Abstract

Giant magnetoimpedance (GMI) has been measured in pieces of silicon steel (4.5% Si) as functions of axial static magnetic field, sample width, frequency and magnitude of the AC driving current. The samples, 0.5×35mm with widths ranging from 0.122 to 1.064mm, were cut from sheets of commercial transformer cores. The impedance decreased with an applied magnetic field and saturated under 1.5kOe. GMI ratio (ΔZ/Z) increased at low frequencies, reached the maximum at the characteristic frequency and decreased at frequencies above the characteristic value. With increasing width of the samples, the characteristic frequency decreases but the GMI ratio increases. The maximum 300% GMI ratio was observed at the frequency about 200kHz for a 1.064mm wide sample. A rise of GMI ratio started and reached the maximum at lower frequencies for wider samples. Finally, GMI ratio increased with increasing AC current from 2.5 to 10mA but this variation is modest in a high-frequency regime. The results can be explained by the dependence of the transverse permeability on the magnetic field, frequency and magnitude of AC current. © 2004 Elsevier B.V. All rights reserved.