High permeability iron-based metallic glasses for line frequency applications

Abstract

The addition of 2–3 at. % of Cr or Mo to FeBSi-base metallic glasses results in a substantial improvement in line frequency magnetic properties. The saturation magnetization and magnetostriction are reduced by approximately 0.1 T and 5–7×10−6/at. %, respectively. When annealed in longitudinal field, these alloys exhibit dc coercivities of 0.3–0.7 A/m and maximum 60 Hz impedance permeabilities of 300 000–400 000, compared with 1 A/m and 200 000 typically seen in FeBSi glasses. By transversely annealing the alloys, the dc remanence ratio can be reduced to ∼0.3, resulting in nearly equal permeabilities under either bipolar or unipolar 60-Hz excitation. Loss separation measurements show that the improvement in 60 Hz properties resulting from addition of Cr or Mo is largely due to the decrease in the hysteresis component of loss. By annealing the Cr- or Mo-containing glasses at higher temperature to produce a slight precipitation of α-Fe particles, the eddy current component of loss is decreased at the expense of hysteresis loss. The resulting alloys thus show lower losses at 10–100 kHz but higher losses in the line frequency regime than alloys without the α-Fe precipitates.