Magneto-optical investigation of magnetization reversal in nearly zero magnetostrictive Co-rich wire and microwire

Investigations of the magnetic reversal in amorphous wire of nominal composition (Co94Fe6)72.5Si12.5B15 and microwire of nominal composition (Co1-xMnx)75Si10B15 (X=0.07; 0.11) using transverse and longitudinal magneto-optical Kerr effect have been performed. Changes of the surface hysteresis loops 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 domains, in contrast to the annealed wire displaying the domain structure with magnetization directed along the wire axis. Such a modification of the domain structure with 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 on the shape of the hysteresis loops of the amorphous wire has also been investigated. The results obtained for this case can be understood by considering the formation of the helical magnetic structure in the wire. The Kerr effect measurements of Co-rich microwires with different Mn content demonstrate the variety of the shapes of magnetization reversal loop, which can be attributed to the change of sign 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 in axial magnetic field of the microwire with X=0.11 could be attributed to the large Barkhausen jumps within the axial domain structure