Synthesis of L12-FeNi Nanoparticles by Nitrogen Insertion and Topotactic Extraction Method

The nitrogen insertion and topotactic extraction (NITE) method was used to explore an unknown metastable phase of an FeNi alloy with an Fe:Ni ratio of 1:1. We found that partly ordered non-equilibrium L1 2 -FeNi can be obtained through Fe 2 Ni 2 N as the intermediate nitride phase. The experimental results of both x-ray diffraction and transmission electron microscopy with energy dispersive x-ray spectrometry are consistent in identifying the denitrided material as L1 2 -FeNi. Ni atoms preferentially occupy the corner sites in an estimated 96% of cases. No significant difference was found in the magnetization curves between the precursor of A1-FeNi and L1 2 -FeNi particles. Our results suggest that the NITE method is not only a useful way for synthesizing fully ordered alloys of equilibrium phases such as L1 0 -FeNi but also for creating metastable phases like L1 2 -FeNi.