Two magnetic phases in cold-drawn Fe-rich amorphous wire

Magnetic properties have been studied in ferromagnetic amorphous wires of nominal composition Fe77.5B15Si7.5 and diameter 0.05 mm prepared by cold-drawing technique. Conventional and surface hysteresis loops were measured by fluxmetric method and by magneto-optical Kerr effect method, respectively. Saturation magnetization dependence with the current density has been obtained. Two Curie points were clearly distinguishable on this dependence that could be associated with the existence of two ferromagnetic phases. On the other hand, two successive jumps of magnetization have been observed in fluxmetric as well as in magneto-optical curves. The joint analysis of the bulk and surface hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and, also, in the volume of the wire. We consider that the helical magnetic structure forms the separate magnetic phase that finds the reflection in the two Curie points behavior