Distribution in strength of the particle anisotropies in a ferromagnetic aggregate

Abstract A particle anisotropy distribution in a ferromagnetic aggregate is explored via the effects of transverse magnetic fields ( H ) on a remanent magnetization ( M R ) previously established. Pertinent to this unconventional property, we have extended the Stoner–Wohlfarth model for a ferromagnetic aggregate of single-domain particles with randomly oriented anisotropy axes. If all the particle anisotropies are identical in strength, it is predicted that the magnetization normal to H stays nearly constant at M R as H is raised up to a critical value and then drops very rapidly as H is raised further. Deviations from this sharp behavior can be readily interpreted in terms of a spread in the size of the particle anisotropies. Thus, from experimental data on a commercial magnetic-memory material, it is deduced that the anisotropy spread is nonzero but fairly narrow. However, the narrowness of this deduced effect may result in part from interparticle exchange coupling, which is ignored in the model.