Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)81+xB12Nb4−xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x = 0, 1, 1.5, 2, and 3, we report field induced anisotropy, KU, after annealing at temperatures of 340–450 °C for 1 h in a 2 T transverse magnetic field. The anisotropy field, HK, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher HK than the crystalline phase. A high saturation induction nanocrystalline phase and high HK amorphous phase were achieved by low temperature annealing resulting in a value of KU exceeding 14 × 103 erg/cm3, more than twice that reported previously for Fe-rich amorphous and nanocomp...