[en] A numerical framework is presented for the solution of the Landau - Lifshitz - Gilbert equation of magnetization motion using a semi-implicit Crank - Nicholson integration scheme. Along with the details of both space and time domain discretizations, we report on the development of a physically based self-consistency criterion that allows for a quantitative measurement of error in dynamic micromagnetic simulations. In essence, this criterion relies in recalculating from actual magnetization motion the imposed phenomenological damping constant. Test calculations were performed with special attention paid to the determination of suitable integration time steps. [copyright] 2001 American Institute of Physics

[en] We have calculated temperature-dependent switching curves using the stochastic Landau-Lifshizt-Gilbert equation for a macrospin with a uniaxial anisotropy. As in experimental results, we obtained curves that shrink with increasing temperature. We find that an Arrhenius law for the relaxation time τ corresponds well to calculations, thus allowing for a determination of the attempt frequency. The results are also found to compare favorably with Coffey's formulae for τ in the low and high damping limit

[en] Based on specific examples, we examine the consequence of spin-polarized current injection into confined model micromagnetic configurations, namely a high remanence state known as the S state and a low, though nonzero, remanence state called the Leaf state. Magnetization dynamics is solved in the space and time domain owing to the Landau - Lifshitz - Gilbert equation. It is shown that, within model bounds, the S state is not propitious to fast switching under the sole influence of a polarized current, even if disregarding the current induced field, whereas Leaf state switching characteristics become extremely complex as soon as due account is made for the latter. [copyright] 2001 American Institute of Physics

[en] Ion implantation in ferrimagnetic garnet epilayers containing bubbles suppresses hard bubbles and defines the propagation tracks for moving bubbles. It has been recognized that the existence of a strain/stress gradient in the vicinity of an implantation boundary is responsible for the deformation of charged walls to which bubbles are attached. Two elastic models describing the stress/strain distribution around an implantation boundary are presented. They rely on densities of defects, infinitesimal dislocations and point defects in the continuum approximation. Assuming a ribbon geometry reduces the elastic problem to a plane-strain one. Very compact expressions can be deduced from the point-defect model if the half-space is restricted to a plane. The dislocation model indicates that most of the elastic strain/stress is due to the lateral thrust exerted by the implanted ribbon on the surrounding elastic medium. (author)

[en] Two examples of in situ dynamic experiments using synchrotron white beam X-ray topography are described. The first is concerned with the plastic deformation of Fe-Si single crystals and the second with the recrystallisation of aluminium polycrystalline samples. Only partial but representative results are presented. The main advantages and shortcomings of the technique are discussed. (Auth.)

[en] Dynamic X-ray diffraction theory in elastically distorted crystals is used to simulate the rocking curves of ion-implanted ferrimagnetic garnet epilayers. It is found that excellent agreement between experimental and simulated rocking curves may be obtained in the case of a standard neon implantation. On the other hand, despite numerous attempts, only a poor fit has been achieved in the case of hydrogen implantation. Peak and sub-peaks broadening suggests that Huang scattering takes place, at least at a precursor level. Finally, the (plastic) strain profiles deduced from the rocking-curve analysis provide a means of computing the elastic strains associated with implantation boundaries, according to the model developed in the first part of this work. Satisfactory agreement between theory and the experimental determination of these strains is obtained by means of plane-wave X-ray imaging. (author)

[en] Magnetic force microscopy (MFM) studies concerning electrodeposited nanowires are reviewed. It is shown that Co nanowires with 35 nm diameter can exhibit single domain states, opening the way to their potential use as MFM probes. Besides, special attention is devoted to the MFM imaging process of soft magnetic samples. Different observations proving the tip influence when analyzing patterned permalloy elements are presented. Experimental results and numerical simulations using a general framework for reversible perturbations are shown to agree quantitatively

[en] The distribution of strain-induced magnetization directions around a non-implanted disc in an ion-implanted ferrimagnetic garnet epilayer supporting bubbles is derived from the elastic model developed by the author. It is shown that when an in-plane field is applied along a direction close to an in-plane easy-axis, the depth-dependent morphology of charged walls varies strongly with the relative magnitudes of the magnetostriction constants. For λ₁₀₀ = λ₁₁₁ (λ₁₁₁ < 0), the largest charged-wall jump (flip) is expected to occur at the interface between implanted and non-implanted thicknesses. For λ₁₀₀ = -1/2λ₁₁₁, the negative shear strain is demonstrated to favour charged walls pivoting around the in-plane easy-axis in the interface region. A switching mechanism is proposed which explains charged-wall rearrangement at the surface during flip when λ₁₀₀ is positive. (author)

[en] The subject is discussed under the headings: introduction; basic physics of Bloch wall statics (magnetization (a) parallel (b) perpendicular, to the surface); magnetostrictive strains; detectability of magnetostrictive strains by means of X-ray imaging techniques; interactions of individual lattice defects and moving walls (optical studies; X-ray studies); conclusion. (U.K.)

[en] White beam synchrotron X-ray topography has been used to conduct in situ studies of the influence of applied elastic tensile stress on magnetic domain configurations in Fe 3.5 wt% Si single crystals. Specimens of [011] tensile axis, and either (100) or (0anti 11) surface orientation were utilized. Tensile stress was applied using a specially designed miniature tensile stage. In specimens of (0anti 11), surface the characteristic Dijkstra and Martius type I structure is included upon application of stress, eventually to be replaced by the type II structure. The transition is understandable in terms of stress-induced anisotropy. On the other hand, in specimens of (100) surface, the initial structure, which essentially consists of 90⁰ was perpendicular to the tensile axis, changes to one which mainly consists of (010) and (001) 180⁰ walls. Both structures have approximately equal volumes magnetized along [001] and [010]. This suggests that the transition is not driven by induced anisotropy. Alternative explanatiions are discussed. Changes in domain configurations around inclusions are also discussed. (orig.)