A new metal-spinel composite (Fe0.2Co0.8)0.8[Fe2.38Co0.62 O4]: thermal behaviour under vacuum

Abstract An original method based on disproportionation in liquid medium leads to the formation of metal oxide composites such as (Fe0.2Co0.8)0.8[Fe2.38Co0.62O4]. The metal alloy Fe0.2Co0.8 exhibits a b.c.c. structure and the oxide part consists of cobalt-doped magnetite. The hysteresis curve exhibits a saturation magnetization of 90 A m2 kg−1 and a coercive field of 1200 Oe. Thermal treatment above 400 °C under vacuum leads to the formation of another composite Co0.8[Fe2.38Co0.62O4] for which metallic cobalt exhibits an f.c.c. structure and the oxide a spinel structure. This composite is characterized by a saturation magnetization of 100 A m2 kg−1 and a coercive field of 400 Oe. At 840 °C, it undergoes a reversible crystallographic transition into a cubic phase isomorphic with FeO.