Galvanomagnetic Effects Research Articles

Anisotropic Galvanomagnetic Effects in Single Cubic Crystals: A Theory and Its Verification.

A theory of anisotropic galvanomagnetic effects in single cubic crystals and its experimental verifications are presented for the current in the (001) plane. In contrast to the general belief that galvanomagnetic effects in single crystals are highly sensitive to many internal and external effects and have no universal features, the theory predicts universal angular dependencies of longitudinal and transverse resistivity and various characteristics when magnetization rotates in the (001) plane, the plane perpendicular to the current, and the plane containing the current and [001] direction. The universal angular dependencies are verified by experiments on Fe_{30}Co_{70} single cubic crystal film. The findings provide new avenues for fundamental research and applications of galvanomagnetic effects, because single crystals offer advantages over polycrystalline materials for band structure and crystallographic orientation engineering.

Study on the surface integrity in ultrasonic vibration and magnetic field complex assisted low speed WEDM under different magnetic field coupling

In this paper, a complex process of ultrasonic vibration (USV) and magnetic field (MF) complex assisted WEDM-LS is proposed, which provides a new method to solve the problems of low machining efficiency and poor machining surface integrity of traditional WEDM-LS. The self-generated MF of wire electrode is taken as the medium, and the influence mechanism of USV and additional MF on the intensity of self-generated MF is explored. Firstly, combined with the Galvanomagnetic effect and Biot-Safar Law, the mathematical models of self-generated MF under USV assisted WEDM-LS and USV-MF assisted WEDM-LS were deduced respectively. And then the MF coupling law between inter electrode was revealed; Secondly, the distribution of self-generated MF of wire electrode under different working conditions was simulated and analyzed. The results showed that compared with traditional WEDM-LS, the self-generated magnetic density under USV assisted WEDM-LS and USV-MF assisted WEDM-LS was increased by 12.1 % and 17.5 % respectively. As a result, the volume of single discharge crater was increased by 12.3 %; Finally, Taguchi orthogonal method was used to complete the USV-MF assisted WEDM-LS orthogonal experiment and the MF coupling verification experiment. The results showed that the Ra was reduced by 23.8 % and the MRR was increased by 25.1 % compared with the traditional working condition. The number of microcracks and micropores on the workpiece surface was significantly reduced, and the degree of workpiece surface burn was effectively reduced, which showed that the surface integrity of the workpiece had been greatly improved. The verification experiment results showed that compared with the opposite coupling of the self-generated MF and the additional MF, when the self-generated MF and the additional MF were coupled in the same direction, the Ra of the workpiece surface was reduced by 18.21 % and the feed speed was increased by 16.68 %. In addition, the removed particles were more evenly adsorbed on the surface of the wire electrode, which increased the normal discharge probability, indicating that the inter electrode MF coupling was the main effect model of ultrasonic vibration and MF recombination.

Перенос заряда в твердых растворах Bi-=SUB=-0.9-=/SUB=-Sb-=SUB=-0.1-=/SUB=-, легированных Mn

Electrical and galvanomagnetic effects in single crystals of Bi0.9Sb0.1 solid solutions doped with 1 and 3 at.% Mn have been studied. It is shown that in single crystals of Bi0.9Sb0.1 solid solutions doped with 1 at.% Mn at temperatures below 180 K, activation conductiity with an activation energy of 10 meV is observed. After thermal annealing, in addition to activation conductivity, at temperatures below 20 K, a “metallic” character of conductivity is observed, which is due to conduction over the impurity band. It was found that in single crystals of Bi0.9Sb0.1 solid solutions doped with 3 at.% Mn, a “metallic” character of conductivity is observed with a feature at low temperatures of about 25 K, which reacts to applied external magnetic fields. After thermal annealing, the “metallic” nature of the conductivity is retained, but this feature practically disappears. The mobility and concentration of charge carriers are estimated.

CHOICE OF A MATHEMATICAL MODEL OF A CURRENT CONVERTER BASED ON A GALVANOMAGNETIC EFFECT

The article is devoted to the analysis and selection of a mathematical model of a current converter based on a galvanomagnetic effect. The dependences of the design parameters of the converter on the parameters of the magnetic material are obtained. The accuracy of calculating the magnetic circuit of a current converter based on the galvanomagnetic effect, which is determined depending on the accuracy of the mathematical model of magnetic induction from magnetic voltage, is investigated.

