Low field sensitivity for gigahertz magneto-impedance sensors

In this work we present Giant Magneto-Impedance measurements of a NiFe-Au multilayer film at frequencies up to 3 GHz, using RF techniques, complemented with a derivative of the microwave absorption spectrum at 9.4 GHz. The curves allow to identify two different type of peaks: ones at low fields, associated to transverse permeability and others at fields increasing with frequency, caused by the ferromagnetic resonance. Usual data reduction consists on subtracting the impedance of the elements of the measuring circuit. If more accurate calculations are made, we can also eliminate the contributions to the impedance due to the interaction between the sample itself and the circuit. The results obtained using this technique display extraordinary sensitivities and Magneto-Impedance ratios. Besides, the derivative of the microwave absorption spectrum proves the existence of a low field contribution even at higher frequencies.