Design of quaternary FeSiCoNi soft magnetic alloys towards large-power and high-frequency applications

Abstract

The growing trend of large power and high frequency in electromagnetic conversion applications urges advancements in the saturation magnetization (Ms), effective permeability (μe) and core loss (Pcv) of soft magnetic composites (SMCs). Such performance depends largely on the Ms and coercivity (Hc) of the magnetic alloys as the main component of the SMCs. It is however, difficult to simultaneously achieve large Ms and low Hc via binary and ternary alloy systems. Here, quaternary Fe81-xSi15Co4Nix (x = 0, 3, 6 at%) soft magnetic alloys have been designed with the effect of Ni addition on the microstructure and magnetic properties of the alloy revealed. On one hand, rational incorporation of Co and Ni maintains the relatively large Ms. On the other hand, the Ni enters into the A2 lattice and promotes its transition into DO3 ordered phase as confirmed by both experimental characterization and first-principles calculations. Such microstructural evolution gives rise to initially decreased magnetocrystalline anisotropy (K1) followed by increasing due to the competitive reduction effect of Ni addition and increment effect of DO3 formation. The magnetostriction constants (λs) increases monotonously from negative to positive values with raised Ni content. This is accompanied with the decrease in 90° domain walls and increase in 180° domain walls as revealed by Lorentz microscopy. Combined lowest K1 and λs as well as optimized domain structure result in the lowest Hc for the Fe78Si15Co4Ni3 alloy. The corresponding SMCs exhibit excellent performance with the μe of 160.6 and the Pcv of 288.4 mW/cm3 (50 mT, 100 kHz) combined with high Ms of 177.3 emu/g, superior to other FeSi-based SMCs.