Elongated single-domain ferromagnetic particles

Abstract

The ‘‘fundamental theorem’’ of Brown on spherical particles is extended to prolate spheroids, whose long axis is also an easy axis for a cubic or uniaxial anisotropy. It is rigorously proven that for such a particle, with a minor semiaxis a, the lowest free-energy state is that of a uniform magnetization, if a<ac 0, and an expression is given for this ac 0. Typical recording particles are thus shown to be single domains in their remanent state, with their magnetization reversing by the curling mode.