Magnetism of Uranium compound under Pressure studied by the X-ray Magnetic Diffraction

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We have developed an experimental system of X-ray magnetic diffraction under multiple extreme condition (low temperature(4.2K)・high magnetic field(6T)・high pressure(20GPa)) on BL39XU at the SPring-8, by utilizing a super-conducting magnet and a diamond-anvil cell. We have developed a new method of X-ray magnetic diffraction by switching helicity of synchrotron radiation utilizing a phase plate.In the first experiment of X-ray magnetic diffraction with a super-conducting magnet we could enclosed a very small crystal of UTe (〜200 μm in size) in the anvil cell, which was installed to the magnet. We succeeded in measuring the lattice constant of UTe at 4.2K under ambient pressure. However, in this experiment, leak magnetic field from the magnet turned out to alter the electron-beam orbit in the storage ring and change the intensity of synchrotron radiation in the configuration of the magnetic field direction perpendicular to the synchrotron beam. So this configuration was prohibited, and the LS separation by the X-ray magnetic diffraction could not be performed. We tried the X-ray MCD (magnetic circular dichroizm) measurement of Fe and Ni under pressure, which could be made only in the parallel configuration. For Ni, the observed curve of MCD signal vs. pressure was reproduced well by the curve of the orbital moment vs. pressure by the band calculation. This result suggested that the MCD signal is strongly correlated with the orbital moments.