Magnetoresistance and Quantum Oscillations in WTe2 Semimetal

Physics of the Solid State - The discovery of extreme magnetoresistance (MR) in nonmagnetic materials attracted attention to WTe2 semimetal. We studied MR in a single crystal of tungsten...     

Ultrasonic attenuation in a LiIO3 crystal

The temperature dependences of the attenuation of longitudinal acoustic waves along the x axis of a LiIO₃ crystal are studied experimentally by the method of Bragg diffraction of light by ultrasound. The measurements are performed in the temperature range from 215 to 335 K at frequencies of 400–690 MHz. Above 260 K, the attenuation is found to exhibit a frequency-independent growth of a relaxational character, which is used to calculate the enthalpy of the activation of ionic motion in the direction normal to the hexagonal axis. In addition, resonance attenuation peaks are observed; as the frequency increases, the peaks are shifted toward lower temperatures. A phenomenological model is proposed to explain the origin of the resonance absorption.     

Phase transition in a NaBi(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal: Acoustic investigations

This paper reports on the results of acoustic investigations of a NaBi(MoO₄)₂ crystal in the temperature range from 20 to 70°C. The temperature dependences of the velocity of longitudinal ultrasonic waves propagating along the crystallographic axes z and x are measured at a frequency of 4 MHz. The results obtained demonstrate that a structural phase transition occurs in the NaBi(MoO₄)₂ crystal at a temperature of 309 K. The experimental findings are consistent with the assumption that the observed phase transition is either a second-order ferroelastic transition or a first-order ferroelastic transition that is very close to being a second-order phase transition.     

NMR line shift of gallium in GaAs crystals in the temperature range 160–360 K

The shift in the nuclear magnetic resonance (NMR) line of ⁷¹Ga isotopes in GaAs crystals is investigated in the temperature range 160–360 K. It is observed that the position of the resonance line is temperature-independent. The value of the shift relative to an isolated nucleus is 440 and 420 ppm for the three samples investigated. The roles of various contributions to the NMR line shift are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1418–1419 (August 1998)     

Size effect in nuclear spin-lattice relaxation and atomic mobility for molten gallium particles

The spin-lattice relaxation rate of gallium isotopes in a melt was shown by NMR to increase considerably with a decrease in gallium particle size. The dominant relaxation mechanism of gallium embedded in an synthetic opal matrix changes from magnetic dipole to electrical quadrupole. The increase in the correlation time of atomic motion in gallium particles with a decrease in their size was estimated. For gallium in opal, the correlation time was found to increase by more than an order of magnitude. It was shown that a variation in atomic mobility becomes noticeable already in gallium particles about 5 μm in size. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 12, 2003, pp. 2242–2246. Original Russian Text Copyright ? 2003 by Tien, Charnaya, Sedykh, Kumzerov.     

NMR of mercury in porous carbon and silica gel

The temperature dependences of the integrated intensity and of the Knight shift of ¹⁹⁹Hg NMR signals are measured for liquid and solid mercury introduced into porous carbon and silica gel. A decrease in the temperature of completion of crystallization and a small temperature hysteresis (from 4 to 9 K) between melting and crystallization are observed. The melting temperature of mercury in pores coincides with that in the bulk. The ¹⁹⁹Hg NMR signal from crystalline mercury under the condition of restricted geometry is observed for the first time. It is established that the Knight shift for liquid and crystalline mercury in pores is smaller than in the bulk.     

Dielectric and NMR Studies of the superionic conductor AgI embedded in mesoporous silicate matrices

This paper reports on the results of studies of small particles of the superionic conductor AgI embedded in MCM-41 and SBA-15 molecular sieves with different sizes of pores (channels). The studies are performed by the dielectric and nuclear magnetic resonance techniques. The temperature of the superionic phase transition is shown to increase monotonically with decreasing pore size. The enthalpy of activation of the ion motion in β-AgI in restricted geometry is determined. It is shown that introduction of AgI into pores does not noticeably affect its structure.     

Transport characteristics of phonons and the specific heat of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:ZrO<Subscript>2</Subscript> solid solution single crystals

The temperature dependences of the specific heat and transport characteristics of phonons in single crystals of yttrium-stabilized zirconium dioxide Y₂O₃:ZrO₂ solid solutions have been studied. It has been shown that the temperature dependences of the specific heat at T > 5 K are almost identical at the degree of stabilization of a solid solution with an Y₂O₃ content of 5–20 mol %. Differences in the temperature dependences of the specific heat of samples from different sources at T < 5 K are due to the presence of low-energy two-level systems. The features of the transport characteristics of thermal phonons at liquid helium temperatures reflect not only the presence of two-level systems but also the scattering of phonons on low-dimensional domains of another phase coherently conjugate to the main phase of the Y₂O₃:ZrO₂ solid solution.     

Field-induced magnetic transition in a mixed rare-earth aluminum garnet Er<Subscript>2</Subscript>HoAl<Subscript>5</Subscript>O<Subscript>12</Subscript>

The temperature dependence of the ac magnetic susceptibility of a single-crystal mixed rare-earth garnet Er₂HoAl₅O₁₂ has been investigated within the range from 1.8 to 300 K in a zero constant field and in applied bias fields of up to 9 T. In the absence of a constant magnetic field the magnetic susceptibility followed the Curie–Weiss law. The application of a constant magnetic field caused a magnetic phase transition, the temperature of which increased with increasing magnetic field. The temperature of the maximum of the ac magnetic susceptibility, which is a characteristic of the phase transition, did not show a noticeable dependence on the frequency of the alternating magnetic field.     

Acoustic studies of melting and crystallization of nanostructured decane

Acoustic studies of melting and crystallization of decane loaded in porous glasses (Vycor and laboratory-produced glass) have been performed. Measurements of the temperature dependences of the ultrasound velocity have revealed a decrease in the melting and crystallization temperatures of decane as compared to the melting point of bulk decane and a diffuseness of these phase transitions. The results obtained are compared with the predictions of the models describing melting of individual small particles. The specific features revealed in the acoustic properties of nanocomposites based on decane-loaded porous glasses are discussed.