Frequency dependence of GMI effect in nanocrystalline Fe86Zr7B6Cu1 ribbons

Giant magnetoimpedance effect (GMI), Delta Z/Z, has been studied in Fe86Zr7B6Cu1 ribbons after heat treatment at 550 degrees C and 600 degrees C for 1 h (samples A and B respectively). Measurements were performed at frequencies, f, of the AC driving current ranging between 50 and 1400 kHz and under an axial magnetic field, H, up to 1440 A/m. Increasing the frequency results in the appearance of a maximum on axial field dependencies of the total magnetoimpedence, Z and its change, Delta Z/Z. Besides, both samples showed frequency dependence of maximum Delta Z/Z ratio, Delta Z/Z(m). Delta Z/Z(m) has a maximum at 300 kHz for sample A when Delta Z/Z(m) = 12.5% and at 200 kHz for sample B when Delta Z/Z(m) reaches 17.5%. Observed dependencies were interpreted in the classical way, taking into account the change of the penetration skin depth of the AC driving current in a magnetic conductor with high circular magnetic permeability. (C) 1999 Elsevier Science B.V. All rights reserved.