Magnetic Properties of L10 FeNi Phase Developed Through Annealing of an Amorphous Alloy

Chemically ordered L1(0) FeNi phase observed in Fe-based meteorite has the potential to replace high-cost rare-earth-based permanent magnets in the future. However, artificial production of this phase is extremely difficult due to negligible atomic diffusion around order disorder transition temperature (similar to 320 degrees C). Here, we report a method for producing high-quality 1,10 FeNi phase and its magnetic properties. We show that a highly disordered metastable state, that is, amorphous can he utilized to produce a highly ordered state, which is not possible with the conventional processing techniques. Amorphous Fe42Ni41.3SixB12-xP4Cu0.7 (x = 0 to 8 at.%) alloy ribbons were studied. Crystallization of amorphous ribbons at 400 degrees C results in adequate atomic diffusion at low temperatures to precipitate L1(0) FeNi grains. Structural characterization revealed a high degree of chemical ordering (S > 0.8), but the volume fraction of precipitated L1(0) grains is low. The crystallized ribbons of FeSiBPCu are composed of two magnetic phases (hard magnetic L1(0) FeNi grains embedded in a soft magnetic matrix). Alloys with higher concentration of Si are shown to produce high coercivity (H-e similar to 700-750 Oe). The soft magnetic matrix strongly influences the He. The actual switching field (>3.7 kOe) of L1(0) FeNi has been found to be much higher than that of He. In this paper, the Lip FeNi phase is shown to form at temperatures higher than the reported order disorder temperature. Our results of temperature-dependent magnetization and thermal analyses suggest that the Llo FeNi phase can survive at temperatures <= 550 degrees C. The magnetization reversal mechanism was understood by angular dependence of He, and it is shown to be a domain-wall pinning type. Due to structural and magnetic similarities between L1(0) FeNi and L1(0) FePt, ribbon samples with low-volume fraction of L1(0) FePt grains in a soft magnetic matrix were prepared with a similar technique. Magnetization behavior of L1(0) FeNi is shown to be similar to that of L10 FePt.