Structure and magnetic properties of nitrides in FeNi and FeNiCo alloy particles synthesized via co-precipitation, reduction, and nitriding

Abstract

Nitriding of FeNi and FeNiCo alloy particles was attempted. Precursor particles were synthesized by co-precipitates of Fe, Ni, and Co ions with the following compositions: Fe/Ni: 0.5/0.5 and Fe/Ni/Co: 0.5/0.45/0.05. The precursor particles were first reduced in hydrogen gas to obtain FeNi and FeNiCo alloy particles. Both the alloy particles were confirmed to have face-centered cubic (fcc) structures. Nitriding was subsequently performed using a mixture of ammonia and nitrogen gases. The formation of monophase (Fe0.5Ni0.5)4N and (Fe0.5Ni0.45Co0.05)4N was observed by the nitriding of the FeNi and FeNiCo alloy particles. No significant change in particle shape was observed by nitriding. Both the coercive force and saturation magnetization decreased by nitriding compared with those of the FeNi and FeNiCo alloy particles. Mössbauer analyses showed that Site I was preferentially occupied by Ni, and Site II was occupied by Fe and Ni with a Ni/Fe: 1/2 ratio in FeNi nitride particles. A similar spectrum to that of the FeNi nitride particles was observed in the FeNiCo nitride particleswith a slightly increased average hyperfine field corresponding to the increase in magnetization.