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Presents information on a study which performed direct current-magnetization measurements on cobalt-chromite and iron-alumite thin film media. Insight on the phenomenon of magnetic viscosity in recording media; Methodology of the study; Results and discussion.

Presents convenient and inclusive tables for the demagnetization factors of general ellipsoids. Discussion on general ellipsoidal cases for magnetization; Details of a mathematical derivation of the demagnetization factors; Application of the magnetization factors to rectangular parallelopipeds.

Presents a study that measured the photoconductivity of diluted magnetic semiconductors. Analysis of the frequency dependence of the photoconductivity and magnetization of the samples; Evaluation of the magnetic field dependence of excitonic photoconductivity; Methodology.

A 2-D vector hybrid hysteresis model for a soft magnetic composite (SMC) material is established, which is combined with classical Preisach model and Stoner-Wohlfarth (S-W) model. The rotational magnetic properties of SMC materials were studied using the vector model, and the computed results were compared with the experimental measurement. It is shown that the vector hybrid model can effectively simulate the rotational magnetic properties under low magnetization fields. [ABSTRACT FROM AUTHOR]

In studying interface anisotropy, it is common to use a simple model in which the magnetization is assumed uniform (coherent). There are then only two parameters, the bulk anisotropy energy σbulk and the surface anisotropy energy r, which can be extracted from the thickness-dependence of the effective anisotropy. This procedure depends on assuming the magnetization is coherent-we show here that incoherence will bias the extracted anisotropy and suggest a method for decreasing this bias. We also suggest an alternative model (also with only two parameters) which includes incoherence effects and may be closer to real systems. [ABSTRACT FROM AUTHOR]

We investigate the influence of spin-valley polarized transport channel (SVPTC) mismatch modulated by the perpendicular electric field and the exchange field in a silicene-based ferromagnet/ferromagnet/superconductor junction and the barrier strength in a ferromagnet/insulator/ferromagnet/superconductor junction. In the former junction, due to the mismatch of SVPTC caused by the different electric fields applied in the two ferromagnet (F) layers, the zero-bias Andreev reflection and zero-bias conductance peak (ZBCP) are suppressed. Moreover, by shifting the band, the exchange field can lead to the different mismatch of SVPTC between the two F layers with opposite magnetization orientations, and thus, the conversion from ZBCP to a zero-bias conductance valley can be observed. For the latter junction, due to the electrically tunable SVPTC, the phase shift of conductance oscillation with barrier strength is created by changing the electric field but not by altering the exchange field. Particularly, for the variation from the parallel to the antiparallel magnetic configuration, there is a phase shift π / 2 of conductance vs the barrier strength. [ABSTRACT FROM AUTHOR]

We report magnetoresistance measurements on epitaxial films of the intrinsic ferromagnetic semiconductor GdN electron doped with ∼ 10 20 cm − 3 to ∼ 10 21 cm − 3 . The magnetoresistance across the temperature range of 10–300 K is dominated by a reduction of spin-disorder scattering in the presence of a magnetic field, imposing a resistance reduction of 27% in a field of 8 T. We show that the magnetoresistance closely follows the magnetic disorder as signaled by the departure of the magnetization from its fully saturated value M s of 7 μ B / G d 3 + . [ABSTRACT FROM AUTHOR]

Nanomagnets form the building blocks for a gamut of miniaturized energy-efficient devices including data storage, memory, wave-based computing, sensors, and biomedical devices. They also offer a span of exotic phenomena and stern challenges. The rapid advancements of nanofabrication, characterization, and numerical simulations during the last two decades have made it possible to explore a plethora of science and technology applications related to nanomagnet dynamics. The progress in the magnetization dynamics of single nanomagnets and one- and two-dimensional arrays of nanostructures in the form of nanowires, nanodots, antidots, nanoparticles, binary and bi-component structures, and patterned multilayers have been presented in detail. Progress in unconventional and new structures like artificial spin ice and three-dimensional nanomagnets and spin textures like domain walls, vortex, and skyrmions has been presented. Furthermore, a huge variety of new topics in the magnetization dynamics of magnetic nanostructures are rapidly emerging. A future perspective on the steadily evolving topics like spatiotemporal imaging of fast dynamics of nanostructures, dynamics of spin textures, and artificial spin ice have been discussed. In addition, dynamics of contemporary and newly transpired magnetic architectures such as nanomagnet arrays with complex basis and symmetry, magnonic quasicrystals, fractals, defect structures, and novel three-dimensional structures have been introduced. Effects of various spin–orbit coupling and ensuing spin textures as well as quantum hybrid systems comprising of magnon–photon, magnon–phonon, and magnon–magnon coupling and antiferromagnetic nanostructures have been included. Finally, associated topics like nutation dynamics and nanomagnet antenna are briefly discussed. Despite showing great progress, only a small fraction of nanomagnetism and its ancillary topics have been explored so far and huge efforts are envisaged in this evergrowing research area in the generations to come. [ABSTRACT FROM AUTHOR]

