Effect of Surface Microstructure on Magnetization Process in Fe $_{80.5}$ Cu $_{1.5}$ Si

The magnetization processes of the Fe_80.5Cu_1.5Si₄B₁₄ nanocrystalline alloy were observed by Kerr effect. In the specimen annealed with heating rate of 0.3°C/s (NA), the pinning of domain walls was observed. Owing to such pinning effect in the NA specimen, high remanent magnetic flux density Br was obtained, and the hysteresis was observed in the B-H loop in the region of B > 1.5 T. Whereas, the smooth domain wall displacement was observed in the specimen annealed with the heating rate of 3°C/s (HA). The coarser grains near the surface observed in the NA specimen are considered to be the pinning site of the domain walls. In the HA specimen, grain growth in the heating process of annealing is suppressed.