Magnetotransport properties of the nanogranular SnO_2 films were invesigated. Non-linear current-voltage (I-V) characteristics were observed at low temperatures. The temperature dependence of the resistance and non-ohmic I-V curves can be well approximated by fluctuation-induced tunnelling model, indicating importance of the contacts barriers between SnO_2 grains. Magnetoresistance was measured within temperature range 2-15.3 K and could be consistent with the variable-range hopping conduction mechanism due to existence of localized states on the surface of SnO_2 grains.
We present the magnetoconductivity measurements of a high mobility two-dimensional electron gas confined at GaN/AlGaN interface. The sensitive measurements of low field conductivity revealed both quantum corrections, the weak localization and antilocalization effects. It indicates the importance of the spin-orbit coupling in this wide band gap material. The analysis of the data provided the information about the temperature dependence of the dephasing time and total spin-orbit relaxation time. The conduction band spin splitting energy amounts to 0.23 meV and 0.35 meV at electron densities 2.2×10¹² cm¯² and 5.7×10¹² cm¯², respectively.
We measured the activation of resistivity at quantum Hall minima in high mobility two-dimensional electron gas confined at AlGaN/GaN interface. The effective g-factor and effective mass was deduced. The electron-electron interactions modify both quantities compared to their bare band values. It is found that the influence of interactions is much more pronounced onto g-factor than effective mass. The relative spin susceptibility was also calculated and compared with available theories. The best agreement was found with the ideal two-dimensional gas model in random phase approximation.
Electrical resistivity and low temperature magnetoresistivity measurements made on a single crystal of UCu_2Si_2 are reported. By using as a phonon reference the temperature dependence of the electrical resistivity of ThCu_2Si_2 we could establish that UCu_2Si_2 has both a ferromagnetic and a Kondo behaviour. Such a phenomenon can be described by the underscreened Kondo lattice model. The magnetoresistivity revealed the presence of magnetic fluctuations within the ferromagnetic order as it was reported previously for UGe_2. Also one of the calculated Fermi surface sheets exhibits nesting properties, being in perfect agreement with the previous neutron diffraction data, supporting the possibility of a presence of the spin density wave phase. In this ternary silicide, where the strong ferromagnetic behaviour exists, this phase is signalised by magnetic fluctuations.
Double-grating-gate field-effect transistors have a great potential as terahertz detectors. This is because the double grating gate serves not only for carrier density tuning but also as an efficient THz radiation coupler. In this paper, we present characterization of these transistors using high magnetic fields. Low and high magnetic field data are used to determine the electron mobility and electron concentration, respectively, in different parts of the transistor channel.
We have used a three term polynomial expression to approximate electrical and magneto transport properties of epitaxial La_{0.67}Sr_{0.33}MnO_{3} (LSMO) thin films in wide temperature range (2-350 K) and in magnetic field up to 9 T. The first term is determined by a low temperature (T<20 K) residual resistivity ρ_{0} and this term is magnetic field independent. The second term describes the electron-electron scattering in LSMO, it shows ~ T^{2} dependence of resistivity up to temperature about 160 K and depends only weakly on magnetic field. The third term, proportional to ~ T^{4.5} dependence, describes a significant increase of resistivity in temperature range 160-350 K and due to its sensitivity to applied magnetic field it is possible to approximate temperature dependence of magnetorestivity below 350 K.
This is an analytical study of magnetic fields effects on the conductance, the shot noise power, and the third charge-transfer cumulant for the Aharonov-Bohm rings and the Corbino disks in graphene. The two distinct physical mechanisms lead to very similar magnetotransport behaviors. Differences are unveiled when discussing the third-cumulant dependence on magnetic fields.
Effects of local vibrational modes on electron transport through a quantum dot attached to ferromagnetic electrodes are studied in the Kondo regime by the non-equilibrium Green function formalism based on the equation of motion method. Differential conductance is calculated for parallel and antiparallel configurations of the leads' magnetic moments, and well defined Kondo resonance peaks and their phonon satellites are found. The influence of a compensating magnetic field on the peak positions is also discussed.
We have investigated magnetic and magnetocaloric properties of Pr_{0.7}(Ca_{1-x}Sr_{x})_{0.3}CoO_{3}, when the average size of the interpolated cation was changed. Pr_{0.7}Ca_{0.3}CoO_{3} has an orthorhombic Pnma symmetry and it shows a magnetic cluster-glass behavior below 70 K. When Sr partially replaces Ca in this compound, its magnetic properties are improved, and it begins to have ferromagnetic-like behavior. The magnetic transition temperature, gradually, increases with increasing Sr content, up to 170 K, for x=1. The electrical conduction also improved when Sr content increased. All the samples show negative magnetoresitance. Magnetic entropy change ΔS_{M} was estimated from isothermal magnetization data. We have found that it had higher values for the samples with x>0.5, around 1 J/kg K for Δ B=4 T, with reasonable good relative cooling power.
