Quantum mechanical design of rare-earth-free ferromagnetic material incorporating 2p element doping for permanent magnet applications

This study investigates the magnetic properties of non-rare-earth ferromagnetic materials, L1₀-ordered FeNi, Fe₂Ni₂N, and Fe₂Ni₂B, using the Kohn-Sham (KS) equation, mean field theory (MFT), Brillouin function (BF), and Callen-Callen (CC) semiempirical relation. We obtained electronic structures, electron density maps, and magnetocrystalline anisotropy energy (MAE) from first-principles calculations. The Curie temperature (T_C) was determined using MFT, while the thermomagnetic properties of L1₀-ordered FeNi and tetragonally ordered Fe₂Ni₂N and Fe₂Ni₂B were obtained from the BF and CC relation. The crystal structure and electron density map for L1₀-ordered FeNi have identified the interstitial sites for the 2p element doping. The addition of interstitial nitrogen (N) has decreased the c/a ratio to 0.992 from 1.007 and saturation magnetization (μ₀M_S) to 1.35 from 1.67T at 0 K. However, nitrogen doping has led to a significant increase in the magnetocrystalline anisotropy constant (K_u) to 1.94 from 0.47MJ/m³, while lowering T_C from 908 to 634 K. Boron (B) doping resulted in an even higher K_u of 2.75MJ/m³ at 0 K. The μ₀M_S for Fe₂Ni₂N is 1.20T (36 MGOe) at 300 K and 0.97T at 450 K. For Fe₂Ni₂B, the μ₀M_S is 0.97T (23 MGOe) at 300 K and 0.74T at 450 K. Fe₂Ni₂N demonstrates a higher saturation magnetization compared to commercial Sm-Co and Alnico, suggesting its potential as a non-rare-earth permanent magnet, filling the 10–30 MGOe gap in magnets. Our computational analysis indicates that B-doped FeNi has the potential to be a high-energy anisotropy permanent magnet with a significant hardness parameter κ of 1.67.