Longitudinal magnetoresistance of uniaxially deformed n-type silicon

The study of Galvano-magnetic effects (as well as tensoeffects) in silicon under extreme conditions allows not only to identify the mechanisms of these effects but also to identify the possibility of creating gaussmeters, infrared detectors, sensitive strain gauges, amplifiers and generators of a wide frequency range. The reliability of the mechanism of negative magnetoresistance was verified using uniaxial elastic deformation of the studied crystals. Uniaxial deformation excludes interline transitions of electrons, as a result of which negative magnetoresistance disappears with an increase in uniaxial pressure. When cubic symmetry is violated, anisotropic phenomena occur in such crystals. The multipath of the isoenergetic surface of the bottom of the silicon conduction band causes anisotropies of the effective mass and relaxation time, which are associated with the features of the transfer phenomenon. In particular, magnetoresistance (piezoresistance), which is the most sensitive to the anisotropy of the iso energy surface. The influence of the latter on magnetoresistance is most clearly revealed in the region of strong magnetic fields, where the magnetoresistance is saturated since the longitudinal magnetoresistance is entirely due to the anisotropy of electron mobility.

Longitudinal magnetoresistance of uniaxially deformed n-type silicon

The study of Galvano-magnetic effects (as well as tensoeffects) in silicon under extreme conditions allows not only to identify the mechanisms of these effects but also to identify the possibility of creating gaussmeters, infrared detectors, sensitive strain gauges, amplifiers and generators of a wide frequency range. The reliability of the mechanism of negative magnetoresistance was verified using uniaxial elastic deformation of the studied crystals. Uniaxial deformation excludes interline transitions of electrons, as a result of which negative magnetoresistance disappears with an increase in uniaxial pressure. When cubic symmetry is violated, anisotropic phenomena occur in such crystals. The multipath of the isoenergetic surface of the bottom of the silicon conduction band causes anisotropies of the effective mass and relaxation time, which are associated with the features of the transfer phenomenon. In particular, magnetoresistance (piezoresistance), which is the most sensitive to the anisotropy of the iso energy surface. The influence of the latter on magnetoresistance is most clearly revealed in the region of strong magnetic fields, where the magnetoresistance is saturated since the longitudinal magnetoresistance is entirely due to the anisotropy of electron mobility.

Negative magnetoresistance and sign change of the planar Hall effect due to negative off-diagonal effective mass in Weyl semimetals

We theoretically investigated the magnetoresistance (MR) and planar Hall effect (PHE) in Weyl semimetals based on the semiclassical Boltzmann theory, focusing on the fine structure of the band dispersion. We identified that the negative longitudinal MR and sign change in the PHE occur because of the negative off-diagonal effective mass with no topological effects or chiral anomaly physics. Our results highlight the important role of the off-diagonal effective mass, which can cause anomalous galvanomagnetic effects. We propose that the PHE produces a dip in the temperature dependence, which enables the experimental detection of the singularity of effective mass, i.e., the Weyl point.

A Theory for Anisotropic Magnetoresistance in Materials with Two Vector Order Parameters

Anisotropic magnetoresistance (AMR) and related planar Hall resistance (PHR) are ubiquitous phenomena of magnetic materials. Although the universal angular dependences of AMR and PHR in magnetic polycrystalline materials with one order parameter are well known, no similar universal relation for other class of magnetic materials are known to date. Here a general theory of galvanomagnetic effects in magnetic materials is presented with two vector order parameters, such as magnetic single crystals with a dominated crystalline axis or polycrystalline non-collinear ferrimagnetic materials. It is shown that AMR and PHR have a universal angular dependence. In general, both longitudinal and transverse resistivity are non-reciprocal in the absence of inversion symmetry: Resistivity takes different values when the current is reversed. Different from simple magnetic polycrystalline materials where AMR and PHR have the same magnitude, and π/4 out of phase, the magnitudes of AMR and PHR of materials with two vector order parameters are not the same in general, and the phase difference is not π/4. Instead of π periodicity of the usual AMR and PHR, the periodicities of materials with two order parameters are 2π.

