Metal-Spinel Composites (M⁰_xFe⁰_1-x)_α-(M_yFe_3-y)_1-α with M=Co, Ni Synthesis and Physical Properties

Abstract
Composite materials made up of cobalt-iron alloy (or nickel -iron alloy) and Co (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 Fe⁰ and 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 reagents and KOH. Pure cobalt - containing composites are obtained in a narrow range of KOH concentration. The metallic phases have the α-Fe (b.c.c. structure) or α-Mn structure, and the lattice parameter of the cobalt - containing magnetite lies between 8.396(2)Å and 8.405(2)Å. Nickel - containing composites without hydroxides are obtained for higher KOH concentrations, 14-15 mol/liter. For lower and higher KOH concentration, hydroxides or amorphous phases precipitate. The coercive field increases when [Co]/[Fe] increases.