FeNi and Fe16N2 magnets prepared using leaching

Abstract

L10-type FeNi alloys and ¡AA-Fe16N2 are candidates for permanent magnets without precious metals, but they are difficult to prepare because atomic diffusion is extremely slow below the orderdisorder transition temperature of L10-FeNi (320°C) and because ¡AA-Fe16N2 is a metastable phase. Here, we report trials for preparing them using leaching, which is a method to obtain porous metals with a high surface area. We used such chemically active porous alloys as precursors for preparing L10-FeNi using the driving force of atomic diffusion and for preparing ¡AA-Fe16N2 using high reactivity with ammonia. No proofs for obtaining the L10-FeNi phase were observed, likely due to an Al impurity of 10 mol% and/or too small of a grain size. An Fe16N2 with ¡AA phase was obtained. Although the saturation magnetization was smaller than that of Fe, a large coercivity (up to 121kAm11) was obtained.