Galvanomagnetic Effects Research Articles

Direct-current voltages in (Ga,Mn)As structures induced by ferromagnetic resonance

Spin pumping is the phenomenon that magnetization precession in a ferromagnetic layer under ferromagnetic resonance produces a pure spin current in an adjacent non-magnetic layer. The pure spin current is converted to a charge current by the spin-orbit interaction, and produces a d.c. voltage in the non-magnetic layer, which is called the inverse spin Hall effect. The combination of spin pumping and inverse spin Hall effect has been utilized to determine the spin Hall angle of the non-magnetic layer in various ferromagnetic/non-magnetic systems. Magnetization dynamics of ferromagnetic resonance also produces d.c. voltage in the ferromagnetic layer through galvanomagnetic effects. Here we show a method to separate voltages of different origins using (Ga,Mn)As/p-GaAs as a model system, where sizable galvanomagnetic effects are present. Neglecting the galvanomagnetic effects can lead to an overestimate of the spin Hall angle by factor of 8, indicating that separating the d.c. voltages of different origins is critical.

Intrinsic domain-wall resistivity in half-metallic manganite thin films

Deciphering the intrinsic magnetic domain-wall (DW) resistivity of manganite materials by typical low-field magnetoresistance measurement is flawed due to the addition of different galvanomagnetic effects such as, colossal magnetoresistance, Lorentz force magnetoresistance, and anisotropic magnetoresistance (AMR). In this paper, by taking the advantage of rotational anisotropy and the stable rotation of the DW planes in half-metallic manganite La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ film, we deploy a remanent state resistance measurement technique to exclude all the field-dependent spurious effects from the intrinsic DW resistivity. To further refine its magnitude, we calculate the remanent state DW AMR by exploiting the three-dimensional micromagnetic simulation, which reveals a comparable but opposite contribution to the positive DW resistivity. From these results, we estimate the intrinsic DW resistance-area product in La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ to be $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{0.16em}{0ex}}\ensuremath{\Omega}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{m}}^{2}$.

Vanadium deep impurity level in diluted magnetic semiconductors Pb1 − x − y Sn x V y Te

The crystal structure, Sn and V distribution over the length of single-crystal ingots, and galvanomagnetic effects in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb1−x−y Sn x V y Te alloys (x = 0.05−0.21, y ≤ 0.015) are studied. It is shown that all the samples are single-phase, while the Sn and V concentrations exponentially increase from the beginning to the end of the ingots. Upon doping with V, a decrease in the concentration of free holes and a metal-insulator transition are found. They are related to the appearance of a deep impurity level of V in the band gap, electron redistribution between the level and the valence band, and pinning of the Fermi-level to the impurity level. The shift rate of the V level relative to the conduction band bottom is determined and a diagram of the reconstruction of the electronic structure of the Pb1 − x − y Sn x V y Te alloy upon varying the host composition is suggested.

Peculiarities of galvanomagnetic effects in GaN epilayers and GaN/InGaN quantum wells

AbstractTemperature dependent Hall effect, magnetoresistivity and time resolved photoconductivity studies have been performed on GaN epilayers and GaN/InGaN multiple quantum wells (MQWs) grown on sapphire films by Metal Organic Chemical Vapor Deposition (MOCVD) method. The MQW structures consisted of different width or different amount of quantum wells. We related the electrical parameters with the quantum structure parameters and found that the geometrical variation of the quantum wells may be substituted by the variation of the amount of the quantum wells. The Hall and the magnetoresistivity measurements showed the complex behavior, which was attributed to the inhomogeneities of the samples, similarly to the case of the crystals with great size defects (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental evidence of magnetically controlled surface current in hall devices

A previously unknown galvanomagnetic effect in semiconductors (conducting materials) within wide temperature range (77–300K) has been experimentally observed, which is expressed by the appearance of magnetically controlled currents on the opposite lateral boundaries of structures between which Hall voltage is also generated. Surface currents are a linear and odd function of the strength and direction of both the bias current and the magnetic field – if the direction of the magnetic field or the supply current is reversed, the polarity of the surface current will also change. This unexpected surface phenomenon is a direct demonstration of the action of the Lorentz force on the moving charges in semiconductors. The discovered mechanism can enrich the possibilities for surface characterization and rapid determination of the main parameters in solids, such as conductivity type, carrier concentration and carrier mobility. The dependence of the surface current in solids on various nonelectrical quantities is useful for development of new types of sensors for pressure, light, chemical composition etc.

Galvanomagnetic phenomena in a longitudinal autosoliton in p-InSb in transverse and longitudinal magnetic fields

The behavior of a longitudinal autosoliton in p-InSb in transverse and longitudinal magnetic fields has been studied. It is shown that the motion of a current filament in the samples that occurs in a transverse magnetic field is absent under the effect of a longitudinal magnetic field. The conclusion is suggested that the emerging Ettingshausen galvanomagnetic effect in a longitudinal autosoliton in a transverse magnetic field is completely blocked by a diamagnetic effect emerging in the autosoliton during θ-pinch.

