Tohoku University

个人简介：

Professor Nojiri had been the Director of High Magnetic Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. He currently serves as the chair of the Condensed Matter Physics Division of Association of Asia Pacific Physical Societies (AAPPS). He received his Ph. D. from Department of Physics, Osaka University. He has worked at Kobe University, University of Tokyo, Tohoku University and Okayama University.

Professor Nojiri’s primary research interest lies in the study of quantum magnetism in low-dimensional quantum spin systems, strongly correlated electron system and molecular magnets, high magnetic field and high frequency THz-electron spin resonance in magnetic compounds X-ray and neutron scatterings in high magnetic field, study of field induced phase transitions.

报告摘要：

Recently, the installation of a pulsed magnet has brought a new breakthrough in x-ray experiments in high magnetic fields. It expands the magnetic field range from 10-15 Tesla to 30-50 Tesla. In such strong magnetic fields, the effect of a magnetic field is not a weak perturbation but is a cause of the intrinsic and significant phenomena in many cases. We report recent progresses in high magnetic field X-ray experiments with SR and XFEL sources.

X-ray diffraction for fundamental peaks is useful to determine the magnetic field dependence of lattice constants and volume in valence transitions in 4f-intermetallics, spin-crossover transitions in 3d-magnetic-complexes, and in charge density wave transitions. The information of x-ray diffraction is complementary with magnetostriction and sound velocity measurements. In frustrated magnets, a magnetic transition is, in many cases, accompanied with a symmetry change. Such lowering of symmetry can stabilize the related ground state by lifting the degeneracy originated from the frustration. The observation of the breaking of extinction rule by x-ray is the key to investigate such anomalies. A sizable lattice deformation is also observed in multi-ferroic, in which the local distortion of atoms generates ferroelectricity. With strong SR source, one can measure the field dependence of the Bragg peak position and intensity under a pulse field of msec- to several tens ms-pulse-width by time-dependent measurement. This has an advantage in the capability of monitoring the field dependence continuously. However, the availability is limited by the short accumulation time for weak peaks appearing in small symmetry changes. Moreover, the observation of weak super-lattice peaks caused by electronic transitions such as CDW, Fermi surface nesting and others is very difficult in SR source. The breakthrough has been made by the combination of the high intense XFEL beam and the single shot pulsed field. A tiny CDW peaks in YBCO have been observed successfully in a single short diffraction. It will extend the application of pulsed field x-ray diffraction for systems with weak spin-charge-lattice couplings.

In this talk, the technical developments, recent examples of experiments, and the future development such as resonant scattering will be presented.

邀请人：吕力（8125 9151）

联系人：胡颖（8264 9361）