Coercivity of anisotropic γ-[Fe.sub.2][O.sub.3] particles at high temperatures

The coercivity of five different samples of anisotropic γ-[Fe.sub.2][O.sub.3] particles is studied in the temperature range 0°-600°C. It is found that their relative coercive force [h.sub.c] = [H.sub.c](T)/[H.sub.c](0) is almost a linear function of the relative magnetization of the particles [m.sub.s] = [M.sub.s](T)/[M.sub.s](0), where [H.sub.c](0) and [M.sub.s](0) are the values of [H.sub.c] and [M.sub.s] of the particles at 0°C. It is experimentally found that [h.sub.c] = β[m.sub.s] + α, where β = 1.103 ± 0.015 and α = -0.114 ± 0.009. This character of the dependence of [h.sub.c] on [m.sub.s] suggests that, at high temperatures, [H.sub.c] of anisotropic γ-[Fe.sub.2][O.sub.3] particles can depend on both their shape anisotropy and other factors. It is assumed that, as the temperature increases, anisotropic γ-[Fe.sub.2][O.sub.3] particles in a zero magnetic field are divided into small structurally and magnetically unstable nanoclusters with magnetization spontaneously changing its direction. As a result, [H.sub.c] disappears near the Curie temperature, although the saturation magnetization of the particles in a field of 1 T is still retained at this temperature. DOI: 10.1134/S1063784214090229