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A great number of useful and practical devices benefit from the use of Nd2Fe14B magnets because of their good magnetic properties and relatively low cost. However, Nd2Fe14B presents a spin-reorientation transition (SRT) at cryogenic temperature that constitutes a challenge for engineers aiming to design devices for use in this environment. Although the spin reorientation transition is well-known for single crystals, there are very few papers describing experiments with polycrystalline samples. In this paper we show the effects of the SRT in macroscopic commercial samples, providing useful experimental data for designers. It has been proven that the macroscopic axis of magnetization in polycrystalline magnets of Nd2Fe14B remains invariant under spin reorientation transition whenever it occurs at H = 0 T. However, the transverse magnetic susceptibility slightly increases after the spin reorientation transition. This makes Nd2Fe14B suitable for cryogenic applications in which permanent magnets with defined axis of magnetization are required. [ABSTRACT FROM AUTHOR]

It is well known that applied mechanical stresses could have a strong adverse effect on the magnetic properties of ferromagnetic media. In power devices, mechanical clamping mechanisms of core lamination stacks could, thus, alter their overall performance. This paper presents an automated approach through which field computation of nonlinear media subject to mechanical stress may be performed. In this approach, clamped zones are assumed to posses zero strain and magnetization induced stresses are deduced from prohibited magnetostriction. Details of the approach as well as simulation results are given in the paper. [ABSTRACT FROM AUTHOR]

This paper presents the first report on Gd doping (0%-4%) of GaN thin films by metal organic chemical vapor deposition. The Ga1-xGdxN films grown in this study were found to be of good crystalline quality, single-phase, and unstrained, with a high saturation magnetization strength of 20 emu/cm3 being obtained for GaN films doped with 2% Gd at room temperature. Furthermore, these films were found to be conductive with an enhanced n-type behavior suggesting that unintentional donors are responsible for stabilizing the ferromagnetic phase in as-grown Ga1-xGdxN. Additionally, it was found that this magnetization can be enhanced by n-(Si: 1018 cm-3) and p-(Mg: 1019 cm-3) doping to 110 emu/cm3 and ∼500 emu/cm3, respectively. This paper shows empirically that holes are more efficient in stabilizing the ferromagnetic phase as compared to electrons. Overall, this research has resulted in a room temperature ferromagnetic dilute magnetic semiconductor that is conductive and whose magnetic properties can be tuned by carrier doping thus providing a path towards realizing spintronic devices. [ABSTRACT FROM AUTHOR]

This paper presents a general theoretical model of constitutive relationships for the soft ferromagnetic and/or the giant magnetostrictive rods under a prestress and a bias magnetic field on the basis of Gibbs’ free energy function. After Gibbs’ free energy function is expanded by Taylor’s series expansion with the stress and the magnetization in the materials as the independent variables, a transcendental function is appropriately selected to replace the first terms with higher order up to six on the basis of the meaning of mechanics and physical theory of magnetic domains, from which a set of closed and analytical expressions of the constitutive relationships for the soft ferromagnetic material rods are obtained, and the parameters appearing in the relationships are determined by those measurable experiments in mechanics and physics. It is found that the predictions from this model are in good accordance with the experimental data given by Kuruzar and Cullity [Int. J. Magn. 1, 323 (1971)] and Jiles and Atherton [J. Phys. D 17, 1265 (1995)] and that this model can be degenerated into the relevant constitutive relationships for the giant magnetostrictive materials obtained by Zheng and Liu [J. Appl. Phys. 97, 053901 (2005)]. Comparing this model with other existing models in this field, the quantitative results exhibit that the relationships obtained here are more effective to describe the effect of the prestress on the magnetostrictive strain and the magnetization, and the effect of the stress and the magnetic field on Young’s modulus. [ABSTRACT FROM AUTHOR]

