FeNi and Fe16N2 Magnets Prepared Using Leaching

L1(0)-type FeNi alloys and alpha ''-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 L1(0)-FeNi (320 degrees C) and because alpha ''-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 L1(0)-FeNi using the driving force of atomic diffusion and for preparing alpha ''-Fe16N2 using high reactivity with ammonia. No proofs for obtaining the L1(0)-FeNi phase were observed, likely due to an Al impurity of 10 mol% and/or too small of a grain size. An Fe16N2 with alpha '' phase was obtained. Although the saturation magnetization was smaller than that of Fe, a large coercivity (up to 121 kAm(-1)) was obtained.