Synthesis of nanocrystalline equiatomic nickel-cobalt-iron alloy powders by mechanical alloying and their structural and magnetic characterization

Mechanically alloying equiatomic Ni, Co, and Fe powder blends for 9 h resulted in the formation of nanocrystalline equiatomic NiCoFe alloy powders comprised of γ-phase. The crystallite size and the lattice parameter was ∼20 ± 5 nm and 0.3597 ± 0.0005 nm, respectively. The mode of the powders was 3-7 μm. The saturation magnetization (MS) and the intrinsic coercivity (HCI) of the alloy, at 300 K, was ∼136 ± 5 Am2/kg and ∼2.0 ± 0.2 kA/m, respectively. Both MS and HCI, irrespective of the milling media and milling atmosphere, decreased with increase in temperature from 60 K to 300 K. At elevated temperatures (400 K to 880 K), the alloy powders maintained the γ-phase up to 640 K, thereafter it was comprised of γ-phase and α-Fe. In the temperature regime 300-640 K, the percentage decrease in MS and HCI was ∼12% and ∼30%, respectively. The MS and HCI at 300 K, after the magnetization versus applied magnetic field (M-H) run at 640 K, was ∼136 Am2/kg and ∼1.5 kA/m, respectively; while the same after the M-H run at 880 K was ∼154 Am2/kg and ∼1.0 kA/m, respectively. Annealing of the nanocrystalline alloy powders is likely to improve its soft-magnetic properties.