High frequency measurement of thin film magnetoresistance

A system to measure the high frequency MR curve of thin films was developed. Two problems had to be solved to realize MR measurement at frequencies above several MHz, namely, to produce a high amplitude magnetic field and to develop electrodes less sensitive to inductive high frequency noises than the conventional four probe electrodes. These problems were solved by making use of the resonance of a coil with a ferrite core connected in parallel with to a capacitor, and by contacting patterned thin film electrodes to the sample surface with a suitable pressure. The result was an appreciable reduction of inductive noises. Using the resonance circuit and electrodes we could obtain AMR curves of Permalloy films at frequencies up to 1.8 MHz in a field of 110 Oe pp.