Quantitative determination of the local Kerr rotation by scanning near-field magneto-optic microscopy

By using a polarization-modulation technique in combination with reflection-mode scanning near-field optical microscopy we are able to determine quantitatively the local polar Kerr rotation on thin magnetic films. As an example, the magneto-optic contrast of magnetic domains thermomagnetically written on a Co/Pt sample is discussed. The size of the magnetic domains is 3×0.5 μm2 and the angular resolution of the local Kerr rotation is better than 0.1°. This measurement technique will make it possible to investigate, e.g., the fine structure of domain walls by scanning near-field optical microscopy.