FePt-based exchange-coupled composites consisting of a magnetically hard L10-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in²) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mechanical systems, among others. In this paper, the effect of the thickness of a soft Co layer (3 < thCo < 20 nm) on the magnetic behavior of ledge-type fcc(100)-Co/L10(001)-FePt composites deposited on an MgO (100) substrate is systematically studied by combining morpho-structural analyses and angular magnetization measurements. Starting from a film consisting of isolated L10(001)-FePt islands, the ledge-type structure was obtained by depositing a Co layer that either covered the FePt islands or filled-up the inter-island region, gradually forming a continuous layer with increasing Co thickness. A perpendicular anisotropy was maintained up to thCo ∼ 9.5 nm and a significant reduction in the coercivity (about 50% for thCo ∼ 3nm) with the increase in thCo was observed, indicating that, by coupling hard FePt and soft Co phases in a ledge-type configuration, the writability can be greatly improved. Recoil loops' measurements confirmed the exchange-coupled behavior, reinforcing a potential interest in these systems for future magnetic recording media. [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]

During the last years, cylindrical structures like dots, wires, and tubes have been intensively investigated. However, stadium-shaped particles have been scarcely investigated because of the complexity associated to the control of its geometry. In this paper, we used a scaled atomistic representation with Monte Carlo simulations to investigate systematically the magnetization reversal process in stadium-shaped magnetic structures as a function of the size of the central volume. Different reversal mechanisms have been identified and its existence has been explained. The reversal process for short, almost circular, stadium structures occurs via the formation of a single vortex, whereas for longer stadium structures the reversal process involves either single vortices or vortex pairs. For the longest structures investigated, the reversal always involves two vortices that generate a central diamond region or a central antivortex, depending on the region of the nucleation of the vortices. Our results provide guidelines for the use of stadium-shaped particles in the control of vortex motion when a magnetic field is applied. [ABSTRACT FROM AUTHOR]

This paper describes a full micromagnetic characterization of the magnetization dynamics driven by spin-polarized current in anisotropic spin-torque oscillators (STOs). For field angles approaching the hard in-plane axis, the excited mode is uniform and a super-critical Hopf-bifurcation takes place at the critical current density JC. For field angles close to the easy axis of the free layer, the excited mode is localized (non-uniform) and a sub-critical Hopf-bifurcation occurs at JC. In this latter region, a hysteretic behaviour is, therefore, found. We demonstrate numerically that the non-linearities of the STO are strongly reduced when the oscillation frequency at the critical current is near the ferromagnetic resonance (FMR) frequency computed at zero bias current, and in particular, this condition corresponds to the field orientation at which a minimum in the FMR-frequency is achieved. [ABSTRACT FROM AUTHOR]

In this paper, we present an analytical method to study the magnetization processes of two magnetic particles with ferromagnetic or antiferromagnetic coupling by using a modified expression for the anisotropy free energy. By considering a system consisting of two uniaxial particles, coupled by a simple exchange interaction, we describe analytically: the particles orientations, switching points and hysteresis loops for different ferromagnetic or antiferromagnetic couplings and for different orientations of the applied field. [ABSTRACT FROM AUTHOR]

The magnetization orientation of the polarizing reference layer would fluctuate between the parallel and antiparallel states when the reference layer loses stability. In this paper, a combined analytical and simulation study is presented to predict the magnetic dynamics of the spin valve element with single-domain magnets as the free and reference layers. We acquire a complete phase diagram that includes the normal spin-torque switching and random magnetization fluctuations by tuning the spin torque strength between the free and reference layers. The phase dynamics strongly depends on the magnetization state of the reference layer, showing that the instability of the reference layer could be responsible for the random fluctuation events. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of the dipolar magnetic interaction on the current-driven vortex dynamics in a two-dimensional array of nanodisks. A general formula is established for the prediction of the correlation between the restoring force of the target nanodisk and the polarities and circulations of the neighboring vortices. Large numbers of possible magnetization configuration combinations among the target and the surrounding neighbors are reduced into four groups under an extreme condition. The maximum and minimum restoring forces are analytically derived, which can be used to predict the critical switching current dependence on the magnetic configuration combinations of vortices. [ABSTRACT FROM AUTHOR]

Traditional magnetic/stress coupling models are based on the magnetoelastic theory, which cannot explain magnetic phenomena when ferromagnetic materials are subjected to a plastic deformation. To promote the development of magnetomechanical theories, a new physical-based magnetic/stress coupling model was proposed in this paper, where the effects of the applied magnetic field, elastic and plastic deformations on the magnetization are, respectively, considered in terms of different acting mechanisms. Moreover, the influences of variants on the strength in different magnetization stages are also calculated. [ABSTRACT FROM AUTHOR]

