Crystal Dislocations and Coercivity in Fine Grained Magnetite

Abstract

Interaction of the stress field of a favourably oriented edge dislocation with the magnetostriction in a ferromagnetic domain wall in magnetite causes the dislocation to act as a potential well for the domain wall. The coercivity of 20 pm. grains, in which the domain structure is considered to be particularly simple, can be explained on this basis if the dislocations are arranged so that the effects of several of them are additive. The required density of edge dislocations is 109 cm-2, which is entirely reasonable; screw dislocations are not effective in magnetite. To explain the variation of coercivity with grain size it appears necessary to assume that the arrangement of dislocations is neither regular nor random but is partially ordered.