Ultrahigh saturation magnetization and optimized magnetic softness in a soft magnetic composite through nanoscale iron nitride

The miniaturization of modern devices demands soft magnetic composites (SMCs) with high saturation magnetization (Ms). However, further enhancing Ms through the α-Fe phase is challenging. This study explores the potential of iron nitrides particularly the Fe4N phase for addressing this limitation. A distinctive SMC with high Fe content (84 at.%) and nanoscale Fe4N phase was prepared using the mechanical alloying (MA) method based on pure Fe and BN powders, and subsequent facile heat treatment. By prolonging the MA period up to 100 h, the amorphous-nanocrystalline structure and refined particle size of 1.9 μm were achieved, thus promoting nitrogen doping through the open atomic packing and metastable thermodynamics. Subsequently, the nanoscale Fe4N phase with a volume fraction of 31.4% was formed by annealing the milled sample at 650°C for 2 min, resulting in an ultrahigh Ms of 226 emu/g, which is higher than those of amorphous-nanocrystalline and FeSi systems. Additionally, the SMC with Fe4N phase shows optimized magnetic softness, whose core loss (Pcv) was reduced by 67.2% compared to the SMC without Fe4N nanocrystals. Our study not only provides a simple and effective method for introducing iron nitrides into SMCs but also presents another alternative path for significantly enhancing the Ms of SMCs.