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There has been a strong demand for observing magnetic domains inside materials for a long time, because these magnetic microstructures are definitely responsible for superior magnetic properties in various functional magnetic materials, such as Nd-Fe-B permanent magnets and recent highly efficient electrical steel. However, major techniques for magnetic domain observation, such as mageto-optical Kerr effect (MOKE) microscopy and x-ray magnetic circular dichroism (XMCD) microscopy in the soft x-ray region, are sensitive to the surface magnetic microstructures and it is not easy to obtain information of magnetic domains well below the sample surface. Accordingly, the development of bulk sensitive magnetic microscopy is a very active research area recently. Non-resonant magnetic x-ray diffraction (NRMXRD) is a candidate for such three-dimensional magnetic microscopy. A small focus size less than 1 μm can be easily achieved by using synchrotron radiation. A long penetration length more than 100 μm is obtained by using high energy x-rays. A drawback is low magnetic contrast in the order of a few tenths of percent for high energy x-rays. In principle, the magnetic contrast in NRMXRD increases with increasing the total polarization of incident x-rays. In this study, we employ a channel-cut linear polarizer as a device that improves incident linear polarization and experimentally examine enhancement of the magnetic contrast.
NRMXRD is a phenomenon that the intensity diffracted at the scattering angle 90° from ferromagnets depends on the helicity of the incident elliptically polarized x-rays. Literally, the process is non-resonant, hence arbitrary high-energy x-rays can be used. Experiments were carried out at the beamlines BL22XU and BL11XU in SPring-8. The energies of the incident x-rays were 8.7 keV, 13 keV, 17.3 keV and 26 keV. In order to increase the incident linear polarization, we used Si(110), Si(111), Ge(110) and Si(100) channel-cut linear polarizers. Elliptically polarized x-rays were generated by using a 500 μm-thick diamond phase plate. The sample was an iron single crystal and an electrical steel sheet. At 8.7 keV and 13 keV, we successfully observed enhancement of the magnetic contrast. However, at 17.3 keV and 26 keV, enhancement was very small. It seems that it is difficult to achieve high magnetic contrast in NRMXRD for high energy x-rays using channel-cut linear polarizers.
会議概要（会議名, 開催地, 会期, 主催者等）
4th QST International Symposium -Innovation from Quantum Materials Science-
Observation of magnetic domains by means of non-resonant magnetic x-ray diffraction
