Analysis of magnetoimpedance measurements at high frequency using a microstrip transmission line

The impedance as a function of the frequency, up to 3 GHz, and its dependence with the applied magnetic field, have been measured in a ferromagnetic amorphous ribbon. We describe the experimental procedure that allows to obtain accurate impedance values in a relatively simple way. In the configuration used, the sample is included in a microstrip, line, like the ones used in radio-frequency applications, and its impedance determined from the reflection coefficient of the whole fixture, after proper calibration and adequate data reduction aimed to eliminate propagation contributions. The results are discussed and compared with theoretical predictions in order to determine the frequency range in which the method is applicable. This experimental procedure provides very detailed features of the impedance curves as a function of the applied magnetic field, that are shown to change drastically with increasing frequency. This behavior is discussed in terms of the magnetization process of the sample. All these results are very useful to investigate the magnetoimpedance effect and the magnetic sensor devices operated at high frequency that use this effect. (C) 2004 Elsevier B.V. All rights reserved.