Kitazawa Hideaki

Metal–Insulator Transition of Filled Skutterudite Compound SmRu4P12

Filled skutterudite SmRu 4 P 12 exhibits a metal–insulator (M–I) transition near 16 K (= T MI ). We have measured in detail the specific heat C ( T ), electrical resistivity ρ( T ) and magnetization M ( T ) under high magnetic field around M–I transition. The detailed measurements have revealed that this M–I transition is caused by two successive transitions. The single peak in C ( T ) at zero field changes into a double peak with increasing field. (-dρ/d T ) and d M /d T exhibit two anomalies at almost the same positions as the specific heat peaks. The magnetic entropy estimated at zero field reaches R ln 4 below T MI . The crystalline electric field (CEF) ground state is a quartet in cubic symmetry. It is suggested that the M–I transition of SmRu 4 P 12 is related to an orbital ordering originating from the CEF ground state quartet.

Observation of Energy Gap in FeGa3

The existence of an energy gap around the Fermi energy is established experimentally for the intermetallic compound FeGa 3 . 57 Fe Mossbauer spectra measured at room temperature confirmed the absen...

Rattling in Clathrate Compounds of ROs4Sb12 and R3Pd20Ge6

We have performed ultrasonic experiments on clathrate compounds ROs 4 Sb 12 and R 3 Pd 20 Ge 6 to explore rattling and tunneling of a guest rattlers motion. We have found frequency dependence of the elastic constants and ultrasonic attenuations, which is called as ultrasonic dispersion, due to thermally activated rattling. At low temperatures, Curie-type elastic softening obeying 1/ T with antiferro-type intersite interaction, which corresponds to quantum tunneling, appears and continues even to the lowest 20 mK in LaOs 4 Sb 12 and La 3 Pd 20 Ge 6 . The understanding of the local charge fluctuation, rattling and tunneling, being coupled to conduction electrons in metals is a basic issue in the aspect of electron–phonon interaction in strongly correlated phenomena such as heavy fermion state, superconductivity and multi-channel Kondo screening effect.

Elastic Constants and Multipolar Effects in PrNi5

We report the temperature dependence of elastic constants in PrNi 5 measured by the ultrasonic technique and analyzed by the quadrupole response. The experimental result of C 66 was well reproduced by the quadrupolar susceptibility including the higher-order multipolar effects. We obtained the higher-order multipolar coupling δ=-0.03 for C 66 mode.

Single Crystalline MgB2 Superconductor

We describe the details of single-crystal growth of magnesium diboride (MgB 2 ) using the vapor transport method. A T c onset temperature of 38.6 K was confirmed, and anisotropic superconducting properties were discussed through the transport and magnetization measurements on the MgB 2 single crystal. The positive curvature in H c2 ( T ) near T c and the linear behavior of H c2 ( T ) at low temperature give clear evidence for clean limit type-II superconductor.

f-Electron States in PrPd5Al2

The crystalline electric field (CEF) excitation spectra of PrPd5Al2 have been studied by neutron inelastic scattering in order to reveal the f-electron states, where PrPd5Al2 is a Pr-based isostruc...

Electric Quadrupole Effect in Clathrate Compound Pr3Pd20Si6

Electric quadrupole effects in a Pr-based clathrate compound Pr 3 Pd 20 Si 6 have been investigated by ultrasonic measurements. Elastic constants of ( C 11 - C 12 ) /2 and C 44 in Pr 3 Pd 20 Si 6 show curie-type softenings with decreasing temperature below 20 K, which are described in terms of quadrupole effects of 4f-electron for the ground state either Γ 3 doublet or Γ 5 triplet. H – T phase diagram of Pr 3 Pd 20 Si 6 under the magnetic fields along [110] is obtained from elastic anomalies in ( C 11 - C 12 ) /2 mode.

Low Temperature NMR Studies of YbSb

Nuclear Magnetic Resonance of YbSb was measured below 1 K to investigate a phase transition around 0.5 K including sample dependence. The observed broadening of spin echo spectra below 0.4 K demonstrates the existence of a phase transition clearly. The width of spin echo spectra are comparable to those of YbAs below 0.4 K, which is suggests the ordered moments are also comparable although the shape of spin echo spectra are quite different. The temperature dependence of relaxation rate shows rather abrupt decrease below 0.4 K. This is not consistent with the previous µSR measurements.

Photoemission Study of Ce2Sb

Ultraviolet photoemission spectra have been measured for Ce 2 Sb, CeBi 0.9 Te 0.1 and CeSe by use of synchrotron radiation to study their electronic structures especially to study the origin of the double peak structures. We have observed the same double peak structure in CeBi 0.9 Te 0.1 as in CeBi. A remarkable triple peak structure is observed in CeSe attributed to the p , f and d bands respectively. Ce 2 Sb is more complicated but it was shown that the band structure is rather similar to CeSb except for a pseudo-gap between the p and d bands and that the f level is at the pseudo-gap causing no double peak structure.