Kerr-effect based magneto-optic imaging with sub-100 nm resolution (abstract)

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Abstract
Magneto-optic imaging based on Faraday rotation with lateral resolution of about 60 nm was successfully demonstrated recently using scanning near-field optical microscopy.1 Magnetic contrast based on the Kerr effect with similar resolution still remains a challenge. Due to numerous applications of the Kerr effect this problem is of significant technical and scientific interest. Demonstration of such a contrast based on Kerr effect obtained using near-field optics is the subject of the present work. We have developed a reflection-mode scanning near-field optical microscope (SNOM) that is routinely capable of imaging with 30–50 nm resolution. It is based on a metalcoated fiber probe with the light of a diode laser (λ=635 nm) coupled into it. Distance between the scanning probe and the sample is maintained constant at 5–10 nm using a shear force based feedback. Light reflected from the sample is collected with an elliptic mirror and a photomultiplier. We have studied the dependence of polarization of light reflected from the various nonmagnetic metal and dielectric surfaces upon the distance between the probe and the surface. Mechanisms responsible for the change in polarization of the reflected light are analyzed. Finally a periodic array of domains was written in a Co/Pt multilayer film using optical thermomagnetic recording. The domains were imaged using a magnetic force microscopy technique that indicated that the size of the domain was about 400 nm. The domains were then imaged using our reflection-mode SNOM. Features of domains smaller than 100 nm in size are clearly resolved. Values of conventional polar Kerr rotation are compared with ones detected using the SNOM.

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