High-field galvanomagnetic properties of graphite

Measurements of the galvanomagnetic properties of graphite show structure in a region well above the quantum limit (10–23T). The first measurements of the longitudinal magnetoresistance in this field range are reported. The conductivity anisotropy, $\text{σ}{}_{\mathrm{<mtext>xx</mtext>}}\text{σ}{}_{\mathrm{<mtext>zz</mtext>}}$, shows strong field dependence, resulting in the lowest anisotropy values ever reported for any highly oriented graphite.     

The galvanomagnetic properties of short-period superlattices

(001) oriented superlattices (SLs) with the period in the range of 9–60 nm are grown. The temperature dependence of the conductivity, the Hall coefficient and the magnetoresistance anisotropy are investigated in the SLs in the temperature range of 1.5–300 K and magnetic fields up to 1.5 T. The SLs are of n-type with the apparent electron concentration in the range of 10¹⁹–10²⁰ cm⁻³. The type II band ordering is concluded for the SLs. Below 6 K the SLs exhibit superconductivity. The superconductivity is suggested to have a local character and to be associated with the strained pseudomorphic SnTe layers.     

Electrical and galvanomagnetic effects in new sodium-doped fullerene composites

The Hall effect, magnetoresistance, the temperature dependence of the electrical resistance, and the current-voltage characteristics of new C₆₀-based carbon-carbon composites were studied in magnetic fields of up to 28 kOe at temperatures T = 1.8–336 K. Sodium-doped samples were used. It is shown that there is weak localization of charge carriers and strong electron-electron interactions. Superconductivity occurs in the range T ≤ 15 K. A mixed current may exist at higher temperatures. Cooper pairs are assumed to form due to the interaction of the conduction electrons with the π-electron system of a C₆₀ molecule.     

On galvanomagnetic size effects in metals

The importance of open electron trajectories formed by specular reflections of charge carriers by the sample boundary to the metal electric conductivities in the strong magnetic fieldH is analyzed. It is shown that the electric conductivity of the near-surface layer _skin is rather sensitive to the state of the conductor surface. The electron-hole Umklapp processes during the surface scattering of charge carriers do not change the dependence _skin(H), while skipping from the closed Fermi surface section to the open one is able to affect _skin essentially only in bulk samples. The method is proposed to restore the indicatrix of conduction electron scattering by the sample boundary through an experimental investigation of the Sondheimer effect and the static skin effect.     

Temperature dependence of the galvanomagnetic and thermomagnetic properties of palladium

The Hall and Nernst-Ettingshausen emfs, the thermo-emf, and electrical resistance in polycrystalline palladium in the temperature range 77 to 750°K are studied. On the basis of the two zone theory, the experimental data are utilized to calculate charge carrier mobility and relaxation time in the indicated temperature interval.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 95–97, August, 1973.The authors express their deep gratitude to E. I. Kondorskii for his interest in the study and evaluation of the results.     

Structural and galvanomagnetic properties of CuInS2 films

Thin copper-indium-disulphide films were prepared by thermal evaporation technique. X-ray diffraction analysis of the compound used for evaporation showed a tetragonal polycrystalline structure. Differential Thermal Analysis (DTA) of this compound showed two exothermic peaks at 585 and 632 °C. Thin films with thicknesses of 0.14 and 0.27 nm have a deposition rate 10 nm/min, while those with thicknesses of 0.54 and 0.56 nm have a deposition rate 48 nm/min. The obtained films have polycrystalline structure as shown from the electron diffraction study. A growth process was detected in the films by transmission electron microscopy as the film thickness increases. The surface topography was revealed by scanning electron microscopy. The variations of Hall mobility and carrier concentration with magnetic induction were studied. The resistivity-temperature relationship was investigated, from which the activation energies before and after annealing were found to be 0.2, 0.3 and 0.055 eV, respectively.     

On the origin of the galvanomagnetic effect in Ne plasma

The interrelation between the width of a magnetogalvanic signal and the alignment of the highly excited level 2s ⁵ (4s [3/2]⁰) has been found experimentally.     

