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We investigated the effect of thermal relaxation on reversible transverse susceptibility (RTS), χ, of single domain Stoner–Wohlfarth particles. We studied such an effect as a function of the orientation β of the easy axis with respect to the drive field (the z axis) within a non‐interacting bi‐state model. At β=00 one prominent cusp occurs for both χt1 and χt2 along the direction perpendicular to the drive field at H≂HC

Field angles and sweep rate dependence of coercivity of the Stoner–Wohlfarth (S‐W) particles are studied based on the decay‐rate model. An analytic expression of the hysteresis loops based on the model is obtained as a function of applied field for various frequencies at various field angles with respect to the easy axis. Variation of the coercivities versus the sweep rate (measurement frequency), field angles, anisotropy constant, activation volume, and the combination thereof, and the distribution of easy axis, etc., have been obtained. Comparison with the thermal‐equilibrium and S‐W hysteresis loops are made. Coercivities of such a system generally increase with increasing sweep rate, anisotropy constant and activation volume, etc., hence decreases with increasing sweeping period. As a function of the field angles, the coercivity curve turns flat with increasing field angles and sweeping period.

Comprehensive analysis of the influence of a weak in‐plane field on the dynamics of a planar domain wall in a uniaxial ferromagnet with a small quality factor has been carried out. The peculiarities of the domain‐wall movement in both subcritical Hz

We study the ground state of magnetization orientation inside domains on both sides of a domain wall. In a uniaxial ferromagnet, the orientation becomes asymmetric with respect to the normal to domain‐wall plane when a magnetic field is applied. As a result, the Kondorsky switching‐field distribution function is modified when the magnetization distribution across the wall proper becomes asymmetric and the wall is charged. The variation of the domain‐wall structure, wall‐shape function, and wall‐energy density function γ versus the magnitude and orientation of the external field is examined and discussed. The extra energy associated with the charged wall is expected to enhance domain‐wall relaxation, generating wiggles in thin‐film head readout waveforms.

Energy barrier height and coercivity variation of a pair of interacting particles has been studied as a function of the bonding angle β for 0°⩽β⩽π/2 and applied field using the fixed step Monte Carlo simulation approach supplemented by the perturbation method. Coercivity Hc(β) of the system has local maxima at β=0 and π/2, and a global minimum at β≃65°, and remains depressed compared to the noninteracting case for β⩽30° at any temperature. The barrier height behaves similarly. Due to the random nature of distribution dipole interaction, on average, leads naturally to a reduction in coercivity and energy barrier height in comparison with the noninteracting case.

The pinned domain‐wall (DW) structure is investigated using a perturbational approach in terms of the inverse quality factor 1/Q and the ratio of H∥/Hk (H∥ being the component magnetic field parallel to the anisotropy axis, Hk being the anisotropy field). The parallel component field gives rise to asymmetric boundary conditions which asymmetrize the DW structure. Dependence of the DW energy, static DW structure, and width on the orientation and the strength of the magnetic field has been evaluated and the corresponding Kondorsky function obtained.

Generalized domain wall dynamic equations have been derived. The influence of the external magnetic field normal to the anisotropy axis on the critical parameters of the domain wall motion has been studied and illustrated.

The response of a system to an infinitesimal perturbation becomes singular if the system changes its degree of metastability, i.e., if it has an inflection point. This theory is used to calculate the reversible transverse susceptibility χt of a single domain particle executing a major hysteresis loop under the influence of a field H(t) applied at an angle β to the easy axis. Thermal relaxation is taken into account and the response of the nonequilibrium system to the infinitesimal field h(t)=h sin ωt, h⊥H, is found. The resultant χt is studied as a function of β, temperature, and of the frequency Ω of the biasing field H.

The dynamics and relaxation of magnetization M(r,t) is usually described phenomenologically by the Landau–Lifshitz (LL) equation with relaxation term M=−γ[M×F]+R, where γ is the gyromagnetic ratio (γ≳0), F is the effective field, and R describes the relaxation of the magnetization toward its equilibrium value. It is already well known that the relaxation term of either the LL or Gilbert form does not give a correct description of the dependence of spin‐wave damping on the wave vector at small wave vectors for the models of an isotropic and easy plane ferromagnet. The correct behavior of the spin wave damping may be obtained by taking into account the spatial dispersion of the relaxation caused by the exchange interaction and correct symmetry structure of the relativistic part of the relaxation term which now has to be represented as a sum of the exchange and relativistic parts by R=Rex+Rτ. A review of the recent results on the relaxation obtained in the frames of the LL equation with the relaxation term s...

