A method for the magneto-optic imaging of magnetization time evolution in thin films

We describe a digital imaging technique with a spatial resolution of less than 0.5 μm that allows the observation of the nucleation and growth of magnetic domains in metallic films whose surfaces are under less than ideal conditions. A diffraction limited laser spot is scanned across the surface of interest while a periodic magnetic field of saturation strength is applied. The local magnetization curve under each point of the laser scan is measured through the longitudinal magneto-optic Kerr effect and recorded in a computer. From the stored data, the spatial distribution of the magnetization component in one direction as a function of time is obtained. Digital averaging and data normalization are used to enhance the quality of the images which allows the optical imaging of very rough surfaces. To demonstrate the technique, the pole tip region of a film recording head was imaged and the magnetization distribution in that region was observed as a current waveform was applied to the coils of the head. In the present implementation, a time resolution of 50 ns was achieved.