Kiyoichiro Motoya

Spin-Glass Behavior and Magnetic Phase Diagram of La1-xSrxCoO3 ( 0 ≤x ≤0.5) Studied by Magnetization Measurements

Magnetic properties of La 1- x Sr x CoO 3 (0 ≤ x ≤0.5) have been studied by magnetization measurements in low magnetic fields. It has been found that there exist spin-glass (0< x ≤0.18) and cluster-glass (0.18 ≤ x ≤0.5) regions. Ferromagnetic long-range order previously reported does not take place. Spin-glass behavior is ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co 3+ and Co 4+ and the antiferromagnetic one between like spins.

Structural and electronic transport properties of polycrystalline p-type CoSb3

The structural and electronic transport properties of polycrystalline p-type CoSb3 with different grain sizes (about 3 and 3×102 μm) were investigated. The magnetic susceptibility was also measured. Samples were characterized by x-ray diffractometry, electron-probe microanalysis, and optical microscope observation. Samples were found to be stoichiometric and homogeneous. The Hall carrier concentration of the samples is of the order of 1018 cm−3 and weakly dependent on the temperature. The temperature dependence of the Hall mobility suggests that the predominant scattering mechanism drastically changes depending on grain size: for large grain size a combination of the neutral impurity scattering and the acoustic phonon scattering, and for small grain size the ionized impurity scattering. The magnetic susceptibility was found to be essentially diamagnetic independently of grain size, and to vary slightly with temperature. The weak temperature dependence of the susceptibility can be explained by taking into ...

Formation of a Hybridization Gap in a Cage-Like Compound CeFe2Al10

We report on the magnetic, transport, and thermal properties of a cage-like compound CeFe 2 Al 10 that crystallizes in the orthorhombic YbFe 2 Al 10 -type structure. A broad peak in the magnetic susceptibility at 70 K indicates that CeFe 2 Al 10 is a valence fluctuation compound. The electrical resistivity and the Hall coefficient exhibit sharp upturns below 20 K, where the thermopower shows a rapid decrease. These low-temperature anomalies in the transport properties resemble those of a typical Kondo semiconductor CeRhSb. These features indicate the formation of a hybridization gap in CeFe 2 Al 10 on cooling below 20 K. The energy gap is estimated as 15 K from the thermal activation energy of the resistivity. The magnetic contribution of the specific heat shows a Schottky-type maximum at 30 K that provides another evidence for the gap formation in CeFe 2 Al 10 .

Spin State and Hyperfine Interaction in LaCoO3 : NMR and Magnetic Susceptibility Studies

59 Co and 139 La NMR measurements have been performed to study the microscopic magnetic properties closely related with the spin state of a trivalent cobalt ion in LaCoO 3 . The temperature-independent 59 Co and 139 La Knight shifts below ∼ 30 K clearly revealed the presence of a nonmagnetic ground state at low temperatures. We calculated the temperature dependence of the magnetic susceptibility χ and the 59 Co Knight shift 59 K in a single ion model with the low-spin 1 A 1 ground state above which the high-spin 5 T 2 state is located. Then, both the trigonal crystal-field and spin-orbit interactions are taken into account. From this analysis, we infer the presence of an antiferromagnetic exchange interaction between the high-spin states. The characteristic temperature dependence of the 59 Co hyperfine coupling constant is also discussed.

Orbital Ordering and Local Magnetic Properties of Mott-Hubbard Insulators YTiO3 and LaTiO3. NMR Study.

47,49 Ti, 89 Y and 139 La NMR measurements have been performed to study local magnetic properties of the Mott-Hubbard insulators YTiO 3 and LaTiO 3 . In particular, the magnetic structure of the ferromagnetic (antiferromagnetic) state of YTiO 3 (LaTiO 3 ) is discussed based on the analysis of 47,49 Ti frequency-swept NMR spectra. We found that the Ti NMR spectrum in YTiO 3 is successfully explained by an orbital ordering model proposed by the unrestricted Hartree-Fock and the band calculations. On the other hand, the Ti NMR spectrum in LaTiO 3 is explained without orbital ordering. The internal field H n at the Y site in YTiO 3 is due to the supertransferred hyperfine interaction, whereas the H n at the La site is canceled out because of the local symmetry in the antiferromagnetic state of LaTiO 3 .

