Influence of core current on magnetization processes in amorphous and nanocrystalline Fe73.5Cu1Nb3Si15.5B7 ribbons

The model for the influence of surface fields Hp generated by the core currents has been employed for the investigation of the magnetization processes and the domain structure in an initially amorphous Fe73.5Cu1Nb3Si15.5B7 ribbon which was successively annealed at selected temperatures Ta up to 540 °C. The analysis of the dM/dt vs. F curves and the M-H loops showed that in the as-received state only a fraction of inner domains with magnetizations I nearly parallel with the ribbon axis (i.e. with small angles 〈δ〉 between I and ribbon axis) participate in magnetization process. The analysis of the effects of Hp on the coercive field Hc and the shift of the center C of the M-H loop shows that the annealing up to Ta = 450 °C reduces the average strength of pinning 〈Su〉 of the domain walls whereas the angle 〈δ〉 changes only a little with Ta. For Ta ≥ 400 °C the maximum magnetization Mm practically reaches the saturation magnetization Ms ( 1.3 T) already in the magnetizing field H0 = 100 A m−1 which indicates rather simple domain structure with I mostly along the ribbon axis. At Ta = 450 °C Hc reached its minimum value, probably associated with the formation of nano-sized Fe-Si particles. Further annealing (Ta > 450 °C) leads to rapid increase in both 〈Su〉 and 〈δ〉, hence also in H, as already observed in the previous studies.