Susumu Shimomura

Effect of Magnetic Transitions and Charge-Ordering on Crystal Lattice in Nd0.5Sr0.5MnO3

X-ray diffraction measurements have been performed on Nd 0.5 Sr 0.5 MnO 3 single crystals at various temperatures and magnetic fields. The temperature dependences of the lattice parameters show abr...

Lattice Constants, Electrical Resistivity and Specific Heat of RNiC2

Anomalous temperature dependence of electrical resistivity was found to be ubiquitous among the compounds RNiC 2 with R = La, Ce, Nd, Sm, Gd, Tb and Er. Lattice parameters were also observed to exhibit anomalous temperature dependence for some of the compounds studied by X-ray diffraction. It is argued that the existence of charge modulated structures is the cause of the former anomalies. The latter anomalies, on the other hand, are likely to be related to the coupling between the lattice and the f-electrons. Results of heat capacity measurements are used to estimate crystal field levels in NdNiC 2 and SmNiC 2 .

Pseudogap of Charge-Density-Wave Compound SmNiC2 Studied by High-Resolution Photoemission Spectroscopy

We have performed high-resolution photoemission spectroscopy of a rare-earth inter-metallic compound SmNiC 2 which undergoes a charge-density-wave (CDW) transition at T CDW = 148 K and a ferromagnetic transition at T c = 17.5 K. We have determined the valence-band and near-E F (Fermi level) electronic states, and observed a marked suppression of the spectral density of states (DOS) within 60-70 meV with respect to E F below T CDW , indicative of a partial gap (pseudogap) opening due to the CDW formation. Finite DOS at E F in the CDW state suggests an imperfect nature of the Fermi-surface nesting.

Synchrotron X-ray Diffraction Studies of α-Gd2S3

Non-resonant X-ray Bragg diffraction measurements on a small, single crystal of α-Gd 2 S 3 in zero and non zero applied magnetic fields are reported. From independent neutron diffraction measurements, the magnetic unit cell is found to be the same as the chemical unit cell. Therefore, the observation of magnetic X-ray diffraction by this compound is particularly challenging. We observe a change in the intensity around the Neel temperature in zero field, as well as around the phase boundaries at finite magnetic fields. The X-ray diffraction intensity is calculated based on the previously established magnetic structure. A reasonable amount of intensity from the interference between magnetic and charge scattering is predicted, and it provides a satisfactory account of our observations.

Manipulating the Multipole Moments in CeB6 by Magnetic Fields

Results of non-resonant X-ray Bragg diffraction measurements in the phase II of CeB 6 under an applied magnetic field, H , are reported. The intensity of the superlattice reflection ( n /2, n /2, n /2) increases dramatically with H applied along the [111] axis, where n is odd. On the other hand, the superlattice intensity decreases with H along the [\bar211] axis normal to the scattering vector. These behaviors of the superlattice intensity in H are explained qualitatively by the combined effects of the magnetic moments tending to align parallel to H and the spin orbit coupling which tends to align the extended wave function of the f electron normal to H . Using this relation, one can manipulate the multipole moments in rare-earth compounds by magnetic fields.

High-Resolution X-Ray Diffraction Study of Commensurate-Incommensurate Phase Transition in (N(CH3)4)2MnCl4 under Pressure.

Using synchrotron radiation, we have performed a high-resolution X-ray diffraction study of a phase transition between the incommensurate phase and the commensurate phase characterized by the wave vector q =3 c * /7 in [N(CH 3 ) 4 ] 2 MnCl 4 under pressure. The pressure dependence of the wave vector q exhibits an “incomplete devils staircase.” The high-resolution capability of the synchrotron radiation reveals that the incommensurate satellite reflection shows an asymmetric and broad line shape along the modulation direction, while the q =3 c * /7 commensurate superlattice reflection is symmetric and its width is equal to the instrumental resolution. Such a profile of the incommensurate satellite reflection is found to depend on the history of the crystal.

Structural Change on the Magnetic Field-Induced Insulator-to-Metal Transition in Distorted Perovskite Eu0.6Sr0.4MnO3

Structural feature of Eu 0.6 Sr 0.4 MnO 3 through the magnetic-field-induced insulator-to-metal (IM) transition has been investigated by X-ray powder diffraction in a magnetic field using synchrotr...

Successive Transition in Rare-earth Intermetallic Compound GdNiC2

In GdNiC2, the magnetic state is investigated under the high magnetic fields and the low temperatures. We find the intermediate phases, in which the magnetization value is close to a half of the full moment, and the successive transition in the phase boundary between the antiferromagnetic, the metamagenetic, and the paramagnetic phases. The mechanism of the intermediate phase is discussed.

Crystal-Site-Selective Spectrum of Fe3O4 Obtained by Mössbauer Diffraction

We have succeeded for the first time in obtaining a crystal-site-selective Mossbauer spectrum of Fe3O4 using the Mossbauer diffractometer at SPring-8 BL11XU. In order to extract the nuclear resonant scattering, which provides the crystal-site-selective emission spectrum, reflections having a Bragg angle near 45° were used. The 666 and 10 10 0 reflection spectra reveal only B- and A-site spectra, respectively. Mossbauer diffraction spectroscopy enables us to measure the crystal-site-selective spectrum and to determine the precise hyperfine structure. This technique provides new possibilities for studying the local crystallographic and magnetic structure on iron sublattices in various multisite materials.

Double Bragg scattering observed in small-angle X-ray scattering from highly oriented pyrolytic graphite

In small-angle X-ray scattering from highly oriented pyrolytic graphite, radial streak patterns are observed. The streaks change their direction with sample rotation and appear and disappear in pairs. This streak pattern can be explained by double Bragg scattering. The directions of the streaks calculated as functions of the rotation angle are in good agreement with experiment. In addition, asymmetry in the intensity of the streaks and a small deviation from the radial pattern are observed, and they can be explained by the finite sample-size effect. The necessity of taking double Bragg scattering into account in small-angle X-ray scattering studies of crystalline materials is emphasized.