This paper reports effects of inter-film interactions on static and dynamic magnetization behavior at film edges in magnetic trilayer stripe arrays under transverse applied fields. The trilayers consist of two magnetic films of Ni80Fe20, 10 nm and 20 nm thick that interact via dipolar fields across thin, nonmagnetic spacers from 1 nm to 20 nm thick. These trilayer films are patterned into stripe arrays by optical interference lithography. Ferromagnetic resonance spectra exhibit separate edge modes that are identified as excitation of edge modes primarily in one magnetic film or the other. When interlayer exchange is negligible, we observe several effects of dipolar edge-edge coupling including shifts of the edge saturation fields and changes in the mode intensity ratio relative to single-film edges. These interaction effects are reproduced by micromagnetic modeling and explained by simple models. [ABSTRACT FROM AUTHOR]

We present a three-dimensional study of the torque transmitted between tile permanent magnets uniformly magnetized. All this study is based on the Coulombian model. The torque is calculated semianalytically by considering all the surface densities that appear on the tiles. In addition, no simplifying assumptions are done in the expressions given in this paper. Consequently, the evaluation of the torque is very accurate and allows us to show the drawbacks of using tile permanent magnets uniformly magnetized instead of using tile permanent magnets radially magnetized. Such an approach is useful because it allows us to realize easily parametric studies. [ABSTRACT FROM AUTHOR]

We present a detailed numerical simulation study of the effects caused by the magnetodipolar interaction between ferromagnetic (FM) layers of a trilayer magnetic nanoelement on its magnetization dynamics. As an example, we use a Co/Cu/Ni80Fe20 element with a square lateral shape where the magnetization of FM layers forms a closed Landau-like domain pattern. First, we show that when the thickness of the nonmagnetic (NM) spacer is in the technology relevant region h∼10 nm, magnetodipolar interaction between 90° Neel domain walls in FM layers qualitatively changes the equilibrium magnetization state of these layers. In the main part of the paper, we compare the magnetization dynamics induced by a sub-nsec field pulse in a single-layer Ni80Fe20 (Py) element and in the Co/Cu/Py trilayer element. Here, we show that (i) due to the spontaneous symmetry breaking of the Landau state in the FM/NM/FM trilayer, its domains and domain walls oscillate with different frequencies and have different spatial oscillation patterns; (ii) magnetization oscillations of the trilayer domains are strongly suppressed due to different oscillation frequencies of domains in Co and Py; (iii) magnetization dynamics qualitatively depends on the relative rotation sense of magnetization states in Co and Py layers and on the magnetocrystalline anisotropy kind of Co crystallites. Finally, we discuss the relation of our findings with experimental observations of magnetization dynamics in magnetic trilayers, performed using the element-specific time-resolved x-ray microscopy. [ABSTRACT FROM AUTHOR]

The high temperature magnetization behavior of an air sintered nanocrystalline ZnO:Co (5 at. %) sample while it is subjected to thermal cycles in vacuum/air ambient is reported in the present paper. The pristine air sintered sample exhibits intrinsic room temperature ferromagnetism. Upon vacuum annealing, the magnetization of this sample increases significantly and the sample remains ferromagnetic up to 630 °C. This has been attributed to the formation of Co clusters, and thus, the ferromagnetic ordering is extrinsic in nature. The subsequent air annealing of the vacuum annealed ZnO:Co (5 at. %) sample, however, reverts back the magnetization to a value that was observed in the pristine air sintered sample. This is due to complete oxidation of the cobalt clusters. Furthermore, the sample’s magnetization at room temperature and also its temperature dependence up to 630 °C remain unaffected by further annealing in vacuum or air, a feature required of a material for its device applications. The Curie temperature of this robust sample is ∼450 °C. [ABSTRACT FROM AUTHOR]