Electric field modulation of galvanomagnetic properties of mesoscopic graphite

Electric field effect devices based on mesoscopic graphite are fabricated for galvanomagnetic measurements. Strong modulation of magnetoresistance and Hall resistance as a function of the gate voltage is observed as the sample thickness approaches the screening length. Electric field dependent Landau level formation is detected from Shubnikov-de Haas oscillations. The effective mass of electron and hole carriers has been measured from the temperature dependent behavior of these oscillations.     

Electrical and galvanomagnetic properties of nanoporous carbon samples impregnated with bromine

Nanoporous carbon samples with a large specific surface area can be filled with heavier elements or their compounds, which makes it possible to investigate the interaction of their electronic subsystems with carbon. One of the elements convenient for filling pores of carbon materials is bromine. Impregnation of nanoporous carbon samples with bromine causes the occurrence of the processes of micropore filling, monolayer adsorption, and intercalation. It has been found that samples impregnated with bromine substantially change their electrical and galvanomagnetic properties, and these changes depend on the structure of the samples. It has been shown that, if in the skeleton of a porous carbon sample there is a fraction of graphite clusters, the impregnation of the sample with bromine increases the concentration of charged carriers (holes). But when the sample has a quasi-amorphous structure, the injection of bromine into the sample leads to the appearance of a certain concentration of electrons in addition to charged mobile holes of the initial sample; i.e., the electrical conductivity becomes bipolar. In the former case, bromine molecules intercalate graphite clusters and, since bromine is an acceptor during intercalation of graphite, the hole concentration in the carbon skeleton network increases. In the latter case, bromine molecules can only be adsorbed on pore walls. As a result, the adsorption interaction between the electron shells of bromine molecules and the carbon surface leads to the formation of a donor layer near the surface and to the generation of electrons in the carbon skeleton network.     

On the theory of the dynamical properties of nematics

The Leslie–Ericksen coefficients of a thermotropic nematic are determined by using an approximate solution of the Fokker–Planck equation for the one-particle distribution function over orientations of the nematic molecules. The results show that the well-known Doi–Edwards theory of the dynamical properties of nematics leads to a qualitatively wrong result for the Leslie angle. The “isotropic medium - nematic” (I–N$I–N$) transition induced by the shear flow is considered. When the temperature decreases, the I–N$I–N$ transition in the shear flowing system takes place at the temperature _T1$T_1$ higher than the temperature _Tc$T_c$ of the equilibrium transition in the motionless system. The interface boundary in this case is parallel to the plane formed by the flow velocity and its gradient. When the shear flowing nematic phase is heated, the N–I$N–I$ transition occurs at another temperature _T2$T_2$, and the following inequalities _T1>_T2>_Tc$T_1>T_2>T_c$ hold. In this case the boundary between the isotropic and nematic phases is perpendicular to the flow velocity. Thus, unlike the equilibrium phase transition, a temperature hysteresis of the phase transition is expected.     

Electrical and galvanomagnetic properties of biocarbon preforms of white pine wood

The electrical and galvanomagnetic properties of high-porosity biocarbon preforms prepared from white pine wood by pyrolysis at carbonization temperatures T _carb = 1000 and 2400°C have been studied. Measurements have been made of the behavior with temperature of the electrical resistivity, as well as of magnetoresistance and the Hall coefficient in the 1.8–300-K temperature interval and magnetic fields of up to 28 kOe. It has been shown that samples of both types (with T _carb = 1000 and 2400°C) are characterized by high carrier (hole) concentrations of 6.3 × 10²⁰ and 3.6 × 10²⁰ cm⁻³, respectively. While these figures approach the metallic concentration, the electrical resistivity of the biocarbon materials studied, unlike that of normal metals, grows with decreasing temperature. Increasing T _carb brings about a decrease in electrical resistivity by a factor 1.5–2 within the 1.8–300-K temperature range. The magnetoresistance also follows a qualitatively different pattern at low (1.8–4.2 K) temperatures: it is negative for T _carb = 2400°C and positive for T _carb = 1000°C. An analysis of experimental data has revealed that the specific features in the conductivity and magnetoresistance of these samples are described by quantum corrections associated inherently with structural characteristics of the biocarbon samples studied, more specifically with the difference between the fractions of the quasi-amorphous and nanocrystalline phases, as well as with the fine structure of the latter phase forming at the two different T _carb.     

