V. V. Sumarokov

A simple low-temperature adiabatic calorimeter for small samples

A simple adiabatic calorimeter has been built to investigate the heat capacity of small (≤1 cm3) samples of carbon nanomaterials at temperatures ranging from 1 to 300 K. It enables (i) rapid mounting of samples (ii) doping of samples with gases directly in the calorimeter, and (iii) rapid cooling of samples to liquid helium temperatures. It can be placed in the helium vessel of a portable Dewar or in a helium cryostat. The heat capacity of a fullerite sample is measured in the temperature range 1–30 K.

Quantum melting in a system of rotors

The authors consider a simple system of interacting rotators and show that such a system could display properties of quantum crystals. The possibility of realizing new quantum systems is discussed.

The peculiarities of heat transfer in CO2 and N2O solids at low temperatures

The thermal conductivities of CO2 and N2O solids are investigated in the low-temperature range 1–40K. The thermal conductivities of CO2 and N2O are large compared with those of simple molecular crystals such as N2, CO, or O2 in the whole investigated temperature range. Analysis of the experimental data by the Callaway method shows that a relatively large size of the crystalline grains, low density of dislocations, and weak phonon–phonon interaction might be the reasons for the good thermal conduction in these crystals at temperatures near the maxima. A comparison between calculated values of the intensity of normal phonon scattering processes and experiment gives evidence that in N2O there is an additional (in comparison with CO2) giant scattering of phonons. This scattering is described in the frameworks of the soft potential model by the resonance phonon scattering on tunneling states and low-energy vibrations.

Temperature dependence of the magnetic susceptibility of solid oxygen

The temperature dependence of the magnetic susceptibility of polycrystalline oxygen samples is measured in the range from 1to54K. The measurements are performed using our home-designed SQUID-based gradiometer. The sensitivity of the instrument with respect to susceptibility reaches values of the order of 10−13. The results are compared with data in the literature.

Theory of the thermal expansion anomaly in solid nitrogen due to O2 impurity

Two mechanisms are considered which contribute to the observed thermal expansion of the N2-O2 solid solution. One of them, connected with the renormalisation of the effective spin-figure coupling constant by the spin-libron interaction, is linear in impurity O2 concentration. The second one is due to formation of clusters of exchange-bound molecules and in the case of pair clusters is quadratic in concentration. The contributions from both the mechanisms are equalised for the O2-molecule concentration of about 1%. The data on the O2-O2 exchange interaction is obtained from comparison between the theoretical and experimental results on the excess thermal expansion of the N2-O2 solid solution. The theoretical model permits the explanation of the main features of the observed anomalies, but only a more sophisticated theory will be able to give a close fit to the experiment.

Investigations of thermal conductivity of simple van der Waals crystal-based nanocomposites

The experimental setup for obtaining and determination of the thermal conductivity of simple van der Waals crystal-based nanocomposites is described. Preliminary thermal conductivity results of measurements carried out in the temperature range 1–40 K on two samples of methane crystals containing nanoparticles of hydroxyapatite are presented. These results confirm usability of the setup and its suitability as a proper experimental method for investigations of the thermal conductivity of the nanocomposites.

Structure and thermal conduction in solid O2 with nonmagnetic impurities

Thermal conductivities of solid oxygen doped with nonmagnetic impurities of nitrogen and argon were measured in the 1–35 K. The antiferromagnetic α-O2 doped with this impurities exhibits a strong thermal conductivity anomaly, which is assumed to be a result of supperpression of the magnon contribution to the heat transport by impurities. At the same time, the jump in the thermal conductivity at the α-β transition and th thermal conductivity in the β-O2 are insensitive to the doping effect, which we ascribe to strong magnetostriction effects. The halfwidth of the x-ray reflexes indicates that doping with Ar and Kr enhanced magnetostriction effects while doping with N2 weakens.

The influence of the disordered dipole subsystem on the thermal conductivity of solid CO at low temperatures

The thermal conductivity of solid CO is investigated in the temperature range 1–20K. The experimental temperature dependence of thermal conductivity of solid CO is described using the time-relaxation method within the Debye model. The comparison of the experimental temperature dependences of the thermal conductivity of N2 and CO shows that in the case of CO there is an additional large phonon scattering at temperatures near the maximum. Analysis of the experimental data indicates that this scattering is caused by the frozen disordered dipole subsystem, similar to a dipole glass. The scattering is described by resonant phonon scattering on tunneling states and on low-energy quasi-harmonic oscillations within the soft potential model.

Thermal conductivity of solid parahydrogen with methane admixtures

The thermal conductivity of a solid parahydrogen crystal with methane admixtures was measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixtures at 13 K. The concentration of CH4 admixture molecules in the gas varied from 5 to 570 ppm. A very broad thermal conductivity peak with an absolute value of about 110 W/(m⋅K) was observed at 2.6 K. The data were interpreted using Callaway’s model with resonance scattering of phonons by quasilocal vibrations of CH4 molecules and phonon–grain boundary and phonon–phonon scattering. As grain boundary scattering increases, the broadening of the peak decreases. The analysis shows that a solid mixture of p-H2 and CH4 is a heterogeneous solution for CH4 concentration higher than 0.1 ppm.

Magnetic properties of oxygen clusters

Magnetic properties of oxygen pair clusters are investigated theoretically for different geometries of clusters which can be realized by doping molecular cryomatrices with oxygen. Anomalous temperature and pressure behavior of the magnetic susceptibility, magnetic heat capacity and magnetic entropy is predicted. It is shown that the low-temperature magnetic susceptibility of these solid solutions is very sensitive to the orientational structure of impurity oxygen clusters, which makes it possible to use the susceptibility data for studying structural and dynamics properties of the host lattice, including high-pressure phases of simple molecular crystals.