Surface magnetic behavior of nearly zero magnetostrictive Co-rich amorphous microwires

Abstract

Investigations on the magnetic reversal in amorphous wire (diameter 125 μm) of nominal composition (Co 94Fe 6) 72.5Si 12.5B 15 and glass-covered microwires (diameter around 20 μm) of nominal composition (Co 1− x Mn x ) 75Si 10B 15 (0.07< x<0.11) using transverse and longitudinal magneto-optical Kerr effect are reported. Changes of the surface magnetic behavior of the amorphous wire after annealing (without and under torsion stress) have been studied. The analysis of the obtained results allows to establish that the outer shell of the as-quenched wire consists of circular bamboo domains, in contrast to the annealed wire displaying the existence of domain structure with magnetization directed along the wire axis. Such modification of the domain structure with the thermal treatment could be related to the change of the sign of magnetostriction from negative to positive. The effect of a thermal treatment under torsion stress (torsion annealing) on the shape of the hysteresis loop of the amorphous wire has been also investigated. The Kerr effect measurements of Co-rich microwires with different content in Mn demonstrate the variety of the shape of magnetization reversal loop, which similarly can be attributed to the change of sign and value of the magnetostriction. The rectangular shape of the hysteresis loop in circular magnetic field of the microwire with x=0.07 can be interpreted by considering that the magnetization process takes place by large Barkhausen jumps of circular domain structure, while the rectangular shape of the hysteresis loop with axial magnetic field of the microwire x=0.11 could be connected to large Barkhausen jumps inside the axial domain structure.