Near-field Magneto-optical Microscope for Observation of Nano-spin Structure

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This report describes the research and development of a scanning near-field magneto-optical microscope conducted under the support of Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture (Category No.07555099).Recently the rapid development in the nano-fabrication technique has lead to the realization of magnetic materials with a sub micron structure, which requires development of observation technology for the Sub-micron to nanometer region. There have been studied various observation techniques such as the magnetic force microscopy (MFM), the electron beam holography (EBH), and the spin-polarized scanning electron microscope (SPSEM). Although MFM and EBH provide ample information on the magnetic field around the magnetic materials, they do not give information of the sample magnetization directly.SPSEM is an excellent technique to observe the spin polarization of the surface directly, it still requires much fundamental studies in order to g … More et a position as a versatile measuring technique, since it is too sesitive to the surface condition of the sample. Compared with these sorts of microscopy the scanning near-field optical microscopy (SNOM) can provide direct information of the magnetization in the material itself.First we took attention on the polarization transmission properties in the bent-fiber probe, which simultaneously work as a cantilever for AFM in the system we employed. It is found that careful selection of the fiber-probe and optimization of the compensating optics can provide a good polarization characteristics. Using the fiber probe with optimized optics we successfully observed magneto-optical-images of the recorded marks on a MO disc with the dysprosium iron garnet film under the crosspolarizer configuration.Next in order to increase sensitivity of the magneto-optical signal we introduced the polarization-modulation technique using the photoelastic modulator (PEM). We successfully obtained the chevron-shaped marks on the platinum/cobalt disk with submicron length. The resolution attained was 90nm.We prepared microstructures of cobalt with sub-mirometer size using focused ion beam (FIB) technology. We obtained magneto-optical images of the microstructure. It is confirmed that the microstructure can be used as a standard pattern for the magneto-optical SNOM. Less