A. Tamaki

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.

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.

Elastic properties of the kondo lattice compound CeCu6

Abstract Elastic properties of the Kondo lattice compound CeCu 6 grown in a boron nitride crucible have been measured by an ultrasonic method. The soft elastic mode C 66 associated with the structural phase transition D 16 2h -C 5 2h has been observed at the transition point T c = 218 K . The anisotropic magnetic field dependences of elastic constants have been found at low temperatures.

Elastic softening and CEF effects of NdB6 and PrB6

Abstract Elastic properties of NdB 6 and PrB 6 have been measured by the ultrasonic method. The observed large elastic softenings of the C 44 modes of NdB 6 and PrB 6 are understood by the co-operative Jahn-Teller instability due to the quartet Г 8 + ground state of NdB 6 and the triplet Г 5 + ground state of PrB 6 . The magnetic field dependences of the elastic constant C 44 of NdB 6 were also investigated. The anisotropy and acoustic Voigt-Cotton-Mouton effects have been found in the antiferromagnetic phase of NdB 6 .

Critical slowing down in the one-dimensional ferroelectric CsH2PO4

Dielectric measurements on the ferroelectric CsH2PO4 with chain-like hydrogen bonds have been performed in the frequency region below 1 GHz. The temperature dependence of the dielectric constant and loss were explained well by the Debye equation with single relaxation time. The relaxation time obtained near the ferroelectric phase transition point exhibits a pronounced critical slowing down. This characteristic divergence of relaxation time has been explained very well using the results of the pseudo-one-dimensional kinetic Ising model. The parameters obtained in this experiment have considerable anisotropy of interactions: J/sub ////k=234K of intrachain and Jperpendicular to /k=6.78K of interchain. The marked long relaxation time compared with that of KH2PO4 is well understood with the critical dynamics of the hydrogen motion in the weakly-coupled one-dimensional chains.

Acoustic de Haas-van Alphen Effect of CeB6 and LaB6

All of the main orbits of LaB6 have been observed successfully by the ultrasonic measurement of dHvA oscillations of elastic constants without field modulation technique, where the high resolution important. Adopting the ultrasonic technique in a dilution refrigerator, the acoustic dHvA oscillation of CeB6 is obtained for the heavy fermion with effective cyclotron mass ~7.2m0 of the extremal orbit 0.012 A-2(1.26MG)

Elastic Properties of CeCu6 at Low Temperatures

Elastic constant C33 of Kondo lattice compound CeCu6 has been measured down to 30 mK by ultrasonic method, where a remarkable softening below Kondo temperature has been found. A characteristic oscillation of C33 under magnetic field below 500 mK will be discussed.

Critical slowing down of dielectric relaxation in ferroelectric NH4HSO4

Dielectric constant and dielectric loss of NH4HSO4 along the ferroelectric c axis have been measured at 100 kHz, 300, 660, 1145, and 1440 MHz as a function of temperature. It was found that the Curie–Weiss law held both in paraelectric and in ferroelectric phases of the upper Curie point which was T0=−2.3 °C. Dielectric relaxation was observed both in paraelectric and in ferroelectric regions. The former relaxation was of the Debye type with a single relaxation time, which was expressed by a relation: τ=1.70×10−10/(T−T0) sec in the temperature region down to T−T0?0.5 °C. It was found that after the same specimen was repeatedly cooled and heated through the upper Curie point, this relaxation gradually changed into that with distributed relaxation times. The dielectric relaxation in the ferroelectric region was complex; that is, the characteristics of the relaxation differed with every specimen.

Transport properties in valence fluctuation compound Sm3Se4

Abstract The ac resistivity of single crystal Sm 3 Se 4 has been measured in the frequency up to 1.5 GHz. Tunneling conduction of the 4f electrons of the Sm 2+ ions has been revealed at low temperatures.

Enhanced Nuclear Antiferromagnetic Resonance of Ho in Cs2NaHoCl6

Hyperfine enhanced nuclear antiferromagnetic resonance of 165Ho(I=7/2) in Cs2NaHoCl6 was observed below about 4.8mK following demagnetization cooling. The measurements were made at several frequencies by CW NMR with a low field sweep. From the observed resonance fields the zero field resonance frequency ωo was deduced to be 272MHz, not far from the expected frequency from the calculation of the dipole interaction among the enhanced nuclear spins. This experiment is the first observation of the enhanced nuclear antiferromagnetic resonance.