Synchrotron X-Ray Diffraction Studies of Magnetic Materials under Extreme Conditions

Abstract

The synchrotron x-ray diffraction studies of magnetic materials under extreme conditions performed at the beam-line BL19LXU at SPring-8 are reviewed. After a description of the experimental setup, we report recent results of non-resonant x-ray magnetic and charge scattering measurements on some antiferromagnets obtained in high magnetic fields and low temperatures. The first result is the observation of the spin-flop transition in the prototypical uniaxial antiferromagnet MnF2 and we find that the intensity of the magnetic x-ray diffraction depends on the angle the magnetic moment in the sample makes with the scattering vector. The second result is the synchrotron x-ray diffraction measurement of the high field phase of a spin-Peierls system. We have measured the x-ray diffraction by CuGeO3 in magnetic field, H, up to 15 T. We find that the temperature, T, dependence of the incommensurate peak is quite different at lower H from that at higher H. At magnetic fields slightly above the critical field, HSP, for the commensurate to incommensurate transition, the incommensurability, δl, depends much on T, whereas at H well above HSP, δl is almost independent of T. We interpret this finding as due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations. The third one is the synchrotron x-ray diffraction measurement at a very low temperature. We have observed a jump in the lattice constant of the ladder-like compound Cu2(C5H12N2)2Cl4 at about 40 mK associated with the field induced magnetic ordering from the non-magnetic spin-liquid state. This is the first experimental confirmation of the theoretical prediction on the generalized spin-Peierls phenomenon in quantum magnets.