Reduction of High-Frequency Core Loss of a Fe_77.2Si₁₁B_8.5Cu_0.8Nb_2.5 Soft Magnetic Nanocrystalline Alloy by Minor Alloying

Enhancing saturation magnetic flux density (B_s) while reducing high-frequency core loss in Finemet-type nanocrystalline alloys is of great significance in achieving the miniaturization, high-frequency, and energy-saving of modern power electronic devices. In this work, we first designed a high-B_s Fe_77.2Si₁₁B_8.5Cu_0.8Nb_2.5 alloy by appropriately reducing the non-magnetic elements in typical Finemet nanocrystalline alloys, and subsequently alloyed 2 at% Co, Al, and Mo, respectively. The effects of alloying elements on structure and static and high-frequency magnetic properties were studied. The results reveal that, alloying Al or Mo reduces the average α-Fe grain size (D_α-Fe) in the nanocrystalline alloys, while Co exhibits a slight influence. The added Al or Mo results in decreases in both the B_s and coercivity (H_c) of the nanocrystalline alloys, whereas Co increases the B_s without changing H_c, and meanwhile, all alloying elements show minimal effects on effective permeability (μ_e). Furthermore, the addition of Co, Al, or Mo lowers the core loss (P_cv) at 0.2 T/100 kHz of the based nanocrystalline alloy with reductions of 10.9%, 29.6%, and 26.8%, respectively. A Fe_75.2Si₁₁B_8.5Cu_0.8Nb_2.5Al₂ nanocrystalline alloy exhibits outstanding soft magnetic properties with B_s, H_c, μ_e at 10 kHz and 100 kHz, and P_cv at 0.2 T/100 kHz of 1.34 T, 0.8 A/m, 27,400, 18,000, and 350 kW/m³, respectively. The reduction in P_cv is primarily attributed to the decreased eddy current losses, originating from the increased electrical resistivity by elements alloying.