This paper describes a method for evaluating the magnetization-induced element in a third-order nonlinear optical susceptibility tensor. One difficulty in estimating this element is that the Faraday effects at fundamental and harmonic wavelengths are entangled with the polarization state of the outgoing harmonic wave. Using our method, the contribution of the Faraday effects can be isolated and removed from the rotation angle and the ellipticity of the outgoing harmonic wave. The theoretical expressions for the right- and left-handed circularly polarized components of the outgoing harmonic wave from magnetic media are derived. A formula for evaluating the magnetization-induced element is then determined from these expressions. Applying this formula to a bismuth-aluminum-doped yttrium-iron garnet thin film gives the magnetization-induced element |χxyyy(3),m|=4×10-21 m2/V2 at the fundamental wave of 1.17 eV (third-harmonic wave: 3.50 eV) in a magnetic field of +1 kOe. [ABSTRACT FROM AUTHOR]

The usual skin effect observed in magnetically linear medium (l = const.) is absent in a magnetically non-linear medium, leading to wrong predictions of the eddy current field using the classical approach. For this reason, this paper proposes a thin sheet model, improving the eddy current field description on the basis of physical ideas in the framework of the saturation wave model, which describes the dynamic magnetization of the material with rectangular hysteresis loop. Therewith, the layer-to-layer nature of the magnetization reversal is taken into account. The hysteresis is modeled by means of a static history-dependent hysteresis model. This leads to a simplified model of conducting ferromagnetic sheet, which describes magnetization of isotropic electrical steels. [ABSTRACT FROM AUTHOR]

Spin torque majority gate (STMG) is one of the promising options for beyond complementary metaloxide- semiconductor logic. Improvement of its performance-switching speed vs. required current- is critical for its competitiveness. In this paper, (a) we identify an optimized layout of the gate comprised of thin magnetic wires with in-plane magnetization; (b) we optimize geometries of perpendicular magnetization spin torque majority gates. Micromagnetic simulations demonstrate an improvement in switching current for in-plane magnetization (with less than 1 ns switching time) from 6mA in the original scheme to 1.5mA in the present one. Additionally, failures of switching caused by vortex formation are eliminated and desired output magnetization is achieved. Various geometries of STMG with perpendicular magnetization are explored. The scheme with a straight cross proves to be the most advantageous. It is predicted to operate with the switching current of 50 lA and less than 4 ns switching time. [ABSTRACT FROM AUTHOR]

The characterization of magnetic memory effect is the primary task of the metal magnetic memory (MMM) technique used in quantitative evaluation, and it has been characterized by the Jiles-Atherton (J-A) model in recent papers. The feasibility of using the MMM field to characterize magnetization intensity M and the feasibility of using the J-A model in MMM detection are discussed in this paper to clarify the magnetic memory effect in the elastic stage. According to analysis with the J-A model and the results of a rotating bending fatigue experiment, the MMM field follows the law that the state approaches equilibrium under the action of cyclic stress. This is similar to what the J-A model shows, only with replacement of the global equilibrium state Man in the J-A model with the local equilibrium state M0. The expression of M0 is obtained by considering the energy balance in the process of magnetization. M0 changes with the pinning resistance, external field, and type of stress cycle. Additionally, the M0-σ curve is a loop around the Man-σ curve, which is consistent with experimental results. How the modified J-A model describes the variation in MMM field in the process of fatigue is also discussed. This paper shows that the J-A model can be used to analyze the magnetic memory effect in the process of fatigue after replacing Man with M0. [ABSTRACT FROM AUTHOR]

