Temperature dependence of magnetic anisotropy of Ga-substituted cobalt ferrite

Abstract

The temperature dependence of magnetization, magnetic anisotropy, and coercive field of gallium-substituted cobalt ferrite was investigated for a series of compositions of Co Gax Fe2-x O4 (0≤x≤0.8). Hysteresis loops were measured for each sample over the range of -5 T≤ μ0 H≤5 T for selected temperatures between 10 and 400 K. The magnetization at 5 T and low temperatures was found to increase for the lower Ga contents (x=0.2 and 0.4) compared to pure Co Fe2 O4, indicating that at least initially, Ga3+ substitutes predominantly into the tetrahedral sites of the spinel structure. The high field regions of these loops were modeled using the law of approach to saturation, which represents the rotational process, together with an additional linear forced magnetization term. The first order cubic magnetocrystalline anisotropy coefficient K1 was calculated from curve fitting to these data. It was found that K1 decreased with increasing Ga content at all temperatures. Both anisotropy and coercivity increased substantially as temperature decreased. Below 150 K, for certain compositions (x=0, 0.2, 0.4), the maximum applied field of μ0 H=5 T was less than the anisotropy field and, therefore, insufficient to saturate the magnetization. In these cases, the use of the law of approach method can lead to calculated values of K1 which are lower than the correct value. © 2008 American Institute of Physics.