Domain wall motion under the influences of weak in-plane fields applied along arbitrary directions in an infinite medium with uniaxial anisotropy has been considered. Typically, the azimuthal angle of the magnetization vector along with the domain wall central plane exhibits transient, stationary and oscillatory behavior. The azimuthal angle displays a terrace-like structure at the critical field when subject to a weak perturbation field along the domain wall normal direction. As a result, the domain wall cants out its magnetization vector out of the wall plane and stays in that configuration as it continues to translate onward like a hybrid of Bloch-Néel wall in a quasi-static manner without precession. The in-plane field along the wall normal has limited effect on the domain wall upper bound velocity, while the field parallel to the domain wall can substantially increase it. At a higher drive field, the magnetization (φ) precesses nonuniformly with time and results in nonuniform, anharmonic oscillatory behavior for domain wall motion. Also, as domain wall picks up its velocity, it contracts to reduce its surface demagnetization energy and at the same time interchanges between Bloch type and Néel type in an oscillatory manner.

The time‐dependent temperature distribution of a thin‐film stripe has been solved rigorously using two successive Laplace transforms on both time and coordinate. For a good conducting stripe with a δ‐shaped crack it is shown that the temperature distribution can be very adequately described by the steady‐state solution provided only that the time scale involved is of the order of 10−3 sec or longer. No localized hot spot is possible, for whatever reasons, for a good conductor. However, if heat generation outpaces heat conduction, as would be the case for a poor conductor, a localized temperature becomes quite realizable. Finally, if stripe cracking is developed via grain‐boundary grooving processes somewhere along the stripe, in particular near the anode, void formation there is simply a natural consequence of the temperature‐grandient effect.

The capillarity‐induced surface mass transport has been extended to cases where there is a notch and/or a ridge on a bicrystal system. Changes in the surface morphology caused by capillarity‐induced and electromigration‐induced surface diffusions and grain boundary diffusions have been analyzed. Thermal grooving is shown to develop only when the initial slope of a notch on the crystal surface is less than γb/2γs (γb and γs are, respectively, the grain boundary and the surface Gibbs free energy) or when the initial surface contains a ridge at the grain boundary. The slope of the grooving profile is invariant with time but its depth develops as the one fourth power of time. Surface fluxes due to the electromigration origin change the morphology in an asymmetric manner, biased in the direction of the electron flow. When combined with fluxes from grain boundary diffusion, severe mass depletion and accumulation can occur, giving rise to characteristic electromigration damage of open circuit failures. Finally, ...

A mathematical analysis of the variation of resistance and the electric line of force over a greion in a conducting strupe with a geometrical defect is carried out based on the Christoffel‐Schwarz transformation. The overall resistance of the sripe with a bump‐type defect may turn out to be less than that of homogeneous stripe of the same physical length despite the added resistance due to the current crowding. Possible implications of this effect are pointed out. The electromigration flux divergence at the edige of a void or a cracking is substantially greater than that at the edge of the bump‐type defect. This is in line with the notion that stripe cracking or a faceted void in its embryonic stage first nucleated at the grain‐boundary triple points.

We have derived the static spin configurations of the various kinds of bubble domains using the cylindrical coordinate system. The spin deviation from the wall normal and the variation of the wall width and its characteristic length, etc., have been solved and discussed at some length. The present results can be reduced to the corresponding planar wall results at an appropriate limit, with the exception of the stability condition.

The contribution of a stripe cracking to its resistance is obtained in a closed form by means of Christoffel-Schwarz transformation. It is shown that the cracked region resistance is a sum of two terms in series: one is the typical resistance term which is linearly proportional to the width and inversely proportional to the cross section of the stripe, the other depends sensitively upon the perpendicular depth of the crack, known as the current crowding resistance. Some numerical results for the crack region resistance are presented. The extra local electric field, its corresponding mass flux and their potential implications to electromigration arc also discussed.

The motion of a 180° domain‐wall in pure yttrium iron garnet has been investigated, using the Winter‐Janak domain‐wall excitation spectrum. In particular, the domain‐wall mobility as a function of temperature has been thoroughly studied. It is shown that the demagnetization energy due to the surface roughness of the sample where the domain‐wall plane crosses the sample surface is the main source of resistance to domain‐wall motion; the two‐body part of the surface roughness causes transitions from a uniform translational domain‐wall magnon mode to a degenerate domain‐wall translational magnon mode, and is the predominant process that leads to the domain‐wall motion relaxation. The four‐body interaction intrinsic process contributes very little even at higher temperatures (about 10% of the two‐body interaction at 300°K, much less at lower temperatures). The two‐body process being considered here is, in some sense, similar to the Sparks‐Loudon‐Kittel calculations in which each pit is assumed to scatter inde...

The head field distributions for a conventional ring head and pole-keeper head are shown to be mathematically equivalent, provided that the head pole piece of the ring heads are large compared to the gap length and that the head-field Fourier coefficinets are properly redefined. Despite the equivalence, the ring head write fields are very dissimilar to those of the pole-keeper heads, either within the gap or outside of it in the trailing regions. A total of up to 200 Fourier coefficients was obtained for both heads for several values of the pole-thickness. As an application, the parameters related to the surface-gap field were also evaluated in order to facilitate write-field calculations.