Influence of toroid radius on magnetic properties of iron-based amorphous alloys and 6.5WT%Si-Fe rapidly solidified ribbons

Iron-bases amorpnous alloys (Fe78B13Si9), crystalline 6.5wt% Si-Fe rapidly solidified ribbons and 3wt% silicon steel sheets were wound in to toroid cores of 25mm width and 5∼35mm radius. A stress of 130MPa was applied to the amorphous ribbons by 130MPa. The AC and DC properties were measured, and then the magnetic domain configurations were observed by SEM. The iron loss of amorphous alloys increased inversely proportional to the toroid radius before Stress Relief Annealing (SRA), but were almost independent of radius after SRA. The results on 6.5wt%Si-Fe ribbons were similar to those of amorphous ribbons. The increase in losses were due to hysteresis loss in both cores. A similar effect of the toroid radius was shown on the magnetic domain configurations. The 180° and cross domain configurations were observed on both surfaces of flat ribbons before SRA. A wide 180° domain was observed after SRA. When the specimen was bowed to various radii, wide 180° domains were observed in the longitudinal direction on the convex side and narrow 180° domain was observed in the transverse direction on the concave side. The iron loss was reduced by a factor of 2 with increasing applied stress up to 70MPa before SRA and up to 25MPa after SRA.