Inspired by the research interest on the realization of flatbands and magnetization plateaus in kagome lattices, herein we study the electronic properties and exchange magnetic interactions in quasi-one-dimensional boron triangular kagome lattice (1D-BTKL) models by using the real-space Green’s function approach in a tight-binding model. First, we study the electronic properties of 1D-BTKLs in the presence of staggered sublattice potential, and then, by analyzing the Ruderman–Kittel–Kasuya–Yoshida (RKKY) interaction in these lattice structures, the magnetic ground states of 1D-BTKLs in the presence of two magnetic adatoms are evaluated. It is found that the 1D channels of BTKL show different electronic and magnetic behaviors due to different values of the hopping integrals and spin–orbit couplings. Two important salient features of 1D-BTKLs are the presence of flatbands in their band structures as well as the emergence of the RKKY plateau vs the Fermi energy. To the best of our knowledge, it is the first time that the RKKY plateau is systematically reported and as we will see this idea has been advocated forcefully. It was shown that both the width and location of the magnetization plateaus could be controlled through variation of the staggered potential and the Fermi energy as well as the spatial configuration of the magnetic impurities, enabling a variety of electromagnetic devices to be produced. The other fascinating feature of the present study is the magnetic susceptibility discontinuity, named as magnetization jump, which accompanies with the discontinuity in the magnetization curves. We believe that our results provide significant insights into designing further experiments to search for the realization of the flatbands and magnetization plateau phases in spintronics and pseudospin electronic devices based on TKLs. [ABSTRACT FROM AUTHOR]

The effect of semihard magnetic phases and interfaces on the performance of nanostructured two-phase permanent magnets is investigated by model calculations. In addition to the trivial coercivity increase due to the replacement of soft regions by semihard regions, there is a coercivity enhancement even if the volume-averaged anisotropy is kept constant during the introduction of the semihard phase. A variational approach is used to derive analytical results for representative anisotropy profiles. The improvement is operative on length scales slightly larger than that of the soft phase in hard-soft composites, but the main challenge is to find semihard light or heavy transition metal phases with a high magnetization. There are several Fe- and Co-based phases, but most are thin-film systems and difficult to use in bulk magnets. Very hard nanostructured magnets may also be created from soft phases with negative but large anisotropy constants (hard-magnetic soft-soft magnets). [ABSTRACT FROM AUTHOR]

The magnetization of In1-xMnxSe is calculated and measured from 140 to 400 K in magnetic fields up to 7 T for two crystals with concentrations x=0.014 and 0.027. The Mn ions enter the InSe bulk crystal substitutionally at the In lattice site and are responsible for the observed magnetization of the sample. A singlet model of isolated Mn ions with a spin-orbit coupling parameter of 38 cm-1 fits the experimental data from two different concentration samples for temperatures ranging from 140 to 400 K in fields up to 7 T. This agreement between the experimental magnetization and the theoretical magnetization for In1-xMnxSe expands our theoretical understanding of the III-VI diluted magnetic semiconductor (DMS) by adding a Se-based system and complements previous agreement reported for only two other III-VI DMS (Ga1-xMnxS and In1-xMnxS). [ABSTRACT FROM AUTHOR]

Magneto-optical measurements are used to investigate Pt–Co and Co layers exchange-coupled by a Pt layer. The magnetization precession was measured in a pump-probe experiment using a femtosecond laser with direct optical excitation. The competing magnetic anisotropies of the layers yield a noncollinear spin structure with a field-dependent angle between the layers. Two modes, a ferromagnetic or “acoustic” mode and an antiferromagnetic or “optic” mode, are identified from the Fourier-transformed excitation spectra, and the obtained line positions are used to estimate the interlayer exchange constants. [ABSTRACT FROM AUTHOR]

