Satoshi Iikubo

Finite size effects of nanoparticles on the atomic pair distribution functions.

The finite size effects of nanoparticles on the atomic pair distribution functions (PDF) are discussed by calculating the radial distribution functions (RDF) on nanoparticles with various shapes, such as sheet, belt, rod, tube and sphere, assuming continua. Their characteristics are shown depending on the shapes and the sizes of the nanoparticles. The formulas of a PDF analysis which take account of such effects are presented and are found to reproduce the experimental data.

Antiferromagnetic bipolar semiconductor LaMnPO with ZrCuSiAs-type structure

Electronic and magnetic properties of a layered compound LaMnPO are examined in relation to a newly discovered iso-structural superconductor LaFeAs(P)O. Neutron diffraction measurements, together with temperature dependent magnetic susceptibility, clarify that LaMnPO is an antiferromagnet at least up to 375 K. The spin moment of a Mn ion is determined to be 2.26u2002μB at room temperature, and the spin configuration is antiparallel in the Mn–P plane and parallel between the Mn–P planes, which is rather different from that of LaFeAsO. Optical absorption spectra, photoemission spectra, and temperature dependent electrical conductivity indicate that LaMnPO is a semiconductor. Furthermore, nominally undoped LaMnPO exhibits n-type conduction while the conduction type is changed by doping of Cu or Ca to the La sites, indicating that LaMnPO is a bipolar conductor. Density functional calculation using the GGA+U approximation supports the above conclusions; the electronic band structure has an open band gap and the an...

Antiferromagnetic Fluctuations in Fe(Se1-xTex)0.92 (

Motivated by the discovery of superconductivity in F-doped LaFeAsO, we investigated the magnetic fluctuations in related compounds Fe(Se 1- x Te x ) 0.92 ( x = 0.75, 1) using neutron scattering technique. Non-superconducting FeTe 0.92 shows a pronounced magnetic fluctuation around | Q |≈0.9 A -1 , which is slightly smaller than the magnetic ordering vector | Q |≈0.97 A -1 . In a superconductor Fe(Se 0.25 Te 0.75 ) 0.92 , we observed that a magnetic fluctuation is located at | Q |≈0.9 A -1 at low energies and shifts to a higher value of | Q |≈1.2 A -1 at higher energies. The latter value is close to a reciprocal lattice vector Q = (0.5,0.5,0.5) or (0.5,0.5,0), where the AF fluctuations are observed in other FeAs-based materials. The existence of this common characteristic in different Fe-based superconductors suggests that the AF fluctuations may play an important role in superconductivity.

x = 0.75, 1

The wave vector ( q )- and energy (ω)-dependent magnetic excitation spectra χ( q ,ω), have been studied in the temperature ( T ) range of 10 K≤ T <150 K on single crystals of La 1.48 Nd 0.4 Sr 0.12 CuO 4 , which has the static “stripe” order in the low-temperature phase. The incommensurability δ of the peak of χ( q ,ω) found by the q -scans and the peak width Δ q exhibit characteristic T dependences. The observed profiles show a clear incommensurate structure even at rather high temperatures. The results indicate that effects of the slowly fluctuating “stripes” exist not only in the low-temperature tetragonal (LTT) phase but also in the orthorhombic phase (LTO1) of the present system.

) Observed by Inelastic Neutron Scattering

Magnetic and local structures in an antiperovskite system, Mn3Cu1-xGexN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn3GeN for the broadening of MVE.