Spatially resolved measurement technique of magnetic anisotropy fields using the magneto-optic Kerr effect

Abstract

In this paper a novel method that permits spatially resolved measurements of the anisotropy field and easy axis direction is reported. The technique employs a Kerr based sensor that monitors the direction of magnetization φ of a magnetically soft thin film while an applied field is rotated in the plane of the film. The magnitude of the rotating field is set approximately to twice the anisotropy field (Hk), and thus the film remains saturated at all times and the domain wall artifacts reported previously are eliminated. φ and the direction of applied field β are then independently measured. We show that the amplitude and phase of sin(β-φ) are related to H k and the easy axis orientation (EAO), respectively. The amplitude and phase information can be easily determined by first normalizing and then applying a fast Fourier transform to the digitally captured Kerr signal. Operationally, computer controlled translation stages are used to scan the sample under the Kerr laser beam, which is fixed with respect to the toroidal electromagnet generating the rotating applied field. Because the sample need never be rotated, "maps" of Hk and EAO covering approximately 100 locations can be generated in less than 10 min by a fully automated instrument employing this technique.