In this paper, the real time thermal effect of the heat-assisted magnetic recording (HAMR) on the slider is investigated with the HAMR platform. The net temperature rises of the slider caused by laser absorption and heat radiation of the locally heated recording magnetic disk are studied by monitoring the calibrated read sensor resistances in different rotation speeds. The maximum slider temperature increase of about 3.5 °C caused by the locally heated recording disk is obtained when the media net temperature increase is 85 °C at 2000 rpm rotation speed. A higher temperature case is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the magnetization reversal in single-phase RE2Fe14B and two-phase α-Fe/RE2Fe14B with varying nanoscale grain structures and intergranular exchange interactions produced via controlled segregation during crystallization. We show that the loss of coercivity arises because domain-wall processes dominate the magnetic reversal as the exchange interactions increase. Micromagnetic modeling corroborates a transition to strongly cooperative magnetic reversal as the exchange interactions increase. The magnetic reversal is controlled by the growth of interaction domains via discrete domain-wall motion, and the coercivity is intrinsically limited by the presence of interaction domains. To alleviate this problem, we have built an additional length scale into the structure that is below the interaction domain size but above the limit for intergranular exchange interactions to be significant. These “single-interaction domain” structures retain nucleation-type magnetic reversal and high coercivity. We show experimentally that nanocomposite Sm-Co/Co with this additional length scale has excellent coercivity and nucleation-controlled reversal. [ABSTRACT FROM AUTHOR]

Rare-earth atoms play an important role in determining the magnetocrystalline anisotropy in 4f-3d intermetallic compounds. Recently we reported on the synthesis and magnetic properties of Gd-substituted Mn-Zn ferrite nanoparticles as potentially suitable for magnetic fluid hyperthermia (MFH). In MFH the specific power absorption rate is related to the lossy magnetocrystalline anisotropic properties of the magnetic fluids. In this paper we report the role of Ho substitution in magnetite nanoparticles, which is found to enhance the KV product arising from the large anisotropy of Ho3+ moments. The zero-field-cooled magnetization data is then simulated by assuming noninteracting magnetic particles with uniaxial anisotropy and lognormal particle size distribution. The fit parameters give the values of particle diameter (D) 9 nm, standard deviation 0.3 in ln(D), and the anisotropy constant K to be 3.5×104 J/m3. The value of K thus obtained is an order of magnitude larger than the value known for the undoped for magnetite (104 J/m3). [ABSTRACT FROM AUTHOR]

We present experimental techniques to measure magnetization precession of individual layers in a “spin-valve” trilayer. Precessional motions of individual Ni81Fe19 and Co93Zr7 layers have been separated in Ni81Fe19/Cu/Co93Zr7 using ±45 ps time-resolved x-ray magnetic circular dichroism (tr-XMCD) at Fe and Co edges. We compare the efficacy of two experimental configurations in this paper. Pulsed-field tr-XMCD measurements in reflectivity are compared with resonant-field tr-XMCD measurements in transmission. Despite the order of magnitude larger angles of precession excited in pulsed-field reflectivity measurements, data quality is found to be superior in resonant-field transmission measurements. Relative roles of sample preparation and timing jitter in the different techniques are discussed. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance properties in nanostructured multilayers are numerically investigated for the application of spintronics devices. The resonance frequency can be shifted by switching the magnetization state between a parallel and an antiparallel configuration. These remanent states are selectively initialized by choosing the saturation direction of magnetization. In this paper, the signal independency between the two resonant states, the amplitude of the magnetization rotation at the resonance frequency, and the response time to reach equilibrium resonance are systematically studied as a function of the geometrical and magnetic parameters. [ABSTRACT FROM AUTHOR]

In this paper we discuss some properties of the radial vector model (RVM) proposed as a three-dimensional extension of the classical scalar Preisach model (CSPM). In particular, we prove that the irreversible model of magnetization of the RVM is consistent with the conservation of magnetic energy and with the second law of thermodynamics. The model continues to have these properties even when a reversible component of magnetization is added to the magnetization. [ABSTRACT FROM AUTHOR]

In this paper, a fast algorithm for the rapid calculation of the demagnetization field in micromagnetic modeling is presented. The method is applied to finite element micromagnetic modeling to study the switching phenomenon of perpendicular recording media. The method is shown to provide high efficiency in the numerical simulation with reduced memory requirement. With significant improvement in the computing speed, the practical application of recording physics based simulations can be extended to the investigation of perpendicular magnetic recording processes in various aspects, for instance, a large number of micromagnetic simulations can be carried out to build microtrack model and to predict the performance of perpendicular head and media combinations. [ABSTRACT FROM AUTHOR]

Hysteresis phenomenon is one of the important characteristics of soft magnetic materials. A three-dimensional (3D) magnetic property measurement system has been developed. This system can effectively control the locus of the time-varying magnetic flux density vector B and measure the corresponding magnetic field strength vector H in a cubic sample of soft magnetic material. The sample involved in this study is a soft magnetic composite sample made of highly pure iron powder. This paper investigates the B and H loci in 3D space and the power loss when the B loci are controlled to become circles and ellipses lying in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and losses depend strongly on the orientation, position, and process of magnetization. On the other hand, the H vectors evolve into a unique locus pattern, and the power losses approach a unique value when the B vectors evolve into the same loci through either a series of small circles or ellipses. [ABSTRACT FROM AUTHOR]

