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We have utilized micromagnetic simulations to study the effect of structural defects on the magnetic switching behavior of thin elliptical permalloy films. The nonmagnetic void was found to tend to pin the adjacent magnetic moment, which changes the local equilibrium magnetization configurations and alters the switching behavior of magnetization, leading to a large variation in switching fields. In particular, for the case of voids close to the edge, the curling effect of voids is significant and induces the occurrence of the multiple-stage magnetization reversal, leading to significantly large switching fields. Index Terms--Magnetic switching, micromagnetic simulations, patterned films, structural defects.

We have studied the influence of the surface topology on the magnetostatic coupling between two patterned ferromagnetic layers. By the Fourier series method, we can determine the most suitable geometric parameters of the patterned spin-valve structures with giant magnetoresistance. It was noted that a proper shift between two ferromagnetic layers can change the sign and magnitude of the interlayer coupling. Index terms - Spin valve, patterned structure, magnetostatic coupling.

A causality algorithm is introduced to keep track of all history of interacting magnetic systems since saturation. It reflects the true hysteresis of the interacting system with ambient temperature. Though not entirely self-consistent, it satisfies the requirement of causality and is physically more realistic. Because it contains the evolution due to the interactions, thus the coercivity indeed shifts linearly with the coupling strength.

Exact analytical expressions for the local interaction field produced by an infinite array of rectangular prisms are derived. For tablet-like prisms, the local interaction is positive for certain packing density; while for needle-like prisms, the local interaction is always negative. Moreover, local interaction is not a linear function of packing density.

The magnetic surface anisotropy in ultrathin films with a distribution of surface roughness is calculated with a magnetostatic model. The surface roughness can give the famous 1/t dependence of shape anisotropy for thick films; however, the anisotropy deviates from 1/t dependence for very thin films. It can be concluded that a rougher film results in a larger surface anisotropy. The calculated results are reasonably consistent with the experiment.

An exact solution is derived for the first time for the fields of a thin film head with an underlayer. The Fourier analysis is used to determine the distribution of the fringe field components around the head pole, and the accurate Fourier coefficients are evaluated for a range of head geometries. With an underlayer, it is found that the amplitude of vertical field is higher everywhere than that with no underlayer, and the amplitude of horizontal field is lower in the region above the gap and exhibits an enhanced negative lobe near the outer corner of the head pole.

The fringe field of an asymmetric ring head with an underlayer is obtained using conformal mapping techniques for the first time. The Schwartz-Christoffel transformation is used to determine the magnetic field distribution around the head poles, and an analytical field equation is obtained. It is found that an asymmetric ring head with an underlayer is highly suitable for perpendicular recording.

We have studied the temperature effect on magnetic properties in (001) epitaxial Co-NiMn. The interfacial exchange coupling in Co-NiMn not only induces a unidirectional anisotropy but also a uniaxial anisotropy. Double shifted hysteresis loops could be found along the hard axis, and used to accurately determine the anisotropy constants using the coherent rotation model. The cubic anisotropy of Co decreases monotonically with increasing temperature, while the interface-induced uniaxial anisotropy decreases with increasing temperature up to 180[degrees]C, and then increases with further increasing temperature. A mechanism explaining the enhancement of interface-induced uniaxial anisotropy and coercivity at temperatures above 180[degrees]C is proposed. Index Terms--Anisotropies, coercivity, double shifted hysteresis loop, induced uniaxial anisotropy, thin film, vibrating sample magnetometer, (001) epitaxial Co-NiMn.

Research into in-plane magnetic anisotropy in Co films epitaxially grown on NiMn (001) films is presented. It was found that exchange coupling in NiMn/Co induces a unidirectional anisotropy and a uniaxial anisotropy.

We have studied the influence of interparticle interaction on the switching of recording media under a rapidly varying field. Two parallel particles with dipole-dipole coupling for arbitrary bond angle were treated analytically. Under a rapidly varying field, the oscillatory switching bands were observed before the static limit for small damping constant and bond angle. Interaction modifies the switching band shape but only the damping constant changes the band gap.

A soft-phase based heterostructure magnet has been analyzed with micromagnetics. Calculated energy product critically depends on the diameter of the inner soft-phase. The volume fraction of the hard-phase shell region providing the high coercivity is much less than the inner soft-phase region. It was proven, at least theoretically, the energy product of 70 MGOe can easily be achieved for the 100 [angstrom] diameter of soft-phase materials.

Binary clusters of parallel uniaxial particles having dipole-dipole coupling display four stable configurations for bond angle values of 90 and 0 degrees. Thermal relaxation assumptions help solve a master equation for the occupation probabilities of the stable configurations and yield switching field distribution and coercivity values for the particles. Approximate expressions from an extremal analysis coincide well with the numerical estimates from the master equation.

We present a rigorous micromagnetic study for the nucleation by the magnetization curling mode in acicular coated particles. The calculated nucleation field increases with shell thickness and saturates within observable thickness. It is found that the shell uniaxial anisotropy determines the initial slope and the saturation level depends on both the interfacial coupling and shell anisotropy. The shell surface anisotropy will further increase the nucleation field. A very good fitting of experimental data can be obtained by the present mode.