Helical spin structure in MnSi-NMR studies

Abstract The zero field NMR signals of MnSi have been observed at 1.6 K. From the distribution of the resonance frequency and the external field dependence it is concluded that MnSi has a helical spin structure at zero field. The magnetization process is interpreted as due to the helical→ conical→ ferromagnetic transitions.

Bulk screening in core-level photoemission from Mott-Hubbard and charge-transfer systems

We report bulk-sensitive hard x-ray shn = 5.95 keVd core-level photoemission spectroscopy sPESd of single crystal V1.98Cr0.02O3 and the high-Tc cuprate Bi2Sr2CaCu2O8+d sBi2212d .V 1.98Cr0.02O3 exhibits low binding energy “satellites” to the V 2 p “main lines” in the metallic phase, which are suppressed in the antiferromagnetic insulator phase. In contrast, the Cu 2 p spectra of Bi2212 do not show temperature-dependent features, but a comparison with soft x-ray PES indicates a large increase in the 2p 5 3d 9 satellites or 3d 9 weight in the bulk. Cluster model calculations, including a full multiplet structure and a screening channel derived from the coherent band at the Fermi energy, give very satisfactory agreement with the experiments.

Neutron Scattering Investigation of Itinerant Electron System Fe2P

Neutron elastic and inelastic scattering experiments have been performed on Fe 2 P single crystals in the temperature range from 8 K to 800 K. Fe 2 P is of the hexagonal C-22 type structure and exhibits c -axis ferromagnetism below 130 K. In the intermediate range between 130 K and 217 K, the canted ferromagnetism with a uniform component along the c -axis M 0 and a staggered component in the c -plane M Q appears, and the first order transition takes place at T c =217 K from the canted ferromagnetism to paramagnetism. The most interesting behaviour is the existence of giant short range order up to T =3 T c . It originates in the small stiffness constants D and leads to the strong deviation of susceptibility from the Curie-Weiss law. The amplitude of the spin fluctuation observed In Fe 2 P In the pararnagnetic phase is understood by the simple model with parameters deduced from the spin wave dispersion at low temperature, the magnetization and uniform susceptibility.

Hole-doping effect on magnetic properties of La1−xSrxCoO3 (0 ≤ x ≤ 0.5)

Abstract We performed magnetization, neutron scattering and NMR measurements to reveal the hole-doping effect on magnetic properties of La 1− x Sr x CoO 3 (0 ≤ x ≤ 0.5). A magnetic phase diagram which includes spin-glass (0 ≤ x ≤ 0.18) and cluster-glass (0.18 ≤ x ≤ 0.5) phases is proposed.

Double-Q 120 degrees structure in the Heisenberg antiferromagnet on rhombohedrally stacked triangular lattice LiCrO2

The magnetic ordering of the S=2/3 Heisenberg antiferromagnet on a rhombohedrally stacked triangular lattice LiCrO2 is studied by susceptibility, neutron diffraction and polarization analysis measurements using a single crystal. The temperature dependence of the susceptibility strongly suggests that a 120 degrees structure is established in each quasi-two-dimensional layer, which is parallel to the c plane. Assuming the 120 degrees structure in which magnetic moments are confined in a plane including the c axis because of an Ising-type anisotropy, neutron scattering shows that the magnetic ordering is a double-Q structure with non-equivalent wave numbers q=(1/3 1/3 0) and (-2/3 1/3 1/2). It is characterized by an alternating sequence of rotational direction of the 120 degrees structure along the c axis.