The bulk polycrystalline samples with nominal compositions Zn0.98-y(Mn/Co)0.02(Al/Sb)yO (y=0, 0.01, and 0.03) have been synthesized via solid state reaction route. The x-ray diffraction results reveal the presence of mainly wurtzite structure of pure ZnO in all the Al/Sb codoped ZnMnO and ZnCoO samples. EDAX results confirm the presence of all elements in the samples in the stoichiometric ratio. While the Zn(Mn/Co)O samples show paramagnetic behavior at room temperature, the Al/Sb codoped ZnMnO samples exhibit room temperature ferromagnetism (RTFM) with saturation magnetization (Ms). The M-H curves of Al/Sb codoped ZnCoO samples show almost linear variation with a small kink at the origin, indicating the presence of weak ferromagnetism in the Al/Sb codoped ZnCoO samples. Possible mechanisms of the observed RTFM in Al/Sb codoped Zn(Mn/Co)O samples are discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, two methods for the synthesis of magnetic nanotubes inside the pores of anodic alumina membranes by atomic layer deposition (ALD) are compared. The precursors were nickelocene or cobaltocene, and H2O or O3. The first method consists of a three-step ALD cycle: First, the sample is exposed to the metal-organic precursor, subsequently to water, and finally, to hydrogen. In the second method, metal oxide is deposited by a conventional two-step ALD cycle. After the ALD process, the sample is reduced under hydrogen atmosphere. The magnetic nanotubes obtained by the second method have a smaller grain size and improved magnetic properties. The magnetic nanotubes with diameters ranging from 35 to 60 nm exhibit a preferential magnetization direction along the nanowire axis. The Ni or Co nanotubes with larger diameters (around 160 nm) show a nearly isotropic magnetic behavior, with the magnetic moments arranged in a vortex state at zero field. [ABSTRACT FROM AUTHOR]

Up to this date, the conventional electromagnetic force calculation methods such as Maxwell stress, virtual work, Kelvin’s formula, equivalent magnetic charge, and equivalent magnetizing current produce results where the surface component takes up a major portion of the total force, with the portion of the body force being very small or even none. As the formulation of the above mentioned methods starts from the concept of body or volume force, there has been controversy over the true concept of electromagnetic force identity. In this paper, it is shown that electromagnetic body force, which is also called volume force, can be calculated using virtual air-gap scheme that is derived from the generalized equivalent source methods. For the body force calculation, the application of virtual air gap is extended to calculate the force of each finite element as if an element is an independent body surrounded by virtual air gap. The force calculation methods adopted in this paper include Maxwell stress, magnetic charge, and magnetizing current. The examination of the calculated force distribution shows that the force can be expressed only as body force distribution. The total force calculated by the volume integration of the body force on the magnetized body agrees well with the total force calculated by conventional approaches. [ABSTRACT FROM AUTHOR]

In this paper experimental stress-strain and magnetization versus field curves measured for Ni[SUB2]MnGa alloys are compared with modeling results obtained using a statistical model. The model is based on the assumption of equivalence between the magnetic field and mechanical stress through magnetoelastic interactions. The approach is extended to describe the complex irreversible behavior of strain and magnetization using a statistical distribution of the energy barriers that separate the metastable states of the martensite twins. A theoretical value of the energy conversion coefficient c[SUBme] = 1.57 × 10[SUP-4] MPa (kA/m)[SUP-2] is found, which is in good agreement with the experimentally determined value of 1.25 × 10[SUP-4] MPa (kA/m)[SUP-2]. [ABSTRACT FROM AUTHOR]

The paper proposes the use of a Lorentzian function to describe the irreversible component of the magnetization of soft materials with hysteresis using the Everett's integral. We will derive an analytical formula to compute the irreversible magnetization, and compute the reversible component by the measurements of the major loop. We shall compare the numerical results with experiments on not-oriented-grain magnetic irons. [ABSTRACT FROM AUTHOR]

The approach of using the generalized Meiklejohn-Bean model to derive the antiferromagnetic thickness dependence of exchange bias and coercivity in ferromagnetic/antiferromagnetic bilayers is justified. The mathematical procedure to obtain the analytical expressions through finding the critical fields is illuminated. [ABSTRACT FROM AUTHOR]

The concept of the memory motor is based on the fact that the magnetization level of the AlNiCo permanent magnet in the motor can be regulated by a temporary current pulse and memorized automatically. In this paper, a new type of memory motor is proposed, namely a flux mnemonic double salient motor drive, which is particularly attractive for electric vehicles. To accurately analyze the motor, an improved hysteresis model is employed in the time-stepping finite element method. Both simulation and experimental results are given to verify the validity of the new method. [ABSTRACT FROM AUTHOR]