Vortex motion in tilted magnetic fields in highly layered electron-doped superconductor Nd2-xCexCuO4

The carrier transport and the motion of a vortex system in a mixed state of an electron-doped high-temperature superconductors Nd2-xCexCuO4 were investigated. To study the anisotropy of galvanomagnetic effects of highly layered NdCeCuO system we have synthesized Nd2-xCexCuO4/SrTiO3 epitaxial films with non-standard orientations of the c-axis and conductive CuO2 layers relative to the substrate. The variation of the angle of inclination of the magnetic field, B, relative to the current, j, reveals that the behavior of both the in-plane ρxx(B) and the out-of-plane ρxy(B) resistivities in the mixed state is mainly determined by B⊥, the perpendicular to j component of B, that indicates the crucial role of the Lorentz force, FL∼[j×B] and defines the motion of Josephson vortices across the CuO2 layers.

Correlation among hydrogenation, magnetoelastic coupling, magnetic anisotropy, and magnetoresistance in magnetostrictive, hydrogen-absorbing palladium-cobalt alloy films for hydrogen sensing

Hydrogen-absorbing magnetic alloy films, such as palladium-cobalt (PdCo) alloy films, are expected to play a significant role in the next generation of hydrogen sensors. However, effects of hydrogenation on such films are very complex, since these alloys show strong spin-orbit interaction, i.e., strong magnetoelastic coupling. Accordingly, we conducted integrated research on the hydrogenation, magnetoelastic coupling, magnetism, and galvanomagnetic effect of PdCo alloy films having different magnetic anisotropies of longitudinal and perpendicular magnetic anisotropies. As a result, it was revealed that the stress in the film determines its magnetic anisotropy. The magnetoresistance curves of films, consisting of ordinal and anisotropic magnetoresistance effects, correspond well to the magnetization-magnetic field curves. Hydrogenation results in the compressive stress and decreased magnetostriction, which both have a negative influence on the perpendicular magnetic anisotropy energy of the films. Moreover, the influence is observed also in ordinal and anisotropic magnetoresistances. In addition, the increases in coercivity and electronic resistivity due to the incorporated hydrogen atoms (and related defects) are detected. The results are summarized in a correlation diagram, which shows that hydrogen-absorbing magnetic alloy films are very suitable for use in hydrogen sensors—the films can detect hydrogen via various methods such as magnetic anisotropy, galvanomagnetic effect, coercivity, and resistivity.

Topological Thermoelectric Materials Based on Bismuth Telluride

The main directions of experimental studies of topological insulators based on bismuth and antimony chalcogenides, which are related to the possibility of using the properties of the surface states of Dirac fermions in thermoelectricity, have been considered. The results of studies of the Van der Waals interlayer surface (0001) in single-crystal layered films of solid solutions of n- and p-type conductivity with substitutions of atoms in Bi and Te sublattices performed by micro-Raman spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy have been discussed. The oscillations of galvanomagnetic effects in strong magnetic fields and thermoelectric properties measured under normal conditions and at high pressures have been analyzed. The compositions of solid solutions in which the contribution of the surface states of Dirac fermions increases because of an increase in the surface concentration of fermions and the Fermi velocity depending on the energy of the Dirac point, the value of the Seebeck coefficient, and the power parameter have been determined.

Significant suppression of galvanomagnetic signal under dynamical spin injection in CoFeB/Pt bilayer

An effective detection structure for a dynamical spin injection in a ferromagnetic/nonmagnetic metal bilayer has been developed. We demonstrate a clear detection of a highly symmetric signal, indicating a significant suppression of spurious signals due to the galvanomagnetic effects from the ferromagnetic layer. The angular dependence of the signal amplitude assures that the observed signal is caused by the inverse spin Hall effect due to the dynamical spin injection. We also find the importance of the eddy current that induces spin-rectified signals from a ferromagnetic layer.

