The temperature dependence of coercivity in cobalt-aluminum fine-particle ferromagnets

A model based on coherent rotation has been developed to describe quantitatively the magnetic hardening exhibited by heat-treated β-CoAl alloys. The coercivity of these fine-particle ferromagnets was measured over the temperature range from 77 to 757 K and correlated with the calculated values based on the proposed model. The model incorporates both crystal anisotropy constants, K₁ and K₂, as well as the shape anisotropy of the particles. The unusual minimum observed at elevated temperatures is predicted by the model and shown to derive directly from the interplay between the crystal and shape anisotropies of the elongated single-domain particles. The magnetic properties of the particles are shown to depend critically on the crystallography of the solid-state transformation and particle morphology, which were determined by transmission electron microscopy and diffraction