Measurements of the anisotropy in permalloy

A measurement system is described, which accurately determines the anisotropy field H_k and the orientation of the easy-axis in a permalloy film or in any material showing magnetization induced resistance anisotropy. An accuracy of 0.1% in H_k and 0.1 degrees in easy-axis orientation is reached in permalloy when the applied field strength is 2.5 H_k. Deviations from the Stoner-Wohlfarth single domain model can be recognized after the analysis of the measurement. Four electrical contacts have to be positioned on the permalloy in a planar-Hall configuration. Aluminum contacts realized by a standard lithographic process are used, providing a reference for the easy-axis orientation and an accurate relative orientation of the different planar-Hall elements that can be made out of a single film.