Effect of Si addition on the magnetic properties of FeNi-based alloys with L1₀ phase through annealing amorphous precursor

As a promising candidate of rare-earth free hard magnetic materials, L1₀-FeNi has been paid much attention in the last decades. However, it is difficult to be artificially fabricated due to its low thermal stability and sluggish diffusion ability of atoms below the crucial temperature of 320 °C. In this study, a promising method of annealing amorphous precursor was extensively developed through (Fe₅₀Ni₅₀)_84−xSi_xP₁₆ (x = 0, 4 at%) and (Fe₅₀Ni₅₀)_86−xSi_xP₁₄ (x = 2, 4, 8 at%) alloys. Especially, the effect of Si on the formation of L1₀ phase in annealed FeNi-based alloys was investigated and clarified. It is found Fe₄₂Ni₄₂P₁₆ with a much low crystallization temperature could be an appropriate basic amorphous alloy for the formation of L1₀ phase. The addition of Si enhanced the thermal stability of Fe-Ni-P amorphous alloys. Interestingly, Si could stabilize the L1₀ phase in annealed samples and increase its disordering temperature above which L1₀-FeNi phase could deteriorate into soft magnetic phase. As expected, appropriate Si addition indeed improved the hard magnetic properties of the annealed alloys and samples with high coercivity above 900 Oe was obtained. Further Si addition would deteriorate the magnetic-crystalline anisotropy of L1₀ phase and decrease the coercivity of annealed Fe-Ni-Si-P alloys. Nevertheless, the results indicate that increasing the order-disorder transition temperature through element doping in L1₀ lattice would be a promising strategy for the massive formation of L1₀-FeNi like other ordered phases (i.e. L1₂-FeNi, L1₀-CoPt), and could substantively contribute to the artificial fabrication of FeNi-based rare-earth free magnets in future.