Influence of microstructure and anisotropy on the high-frequency soft magnetic properties of nanocrystalline FeSiBNbCuP alloys

Abstract

Several electronic devices require alloys with excellent soft magnetic properties, for further advancement. The effect of anisotropy and microstructure, particularly concerning grain orientation, on the high-frequency (100 kHz) magnetic properties of nanocrystalline Fe77.8Si11.6B7Nb2Cu0.6P1 toroidal cores has been studied. The field-induced anisotropy (Ku) of the cores was induced by applying transverse field annealing (TFA) with a magnetic field of 0.08 T at annealing temperatures ranging from 320 °C to 540 °C after having been optimally nano-crystallized by normal annealing (NA). The high-frequency magnetic properties were found to be affected by the competition between Ku and the averaged magnetocrystalline anisotropy (<K1 >). The optimal soft magnetic characteristics, i.e., high saturation magnetization of 1.5 T, high permeability of 18,400 (100 kHz, 0.06 A/m), low coercivity of 1.7 A/m, and low core loss of 209 kW/m3 (100 kHz, 0.2 T), were obtained when the < K1>/Ku ratio was approximately 1. With further increase in the TFA temperature, the texture of the α-Fe(Si) grains in the 〈100〉 direction became more prominent, leading to an increase in < K1 > and consequently deteriorating the soft magnetic properties. A bi-anisotropy and microstructure interaction model was established based on the experimental results, it can provide guidance for optimizing the high-frequency magnetic performance of Fe-based nanocrystalline alloys.