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X-ray and Neutron Experiments in High Magnetic Fields

Hiroyuki Nojiri (Tohoku University)

Recent activities in X-ray and neutron experiments in pulsed high magnetic fields are introduced. A magnetic field is one of the most powerful control parameters of strongly correlated systems in which various field induced phase transitions are found to emerge. On the other hand, as probes of the different states of matter, X-rays and neutrons have been used intensively. Recently, the use of pulsed magnetic fields for these experiments has been developed in many different laboratories. This use would open new opportunities in the study of magnetic compounds. In X-ray scattering, structural investigation of spin-lattice coupling in frustrated antiferromagnets is one of the most important subjects. Another important use of X-rays is spectroscopy such as XAS and XMCD for magnetic field driven electronic transitions such as valence state transitions. These methods are unique to examine the electronic and magnetic states in very high magnetic fields in a site- selective manner. Complementary uses of portable mini-coils and of conventional long pulsed magnets are very useful to realize those measurements. In neutron scattering, the determination of magnetic structure is one major use. Among many interesting targets, frustrated antiferromagnets such as TbB4 and CdCr2O4 have been intensively investigated. In such systems, the ground state is highly degenerate and many phases are competing each other. It is notable that highly non-trivial phases often appear. Hence, it is essential to observe the order parameter by some direct means such as neutron diffraction in order to uncover the mechanism of these phase transitions. In this talk, the present status of x-ray and neutron experiments are introduced first. Then recent examples of X-ray diffraction/ spectroscopy and of neutron diffraction in both reactor and pulse sources are presented. The talk includes recent results at ILL for TbB4 and CdCr2O4 and at the Japanese synchrotron source SPring8 for Yb and Eu valence fluctuation compounds.

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