High-pressure magnetic phase transition and galvanomagnetic effects in the high-temperature ferromagnet p-Cd0.7Mn0.3GeAs2

The ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 undergoes a high-pressure ferromagnetic-to-antiferromagnetic phase transition. We have studied this transition at different temperatures. From magnetic-field dependences of the Hall resistance measured at different temperatures, we have derived the normal and anomalous Hall coefficients of the material as functions of temperature. Its transverse magnetoresistance changes from positive to negative near the ferromagnetic-to-antiferromagnetic phase transition.

Electronic structure and structural phase transition in Pb1−xGexTe:Cr under pressure

We investigate galvanomagnetic effects near the insulator-metal transition induced by pressure in Pb1−xGexTe (x=0.10, 0.13) alloys doped with chromium (4.2≤T≤300 K, B≤8 T). We observe nonlinearity in the magnetic field dependencies of Hall voltage and peaks of anomalous scattering in the temperature dependencies of resistivity. These are due to the conductivity via chromium impurity band and to the structural phase transition from the cubic NaCl phase to the rhombohedral GeTe phase. Magnetic field dependencies of the Hall coefficient RH(B) are calculated in the framework of two-band conduction model. The main parameters of charge carriers are determined. Pressure dependencies of the critical phase transition temperature are obtained.

Electronic structure of diluted magnetic semiconductors Pb1−x−ySnxCryTe

Abstract Galvanomagnetic effects in diluted magnetic semiconductors Pb 1− x − y Sn x Cr y Te at temperatures 4.2≤ T ≤300 K under variation of matrix composition ( x =0.06–0.235) and impurity content ( y =0.002–0.045) have been investigated. The p–n-conversion of the conductivity type, induced by the chromium doping, was observed. It is shown that in the heavily doped alloys temperature dependencies of resistivity and of the Hall coefficient have a “metallic” character, indicating pinning of the Fermi level by the chromium deep impurity level, situated in the conduction band. Free electron concentration and Fermi energy were calculated as functions of impurity concentration and of matrix composition by analyzing experimental data in the framework of the two-band Kane dispersion law. The impurity content coefficients of the free charge carrier concentration were determined and the diagram of electronic structure rearrangement under varying the alloy composition was obtained for the alloys under study.

Galvanomagnetic Effects ̈Sen sors based on Hall Effect ̈

Galvanomagnetic Effects ̈Sen sors based on Hall Effect ̈

Galvanomagnetic effects in A2VB3VI

Magnetoresistivity of A2VB3VI-based compounds has been investigated (H∼0÷89 kE, T=0,5÷4,2 K). Oscillation of magnetoresistivity, Shubnikov de Gaas oscillation has been observed at high magnetic fields (H>30 kE). The charge carrier concentration and area of extreme cross section of Fermi surface by plane, perpendicular to magnetic field have been evaluated from oscillation period.A52B63-based compounds are used as high effective thermoelectric transformers [1]. Recently, the interest to these compounds increases due to the perspectivities of widening of working temperature range and increase of thermoelectric efficiency of A52B63 compounds, doped by different impurities [2-6]. Therefore the investigation of fundamental characteristics of these compounds is not only extended our representation on band structure, also has a practical meaning.In the present work the results of investigations of galvanomagnetic effects in layered A52B63 compounds which have rhombohedral structure and crystallize in sp.gr. D3d (R÷m) [1], are given. The layers in A52B63 compounds consist of five monoatomic hexagonal grids alternating in sequence in B(1)-A-B(2)-A-B(1). Atom B(2) has 6 nearest atoms B(1). The bond between B(1)-A-B(2)-A-B(1) layers-quintets is of weak Van-der-Vaals type, but in layers of B(1)-A and A-B(2) bonds have covalent character with small fraction of ionic bond.Single crystals under investigation have been were grown by Bridgman method from components with stoichiometric relationship. It is known, that by synthesis of A52B63 compounds from the melt of stoichiometric structure are characterized by presence of a significant amount of own points defects conditioned by transition of A atoms into the position of B atoms. These antistructural defects are the acceptors. Concentration of holes is p∼1019cm-3. Investigations have been carried out in temperature range 0,5÷300K and magnetic field up to 8 Tl. At galvanomagnetic investigations the sample is placed in the centre of superconductive solenoid. Measurements are carried out by selective method under the alternating current by 20 Hz frequency. The current magnitude does not exceed 1MA. The current is directed along the layer plane, magnetic field is perpendicular to layer plane.

Conductivity anisotropy in the doped Bi2Te3 single crystals

Temperature dependences (temperature range T = 0.5−300 K) of resistivity in the plane of layers and in the direction perpendicular to the layers, and the galvanomagnetic effects in undoped and doped Bi2Te3 single crystals are studied (magnetic field H < 80 kOe, T = 0.5−4.2 K). It is shown that upon doping of Bi2Te3 with the Group III atoms (In and B), conductivity anisotropy increases mainly due to an increase in resistivity in the direction perpendicular to the layers. This fact makes it possible to assume that the atoms of these impurities are incorporated mainly into the van der Waal gaps between the layers upon doping. It is also revealed that, upon doping of Bi2Te3 with In and B, the temperature dependence of conductivity becomes weaker, which indicates an increase in the role of scattering by defects in scattering mechanisms. The concentrations and mobilities of charge carriers, values of the Hall factor conditioned by the anisotropy of effective masses and orientation of ellipsoids with respect to crystallographic axes, areas of the extreme section of the Fermi surface by the plane perpendicular to the direction of the magnetic field, and the Fermi energy are evaluated.

