Field-induced magnetic transition in cobalt-ferrite

We present magnetostriction and magnetization measurements of a cobalt ferrite (Co 0.8 Fe 2.2 O 4 ) single crystal. We observe unusual behavior in the magnetic hard axis of the single crystal which manifests in a jump of the magnetization curve at a critical field. This first order magnetization process (FOMP), which is explained as an anisotropy-driven transition, is visible at temperatures lower than 150 K. By analyzing the anisotropy constants, we found that the higher order anisotropy constant K 2 dominates the anisotropy energy. In the magnetostriction measurements, the FOMP is clearly visible as a huge jump in the [111] direction, which can be explained by means of a geometric model.