Nobuyoshi Wakabayashi

Short-range polaron correlations in the ferromagnetic La1-xCaxMnO3

We use neutron scattering to demonstrate the presence of lattice polarons and their short-range correlations for several samples of La1-xCaxMnO3 in the Ca doping range 0.15</=x</=0.3. We establish the doping dependence of the orientation, commensuration, and coherence length of the polaron correlations and show that the populations of correlated and uncorrelated polarons are intimately related to the transport properties of the materials.

Deformation of Vesicles under the Influence of Strong Electric Fields II

The deformation of vesicles with conducting membranes in external electric fields has been studied in the framework of the perturbation theory. A simple model for dynamics of deformation is proposed, and the results of numerical calculations for typical combinations of the vesicle size and the electric field are presented. When the conductivity inside a spherical vesicle is larger than that of the exterior medium, the deformations, both static and dynamic, are prolate and, otherwise, they are oblate.

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...

Spatial correlations in the valence of metal ions in Ni1-xPdx(chxn)2Br3

X-ray scattering experiments have been performed on a quasi-one dimensional system, Ni 1- x Pd x (chxn) 2 Br 3 . Strong diffuse scattering was observed for x > 0.7, and it was interpreted as due to spatial inhomogeneity in the valence of metal ions. This inhomogeneity takes the form of CDW in which the metal ions within a chain have valences alternating between +2 and +4. Correlations in the valence sequence could be determined parallel as well as perpendicular to the chain direction. Pair correlation functions deduced from the measurements show the existence of strong correlation between the positions of bridging Br ions and those of Br counter ions. It is concluded that the valence of metal ions for x <0.7 is +3. These results are consistent with previous data on optical and magnetic measurements.

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 .

Magnetic Excitations in an Ordered Ferromagnetic Alloy Fe3Pt

Magnetic excitations in an ordered ferromagnetic alloy of Fe 78 Pt 22 have been studied by neutron scattering. Magnetic dispersion relations have been measured in the [001], [110] and [111] directions. The dispersion curve attained to the zone boundary in [001], while in other two directions, well defined magnon groups could be detected up to 80 meV. The dispersions still have steep slopes, sugggesting that magnon energies at zone boundaries would be quite high. The results have been analyzed in terms of the spin wave theory of the four sublattice Heisenberg system, which indicates that any solutions for fitting the observed dispersions could not explain consistently the whole experimental data. An anomalous damping of the magnons in the [001] direction was detected at high temperatures.

Orbital and Charge Ordering in La1-xSr1+xMnO4 (0.4≤x ≤0.5)

Hole concentration dependence of charge order (CO) and orbital order (OO) in layered perovskite compounds La 1- x Sr 1+ x MnO 4 has been studied by means of the resonant X-ray scattering technique. Both CO and OO are observed below 210 K in the compounds having the hole concentration x between 0.5 and 0.48, but neither is observed for x ≤0.46. The transition temperatures are nearly independent of x between 0.5 and 0.48. Correlation lengths ξs for both orders obtained from analyses of superlattice peak profiles are finite at any temperature. Moreover, in contrast to the cubic perovskite, ξ for OO is larger than that for CO. ξ for OO is as short as that for CO at the critical concentration of x =0.48. These results suggest that OO is prerequisite to the forming of CO in this system.

Steady-state deformation of a vesicle in alternating electric fields

Abstract Steady-state deformation of a vesicle with a membrane of arbitrary conductance in an alternating electric field is discussed. A simple formula is obtained for the elongation modulus of the vesicle as a function of the frequency of the applied field. The dependences of this modulus on the conditions in the medium and the membrane characteristics are illustrated in detail. Experimental applicability to the extraction of information on the characteristics of a vesicle are discussed.

Transient and Steady-State Deformations of a Vesicle with an Insulating Membrane in Response to Step-Function or Alternating Electric Fields

Deformation of a vesicle with an insulating membrane under an external electric field is considered. Application of a step-function field, under which the eventual form is prolate, is shown to transientiy induce an oblate deformation, provided that the conditions of the surrounding medium are chosen properly. It is further demonstrated that alternating electric fields induce deformation in a frequency-dependent manner; the deformation at low frequencies is always a prolate one, whereas the steady-state deformation at high frequencies is either prolate or oblate depending on the medium conditions. If this frequency dependence is experimentally observable, the capacitance and curvature elastic modulus of the membrane as well as the intravesicular conductance can be estimated directly from the data. The field-induced deformation may serve as a novel experimental method in cell biology.

Crystal Lattice Changes Induced by Magnetic Field and Helifan Structure in Holmium Metal

An X-ray diffraction study has been made on holmium metal in a magnetic field at several temperatures. In most cases, the c -lattice parameter has been observed to change discontinuously with increasing magnetic field, corresponding to the appearance of various magnetic structures. The result of numerical calculations by a self-consistent mean field method suggests that the effect of the helifan structure on the crystal lattice has been observed in a narrow range of magnetic field.