Murakami Youichi

Symmetry Lowering in LaOBiS2: A Mother Material for BiS2-Based Layered Superconductors

We report X-ray diffraction studies of single-crystal samples of LaOBiS2 and CeOBiS2, which are mother materials for BiS2-based layered superconductors. The structural symmetry in LaOBiS2 is lowere...

Orbital and Charge Ordering in LaSr 2Mn 2O 7 Observed by Resonant X-Ray Scattering

Orbital and charge ordering phenomena in bilayered perovskite manganite LaSr 2 Mn 2 O 7 have been studied by resonant X-ray scattering. Superlattice reflections corresponding to these orderings are observed below 210 K. The in-plane and stacking structure of the orbital and charge order is determined from these reflections. The anisotropy of the anomalous atomic scattering factor of Mn 3+ in the orbital ordered state is observed in the azimuthal angle dependence of the reflections. The anisotropy is attributed to the band dispersion of 4p level due to the layered structure as well as the orbital order. In the course of this study, we have found that charge and orbital orderings collapse simultaneously, maintaining the same correlation lengths with further decreasing temperature.

Resonant Magnetic X-ray Diffraction Study on Successive Metamagnetic Transitions in TbB4

Resonant magnetic x-ray diffraction experiments on the Shastry–Sutherland lattice TbB 4 were carried out under pulsed magnetic fields up to 30 T at 8 K. TbB 4 exhibits a multi-step magnetization process above 16 T below about 20 K when magnetic fields are applied along the c -axis. We examined the intensity of the 010 magnetic reflection as a function of magnetic field and found that the magnetization plateau phases are accompanied by large XY components of magnetic moments. We propose novel magnetic structures which consist of XY spins and Ising spins for the plateau phases. We also propose that energy level crossing and its inherent degeneracy give rise to the successive metamagnetic transitions in TbB 4 .

Resonant X-ray Studies of the Quadrupolar Orderings in RB2C2 (R = Dy, Ho)

We have performed the resonant x-ray scattering experiment on DyB 2 C 2 and HoB 2 C 2 , where the antiferroquadrupolar orders play important roles. The superlattice reflections that appear below the transition temperatures have been investigated by measuring the incident energy, polarization, scattering vector, azimuthal angle and temperature dependences at the L 3 absorption edge. The results are theoretically analyzed with a model of the antiferroquadrupolar order: the azimuthal angle dependences are well explained. The quadrupolar and magnetic contributions to the scattering intensities are also separated: it is deduced that the magnitude of the ordered quadrupolar moments of HoB 2 C 2 is much smaller than that of DyB 2 C 2 .

Resonant X-ray Scattering Experiments on the Ordering of Electronic Degrees of Freedom

Resonant X-ray scattering (RXS) has been developed as a powerful technique for observing orderings of electronic degrees of freedom: charge, spin, orbital, and multipoles. After a brief introduction of the RXS technique, we review some RXS experiments on the orderings in \(d\) and \(f\) electron systems with a strong correlation between electrons. The basic concept of RXS and the recent developments of the technique are described in this review paper. We also present future prospects of the studies using RXS for users.

Magnetic Correlation in the Ordered Phase of CeOs4Sb12

We performed neutron diffraction and magnetization measurements to reveal the nature of phase transition of a Kondo semiconductor CeOs 4 Sb 12 . Weak antiferromagnetic (AFM) reflections characterized by a wave vector q = (1 0 0) were observed, and the ordered moment value is around 0.07µ B /Ce at zero magnetic field. The AFM structure is rapidly suppressed by magnetic field of 1 T, in contrast to the transition temperature suggested to be enhanced by magnetic field. Only ferromagnetic correlation is observed above 1 T. Such drastic variation of the magnetic correlation is closely connected into the transport properties; the AFM ordered phase below 1 T and the induced ferromagnetic state above 1 T correspond to the semiconducting and metallic states, respectively.

Correlation between Tc and Transport Properties in PrFeP1-xAsxO0.9F0.1

We investigated the isovalent P/As substitution effect in iron pnictide superconductor, PrFeP 1- x As x O 0.9 F 0.1 to find the relationship among superconducting transition temperature T c , crystal structure and electronic properties. The lattice constants and the pnictogen height from iron layer show linear x dependence, indicating the continuous change of chemical pressure without the variation of band filling. In contrast to the monotonic change of crystal structure, T c , the temperature dependence of resistivity and Hall coefficient R H show anomalous x dependence. In the region of the As concentration of 0≤ x ≤0.6, the T c continuously increases, and the power of temperature of resistivity ( n ) is gradually changed from 2 to 1 with increasing x . The T c and the power n show distinct correlation, indicating that the antiferromagnetic fluctuation enhances T c . On the other hand, T c and the power n have no correlation in the region of 0.6 < x ≤1.0. These different behaviors in the regions of x < ...

Absence of Magnetic Long Range Order in Ba3ZnRu2O9: A Spin-Liquid Candidate in the S = 3/2 Dimer Lattice

We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.We have discovered a novel candidate for a spin liquid state i n a ruthenium oxide composed of dimers of S = 3/2 spins of Ru, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000times lower than the magnetic interaction scale of around 20 0 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a s pin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance o f interand intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

Field Induced Magnetic Moment Distribution in the Ordered Phase of PrFe4P12

Neutron diffraction experiments have been performed to investigate the electronic phase transitions in the Pr-based filled skutterudite PrFe 4 P 12 . This compound undergoes a transition from a characteristic heavy-electron state to a nonmagnetic phase below 6.5 K. Neutron diffraction experiments reveal an antiferromagnetic alignment of the magnetic-field induced dipole moments. The directions of the antiferromagnetic components are considered to be always parallel to the magnetic field applied along either [0 0 1], [1 1 0] or [1 1 1]. This implies that the symmetry of the ordered state can be categorized as Γ 1 . This phenomenon is consistent with the scenario of a scalar-type order parameter for the Pr 4 f electron state.

Quadrupolar Order and Structural Phase Transition in DyB4 with Geometrical Frustration

Structural phase transition accompanying with quadrupolar ordering in DyB 4 with Shastry–Sutherland type geometrical frustration has been studied by X-ray diffraction. Previous study [D. Okuyama et al. : J. Phys. Soc. Jpn. 74 (2005) 2434.] using resonant X-ray scattering revealed short-range ordering of the O z x -type quadrupolar moments and the c -plane component of the magnetic moments in addition to long-range ordering of the c -axis component of the magnetic moments. The present report focuses on the lattice distortion below the quadrupolar ordering temperature at T N2 =12.7 K. The (0 0 l =integer) fundamental lattice reflection splits into four peaks along the h and k directions and the ( h =even 0 0) reflection becomes broad along the l direction. This indicates that a structural transition from tetragonal to monoclinic takes place below T N2 together with the ordering of the quadrupolar moments.