Improved High Frequency Soft Magnetic Properties in FeSiBCuNb Nanocrystalline Alloys Induced by Additional Low Magnetic Field Annealing

Fe-Si-B-Cu-Nb nanocrystalline alloys have been commercially applied at power electronics. However, few research works are focused on improving high-frequency magnetic properties in the alloys. In this paper, the effect of additional magnetic field annealing temperature on high frequency soft magnetic properties of Si-rich FeSiBCuNb nanocrystalline ribbon was investigated. The as-quenched FeSiBCuNb amorphous alloys were crystallized annealing at 550 °C × 60 min for precipitating nanocrystalline α-Fe(Si) phase. Then the crystallized annealed alloy cores carried out additional transverse magnetic field annealing, and the induced uniaxial anisotropy K_u gradually increases from 9.4 to 21.6 J/m³ with increasing the annealing temperatures from 360 to 520 °C. By comparison with the non-magnetic field annealing sample, the μ_e of nanocrystalline cores with extra field annealing reduces at about the range of 1–30 kHz but gets significant improvement at 50–200 kHz, the Q improves and P_s decrease at all frequencies of 1 ~ 200 kHz. After the magnetic field is annealed at 480 °C, the core achieves optimal high-frequency properties of μ_e = 37.9 k (f = 100 kHz), Q = 0.87, and P_s = 30.94 W/kg. The improvement of high-frequency properties in cores upon transverse magnetic field annealing can be attributed to the fact that the magnetic domains appear in a rectangular band arrangement and are perpendicular to the longitudinal direction of the ribbon. When the magnetic cores operate in a dynamic magnetization field, the periodic magnetization is mainly characterized by domain rotation.