In the paper, a jump-noise process is introduced in magnetization dynamics equations in order to account for random thermal effects. It is demonstrated that in the case of small noise, Landau-Lifshitz and Gilbert damping terms emerge as average effects caused by the jump-noise process. This approach leads to simple formulas for the damping constant in terms of the scattering rate of the jump-noise process. These formulas also reveal the dependence of the damping constant on magnetization. The analysis of random switching of magnetization caused by the jump-noise process is presented. It is shown that the switching rate at very low temperatures may appreciably deviate from the predictions of thermal activation theory, which is consistent with experimental observations of low temperature switchings and is usually attributed to the phenomenon of 'macroscopic tunneling' of magnetization. [ABSTRACT FROM AUTHOR]

In this paper, stochastic magnetization dynamics driven by a jump-noise process is discussed and, under the condition of 'detailed balance,' generalized H-theorems for this dynamics are established. These H-theorems reveal the existence of a class of functionals that monotonically decrease in time during stochastic magnetization dynamics. [ABSTRACT FROM AUTHOR]

This article reports on the influence of the magnetization damping on dynamic hysteresis loops in single-domain particles with uniaxial anisotropy. The approach is based on the Néel-Brown theory and the hierarchy of differential recurrence relations, which follow from averaging over the realizations of the stochastic Landau-Lifshitz equation. A new method of solution is proposed, where the resulting system of differential equations is solved directly using optimized algorithms to explore its sparsity. All parameters involved in uniaxial systems are treated in detail, with particular attention given to the frequency dependence. It is shown that in the ferromagnetic resonance region, novel phenomena are observed for even moderately low values of the damping. The hysteresis loops assume remarkably unusual shapes, which are also followed by a pronounced reduction of their heights. Also demonstrated is that these features remain for randomly oriented ensembles and, moreover, are approximately independent of temperature and particle size. [ABSTRACT FROM AUTHOR]

The substitution of Mn for Fe in Ce2Fe17 suppresses its ferromagnetic ground state completely for Mn contents x>=0.5 Mn/f.u. Ce2Fe16Mn has only an antiferromagnetic phase (incommensurate helix along c axis) below TN=198 K. In this paper, we present and discuss the effects of deuterium insertion (that can be considered as an application of negative chemical pressure) on the magnetostructural properties of Ce2Fe16Mn. Application of (positive) high pressures up to 10 kbar on Ce2Fe16MnDy deuterides (y=1,2.3) allowed us to estimate the role of lattice volume and to divide it from the role of modified electronic band structure that both determines the magnetic states of the deuterated compounds. The results show that a ferromagnetic phase is stabilized by the insertion of D into the antiferromagnetic Ce2Fe16Mn. The Curie temperature TC of Ce2Fe16MnDy deuterides increases with increasing D content reaching TC=258 K for y=2.3 and remarkably decreases with pressure dTC/dP=-5.4 K/kbar and dTC/dP=-3.6 K/kbar for Ce2Fe16MnD1 and Ce2Fe16MnD2.3, respectively. Significant difference between the magnetization of Ce2Fe16MnD1 under pressure and the one of the parent compound at ambient pressure indicates that changes of the volume alone cannot determine the magnetic states upon the initial deuteration. However, the volume expansion becomes dominant when increasing the deuterium content up to 2.3 D/f.u. [ABSTRACT FROM AUTHOR]

This paper is devoted to numerical simulations of the magnetization dynamics driven by a spin-polarized current in extended ferromagnetic multilayers when a point-contact setup is used. We present (i) detailed analysis of methodological problems arising by such simulations and (ii) physical results obtained on a system similar to that studied in Rippard et al. [Phys. Rev. Lett. 92, 027201 (2004)]. We demonstrate that the usage of a standard Slonczewski formalism for the phenomenological treatment of a spin-induced torque leads to a qualitative disagreement between simulation results and experimental observations, and discuss possible reasons for this discrepancy. [ABSTRACT FROM AUTHOR]

The resilience of the exchange bias (Hex) in ferromagnet/antiferromagnet bilayers is generally studied in terms of repeated hysteresis loop cycling or by protracted annealing under reversed field (training and long-term relaxation, respectively). In this paper we report measurements of training and relaxation in NiFe films coupled with polycrystalline FeMn and epitaxial α-Fe2O3. We show that Hex suppressed both by training and relaxation was partially recovered as soon as a field cycling for consecutive hysteresis loop measurement was stopped or the magnetization of the ferromagnet was switched back to the biased direction. In both cases we can model the observed logarithmic time relaxation behavior, and its film thickness and temperature dependence, in terms of a thermally activated reversal of the antiferromagnetic domain configuration to reduce the total magnetic energy. [ABSTRACT FROM AUTHOR]