This paper describes the energy surface model for two exchange coupled magnetic particles and a study of the critical switching field in this coupled system. It is shown that for static switching, the total energy is continuously reduced during the reversal process. The critical switching fields versus applied field angle can be directly obtained from the energy surface model. The results are in good agreement with micromagnetic simulation. For a fast dynamic switching with small damping, the critical switching field may be further reduced. In addition, it is shown that an increase in either Ms or the grain volume of the soft particle will lead to a further reduction of the switching field. This is primarily due to an increase in the Zeeman energy that changes during the reversal. [ABSTRACT FROM AUTHOR]

The paper is dedicated to the micromagnetic study of the real and imaginary parts of the transverse susceptibility (TS) temperature dependence for an interacting particulate system. Due to its fundamental and technological interest, we considered in our study two-dimensional arrays of particles as magnetic patterned media. It is shown that the interactions between particles strongly affect the TS signal. The effects of volume and anisotropy field dispersions are also analyzed. [ABSTRACT FROM AUTHOR]

In this paper we study by means of the spin torque model the fast switching behavior of the Co(20 nm)/Cu(5 nm)/Co(2.5 nm) magnetic multilayers of two different cross sections: ellipse (130×70 nm2) and ellipse (130×40 nm2). Simulations have been performed at zero and room (300 K) temperatures, these point out that the magnetization inversion occurs by nucleation processes in three main steps, for both structures. In particular, for zero temperature the third step of the switching depends on the value of the spin-polarized current. Furthermore, for all of the simulated currents the switching processes are thermally activated and smoother with respect to zero temperature. [ABSTRACT FROM AUTHOR]

It is well known that the energy barrier for magnetization reversal, EB, varies quadratically with the magnetic field for the Stoner-Wohlfarth model. However, the enthalpy H (switching energy) required to reverse the magnetization is the sum of EB and the work Wf done by the Néel fluctuation field. The sum of these two terms gives an enthalpy of reversal. If the fluctuation field is uniaxial and parallel to the holding field, then the enthalpy barrier for switching is linear in the holding field. The linearity is consistent with certain experimental results. If the fluctuation field is anisotropic, then for the same size field, the probability of the particle’s switching will depend upon the direction of that field. The paper discusses the holding field variation of the energy barrier for different fluctuation field directions. [ABSTRACT FROM AUTHOR]

Antiferromagnetic materials have recently gained renewed interest due to their possible use in spintronics technologies, where spin transport is the foundation of their functionalities. In that respect, metallic antiferromagnets are of particular interest since they enable complex interplays between electronic charge transport, spin, optical, and magnetization dynamics. Here, we review the phenomena where the metallic conductivity provides a unique perspective for the practical use and fundamental properties of antiferromagnetic materials. The future direction is outlined with respect to the current advances of the field. [ABSTRACT FROM AUTHOR]

In Cr2O3 thin films doped with Al or Ir, we have discovered a parasitic magnetization, accompanied by the antiferromagnetic order, with tunable direction and magnitude. In this study, by utilizing the parasitic magnetization, the antiferromagnetic anisotropy KAF of the doped Cr2O3 thin films was evaluated. A much greater improvement of KAF was obtained for Al-doped Cr2O3 films than that of bulk. The maximum KAF in this study was ∼9 × 104 J/m3, obtained for the Al 3.7%-doped Cr2O3 film sample. The enhancement of the magnetic dipole anisotropy KMD due to the site-selective substitution is speculated for the dominant origin of the enhancement. Furthermore, based on the obtained KAF, the influence of the parasitic magnetization on the exchange bias blocking temperature TB of the doped-Cr2O3/Co exchange coupled system was discussed. TB greatly increases when the parasitic magnetization is coupled antiparallel to ferromagnetic moment, such as Al-doped Cr2O3/Co systems. [ABSTRACT FROM AUTHOR]

