Electron microscope studies of ferromagnetic ordered structures

Abstract

The magnetic properties of crystallographically ordered ferromagnetic materials are strongly dependent on the presence of crystal defects, because of the effect of defects on the domain structure. Electron microscopy enables the defects and domain walls to be imaged simultaneously, and is therefore capable of giving detailed information about their interactions. In alloys containing Mn, antiphase boundaries (APBs) interact very strongly with domain walls, and tend to act as wall nucleation sites. In MnAl, a possible permanent magnet alloy, in addition to APBs, other defects are also present which tend to behave as wall pinning sites. In some ordered alloys, magnetic anisotropy can be induced by plastic deformation. The resulting changes in the domain structure can be studied by electron microscopy. In spinel ferrimagnets, stacking faults can interact with domain walls.