Sign of bipolar-magnetotransistor sensitivity as dependent on device structure

An experiment is conducted to compare the performance of two designs of dual-collector lateral bipolar magnetotransistor, which are formed in a uniformly doped substrate or a diffused well. Their respective differential collector voltages are found to differ in sign under an applied magnetic field. This effect is interpreted in terms of the sign of magnetic-field sensitivity. A computer simulation is run to investigate the distribution of carrier density, current density, or recombination rate for the latter type of magnetotransistor with a base and a substrate terminal being connected together. A bulk-recombination mechanism of negative sensitivity is revealed for a design with substrate terminals located on the front side only. It is traced to galvanomagnetic effects.

Insulator-metal transition in Pb1-xGexTe doped with chromium under pressure

The galvanomagnetic effects in the n-Pb1-xGexTe (x=0.02-0.13) alloys, doped with chromium, at the temperatures in the range of 4.2≤T≤300 K and under hydrostatic compression of up to 17 kbar have been investigated. The insulator-metal transition, induced by pressure in Pb1-xGexTe: Cr (x=0.10) alloy, was revealed. Using the experimental data in the frame of two-band Kane dispersion relation the pressure dependences of electron concentration and Fermi energy were calculated. The pressure coefficient of chromium deep level energy was obtained and the diagram of the electronic structure reconstruction under pressure was proposed.

Dual-Collector Lateral Bipolar Magnetotransistor: Negative Sensitivity and Galvanomagnetic Effects

The results of measurement of the dual-collector lateral bipolar magnetotransistor, generated in a uniformly doped substrate or in a diffused well were compared and it was established that the collector voltage difference under the influence of a magnetic field has a different sign. The effect is interpreted using the concept of the magnetic sensitivity sign. By means of device-technological simulation we investigated the distribution of charge carriers, current density and recombination speed in a magnetotransistor generated in a well with external connection of substrate and well contacts. It is shown that at a planar arrangement of substrate contacts is responsible for the volumetric concentration-recombination mechanism of negative relative magnetic sensitivity due to Galvanomagnetic effects.

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.

Oscillation galvanomagnetic effect in double-layer metal films

A semiclassical approximation has been used to analyze theoretically the dependence of the conductivity σ (resistivity ρ) of a double-layer film consisting of plane-parallel single-crystal metal layers of different thickness dj ≠ dn and grade lj ≠ ln on the layer thickness ratio d2,1 = d2/d1 and on the magnitude of the magnetic field normal to the layer interface. A general expression (for any d2,1) and asymptotic expressions (for thick and thin (compared to the electron free path lj) metal layers in a weak and a strong magnetic field) for the conductivity of a double-layer specimen have been obtained. A nonmonotonic relation between the conductivity of a double-layer film and the layer thickness ratio at weak magnetic fields has been predicted which is sensitive to the character of the interaction of charge carriers with the conductor boundaries. At strong magnetic fields, ρ becomes an oscillating function of magnetic field (layer thickness). A detailed numerical analysis of the resistivity of a double-layer film on the layer thickness ratio and on the magnetic field strength has been performed for arbitrary values of the parameters that describe the character of the interaction of charge carriers with the specimen boundaries.

Quasi-local states of Sn in Bi2Te3 according to the studies of galvanomagnetic effects in classical and quantizing magnetic fields

The magnetic-field dependences of the Hall coefficient and transverse magnetoresistance are studied experimentally and theoretically in p-Bi2Te3 crystals doped heavily with Sn and grown by the Czochralski method in the case of both classical and quantizing magnetic fields as high as 12 T with the magnetic-field orientation along the C 3 trigonal axis. The Shubnikov-de Haas effect and quantum oscillations of the Hall coefficient were measured at temperatures of 4.2 and 11 K. The six-ellipsoid Drabble-Wolfe model of the energy spectrum and the magnetic-field dependence of the Hall coefficient are used as the basis for the method for determining the Hall factor and Hall mobility. New evidence is obtained in support of the existence of the narrow band of impurity Sn states occupied partially with electrons against the background of the light-hole band spectrum. The parameters of impurity states are estimated including their energy (E Sn ≈ 15 meV), the broadening (Γ « kT), and the radius of localization of the impurity state (R ≈ 30 A).

複合構造Ｐｙ／Ｃｕ／Ｐｙナノリングにおける電流磁気効果

複合構造Ｐｙ／Ｃｕ／Ｐｙナノリングにおける電流磁気効果

The oscillatory galvanomagnetic effect in thin metal layers under the presence of the layer of diffusing impurities

The oscillatory galvanomagnetic effect in thin metal layers under the presence of the layer of diffusing impurities