While most recent studies of the spin-transfer torque effect in nanoscale magnetic structures mainly concern with spin-wave excitation and the magnetization hysteretic switching induced by spin-polarized current, we theoretically investigate the large angle magnetization precessions triggered and sustained by the spin current in great detail using the Landau-Lifshitz-Gilbert equation. The study is conducted particularly on the nanostructures comprising square magnets with an easy-plane anisotropy. A simple nanoscale magnetoelectronic device is proposed based on the structure without mechanical components to function as a motor to convert a dc current into an ac voltage of microwave frequency. The device is unique because the output amplitude and frequency can be continuously tuned by the electrical current in a wide range. Quantitative analysis of the device structure, function, and realization is provided. [ABSTRACT FROM AUTHOR]

We have studied in a systematic way the magnetization reversal processes of single castellated Ni[sub 80]Fe[sub 20] nanowires fabricated by advanced electron beam lithography. The structures consist of two 5 μm wide Ni[sub 80]Fe[sub 20] support wires bridged with a castellated nanowire of width in the range from 80 to 150 nm. We have used the anisotropic magnetoresistance (AMR) effect as a probe of the spin orientations and hence magnetization reversal processes in these complex magnetic structures. When the applied fields are along the horizontal legs of the castellated nanowire, we observe a unique MR response due to the creation of magnetic local easy and hard axes resulting in a number of discontinuous jumps in the magnetoresistance. The magnetoresistance behavior is strongly influenced by spin states at corners of the nanowire for field applied parallel or perpendicular to horizontal legs. These results are in agreement with simple micromagnetic simulations. © 2004 American Institute of Physics. [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 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]

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]

In this paper, the magnetoelectric effect in single-crystalline Sr Z-type hexaferrite materials is reported. The measurements include material characterization and change in remanence magnetization (Mr) versus electric field. In a very low electric field equal to 3.75 V/cm, 14% change in Mr was observed. We deduced a magneto-electric coupling of 55.4 in CGS units or 2.32 × 10-6 sm-1 (SI units) which is the highest value measured to date. [ABSTRACT FROM AUTHOR]

In this paper, the microscopic mechanism for structural, ferroelectric, and magnetic stabilities in displacive perovskite structured multiferroics is investigated by studying BiFeO3-PbTiO3 solid solutions. The results revealed that thermal stability and ferroic orders are intimately connected with the changes in A and B perovskite sites. The breakdown mechanism of the cycloidal magnetic network, which permits to observe the resulting macroscopic magnetization is reveled, compared, and presented for various compositions of the BiFeO3-PbTiO3 system. The delicate energetic balance that stabilizes the electrically polar structures in displacive perovskite multiferroics is proposed and it was showed that it is fully connected to the configuration (atomic occupancy and formal ionic charge) of each individual site of the perovskite unit cell. [ABSTRACT FROM AUTHOR]

Grain-oriented (GO) laminations owing to their crystalline and textured structure exhibit strong anisotropy in magnetic characteristics. GO laminations generally display highly steep, gooseneck, and narrow waist rolling direction (RD) hysteresis loops and complex-shaped transverse direction (TD) curves. The original Jiles-Atherton (JA) model needs improvisation while modeling such characteristics. The paper proposes a modified JA model for the hysteresis modeling of GO laminations with consideration of their crystalline and textured structure. The model is based on single crystal approximation of polycrystalline materials and modifies the anhysteretic magnetization on account of anisotropic energy. It takes into account the domain wall motion as well as domain magnetization rotation. The model provides a better prediction of RD hysteresis loops and also shows ability to characterize of TD hysteresis loops with reasonable accuracy. The model preserves simplicity of the original JA model. [ABSTRACT FROM AUTHOR]

