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

The growing trend of large power and high frequency in electromagnetic conversion applications urges advancements in the saturation magnetization ( M s ), effective permeability (mu e ) and core loss ( P cv ) of soft magnetic composites (SMCs). Such performance depends largely on the M s and coercivity ( H c ) of the magnetic alloys as the main component of the SMCs. It is however, difficult to simultaneously achieve large M s and low H c via binary and ternary alloy systems. Here, quaternary Fe 81-x Si 15 Co 4 Ni x (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 M s . On the other hand, the Ni enters into the A2 lattice and promotes its transition into DO 3 ordered phase as confirmed by both experimental characterization and first-principles calculations. Such microstructural evolution gives rise to initially decreased magnetocrystalline anisotropy ( K 1 ) followed by increasing due to the competitive reduction effect of Ni addition and increment effect of DO 3 formation. The magnetostriction constants (A s ) increases monotonously from negative to positive values with raised Ni content. This is accompanied with the decrease in 90 degrees domain walls and increase in 180 degrees domain walls as revealed by Lorentz microscopy. Combined lowest K 1 and A s as well as optimized domain structure result in the lowest H c for the Fe 78 Si 15 Co 4 Ni 3 alloy. The corresponding SMCs exhibit excellent performance with the mu e of 160.6 and the P cv of 288.4 mW/cm 3 (50 mT, 100 kHz) combined with high M s of 177.3 emu/g, superior to other FeSi-based SMCs.