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 investigated. The samples were stress-relieved by Joule healing with the current 540 mA for 2 min to eliminate internal stresses induced during the 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. The induced magnetic anisotropy was determined from the slope of the longitudinal or circumferential ac hysteresis loops measured at the frequency of 100 Hz. For short stress annealing times an easy-wire-axis anisotropy was observed. After longer times of annealing the anisotropy changed to the hard-wire-axis type. The Giant Magneto-Impedance was studied in the frequency range 10-100 kHz. For the easy-wire-axis anisotropy the field dependence of the impedance change ratio Delta Z/Z shows 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 determined by the magnitude of the creep-induced anisotropy. The experimental results are discussed on the basis of the model introduced by Mohri et al. (C) 1997 Elsevier Science S.A.