Structural and magnetic properties of nanocrystalline Fe–Co–Si alloy powders produced by mechanical alloying

Abstract

We report the structural and magnetic properties of nanocrystalline Fe100−x−yCoySix (x = 10, 15, y = 0–20) alloy powders prepared by mechanical alloying process in a planetary ball mill. All the as-milled powders exhibit non-equilibrium α-Fe(Co,Si) solid solution with average crystallite size of 7–11 nm. The lattice constant increases initially up to 10 at.% Co and then decreases with further increase in Co content due to delay in dissolution of Co into Fe lattice by the introduction of more Si. The variations of structural parameters such as average crystallite size, dislocation density and fraction of grain boundary as a function of Co content show good correlations among them. The substitution of Co in Fe100−x−yCoySix alloy powder increases both saturation magnetization and coercivity due to atomic ordering which induce additional magnetic anisotropy. Thermomagnetization studies reveal that Curie temperature (TC) increases at a rate of 4 K per at.% Co for Co content up to 10 at.% and the rate of increase in TC reduces to 1.4 K per at.% Co for higher Co addition. The variation of structural and magnetic parameters reveals a strong dependence on the composition of Fe–Co–Si alloy. The observed results show the improvement in soft magnetic properties of nanocrystalline Fe–Co–Si alloy powders by proper substitution of Co and Si for Fe.