ZERO COERCIVE FIELD IN TWISTED FE80B20 AMORPHOUS RIBBONS CARRYING AN ALTERNATING-CURRENT

The effects of the direct (J(d)) and alternating (J) core currents on the M-H loops of stress-free and twisted (through 360-degrees over the length of 20 cm) Fe80B20 amorphous ribbons are investigated. Whereas J has little effect on the coercive field H(c) of the stress-free Fe80 B20 ribbons, H(c) of the twisted ribbon decreases linearly with the am plitude J0 of J and reaches zero for J0 = 92 mA. H(c) = 0 occurs when the projection of the self-field of J0 on the domain magnetization (I) reaches the magnitude which is sufficient to unpin the domain walls ( DW) responsible for H(c) at zero magnetizing field H. The effects of J (d) on the M-H loops show that torsion affects the strengths of the DW pinning centres and the directions of I in Fe80B20 ribbon in a way wh ich facilitates the achievement of H(c) = 0. A possible application of H(c) = 0 is mentioned.