Antiferromagnetic materials promise improved performance for spintronic applications as they are robust against external magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. Here, we show that the spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic insulators α − Fe 2 O 3 (hematite) and NiO in bilayer heterostructures with a Pt heavy-metal top electrode. While rotating an external magnetic field in three orthogonal planes, we record the longitudinal and the transverse resistivities of Pt and observe characteristic resistivity modulations consistent with the SMR effect. We analyze both their amplitude and phase and compare the data to the results from a prototypical collinear ferrimagnetic Y 3 Fe 5 O 12 /Pt bilayer. The observed magnetic field dependence is explained in a comprehensive model, based on two magnetic sublattices and taking into account magnetic field-induced modifications of the domain structure. Our results show that the SMR allows us to understand the spin configuration and to investigate magnetoelastic effects in antiferromagnetic multi-domain materials. Furthermore, in α − Fe 2 O 3 /Pt bilayers, we find an unexpectedly large SMR amplitude of 2.5 × 10 − 3 , twice as high as for prototype Y 3 Fe 5 O 12 /Pt bilayers, making the system particularly interesting for room-temperature antiferromagnetic spintronic applications. [ABSTRACT FROM AUTHOR]

We theoretically study the interaction of magnons, quanta of spin waves, and a domain wall in a one-dimensional easy-axis antiferromagnet in the presence of an external magnetic field applied along the easy axis. To this end, we begin by obtaining the exact solution for spin waves in the background of a domain wall magnetized by an external field. The finite magnetization inside the domain wall is shown to give rise to reflection of magnons scattering off the domain wall, deviating from the well-known result of reflection-free magnons in the absence of a magnetic field. For practical applications of the predicted reflection of magnons, we show that the magnon reflection contributes to the thermally driven domain-wall motion. Our work leads us to envision that inducing a finite magnetization in antiferromagnetic solitons such as vortices and skyrmions can be used to engender phenomena that do not occur in the absence of magnetization. [ABSTRACT FROM AUTHOR]

Studies the magnetization patter of cobalt (Co) and permalloy disks. Use of Lorentz microscopy and magnetic force microscopy in the study.

In this paper we report on magnetization reversal processes of pinned layers in different ferromagnetic and anti-ferromagnetic bilayer and spin-valve structures by observing hysteresis, switching field distribution (SFD), and time-dependent effects. The fact that time-dependent coercivity H[sub c] tendency is more pronounced in ordered AF materials than that of disordered AF materials implies a spin reversal of some AF grains with locally low pinning field and low blocking temperature. We propose a simple qualitative model to explain our results in terms of a distribution of the pinning reversal field and temperature in AF layer, which may be due to a grain size distribution in the AF layer and an incomplete and inhomogeneous phase transformation in some ordered AF materials. High resolution electron microscopy (HREM) results reveal that lattice spacing does change from place to place in AF region of some ordered AF materials. The evidence indicates an incomplete and inhomogeneous phase transformation in the ordered AF systems, supporting the results of the magnetization reversal process study. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper describes the experimental results obtained by a broadband permeability measurement method based on the full-wave electromagnetic (EM) analysis of a non-reciprocal transmission line. The method offers a new experimental tool for measuring the broadband dynamic behavior of ferrites whatever their magnetization state. The methodology and experimental setup are presented with the aim of extracting both the permittivity and the two components (diagonal μ and off-diagonal κ) of the permeability tensor. Experimental data on commercial ferrites set in different magnetization states are presented and discussed. Furthermore, this method opens perspectives for the determination of other useful magnetic parameters such as resonance linewidth ΔH. This quantity can be then measured at different frequencies, where conventional resonant methods give a value at a fixed frequency. [ABSTRACT FROM AUTHOR]

This paper presents a finite element model to solve the electromagnetic behavior and the AC loss in round high-temperature superconducting wire with a hole defect both in external field condition and self-field condition. The hole defect is assumed to be infinitely long along the wire. The model is based on the H formulation and the highly nonlinear E-J characteristic. The simulation results for the round superconducting wire with a hole defect and the one without defect are compared. It is found that the existence of the hole defect causes small reduction for the magnetization AC loss and large enhancement for the transport AC loss. The influences of the position and shape of the hole on the AC loss are also investigated. We find that the AC loss in external field condition decreases when the hole defect moves towards the edge of the superconducting wire from its center. However, the feature is opposite in self-field condition. Meanwhile, the influence of the shape of the hole on the AC loss is not strong in both conditions. [ABSTRACT FROM AUTHOR]

