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[摘要]：High-frequency [1-500 MHz] measurements of the magnetoimpedance (MI) of glass-coated Co69.4Fe3.7B15.9Si11 microwires are carried out with various metal-to-wire diameter ratios. A twin-peak, anhysteretic behaviour is observed as a function of magnetic field. A maximum in the normalized impedance, Delta Z/Z, appears at different values of the frequency f, 125, 140 and 85 MHz with the corresponding diameter ratio p = 0.80, 0.55 and 0.32. We describe the measurement technique and interpret our results with a thermodynamic model that leads to a clearer view of the effects of p on the maximum value of MI and the anisotropy field. The behavior of the real and imaginary components of impedance is also investigated; they display a resonance that becomes a function of the dc field H-dc for values larger or equal to H-K the circumferential anisotropy field for each p value. These results are interpreted in terms of a rotation model of the outer shell magnetization. (C) 2007 Elsevier B.V. All rights reserved. |
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