Shingo Araki

Evidence for Magnetic-Field-Induced Quadrupolar Ordering in the Heavy-Fermion Superconductor PrOs4Sb12

Neutron diffraction experiments on the heavy-fermion superconductor PrOs 4 Sb 12 revealed that a small antiferromagnetic moment, parallel to [010] ( y -direction), is induced in the field-induced phase ( H ∥ z ). The analysis, based on the Γ 1 singlet ground state crystal field model, shows that antiferro-order of O y z -type quadrupole moments of Pr ions is formed in the field-induced phase. This strongly suggests that the crystal field ground-state of Pr ions in PrOs 4 Sb 12 is the Γ 1 singlet and the quadrupolar ordering is induced due to level crossing with an excited state under a magnetic field.

Magnetic Excitations in Heavy-Fermion Superconductor PrOs4Sb12

Magnetic excitations in a single crystal of heavy-fermion superconductor PrOs 4 Sb 12 have been studied by inelastic neutron scattering (INS) at low temperatures under high magnetic fields. The crystal field (CF) excitations at 0.7 meV observed in a previous INS study of a polycrystal sample were confirmed in this study on a single crystal. The observed excitations in the zero magnetic field soften around a wave vector (1,0,0), which is the modulation vector of the field-induced antiferro-quadrupolar ordering, suggesting the presence of quadrupolar instability. The observed field dependence of excitations is better reproduced in a singlet ground-state model rather than in a non-Kramers doublet ground-state model. In a high resolution experiment, furthermore, the change of the excitation spectra at (1,0,0) was observed on passing through the superconducting transition temperature, indicating that the excitation and the superconductivity are closely related in PrOs 4 Sb 12 .

Single crystal growth and magnetic properties of CeRh2Si2

We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 by the Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the tetragonal crystal structure. A metamagnetic transition is found for the magnetic field along the [001] direction at 26 T.

Magnetic Properties and Crystalline Electric Field Scheme in RRhIn5 (R: Rare Earth)

A series of ternary compounds RRhIn 5 (R: rare earth) has been grown in the single crystalline form by means of the flux method. The magnetic properties of these compounds were investigated by meas...

Magnetic and Electrical Properties in a Dense Kondo Compound PrSn3.

We measured the specific heat, thermal expansion coefficient, magnetization, electrical resistivity, magnetoresistance and de Haas-van Alphen (dHvA) effect in PrSn 3 . The dense Kondo effect was confirmed from a negative magnetoresistance and the presence of heavy electrons with the cyclotron effective mass of 8–9 m 0 for the main Fermi surface. The magnetic phase diagram was also clarified by the high-field magnetization measurement.

Magnetic and Fermi Surface Properties of the Ferromagnetic Compound UGa2.

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa 2 . The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5 f 2 - and 5 f 3 -CEF schemes, based on the localized 5 f -electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5 f 2 - and 5 f 3 -core models nor by the spin-polarized 5 f -itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m 0 , which is consistent with the electronic specific heat coefficient of 11 mJ/K 2 ·mol.

Fermi surface and magnetic properties of PrTIn5 (T: Co, Rh, and Ir)

We grew single crystals of PrCoIn 5 , PrRhIn 5 , and PrIrIn 5 with the tetragonal crystal structure and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas–van Alphen effect. These Pr compounds reveal no magnetic ordering. The topology of the Fermi surfaces is the same as that of a non-4 f reference compound LaRhIn 5 . The cyclotron mass and/or the electronic specific heat coefficient are also approximately the same as those of LaRhIn 5 . The magnetic susceptibility and magnetization are anisotropic, reflecting the crystal structure, which are well explained by the tetragonal crystalline electric field scheme with the singlet ground state.

Adducts of a series of carbamato-silver(I) with tertiary phosphine: Synthesis and properties in solution

Abstract A series of carbamato-silver(I) complexes having the formula of MePh2PAg(YZCNR2) (1), (Ph3P)2Ag(YZCNR2) (2), (MePh2P)2Ag(YC(O)NR2) (3), Ph3PAg(YC(O)NR2) (4) (YZ = SS, SSe, SeSe; Y = S, Se; R = Me, Et) and (Ph3P)3Ag2(SC(O)NEt2)2 (5) were prepared. Molecular-weight determinations, conductivity measurements, 1H and 31P NMR spectra indicate that 1 exists as a planar three-coordinate complex involving a bidentate carbamato ligand in solution. The complexes 2 and 3 dissociate into the phosphorus ligand and Ph3PAg(YZCNR2) or MePh2PAg(YC(O)NR2) to considerable extents in solution. On the other hand, 4 exists as an equilibrium mixture of monomeric and oligomeric species in solution. The addition of extra Ph3P to a solution of 4, causes the formation of the bis-phosphine complex, (Ph3P)2Ag(YC(O)NR2), which is a predominant species in solution containing three equivalent amounts of Ph3P at low temperature. It is also concluded that 3, 4 and 5 have less tendencies to exist as disilver(I) species in solution than the copper(I) analogs.

Synthesis and 1H and 31P nuclear magnetic resonance spectra of (N,N-dimethyldicalcogenocarbamato)bis(tert-phosphine)palladium(II) and platinum(II) dimethyltin(IV) trichloride

A series of the compounds of formula [M(PR3)2 (XYCNMe2)][Me2SnCl3] (M = Pd(II) and Pt(II); PR3 = PPh3 and PMePh2; X, Y = Se) has been prepared. Conductivity measurements, i.r. and PMR spectra indicate that the complexes are 1:1 electrolytes in solution and the cationic part takes a square planar configuration. The 1H and 31P NMR spectra reveal that abilities of the sulfur and selenium to coordinate with the metal(II) resemble each other closely. The bonding nature of the PR3 Pd(II) and -Pt(II) bonds is also described on the basis of the 31P N MR spectra.

De Haas-van Alphen Effect and RLAPW-Energy Band Calculations in CeNi

We have carried out the de Haas-van Alphen (dHvA) experiments in a valence fluctuating compound CeNi. Forty seven dHvA branches are observed experimentally, which are mainly centered at the symmetrical axes. Most of the dHvA branches are approximately explained by the 4 f -itinerant band model. The cyclotron mass is in the range from 3.0 to 27 m 0 . Branch α, which has the largest cross-sectional area of the Fermi surface in the detected branches along the a -axis, has the cyclotron mass of 27 m 0 . This mass is five times larger than the corresponding band mass of 5.45 m 0 .