In this paper, we report the structural, microstructural, and magnetic properties of nanosized (particle size ranging from 20 to 30 nm) Ni0.35Zn0.65Fe2O4 (MA4) system synthesized via mechanochemical route followed by annealing. The Rietveld refinement is used for the first time to precisely resolve the crystal structure of a ferrite system at nanoscale. MA4 is a cubic spinel of [formula] symmetry. According to XRD and HRTEM studies, it is a well crystalline sample which possesses large microstrain. In spite of its nanometric size, MA4 has displayed some notably distinct magnetic properties like, enhancement of magnetization (64 emu g-1 at 15 K), magnetic order, magnetic ordering temperature, coercivity (1000 Oe at 15 K), magnetic anisotropy energy, and reduction of superparamagnetic relaxation compared with its counterparts synthesized by chemical route. It exhibits clear hysteresis loop (HC = 50 Oe) at 300 K and ferrimagnetic ordering below the blocking temperature (∼250 K). These improvements in magnetic properties of the system are likely to be very helpful for its technological applications. Again, particles in the sample possess a ferrimagnetically aligned core (with small canting) surrounded by a magnetically disordered shell with canted spin structure. The magnetically disordered surface region of MA4 has an equilibrium cation distribution, whereas the ferrimagnetic core region possesses a nonequilibrium cation distribution. Moreover, the infield Mössbauer spectroscopic study reveals that the nearest neighbor ion configuration about [B] site Fe3+ ions is not identical. Thus, there is local chemical inhomogeneity in the sample. The cation redistribution, chemical inhomogeneity, lattice strain are identified as the causes for magnetic enhancement in MA4. [ABSTRACT FROM AUTHOR]

Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers constitute the core of a superconducting spin valve. The switching effect of the spin valve is based on interference phenomena occurring due to the proximity effect at the S/F interfaces. A remarkable effect is only expected if the core structure exhibits strong critical temperature oscillations, or most favorable, reentrant superconductivity, when the thickness of the ferromagnetic layer is increased. The core structure has to be grown on an antiferromagnetic oxide layer (or such layer to be placed on top) to pin by exchange bias the magnetization-orientation of one of the ferromagnetic layers. In the present paper, we demonstrate that this is possible, keeping the superconducting behavior of the core structure undisturbed. [ABSTRACT FROM AUTHOR]

The bit patterned media use one single domain magnetic island to record a bit. It can effectively push the superparamagnetic limit to higher recording densities. In this paper, we present and investigate a composite patterned media structure comprising of soft layer enclosed magnetic islands to significantly improve the writing capability of conventional writer. Systematic micromagnetic simulation studies reveal that the proposed structure has a different domain wall propagation mechanism and has less stringent requirement on the exchange-coupling strength as compared to conventional composite structures. [ABSTRACT FROM AUTHOR]

In this paper we present a phenomenological approach computing the behavior of a cobalt particle by the Della Torre–Pinzaglia–Cardelli (DPC) model. The identification of the model is realized using a suitable numerical procedure and a set of data obtained using a micromagnetic numerical model based on Brown’s equations. In order to simplify the identification, a class of hysterons, which describes the magnetization process of a single domain in agreement with the Stoner and Wohlfarth theory, is used. The accuracy of the reconstructed magnetization cycles using the DPC model and the save of the computation time with respect to the micromagnetic numerical model are shown. [ABSTRACT FROM AUTHOR]

In this paper noise enhanced stability in magnetic systems is studied by both an Ising-type model and a Preisach–Arrhenius model as well as a dynamic Preisach model. It is shown that in one nonequilibrium Ising system noise enhanced stability occurs and that dynamic Preisach model has the capability to predict the occurrence of noise enhanced stability in magnetic systems. On the contrary, in a Preisach–Arrhenius model of a single quadrant magnetic material, noise enhanced stability is not detected. [ABSTRACT FROM AUTHOR]

Complementary nature of coercivity enhancement and exchange bias in a ferro-antiferromagnet (F-AF) exchange coupled system with arbitrary configuration refers to the relation Hsw0-=Ms/χin,max, with Ms being the saturation magnetization of the F part, Hsw0- being the field at which the F magnetization starts to be unstable, applied opposite to the stable direction of the F magnetization in the absence of external field, and χin,max being the maximal initial susceptibility, for which the field is applied perpendicular to that stable direction. This relation is a special case of a more general result for a single domain particle, proved in this paper. In a F-AF system, when the F magnetization behaves coherently, the effect of F-AF coupling can be absorbed into the anisotropy of the F part and the system can be treated as a single domain in an external field. [ABSTRACT FROM AUTHOR]

Attractive features of soft magnetic composites (SMCs) are high resistivity, isotropic three-dimensional flux behavior, and easy compression into the complicated shapes required in electromagnetic devices. Comprehensive understanding of the materials will help optimize design of electromagnetic devices. This paper presents the magnetization processes in a SMC sample in micron scale by means of the magneto-optical imaging technique. The sample was magnetized by magnetic fields tangential or perpendicular to the observation surface. It is observed that the flux density is higher at the particle region but lower at the interparticle space. When a tangential field is applied, the stray fields change polarization at the particle boundaries. Both results suggest that the magnetized sample behaves as a collection of individual magnetized particles rather than as a uniform and continuous magnetic substance such as soft iron although there are some interactions between neighboring particles. [ABSTRACT FROM AUTHOR]

