arXiv subjects

Hiroyuki Kimura

Publications and source records attributed to Hiroyuki Kimura.

3 recordsLinked to original sources

arXiv2024

Toward the theoretically observable limit of electron density distribution by single-crystal synchrotron X-ray diffraction: The case of orbitally ordered Ti-3d^1 in YTiO_3

The theoretically observable limit of electron density distribution by single-crystal X-ray diffraction is discussed. When F_{orb} and δF are defined as, respectively, the partial structure factor for an orbital and the deviation of the observed F from the true F, the accuracy of electron density attributable to F_{orb} is chiefly determined by the number of reflections satisfying the condition F_{orb}/F > δF/F. Since F_{orb}/F, which is generally small for crystals with large F(0,0,0), is constant under a given set of experimental conditions, δF/F must be reduced to increase the number of reflections satisfying F_{orb}/F > δF/F. The present paper demonstrates how to reduce δF mathematically and experimentally, and the following topics are covered: the Poisson statistics, accumulation of errors in the data collection and reduction procedure, multiple diffraction, conversion error from F^2 to F in refinement programs, which is unavoidable when the input quantities have different dimension from F, weighting of reflections, and tips. For demonstration, observation of the electron density of the Ti-3d^1 orbital in YTiO_3 by synchrotron single-crystal X-ray diffraction is presented.

cond-mat.mtrl-sci↗

arXiv2008

Pressure-induced commensurate magnetic order in multiferroic $HoMn_2O_5$

The pressure ($p$) -- temperature ($T$) phase diagram for microscopic magnetism in the multiferroic compound HoMn$_{2}$O$_{5}$ was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate--commensurate--incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The $p$ -- $T$ phase diagram established shows excellent agreement with the recently reported $p$ -- $T$ dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the $p$ -- $T$ magnetic phase diagram is quite similar to the previously obtained magnetic field-temperature phase diagram.

cond-mat.str-el↗

arXiv2006

Incommensurate lattice distortion in the high temperature tetragonal phase of La$_{2-x}$(Sr,Ba)$_{x}$CuO$_{4}$

We report incommensurate diffuse (ICD) scattering appearing in the high-temperature-tetragonal (HTT) phase of La$_{2-x}$(Sr,Ba)$_{x}$CuO$_{4}$ with $0.07 \leq x \leq 0.20$ observed by the neutron diffraction technique. For all compositions, a sharp superlattice peak of the low-temperature-orthorhombic (LTO) structure is replaced by a pair of ICD peaks with the modulation vector parallel to the CuO$_6$ octahedral tilting direction, that is, the diagonal Cu-Cu direction of the CuO$_2$ plane, above the LTO-HTT transition temperature $T_s$. The temperature dependences of the incommensurability $δ$ for all samples scale approximately as $T/T_s$, while those of the integrated intensity of the ICD peaks scale as $(T-T_s)^{-1}$. These observations together with absence of ICD peaks in the non-superconducting $x=0.05$ sample evince a universal incommensurate lattice instability of hole-doped 214 cuprates in the superconducting regime.

cond-mat.supr-con↗