Magnetic properties of fine Fe-Co-B particles prepared by chemical reduction

The effect of chemical composition and particle size on the magnetic properties of Fe-Co-B fine particles has been studied. The powders were produced by chemical reduction of aqueous solutions of ferric chloride and cobalt chloride with sodium borohydride. The structure of the initially reduced powders varied from amorphous to crystalline bcc depending on the boron concentration. Chemical composition analysis showed a boron content in the range 5--30 at. %. The particle size was found to be 25 nm. The magnetization and coercivity of as-made powders were relatively low. After annealing, the maximum values of magnetization and coercivity obtained were about 160 emu/g and 1940 Oe, respectively. The temperature coefficient of coercivity varied from negative to positive with sample composition and packing fraction