H. Nakao

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

A novel structure of orbital ordering is found in a Nd0.5Sr0.5MnO3 thin film, which exhibits a clear first-order transition, by synchrotron x-ray diffraction measurements. Lattice parameters vary drastically at the metal-insulator transition at 170 K (= T(MI)), and superlattice reflections appear below 140 K (= T(CO)). The electronic structure between T(MI) and T(CO) is identified as A-type antiferromagnetic with a d(x2-y2) ferro-orbital ordering. The new type of antiferro-orbital ordering characterized by the wave vector (1/4 1/4 1/2) in cubic notation emerges below T(CO). The accommodation of the large lattice distortion at the first-order phase transition and the appearance of the novel orbital ordering are brought about by the anisotropy in the substrate, a new parameter for the phase control.

Orbital Ordering Structures in (Nd,Pr)0.5Sr0.5MnO3 Manganite Thin Films on Perovskite (011) Substrates

Structural study of orbital-ordered manganite thin films has been conducted using synchrotron radiation, and a ground state electronic phase diagram is made. The lattice parameters of four manganite thin films, Nd0.5Sr0.5MnO3 (NSMO) or Pr0.5Sr0.5MnO3 (PSMO) on (011) surfaces of SrTiO3 (STO) or [(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7] (LSAT), were measured as a function of temperature. The result shows, as expected based on previous knowledge of bulk materials, that the films resistivity is closely related to their structures. Observed superlattice reflections indicate that NSMO thin films have an antiferro-orbital-ordered phase as their low-temperature phase while PSMO film on LSAT has a ferro-orbital-ordered phase, and that on STO has no orbital-ordered phase. A metallic ground state was observed only in films having a narrow region of A-site ion radius, while larger ions favor ferro-orbital-ordered structure and smaller ions stabilize antiferro-orbital-ordered structure. The key to the orbital-ordering transition in (011) film is found to be the in-plane displacement along [011] direction.

Charge-order pattern of the low-temperature phase from a monoclinic single domain of NaV2O5 uniquely determined by resonant x-ray scattering.

The present resonant x-ray scattering from each of monoclinically-split single domains of NaV2O5 has critically enhanced contrast between V4+ and V5+ ions strong enough to lead to unambiguous conclusion of the charge-order pattern of its low-temperature phase below Tc = 35 K. The zig-zag type charge-order patterns in the

Diffuse scattering from an Al72Ni20Co8 decagonal quasicrystal on an order–disorder transformation

ab

Coupling between Orbital and Lattice Degrees of Freedom in Y1-xCaxTiO3 (0 < x ≤0.75): A Resonant X-ray Scattering Study

-plane previously confirmed have four kinds of configurations (A, A, B and B) and the stacking sequence along the c-axis is determined as the AAAA type by comparison with model calculations. By assigning the A and A configurations to Ising spins, one can reasonably understand the previously discovereddevils staircase-type behavior with respect to the modulation of the layer-stacking sequences at high pressures and low temperatures, which very well resembles the global phase diagram theoretically predicted by the ANNNI model.

An inelastic X-ray scattering spectrometer for materials science on BL11XU at SPring-8

Non-uniform distortion induced by superstructure domains has been observed during the ordering process of an order–disorder transformation in a single decagonal quasicrystal of Al72Ni20Co8. The full width at half maximum (FWHM) of the fundamental reflections increased below the transformation temperature, Tc. At the same time, the integrated intensity of the fundamental reflections varied drastically at Tc. A small hysteresis was also observed in the temperature dependences of both the FWHM and the integrated intensity of the fundamental reflections. Peak broadening of the fundamental reflections is predominantly dependent on |G∥ | below Tc. In addition, the weak dependence of the peak broadening with |G⊥ | is extracted from the observed FWHM of the fundamental reflections. After deconvolution, the FWHM of the fundamental reflections appears to be a linear combination of |G∥ | and |G⊥ |. Coexistence of the non-uniform distortion and of the random phason strain contributes to the ordering process below Tc. The diffuse scattering from atomic short-range order (SRO) was distributed around the ideal positions of the superstructure reflections. The SRO diffuse scattering disappeared completely above Tc + 10 K. In addition, a small hysteresis of the SRO diffuse scattering was found in the temperature cycle.

d-f Coulomb and quadrupole-strain interactions in DyB{sub 2}C{sub 2} observed by resonant x-ray scattering

We have studied the orbitally ordered states in Y 1- x Ca x TiO 3 (0 < x ≤0.75) by resonant X-ray scattering (RXS) near the Ti K -edge ( E ∼5 keV) and by powder X-ray diffraction measurements. The ...

Crystal Structure and Charge-Ordering in La1.5Ca0.5CoO4 Studied by Neutron and Resonant X-ray Scattering

Abstract An inelastic X-ray scattering spectrometer on the beamline BL11XU at the SPring-8 is described. The typical energy resolution and energy transfer are 0.1–1xa0eV and ∼30xa0eV, respectively. The main aim of this spectrometer is the measurement of electronic excitations, such as charge-transfer excitation and interband transition, especially using resonant X-ray scattering. As a test experiment, the resonant X-ray scattering spectra of LaMnO 3 including Mn Kβ 5 emission are given.

Resonant X-ray scattering study on the filled skutterudite PrFe4P12

Experimental evidence of the d-f Coulomb interaction responsible for the resonant x-ray scattering (RXS) from antiferroquadrupolar order in DyB{sub 2}C{sub 2} is presented. The energy dependences of the RXS intensity with polarization analysis are analyzed by considering the interference between the resonances of dipolar (E1) and quadrupolar (E2) transition processes. It is found that the structure factors for the E1 and E2 processes have the same sign for {sigma}-{pi}{sup } but the opposite sign for {sigma}-{sigma}{sup } channel. This result, when compared to the calculated structure factors, means that the quadrupolar moments of the 4f and 5d shells have opposite signs to each other. Interference between nonresonant Thomson scattering from the lattice distortion and resonant scatterings is also studied, revealing the relation between the displacements of the B and C atoms and the charge distributions of the 4f and 5d shells.

Periodic Arrangement of Quadrupolar Moments Induced by the Antiferromagnetic Order in TbB2C2: Observation by Resonant X-ray Scattering

Using neutron and resonant X-ray scattering, we studied crystal structure and charge-ordering pattern in La 1.5 Ca 0.5 CoO 4 . Taking A 2 m m with a – b type twin structure into account, Co 2+ /Co 3+ checkerboard charge ordering pattern was suggested in La 1.5 Ca 0.5 CoO 4 by neutron scattering structure analysis. In order to clarify the charge ordering pattern and the valences of the two Co sites, we performed a resonant X-ray scattering (RXS) measurement near the Co K -edge. We found a resonant signal at (3, 0, 0) reflection which corresponds to the charge ordering with a Co 2+ /Co 3+ checkerboard pattern, and the Co valences of charge ordering were fully charge disproportionated. From the X-ray fluorescence spectra, we found the pre-edge peak structures at E =7.710 and 7.713 keV, corresponding to 1 s → t 2 g and 1 s → e g transitions, respectively. The polarization dependence of the latter one suggests that the anisotropy e g orbital is realized in La 1.5 Ca 0.5 CoO 4 .