In this paper one presents a method for statistical characterization of the magnetization processes in two-dimensional networks of single-domain ferromagnetic particles. These systems are similar with the structured materials that are seen as future high-density recording media. The method allows very interesting developments in the characterization of the stability of the magnetic states which is an important factor for a recording medium. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper represents the force performance of a brushless dc motor with a continuous ring-type permanent magnet (PM), considering its magnetization patterns: trapezoidal, trapezoidal with dead zone, and unbalanced trapezoidal magnetization with dead zone. The radial force density in PM motor causes vibration, because vibration is induced the traveling force from the rotating PM acting on the stator. Magnetization distribution of the PM as well as the shape of the teeth determines the distribution of force density. In particular, the distribution has a three-dimensional (3-D) pattern because of overhang, that is, it is not uniform in axial direction. Thus, the analysis of radial force density required dynamic analysis considering the 3-D shape of the teeth and overhang. The results show that the force density as a source of vibration varies considerably depending on the overhang and magnetization distribution patterns. In addition, the validity of the developed method, coupled 3-D equivalent magnetic circuit network method, with driving circuit and motion equation, is confirmed by comparison of conventional method using 3D finite element method. [ABSTRACT FROM AUTHOR]

This paper presents two-dimensional vector measurements of major hysteresis loops of magnetic particle tape measured with a vibrating sample magnetometer. The measurements, presented in magnet and sample coordinates, may be used to evaluate how well the computations of a vector model fit the corresponding measured data. The measurement process is described, and the characteristics of the measurements are discussed. [ABSTRACT FROM AUTHOR]

We study the magnetocaloric effect in layered systems composed of a ferromagnet with a relatively low Curie temperature (TC), which is sandwiched by stronger ferromagnets and exchange coupled to them across the interfaces. Switching of magnetization in the softer ferromagnetic surrounding in an applied magnetic field (H) of the strength in several tens of oersteds provides the isothermal magnetic entropy change (Δs) in the system because of magnetization redistribution in the spacer. Our simulations of these effects we present here reveal the maximal value of Δs, obtained at a realistic interfacial exchange constant, which is in quantitative agreement with this quantity observed experimentally in different heterosystems based on the NixCu100 − x (x ∼ 70 at. %) spacer. [ABSTRACT FROM AUTHOR]

Magnetic domain pattern and magnetic domain wall motion are particularly important to understand the magnetization process. Here, we investigated the magnetization process of perpendicularly exchange-biased Pt/Co/Au/Cr2O3/Pt stacked films based on observations of the magnetic domain. In particular, in contrast to previous studies which use fully exchange-biased state, we used the bi-exchange-biased state. We found that the magnetic domain pattern at the remanent state was robust against magnetic-field cycling, which is relevant to the absence of the training effect. The magnetization process was followed by domain wall propagation in the increasing branch of the magnetization curve. In the decreasing branch, both nucleation of the reversed domain and domain wall propagation were involved. The former was accompanied by latency, suggesting that thermal activation played a significant role in the nucleation of the reversed domain. [ABSTRACT FROM AUTHOR]

Nanosized antiferromagnets show anomalously large magnetization and superparamagnetism, having complicated magnetic properties due to a competition between core and surface spins in addition to the surface-induced effect, the finite size effect, and the magnetic moment distribution. A significant distribution of magnetic moments, which are responsible for the superparamagnetism, can also exist in real ensembles of nanoparticles, making the analysis of magnetization difficult. It has been a key issue for the understanding of the complicated magnetic property to correctly separate a superparamagnetic component from an antiferromagnetic component that linearly depends on magnetic fields in the observed magnetization. Here, we report the separation of these two components observed in the magnetization of antiferromagnetic NiO nanoparticles by applying the scaling law in the magnetization of superparamagnets. The distribution of the magnetic moment was taken into account without a priori assumption of the distribution function. The magnetic moments causing superparamagnetism had a bimodal distribution with different mean values. The contribution of the two different superparamagnetic components could thus be newly clarified and was ascribed to the uncompensated spins in the core and on the surface. The magnetic structure that leads to the bimodal distribution is discussed in light of the inhomogeneity of the surface structure. [ABSTRACT FROM AUTHOR]

