High frequency magnetic properties of some amorphous alloys

Amorphous magnetic alloys, although possessing low coercive forces and high electrical resistivities, have high-frequency losses significantly larger than expected from classical calculations. These high "anomalous" losses are caused by the wide domains in the material. This paper discusses some techniques for lowering the losses by changing the domain size in several amorphous alloy strips. Both DC and AC test (60 Hz, 1-10 kHz) results are reported. Transverse scratching, causing demagnetizing effects, lowered the loss, while longitudinal scratching had no effect. A transverse field during annealing led to a lower loss, as did annealing so that fine crystalline α-Fe precipitates were formed; such precipitates had a much stronger effect than did the induced magnetic anisotropy from field annealing. The application of a transverse DC bias field during testing at high frequency had a profound effect; losses decreased at low levels of bias field and increased at high levels. Application and removal of the bias field lowered the losses at high frequency as much as 40%. These bias fields were found to reduce the domain wall spacing. The observed effects are all consistent with the idea that domain refinement leads to a reduction in losses. Such processes can be used to improve the useful properties of amorphous alloys.