Confirmation of hard magnetic L1₀ FeNi phase precipitated in fenisibpcu alloy by anomalous X-ray diffraction

There is a growing interest in the development of rare-earth element-free hard magnets. The L1₀ FeNi phase found in Fe-based meteorites is promising based on its high-magnetocrystalline anisotropy and saturation magnetization. Not only the production, but also the characterization of L1₀ FeNi phase is challenging due to similar X-ray scattering factors of Fe and Ni. Here, we report on the confirmation of L1₀ FeNi phase precipitated in a multi-phase FeNiSiBPCu alloy by anomalous X-ray diffraction (AXRD). This is a powerful technique, which can differentiate between ordered and disordered phases along with the elements present in a phase. We measured integrated X-ray intensity with energy near the Fe (7-7.2 keV) and Ni (8.25-8.4 keV) absorption edges for superlattice and fundamental reflections of L1₀ FeNi. A drastic change in integrated intensity with energy of X-ray was observed. Increase in intensity around superlattice reflection at Ni-absorption edge clearly confirms the presence of a chemically ordered L1₀ FeNi phase, but the results obtained at Fe edge are surprising. The analysis of AXRD results suggested that (110) diffraction peak of Fe₂B phase overlaps with (001) of L1₀ FeNi. Understanding gained from AXRD results also allows us to estimate the long-range order parameter (S) from X-ray diffraction measurements.