In this paper we present a study of superparamagnetic and superspin glass states of magnetic nanoparticles confined in mesoporous templates. Characterization utilizes dynamic magnetization techniques, ac susceptibility, and ferromagnetic resonance, in addition to dc magnetization curves. In order to differentiate between the intrinsic and collective properties, we considered three magnetic nanoparticles systems with comparable size, shape, and crystallinity but with different intrinsic magnetocrystalline anisotropy. Further, confinement effects were studied by considering three different geometries of nanoparticles. The effect of the geometrical confinement and intrinsic anisotropy of the nanoparticles are discussed based on known theoretical predictions. [ABSTRACT FROM AUTHOR]

In this paper we present the calculated spectra of signals originating from the magnetization reversal of a system of two identical bistable magnetic moments. We show that in contrast to the spectrum characteristic of magnetization reversal in any common ferromagnetic material, the amplitude of the harmonics in the calculated spectra can change periodically. Also, we present experimental spectra of signals induced by the magnetization reversal of two magnetically coupled glass-covered. Periodic variation of the harmonics amplitude predicted by the calculations was observed in the experimental spectra. [ABSTRACT FROM AUTHOR]

Soft FeCo films of high magnetization are a well known integral part of today's magnetic recording heads. Values for the volume exchange, an important parameter since it determines exchange length, domain wall width, and energy are, however, available for few compositions of FeCo in spite of the widespread use of these alloys. This paper presents results for volume exchange on Fe65Co35 determined by means of a detailed Brillouin light scattering study, one of a few methods that permit the measurement of exchange. A set of Fe65Co35 films of various thickness values was examined, and volume exchange was found to be 3.5 × 10-6 erg/cm, far higher than what is often assumed. [ABSTRACT FROM AUTHOR]

This paper shows how to implement a semi-implicit algorithm based on the Adams-Bashforth algorithm as a predictor, and a second order Adams-Moulton procedure as a corrector in the Landau-Lifshitz-Gilbert-Slonczewski equation. We compare the results with a Runge-Kutta scheme of the 5th order, while for the standard problem #4 (and, in general, for the LLG equation) the computational speeds are of the same order, and we found better performance when the thermal fluctuations or the spin-polarized currents are taken into account. [ABSTRACT FROM AUTHOR]

In this paper, we study the effect of mechanical stress on the domain configuration of a NiFe film obliquely deposited on a compliant polyimide substrate. To this end, we have developed a new method combining in situ mechanical tests with magnetic force microscopy (MFM) imaging. This approach allows changing the static magnetization structure of the film by controlling the stress-induced anisotropy. In the absence of applied stress and magnetic field, the sample shows stripe domains with an in-plane tilted direction with respect to the stress axis. After saturating the film, application of an increasing stress regenerates progressively a stripe domains structure with a modified in-plane magnetization direction. [ABSTRACT FROM AUTHOR]

Measurement of first order reversal curves (FORC) is emerging as a common characterization method to understand the exchange and magnetostatic interactions in magnetic films. In this paper, the FORC of the top and bottom layers of an antiferromagnetically coupled (AFC) perpendicular recording media is studied. The AFC media shows four peaks in the FORC contours, as against a single peak observed in the FORC of typical magnetic samples. Moreover, it is also pointed out that the FORC contours may be affected by time-dependent magnetization effects. [ABSTRACT FROM AUTHOR]

This paper presents the results of a high pressure study on the ferrimagnetic compound ErCo2, which exhibits at ambient pressure magnetic ordering below TC = 33 K, where the localized Er magnetic moments order ferromagnetically, and the itinerant moments in the Co sublattice, align antiparallel to the Er moments. In the paramagnetic range, clustering of the Co moments is observed below Tf ∼ 100 K for which the term 'parimagnetism' has been proposed. In contrast to the pronounced peak in the AC susceptibility data at TC only a tiny 'bump' shows up at Tf. The decrease of both TC and Tf with applied hydrostatic pressure has been observed, the first one being in agreement with previously published data. At higher pressures, an asymmetry in the TC-related AC susceptibility peak has been observed owing to a decoupling of the magnetic ordering phenomena in the Er and Co sublattices. Compared to earlier published results, our magnetization measurements at higher pressures above PC reveal a small but clearly observable evolution of both the critical temperature and saturated magnetization. [ABSTRACT FROM AUTHOR]