We report on the field-cooled magnetization (FCM) process under magnetic fields of up to 22 T for the stacked Y-Ba-Cu-O (YBCO) bulk pair reinforced by a stainless steel (SUS316) container. On the basis of the numerically simulated mechanical stress in a bulk during FCM, the SUS316 container was designed by the numerical simulation to offer the sufficient hoop stress tolerance to the bulk trapping the magnetic field of 20 T. As a result, we obtained successfully the trapped field, B T , of 15.1 T by FCM from 18 T at 28 K at the center of the YBCO bulk pair. However, the extremely large-scale vortex jumps and large temperature rise occurred suddenly during FCM from a higher field of 22 T at a lower temperature of 23 K, and then a small crack was confirmed at the periphery of "both" YBCO bulks from the distorted contour maps of B T . The simultaneous break of both YBCO bulks probably in spite of sufficient mechanical reinforcement led us to conclude that the thermal instability triggered off the large-scale vortex jumps and large heat generation. The stress concentration induced thermally at the hot spot brought about the cracking. [ABSTRACT FROM AUTHOR]

The electric field (E) controlled magnetism in the multiferroic heterostructure comprising polycrystalline yttrium iron garnet (YIG) film, Pt electrodes, and lead magnesium niobate-lead zirconate titanate (PMN-PZT) ceramic is presented in this work. The electric-field-dependent magnetization and susceptibility of YIG film reveal the strain-mediated transformation of magnetocrystalline anisotropy. A strong converse magnetoelectric (CME) effect has been observed in the YIG/Pt/PMN-PZT/Pt heterostructure, and the CME coefficient can reach 17 × 10−8 s/m at 0 Oe and 4.2 kV/cm. The reversible magnetization switching by means of a low voltage pulse (±4.6 kV/cm) can be realized at 0 Oe in the YIG/Pt/PMN-PZT/Pt heterostructure, and the E-tunable susceptibility can reach Δχ/χ0+ = 55.5% at 20 Oe and 4 kV/cm. These results show great potential in power-efficient magnetoelectric components for information storage and tunable devices. [ABSTRACT FROM AUTHOR]

We have reinvestigated the magnetization reversal in perovskites La1–xPrxCrO3, GdCrO3, and TmCrO3 and show that spin rotation or reorientation plays a key role in this property. The magnetization of La1–xPrxCrO3 as well as other chromites, including GdCrO3 and TmCrO3, indicates that the disappearance of magnetization reversal when x is increased from ∼0.85 is caused by a flip of Pr3+ paramagnetic moments antiferromagnetically coupled with canted Cr3+ spins. This is due to a Zeeman energy of Pr3+ in analogy with a spin rotation in GdCrO3 and TmCrO3 below ∼25 K, denoted as the spin reorientation transition. Magnetic susceptibility measurements point to either superparamagnetic or single-molecule-magnet-like glassy behavior in all three systems, which is likely linked to a rotation of the R3+-Cr3+ coupling, as seen from magnetocalorimetry (R = La1–xPrx, Gd, and Tm). We also present a characteristic magnetization switching by rotating the R3+ moments with the aid of large Zeeman energies. [ABSTRACT FROM AUTHOR]

We present a simple semiclassical model to sustain that in europium chalcogenides (EuX), Faraday rotation (FR) in the transparency gap is proportional to the magnetization of the sample, irrespective of the material's magnetic phase, temperature, or applied magnetic field. The model is validated by FR and magnetization measurements in EuSe in the temperature interval 1.7–300 K, covering all EuSe magnetic phases (paramagnetic, antiferromagnetic type I or type II, ferrimagnetic, and ferromagnetic). Furthermore, by combining the semiclassical model with the explicit electronic energy structure of EuX, the proportionality coefficient between magnetization and FR is shown to be dependent only on the wavelength and the bandgap. Due to its simplicity, the model has didactic value; moreover, it provides a working tool for converting FR into magnetization in EuX. The possible extension of the model to other intrinsic magnetic semiconductors is discussed. [ABSTRACT FROM AUTHOR]

We fabricated quasiantiferromagnetic (quasi-AFM) layers with alternating antiparallel magnetization in the neighboring domains via 90° magnetic coupling through an Fe-O layer. We investigated the magnetic properties and the relationship between the magnetic domain size and the 90° magnetic coupling via experiments and calculations. Two types of samples with a Ru buffer and a (Ni80Fe20)Cr40 buffer were prepared, and we found that with the NiFeCr buffer, the sample has a flatter Fe-O layer, leading to stronger 90° magnetic coupling and a smaller domain size compared with the Ru buffer sample. This trend is well explained by the bilinear and biquadratic coupling coefficients, A12 and B12, in Landau–Lifshitz–Gilbert simulations, suggesting the possibility of using both AFM and FM properties by controlling the quasi-AFM domain size. [ABSTRACT FROM AUTHOR]