Effect of transverse magnetic field annealing on the magnetic properties and microstructure of FeSiBNbCuP nanocrystalline alloys

Improving the high-frequency magnetic properties of Fe-based nanocrystalline alloys with high-saturation magnetic induction (Bs) has received extensive attention recently. The magnetic properties, microstructure, and magnetic domain structure of Fe76Si12B8Nb2.2Cu0.8P1 ribbons after normal isothermal annealing (NA) and transverse magnetic field annealing (TFA) were investigated. It was found that NA and in situ crystallization TFA (TFA1) have little effects on the Bs and coercivity (Hc) of the ribbons but they significantly affect the magnetic permeability (μ) and optimal annealing window. In contrast, TFA after nanocrystallization (TFA2) enables the ribbons to attain a higher μ in a wide frequency range and a wider annealing temperature range than NA and TFA1. The TFA2 ribbons exhibit a high Bs of 1.45 T, low Hc of 0.8 A/m, and high μ under 1 A/m of 24,000 and 16,600 at 1 and 100 kHz, respectively. The factors causing the improved soft magnetic properties were revealed in terms of magnetic anisotropy and magnetization processes.