Tadao Fujimura

Quadrupolar response and rotational invariance of singlet ground state system; HoVO4

Elastic properties of holmium vanadate, HoVO 4 , have been investigated by means of an ultrasonic method. The elastic constants C 11 , ( C 11 - C 12 )/2 and C 66 exhibited remarkable softenings possessing minimum points around 13.5 K, which are characterized by the quadrupolar responses for the singlet ground state system. Appling magnetic fields along the tetragonal c -axis, the elastic anomalies of ( C 11 - C 12 )/2 and C 66 associated with the level crossing of the singlet ground state at about 10.6 T have been found. The rotational invariance effect has been revealed in the C 44 mode under magnetic fields along c -axis.

Quadrupolar ordering and dense kondo behaviour in SmSn3

Abstract From the specific heat measurement on SmSn 3 , it is found that the ground state of Sm 3+ ( J = 5 2 ) ions is Γ 8 quartet and that the magnetic phase transition at T N ≈ 10 K reported so far is not simple but of successive transitions due to probably quadrupolar ordering. We also observed that SmSn 3 exhibits dense Kondo behaviour. These results are compared with our experimental results on isomorphous compound SmIn 3 .

Elastic properties of dense Kondo compounds: CeB6, Ce0.5La0.5B6 and CeSb

Abstract The elastic softening of (C 11 −C 12 ) 2 and C 44 in CeB 6 and Ce 0.5 La 0.5 B 6 are explained by the strain susceptibility with a Г 8 (0 K)−Г 7 (545 K) level scheme including the quadrupolar exchange interaction. The rotational invariance and the elastic anisotropy effects of C 44 have been found. The elastic anomalies of CeSb are also presented.

Elastic properties in CeB6

Abstract Elastic constants and ultrasonic attenuation of CeB 6 have been measured. The ( C 11 − C 12 )/2 mode exhibited a softening of 1.6% with a peak of 50 K and C 44 of 1% at 25 K. The elastic constant C 12 of CeB 6 has the negative value, C 12 = -9.3x10 11 erg/cm 3 .

Magnetic and elastic properties of (CH3NH3)2FeCl4 and (C2H5NH3)2FeCl4

Abstract Weak ferromagnetism of 0.08 and 0.04μB per Fe2+ in the c-direction of MAFeC and EAFeC, respectively, are discussed based on the Dzialoshinsky-Moriya interaction. Only in EAFeC, weak remanence from 0.66 to 0.05 emu g-1 observed in the c-plane after a field cooling is attributed to the non-compensating moments in domain walls, correlating with a large change of C44 below TN.

Valence fluctuation of Sm3Se4

The fluctuating valence state of Sm3Se4 has been investigated by measurements of ultrasonic dispersion and AC conductivity. A pronounced frequency dependence of the elastic constants and ultrasonic attenuation near 120K is observed, which is caused by the thermally activated hopping of 4f electrons. The AC resistivity also shows marked frequency and temperature dependences, which are governed by the 4f hopping conduction and the thermally assisted quantum mechanical tunnelling among the localised states in the randomly distributed potentials. The 4f hopping rate determined by the present experiments has the activation-type temperature dependence, tau = tau 0 exp(E0/kT), where tau 0=2.4*10-13 s and the activation energy is E0=0.14 eV.

Synchrotron-radiation study of phase transitions in phosphorus at high pressures and temperatures

Results are reported of an investigation using synchrotron radiation into the effects of temperatures up to 1173 K on pressure-induced phase transitions in phosphorus. A cubic type multi-anvil press was employed and a diffraction pattern in an energy-dispersive mode was taken for a period of time, typically 200 s, without suffering from a deterioration of the sample material. The pressure of the first transition, orthorhombic–rhombohedral (As-type), decreases with increasing temperature at a rate of 2.3 MPa K−1 and the As-type structure is stable at a pressure as low as 2.6 GPa at a temperature of 1073 K. The volume discontinuity at the transition, ΔV, is 10% at room temperature and remains almost unchanged with increasing temperature. The axial ratio c/a, when the rhombohedral structure is referred to the hexagonal system, changes mostly with pressure but only slightly with temperature, approaching √6 = 2.45 on going to the second transition, rhombohedral–simple cubic. The pressure of this transition, in contrast to the first one, is independent of temperature but ΔV at this transition, 3.7%, continuously decreases with increasing temperature.

Acoustic de Haas-van Alphen effect and rotational invariance of LaB6

Abstract The acoustic quantum oscillations of LaB 6 are observed in the sound velocity change of (C 11 −C> 12 ) 2 and C 44 modes. The observed oscillations are of the degenerate ρ 3 and ρ 4 branches from the interconnecting necks along the Σ lines in the simple cubic Brillouin zone. Furthermore we find clear evidences of the rotational invariance effect in the quantum oscillations of the (C 11 −C 12 ) 2 mode and the anisotropy effect of the C 44 mode.

Structural Phase Transition of Layer Compound (C2H5NH3)2FeCl4

The sequence of the structural phase transitions of the layer compound (C 2 H 5 NH 3 ) 3 FeCl 4 has been determined with the ultrasonic, dielectric and polarized microscope measurements as following; Phase I ( D 4 h 17 )–(378.8 K)–Phase II ( D 2 h 18 )–(203.5 K)–Phase III–(133.7 K)–Phase IV. The set of the critical exponents obtained with ultrasonic methods are explained by the results of the renormalization group theory on the three dimensional XY model. The ferroelastic domains are observed in the phase II and phse III. The anomaly of he dielectric constant is found near the II-III phase transition point.

Thermal and Elastic Properties of Black Phosphorus

Temperature dependence of specific heat at constant pressure, and temperature and hydrostatic pressure dependence of elastic constants have been measured on single crystals of black phosphorus. Elastic softening is observed in c 55 with decreasing temperature. The elastic constants c 11 , c 22 and c 33 increase with pressure up to 6–7 kbar. Deformation potential effect in this system is discussed.