Torsion annealing influence on the impedance behaviour in amorphous FeSiB and CoSiB wires

An experimental study on the influence of a dc magnetic field on the real and imaginary parts of axial diagonal (ζzz) and off-diagonal (ζϕz) components of the surface magnetoimpedance (MI) tensor in amorphous Fe77.5Si7.5B15 and Co72.5Si12.5B15 wires has been performed. The impedance characteristics have been analysed in the as-cast wires and after being torsion annealed. The ac drive current was 5 mArms flowing along the wires in the frequency range from 0.45 to 0.8 MHz. The MI behaviours can be ascribed to the different domain structures of positive and negative magnetostriction wires, before and after the intrinsic anisotropy distribution has been also modified by the annealing treatment.