High-frequency magnetoimpedance effect in glass-coated amorphous Co83.2B3.3Si5.9Mn7.6 microwires

Measurements of the giant magnetoimpedance (GMI) were carried out in the amorphous Co83.2B3.3 Si5.9Mn7.6 micro-wires at high frequency range from 100 MHz up to 1 GHz of an ac-current flowing along the wire and at varying axial dc-magnetic field in its range of +/-120 Oe. The wires, about 15 mum in diameter, were fabricated by a glass-coated melt spinning technique. The shapes of the impedance curves plotted vs. a dc-field change dramatically with the frequency. The phase angle was also strongly dependent on the field. The maximum value of GMI, around 250%, was reached at the frequency of about 500 MHz. The external dc-magnetic field changes the circumferential permeability as well as the penetration depth, both in turn change the impedance of the sample. The increments of GMI at high frequency can be understood in terms of the LC-resonance phenomena. A sudden change of the phase angle, as large as 180degrees, evidenced the occurrence of the resonance at a given intensity of the external dc-field.