METAL-SPINEL COMPOSITES ((MXFE1-X0)-FE-0)(ALPHA)-(MYFE3-YO4)(1-ALPHA)WITH M=CO, NI SYNTHESIS AND PHYSICAL-PROPERTIES

Composite materials made up of cobalt-iron alloy (or nickel -iron allo y) and Clo (or Ni) doped magnetite are synthesized in an aqueous media . The procedure employed is a low temperature reaction in alkaline KOH solution which involves the disproportionation of Fe(II) into Fe-0 an d Fe(III) and a reduction of Co(II) or Ni(II). The composition of the final product depends on the initial and final concentrations of reage nts and KOH. Pure cobalt - containing composites are obtained in a nar row range of KOH concentration. The metallic phases have the alpha-Fe (b.c.c. structure) or alpha-Mn structure, and the lattice parameter of the cobalt - containing magnetite lies between 8.396(2)Angstrom and 8 .405(2)Angstrom. Nickel - containing composites without hydroxides are obtained for higher KOH concentrations, 14-15 mol/liter. For lower an d higher KOH concentration, hydroxides or amorphous phases precipitate . The coercive field increases when [Co]/[Fe] increases.