Magnetic measurements and transmission electron microscopy investigatIons on Fe–Co ultrafine powders derived from a bimetallic carbonyl cluster

Abstract

The molecular carbonyl cluster HFeCo₃(CO)₁₂(1) affords an ultrafine Fe–Co powder by thermal treatment under inert atmosphere. Several magnetic or magneto–structural transformations have been evidenced by thermomagnetic analysis (TMA) from 20 to 950 °C. Transmission electron microscopy (TEM) investigations on samples treated at an intermediate temperature showed the presence of both mono- and bi-metallic crystallites of nanometric size. The saturation magnetization was found to increase with increasing annealing temperature, while the opposite behaviour was found for coercitivity. A comparison was made with the magnetic properties of the cast FeCo₃ alloy.