Magnetic force microscope study of domain wall structures in magnetite

Abstract

Domain walls (DW) in a small multidomain grain (≊20 μm) of magnetite (Fe3O4) exhibiting a planar domain pattern were studied using a magnetic force microscope(MFM). Most walls were subdivided with one or two Bloch lines and all walls displayed asymmetric MFM responses. Domain walls were observed to have small offsets either at the location of Bloch lines or at other locations without Bloch lines. The experimental data were described by a model in which (1) the easy axis of magnetization is not exactly parallel to the grain surface but is slightly inclined, and (2) there is also some plane dividing the grain in two parts with slightly different inclined easy axis directions. The inclined easy axis produces asymmetric spin distributions across the DW and wall offsets occur to reduce the surface magnetostatic energy of the wall.