EFFECTS OF TORSION ON THE DECREASE OF LOSS BY MEANS OF CORE CURRENT IN FE80B20 AMORPHOUS RIBBON

The effects of torsion (specific twist tau = 0, 5, 10, 15, 20, and 30 pi/m) on the domains and pinning in an as-quenched Fe80B20 amorphous ribbon are studied by means of the direct (J(D)) and alternating (J) core currents. For all twist angles and both J and J(D) the model of the influence of the surface field H-p generated by the core current on the magnetization of amorphous ribbons describes well the observed dM/dt versus H curves and the corresponding M-H loops. The analysis of the effects of H-p on the coercive field H-c and the shift of the center C of the M-H loop shows that torsion increases both the average angle [delta] between the domain magnetizations (I) and the ribbon axis and the pinning of the domain walls. The competition between these effects results in an optimum tau approximate to 10 pi/m for which H-c = 0 is obtained with the lowest amplitude J(0) of J. An explanation of these phenomena in terms of the appearance of an easy axis of magnetization and the increase in stresses due to torsion (tau) is provided.