The magnetic anisotropy of Fe-SiO₂and Fe₂₀Ni₈₀-SiO₂granular solids

Abstract

Fe-SiO2 and Fe20Ni80-SiO2 granular solids have been prepared using a sol-gel method and investigated by X-ray diffractometry, Mossbauer spectroscopy and transmission electron microscopy. The magnetic properties were measured and the coercivity of these granular solid samples was found to be almost independent of temperature in the range 80-300 K. The effective magnetic anisotropy including shape anisotropy and strain anisotropy has been determined from the magnetizing curves of these granular solid samples using the law of approach to saturation. The obtained values of the effective magnetic anisotropy exceed 106 erg cm-3. The almost temperature-independent effective magnetic anisotropy can approximately explain the variation of Hc versus T for the granular solid samples. The shape anisotropy has been estimated assuming that the average axis ratio of the metal particles c/a is 1.2 and the strain anisotropy has been calculated from the effective anisotropy and the shape anisotropy. The magnitude of the strain anisotropy and the variation of the strain anisotropy with temperature are explained for the Fe-SiO2 and Fe20Ni80-SiO2 granular solid samples.