Electrical resistance, transversal magnetoresistance and the Hall effect were studied on polycrystalline CaTi_xRu_{1-x}O_3 (x=0, 0.07) samples using a conventional Quantum Design PPMS-9 equipment in the temperature range 2-300 K and magnetic field up to 9 T. Substantial differences were found between the two samples: (i) opposite to the metallic character of CaRuO_3, the substituted sample has insulating-like electrical resistance;(ii) the magnetoresistance of the substituted sample changes the sign from negative to positive values with increasing temperature. The magnetoresistance of CaRuO_3 is negative, the sign reversal is induced by magnetic field and only at temperatures below 15 K, such a behaviour is predicted for clustered systems;(iii) the Hall voltage in pure CaRuO_3 also changes sign from negative to positive values above 35 K. This temperature coincides with the observed magnetic transition temperature, indicating that the magnetic state and the carrier character interrelate.
A new version of the construction of the extraordinary magnetoresistance effect (EMR) based magnetic sensor has been proposed [2]. The differences between the original three dimensional (3D) construction and proposed 2D (planar) construction are presented. In proposed construction the metallic thin film (shunt) is coplanar with the semiconductor sensitive element. There are advantages of that planar construction like easier way of technological obtaining of the device. Another advantage is its application for EMR sensors based on new electronic materials like graphene and topological insulator thin films. The validity of the planar construction has been experimentally confirmed for model EMR sensors based on InSb/Ag structures. Comparison of the obtained experimental data with computational simulations of the EMR effect on planar model EMR sensors is performed Finite element method (FEM) is used as a tool for obtaining EMR effect simulations.
The in-plane transport of strongly underdoped La_{2-x}Sr_xCuO_4 films was examined in the magnetic fields up to 14 T and in temperatures down to 1.6 K. While at high temperatures the samples display metallic-like resistivity, the low-T transport is governed by variable-range-hopping mechanism. Careful analysis shows that the temperature dependence of pre-exponential factor in Mott's variable-range-hopping law may not be neglected and that the density of states at the Fermi level can be effectively expressed as g(E-E_F)=N_0 (E-E_F)^p, with a small exponent p of the order of 0.1. In the magnetic field parallel to CuO_2 planes one of the variable-range-hopping parameter,ρ_0, increases by about 20-25%, while the other one, T_0, decreases by about 10-15%, resulting in the decrease in total resistivity. This effect may be related to the decrease of the tunneling barrier between different antiferromagnetic clusters in the presence of magnetic field.
We report heteroepitaxial growth of multiferroic BiFeO_3 thin films by RF magnetron sputtering on lattice-matched SrTiO_3 substrates, as well as preparation and electrical properties of the heterostructures formed by growing BiFeO_3 thin films on highly conductive LaNiO_3 films and n-Si substrates. Nonlinear and rectifying current-voltage (I-U) characteristics were revealed for the heterojunctions in a wide temperature range (T=78-300 K).
Samples consisting of a few layers of graphene obtained by thermal decomposition of SiC were studied by means of transport experiments at 4 K and in a magnetic field up to 7 T. Transport data show that the samples have a two-dimensional character. Magnetoresistance has an approximately linear character at high magnetic fields, which has been previously observed in graphite samples, and a negative magnetoresistance, at low magnetic fields. The transverse resistivity ρ_{xy} is nonlinear as a function of B, which can be described using a many-carrier model.
Results of two-probe magnetoresistance studies in GaN:Si/(Ga,Mn)N/GaN:Si prospective spin filter structures are reported. It is postulated that transport characteristics are strongly influenced by highly conductive threading dislocations and that shrinking of the device size partially mitigates the issue. Simultaneously, maxima at ≈1500 Oe on overall weak, up to 2%, negative magnetoresistance are seen at low temperature, whose origin has been tentatively assigned to effects taking place at the contacts areas.
We report the fabrication and investigation of p-n diode structures based on thin hole-doped La_{2/3}Ca_{1/3}MnO_3 films grown on n-type silicon substrates. La_{2/3}Ca_{1/3}MnO_3 films with typical thickness of about 400 nm were prepared using pulsed laser deposition. Reflection high-energy electron diffraction measurements revealed polycrystalline quality of La_{2/3}Ca_{1/3}MnO_3 thin films on Si substrates. The surface roughness of La_{2/3}Ca_{1/3}MnO_3 films investigated by atomic force microscopy was found to be in the range of 25÷30 nm. Studies of electrical properties showed that La_{2/3}Ca_{1/3}MnO_3/Si heterostructures exhibit nonlinear asymmetric I-V characteristics both at room temperature and at 78 K. Furthemore, it was shown that these I-V dependences are sensitive to magnetic field, especially at lower voltages.
The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm_{0.996}Yb_{0.004}B_{12} dodecaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AF-P) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (ρ(H||[110])/ρ(H||[111])~ 1.2 at H~ 20 kOe) and at the critical field of AF-P transition (H_{N}[100]/H_{N}[111]~ 1.25) in this magnetic metal with a simple fcc crystal structure.
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