of the model is the multiaxial character of the anisotropy, that is the magnetic moments may select their lowest energy state from 26 distinct main crystallographic directions. Hysteresis curves and magnetic moment configurations of the model are presented and discussed in this paper. [Copyright &y& Elsevier]

A comprehensive analysis of the giant in-plane uniaxial magnetic anisotropy of exchange biased molecular beam epitaxy grown Cu(1 1 0)/Ni80Fe20/Fe50Mn50 bilayers, discovered by Jungblut et al. (J. Appl. Phys. 75 (1994) 6659) is presented. Cu(1 1 0)/Ni80Fe20 samples have a uniaxial in-plane volume anisotropy with a [0 0 1] easy axis direction. Covering such ferromagnetic (F) layers with an antiferromagnetic (AF) Fe50Mn50 layer introduces an interface contribution to the uniaxial anisotropy that leads to an [1 1¯ 0] easy axis direction for F layer thicknesses below a critical value of 4 nm, and to an enhancement of the [0 0 1] anisotropy for larger thicknesses. The effect occurs only for Fe50Mn50 layers that are thicker than the minimum thickness that is required to obtain the exchange bias effect. From in situ low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) the Ni80Fe20 surface is shown to be corrugated, viz. in the form of elongated 2–4 monolayer high mesas at a distance of typically 4–8 nm in the [0 0 1] direction and a length along the [1 1¯ 0] direction of 25–60 nm. We show that this novel mesoscopic magnetic effect can be explained from the magnetically uncompensated nature of the AF (1 1 0) surface in combination with the corrugation of the F/AF interface. The spatially varying sign of the F–AF exchange coupling then leads to a preferred F layer magnetization direction that is perpendicular to the staggered AF magnetization. The remarkable change of sign of the interface anisotropy indicates that in the thin and thick F layer regimes the staggered AF magnetizations that are frozen in during the growth are different by a 90° rotation. We tentatively explain this from the kinetics of magnetic structure transformations in the bilayer during the growth process. The local exchange bias interaction parameter obtained from a quantitative analysis is Jeb,loc&ap;2.5–10 mJ/m2, which is close to the theoretical upper limit and is two orders of magnitude larger than the sample averaged interaction parameter, Jeb, obtained from the exchange bias field. This provides the first direct experimental proof that the observed value of Jeb of an AF/F bilayer can be the result of much larger but almost completely averaged out opposing local AF–F exchange interactions. The paper contains a brief overview of the recent developments in the field of mesoscopic magnetism. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate spin diffusion in Heisenberg chains with uniaxial nearest-neighbor interactions. The approach followed is based on an analysis of the infinite-temperature longitudinal spin density and spin current correlation functions. For S=1/2, exact results are presented for the time-dependent correlation functions in the XY limit. Away from this limit, the second and fourth moments of the Fourier transform of the spin density correlation function provide information about spin dynamics for arbitrary values of the spin. The moments are used in an assessment of the accuracy of the Gaussian approximation for the spin diffusion constant for S=1/2. The general behavior of the Gaussian approximation when S>1/2 is discussed, and numerical results for the spin diffusion constant are presented for S=1/2, 1, 3/2, 2 and in the classical limit. A moment-based criterion for the boundary in reciprocal space between diffusive and non-diffusive dynamics that applies to arbitrary values of the spin is presented. [Copyright &y& Elsevier]

Abstract: This paper is devoted to the determination of the equivalent anisotropy properties of polycrystalline magnetic materials, modelled by an assembly of monocrystalline grains with a stochastic spatial distribution of easy axes. The mathematical theory of is applied to homogenize the anisotropic term in the Gibbs free energy. The procedure is validated focusing on the micromagnetic computation of reversal processes in polycrystalline magnetic thin films. [Copyright &y& Elsevier]

Abstract: This paper presents the radio-frequency (rf) diagonal conductivity spectra of two-dimensional electrons in the second excited and higher Landau levels, and in particular shows isotropic pinning mode resonances in the bubble phases evolving into a highly anisotropic rf resonance in the stripe phase. The stripe phase resonance is observed for the rf electric field, , along the “hard” direction, in which the dc higher resistivity occurs, but not for along the orthogonal, “easy” direction. The resonance is naturally interpreted as a pinning mode of the stripe phase. [Copyright &y& Elsevier]

Abstract: Strongly correlated electronic systems in two dimensions have constantly been a source of new discoveries. For example, the integer and fractional quantum Hall (QH) effects have emerged when such systems have been subjected to strong perpendicular magnetic fields. Recently, in the transitional regions between QH plateaus, strong magneto-transport anisotropies have been observed below ca. 100mK. In this paper, we explain the emergence of broken rotational symmetry at half-filled valence Landau levels in terms of quantum liquid crystalline states with nematic order. Quantum Monte Carlo simulations indicate that while isotropic states are stable in the lowest and first excited Landau level, there are regions of instability towards liquid crystalline states in higher Landau levels. A possible connection of the recently discovered magneto-transport anisotropy in low magnetic fields and these liquid crystalline states is discussed. [Copyright &y& Elsevier]

Abstract: In this paper we study superconducting gap functions in planar systems with very different hopping frequencies in the two directions. Allowing the carriers to interact via an isotropic superexchange (using a two-dimensional – model) we calculate the gap function amplitudes by solving the BCS gap equation. The lowering of symmetry induced by such hopping anisotropies results in a mixed symmetry state (of s and d-wave) of the gap function. At smaller anisotropies s-wave pairing dominates the phase diagram at lower densities where we believe our calculations are most accurate. As the system is made progressively more anisotropic, it becomes increasingly difficult to distinguish between the gap function amplitudes corresponding to these two symmetries and in the limit of extreme anisotropy they become identical, with a dramatic increase of the d-wave component. Finally, these gap function amplitudes are used to calculate the thermodynamic properties, e.g. the specific heat, which provides robust support for enhanced pairing correlations in presence of hopping anisotropies. [Copyright &y& Elsevier]