Small region magneto-optic measurements of Permalloy I bars

We have developed a Kerr magneto-optic probe capable of examining regions of ∼3 μm diameter and have used it to measure the magnetization distributions within Permalloy I bars. The measurements were made so as to bring into evidence the location and movement of domain walls. By suitable adjustment of the polarizing elements, signals can be observed either from the longitudinal Kerr effect from domains or from the polar Kerr effect of the out-of-plane magnetization of the Bloch wall. This paper reports the use of the polar effect to make precise determinations of Bloch wall locations in Permalloy I bars of 100×12×0.3 μm. Two different domain configurations were studied and wall locations were mapped as a function of applied field for each. Wall curvature is evident from the results. Local saturation and wall nucleation fields were also observed. Both types of domain configuration were found to respond qualitatively as predicted by a series-based continuum calculation but with some notable differences.