On the theory of optical properties of fractal clusters

A theory of optical properties of clusters of spherical metal nanoparticles characterized by an arbitrary size distribution is developed in a quasi-static dipole approximation. The equations for coupled dipoles and general relations are formulated in terms of reduced dipole moments. It is shown that the dipole resonant frequencies and amplitudes, the absorbed power, and the acting-field magnitudes strongly depend on the ratios of particle radii in a cluster. Properties of linear, planar, and three-dimensional systems are examined.     

On the theory of rheological properties of magnetic suspensions

The paper deals with a theoretical study of influence of magnetic field on effective viscosity of suspension of non-Brownian magnetizable particles. It is supposed that experimentally observed magnetorheological effects are provided by chain-like aggregates, consisting of the particles. Unlike previous works on this subject, we take into account that the chains cannot be identical and estimate their size distribution. The following power law (η-η₀)/η₀∼Mn^-Δ, detected in many experiments, is obtained theoretically (η and η₀ are the suspension effective viscosity and the carrier liquid viscosity, respectively, Mn is the so-called Mason number, proportional to the shear rate and inversely proportional to the square of magnetic field). The calculated magnitude of the exponent Δ increases with the applied magnetic field from approximately 0.66 to 0.8-0.9 and slowly increases with the volume concentration ? of the particles. These results are in agreement with known experiments.     

On the theory of conductivity of anisotropic composites: A weakly inhomogeneous medium

The conductivity of a weakly inhomogeneous anisotropic medium is considered. The effective conductivity tensor $ \hat \sigma _e $ \hat \sigma _e is determined in the approximation quadratic in deviation of local conductivity $ \hat \sigma $ \hat \sigma (r) from mean value 〈$ \hat \sigma $ \hat \sigma 〉 for an arbitrary anisotropy of the composite.     

Electrical, galvanomagnetic, and thermoelectric properties of PbSe in the void sublattice of opal

A study of transport phenomena, namely, electrical resistivity, thermopower, Hall coefficient, and magnetoresistance of p PbSe synthesized in opal voids has been carried out in the 4–300 K range. The parameters of the semiconducting material have been determined at different void filling levels. An anomalous behavior of the hole mobility associated with surface scattering from insulating opal-matrix walls has been observed. Fiz. Tverd. Tela (St. Petersburg) 40, 781–783 (April 1998)     

Effect of Ti on the galvanomagnetic properties of single-crystal Sb2−x TixTe3

A study is reported of the lattice parameters, Hall effect, Shubnikov-de Haas effect, and thermopower of single-crystal Sb_2−x Ti_xTe₃ as functions of titanium content within the range 0<x<0.04. An increase in titanium content is shown to decrease the initial hole concentration in a sample without a noticeable change of the energy spectrum. Fiz. Tverd. Tela (St. Petersburg) 40, 441–444 (March 1998)     

The influence of CO adsorption on the galvanomagnetic and magnetic properties of evaporated nickel films

The influence of CO adsorption on the ordinary Hall coefficient, R_HO, the extraordinary Hall coefficient, R_HE, the perpendicular magnetoresistivity ΔR_{mag O} and the saturation magnetization, B_S, of Ni films with thicknesses between 1 and 200 nm has been studies as a function of the CO coverage at 77 and 273 K. There is a maximum in ΔR_HE at a coverage of about half a monolayer. ΔR_HO, ΔΔR_{mag O} and ΔB_S exhibit an oscillating behaviour.