Specificity of the electrophysical properties of elastically deformed p-type germanium

The influence of directional elastic compression deformation on the electrophysical properties of p-type germanium single crystals was investigated. The dependences of the Hall coefficient on the magnetic field strength on samples of different crystallographic orientations in the absence and in the presence of uniaxial mechanical stress were measured at two temperatures (room temperature and liquid nitrogen temperature). On the same samples, the tensoresistance and longitudinal tensomagnetoresistance were studied in a wide range of mechanical stresses (0≤X≤1GPa). The presence of anisotropy of galvanomagnetic effects in p-Ge was revealed both in the absence of deformation and under very strong mechanical loads. Experiments on measuring the longitudinal tensomagnetoresistance make it possible to conclude that the isoenergetic surfaces in p-Ge, which arise as a result of directional elastic compression deformation, cannot be considered as perfect ellipsoids of revolution, at least in the investigated X range.

Angular dependence of magnetoresistance and planar Hall effect in semimetals in strong magnetic fields

The semiclassical transport theory is especially powerful for investigating galvanomagnetic effects. Generally, the semiclassical theory is applicable only in weak fields because it does not consider Landau quantization. Herein, we extend the conventional semiclassical theory by considering Landau quantization through the field dependence of carrier density in semimetals. The extended semiclassical theory is applicable even in strong fields, where Landau quantization is noticeable. Using this new approach, we explain the qualitative change in the angular dependence of transverse magnetoresistance (TMR), anisotropic magnetoresistance (AMR), and planar Hall effect (PHE) in bismuth with an increase in the magnetic field. This unveils the puzzle of nontrivial field-induced changes in TMR, AMR, and PHE observed recently in semimetal bismuth.

Steel 110G13L. Thermomagnetic and Galvanomagnetic Effects in its Films

The article shows the ability to control magnetic properties due to modulation of phases in the film with varying temperature of growth. So, at low growth temperatures, a film is formed with an axis of easy magnetization in plane. An increase in temperature leads to a change in the phase composition of the film. It is shown that the presence of even a small component of the magnetization vector in the perpendicular direction leads to the appearance of a thermomagnetic effect of a large magnitude with respect to thermal noise

STUDY OF THE MAGNETO-RESISTANCE SILICON P-TYPE

The study of galvanomagnetic phenomena in silicon, in strong magnetic fields, is associated with great difficulties due to the high resistance of the samples and the complexity of preparing omics contacts that work well in a wide range of temperatures and magnetic fields. Therefore, until now, all existing data on galvanomagnetic effects in silicon have been obtained only in the region of weak magnetic fields. Given the growing interest in silicon due to its large potential, it seemed appropriate to study the galvanomagnetic effects in the region of strong magnetic fields, where quantum effects play the dominant role. The study of Galvano-magnetic effects (as well as tensoeffects) in silicon under extreme conditions allows not only to identify the mechanisms of these effects, but also to identify the possibility of creating gaussmeters, infrared detectors, sensitive strain gauges, amplifiers and generators of a wide frequency range. Keywords: galvano-magnetic effects, silicon, negative magnetoresistance, uniaxial pressure.

Role of electron-electron collisions for magnetotransport at intermediate temperatures

We discuss galvanomagnetic and thermomagnetic effects in disordered electronic systems focusing on intermediate temperatures, for which electron-electron scattering and electron-impurity scattering occur at similar rates, while phonon-related effects can be neglected. In particular, we explore how electric and thermal currents driven either by an electric field or by a temperature gradient are affected by the interplay of momentum-dependent electron-impurity scattering, electron-electron scattering, and the presence of a magnetic field. We find that the electric resistance, the Seebeck coefficient and the Nernst coefficient are particularly sensitive to the momentum dependence of the electron-impurity scattering rate at intermediate temperatures. A sufficiently strong momentum dependence of the electron-impurity scattering rate can induce a sign change of the Seebeck coefficient. This sign change can be suppressed by a perpendicular magnetic field. The temperature and magnetic field dependence of the Seebeck coefficient can be used for measuring the magnitude of the electron-impurity and electron-electron scattering rates. The Nernst coefficient vanishes for momentum-independent electron-impurity scattering, but displays a maximum at finite temperatures once the momentum dependence is accounted for. By contrast, the Hall coefficient and the Righi-Leduc coefficient display only a weak dependence on the momentum dependence of the electron-impurity scattering at intermediate temperatures.

