GMI EFFECT IN AMORPHOUS WIRES WITH CREEP-INDUCED MAGNETIC-ANISOTROPY

Non-magnetostrictive Co68.15Fe4.35Si12.55B15 amorphous wires (UNITIKA, AC-20) prepared by the in-rotating-water quenching method were invest igated. The samples were stress-relieved by Joule healing with the cur rent 540 mA for 2 min to eliminate internal stresses induced during th e quenching. Then stress annealing with the current 400 mA and tensile stress 400 MPa was performed for various times from 10 s to 45 min. T he induced magnetic anisotropy was determined from the slope of the lo ngitudinal or circumferential ac hysteresis loops measured at the freq uency of 100 Hz. For short stress annealing times an easy-wire-axis an isotropy was observed. After longer times of annealing the anisotropy changed to the hard-wire-axis type. The Giant Magneto-Impedance was st udied in the frequency range 10-100 kHz. For the easy-wire-axis anisot ropy the field dependence of the impedance change ratio Delta Z/Z show s a simple sharp peak at zero magnetic field. After the change of the anisotropy sign the peak at H=0 splits into two symmetric peaks and a local minimum at H=0 appears. The position of the Delta Z/Z peak is de termined by the magnitude of the creep-induced anisotropy. The experim ental results are discussed on the basis of the model introduced by Mo hri et al. (C) 1997 Elsevier Science S.A.