Grain-size dependence of two-dimensional micromagnetic structures for pseudo-single-domain magnetite (0.2-2.5 μm)

Abstract

SUMMARY Micromagnetic modelling with a Monte Carlo method was performed to obtain 2-D micromagnetic structures of pseudo-single-domain (PSD) magnetite (0.2‐2.5 mm). Cubic model grains were subdivided into a 2-D array with a maximum of 100◊100 cells. In order to find an appropriate cell size, the variation of the self-consistency parameter (S) with cell size was examined. We regard solutions with S>0.95, which corresponds to cell sizes 0.03 mm, as representing realistic micromagnetic structures. For saturation remanence states, we found vortex structures for small PSD grains (0.25 mm) and closure domain structures for larger PSD grains (0.6‐2.5 mm). Between 0.25 and 0.6 mm, structures remained chaotic even after a very large number of Monte Carlo steps. In grains with a closure domain structure, domain walls were usually subdivided into several segments with opposite polarities of magnetization rotation.