Spin Dynamics for Antiferromagnets and Ultrafast Spintronics

A brief review is given of the physical properties of antiferromagnets (AFMs) that can be used as active elements of terahertz and subterahertz range nanooscillators based on the excitation of spin oscillations by spin transfer torque. Possible schemes of such devices are considered. The analysis is carried out from a unified point of view on the basis of the nonlinear sigma model for the antiferromagnetic vector with regard to the magnetic symmetry of real AFMs. Specific properties of AFMs, first of all, the possibility of faster (compared to ferromagnets) spin dynamics, as well as the manifestations of antiferromagnetic ordering in galvanomagnetic and optical effects, are described. The history of the development of AFM physics is briefly discussed, first of all, those aspects of it that may be important for the practical application of AFMs, in particular, in ultrafast spintronics.

ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ЭФФЕКТА ХОЛЛА В ЗЕМЛЕ ПРИ ЗОНДИРОВАНИЯХ СТАНОВЛЕНИЕМ ПОЛЯ В БЛИЖНЕЙ ЗОНЕ

В период с 8 по 15 июля 2018 года сотрудниками Лаборатории геоэлектрики ИНГГ СО РАНпроводились полевые исследованияв рамках гранта РФФИ № 17-05-00083 А. Исследования направлены на обнаружение и численную оценку эффекта Холла в геологических средах. Этот эффект должен очень слабо проявляться во всех сигналах электромагнитных зондирований. Комплекс электроразведочных методов был выбран в связи с методической эффективностью и относительной простотой выполнения работ.Задачи исследований:выбор участка работ; измерение четырьмя радиальными линиями MN сигналов зондирований становлением в ближней зоне для регистрации компоненты , вызванной эффектом Холла; измерение линией компоненты для контроля измерений. Актуальность исследованияобусловлена в первую очередьтем, что гальваномагнитные эффекты (в т.ч. и эффект Холла), возникающие в скрещенных электрическом и магнитном полях, хорошо известны в физике, но не исследовались применительно к геологической среде – это значит, что данные эффекты пока неучтенным образом влияют на сигналы в геоэлектромагнитных зондированиях. Цель: обнаружение эффекта Холла в геологических средах. Объект: эффект Холла в геологической среде. Методы: зондирование становлением поля в ближней зоне, магнитотеллурическое зондирование. Результаты. Полевые исследования в 2018 г. являются первыми целенаправленными полевыми исследованиями с целью обнаружения эффекта Холла в геологической среде методами электромагнитных зондирований. Цель работ, по мнению самих исследователей, по предварительным данным, достигнута. Получена оценка холловской проводимости ~1–2·10–3 См/м.

Thermoelectric Properties and Shubnikov–de Haas Oscillations in Bi Wires Doped with Sn

Using a set of glass-insulated Bi–0.02 at %Sn wires with diameters varying in a range of 0.2–1 μm prepared by liquid-phase casting by the Ulitovsky method, a complex of measurements of the temperature dependences of resistivity ρ(T), thermoelectric power α(T), and magnetic field dependences R(H) in range 4.2–300 K and Shubnikov–de Haas (SdH) oscillations in longitudinal and transverse magnetic fields up to 14 T in a temperature range of 2.1–20 K has been conducted. According to the SdH oscillation measurements, the minimum and maximum cyclotron masses, the Dingle temperature, and the position of the Fermi level eF in the Bi–0.02 at %Sn wires have been calculated. It has been shown that, at low temperatures, the conduction occurs only through T-holes, i.e., eF is located in the region of the band gap ΔEg; it has been found that the anisotropy of the Fermi surface of the T-holes does not change after doping. The observed anomalies in the temperature dependences ρ(T), α(T), and on longitudinal magnetic field dependences R(H), which depend on wire diameter d, have been interpreted in terms of the occurrence of galvanomagnetic size effects. From the experimental data, power factor P.f. = α2σ for the Bi–0.02 at %Sn wires with different diameters in a range of 4.2–300 K has been calculated; the maximum P.f. value in different temperature ranges has been calculated. It has been found that the maximum P.f. value is achieved in a temperature range of 75–100 K, when the thermoelectric power has a positive value, which is an important factor for thermoelectric applications at low temperatures.