Effects of normal annealing and magnetic field annealing on the soft magnetic properties of FINEMET-type cores with Nb variation

By adding trace amounts of Nb element and annealing in a magnetic field, the soft magnetic properties (SMPs) of the FINEMET-type alloys were improved. After changing the Nb content to control the grain size (D) of the nanocrystals in the alloy and adjusting the heat treatment temperature gradient, Fe_72.7Si_14.8B_8.2Cu₁Nb_3.3 nanocrystalline ribbon with excellent SMPs was obtained. Further, transverse magnetic field annealing (TA) was performed on nanocrystalline ribbon cores (NCRCs), and detailed comparisons were made between the magnetic properties and magnetic domain structures with normal annealing (NA), clarifying the mechanism by which TA improves the SMPs. The SMPs of the magnetic cores were adjusted by changing Nb addition, annealing temperature, and magnetization temperature. Experimental results show that compared with NA the samples after TA at 450 °C for 60 min, the permeability (μ_e) of NCRCs is increased by 24.6% at a low frequency of 1 kHz, and it has the maximum μ_e value of 18.9712 × 10⁴. At an operating frequency of 5 kHz, compared to core loss (P_s) of NA, the P_s of the cores after TA is reduced by 31.09%. At frequencies of 10 kHz and 100 kHz, the P_s of the cores are decreased by 28.81% and 16.63%, respectively, compared to NA. By adjusting the structure and size of the domains, TA optimizes the SMPs of NCRCs. This work can provide good guidance for the SMP optimization of NCRCs with low P_s at high frequencies.