A new method for the introduction of periodic boundary conditions to the self-magnetostatic (demagnetization) tenn in micromagnetic simulations is described, using an Ewald-like summation method in real space. The long-range character of the dipolar interactions is included without any distance cutoffs. The accumulated errors are carefully monitored to provide easy control of the quality of the results. This allows the calculations to be either accurate up to floating point limitations or less precise when computational speed requirements dominate. This method is incorporated into a full micro magnetic program, and comparisons are made to analytic results.

Bloch points in permalloy cylinders are investigated using a micromagnetic framework, where thermal effects are included via the Landau-Lifshitz-Bloch equation of motion. We show that this enables micromagnetic modeling of a Bloch point avoiding the problem of singularities, which have been rep0l1ed in the literature so far. The details of the Bloch point which we reveal are compared with earlier analytic approximations describing its geometry and the magnetization drop in its center. The temperature dependence of characteristic parameters, like the Bloch point radius or the azimuthal inflow angle is given in the full temperature range.

We study the reversal mechanisms in a self-assembled, hexagonally ordered Fe antidot array with a period of 200 nm and an antidot diameter of 100 nm which was prepared by polystyrene nanosphere lithography. Direction-dependent information in such a self-assembled sample is obtained by measuring the anisotropic magnetoresistance (AMR) through constrictions processed by focused ion beam milling in nearest neighbor and next nearest neighbor directions. We show that such an originally integral method can be used to investigate the strong in-plane anisotropy introduced by the antidot lattice. The easy and hard axis reversal mechanisms and corresponding AMR signals are modeled by micromagnetic simulations. Additional in-field magnetic force microscopy studies allow the correlation of microscopic switching to features in the integral AMR. We find that the easy axis of magnetization is connected to a distinct periodic magnetic domain pattern, which can be observed during the whole magnetization reversal. While this process is driven by nucleation and propagation of reversed domains, the hard axis reversal is characterized by a (stepwise) rotation of the magnetization via the antidot lattice' easy axes.

Inelastic scattering of excitons on Fe++ ions in Cd1-xFexSe was studied by resonant Raman scattering. Polarization measurements were done using a modulation technique, allowing for the first time to determine the full polarization state of the detected light. The obtained results were compared to a simple calculation in an incoherent model of scattering on Fe++ ions.

In a combined experimental and numerical study, we investigated the details of the motion and pinning of domain walls in isolated and interacting pennalloy triangular rings (side 2 /Lm, width 250 nm, and thickness 25 nm). To induce interaction between the rings, they were arranged either in vertical chains with an apex of each triangle in proximity to the edge center of the triangle above it or in horizontal chains where the proximity is between the adjacent corners of the triangles. Using longitudinal and diffraction magneto-optic Kerr effects, magnetic force microscopy, and micromagnetic simulations, we detennined the field dependence of the spin structure in the rings. In all cases the remnant state of each ring is an "onion" state characterized by two domain walls-one head to head the other tail to tail-pinned at the apexes. In isolated rings the magnetization reversal occurs between two onion states via the fonnation of an intennediate vortex state, which arises from the motion and annihilation of the two domain walls. In the case of the horizontal chains the reversal mechanism is unchanged except that the dipolar interaction affects the field range in which the rings are in the vortex state. In the case of vertical chains an additional intennediate state is observed during reversal. The new state involves a domain wall pinned at the center of the edge that is in close proximity to the apex of its neighbor, We show that the domain-wall motion in this last case can be modeled by a triple potential well. Because the new state requires that a domain wall be pinned at the neighboring apex, our observations can be viewed as a very elementary fonn of magnetic logic. PACS number(s): 75.60.Ch, 75.60.Jk, 78.20.Ls