FeNi and Fe₁₆N₂ Magnets Prepared Using Leaching

Abstract

L1₀-type FeNi alloys and α′′-Fe₁₆N₂ are candidates for permanent magnets without precious metals, but they are difficult to prepare because atomic diffusion is extremely slow below the order–disorder transition temperature of L1₀-FeNi (320°C) and because α′′-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 α′′-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 α′′ phase was obtained. Although the saturation magnetization was smaller than that of Fe, a large coercivity (up to 121 kA m⁻¹) was obtained.