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.