Electrical Hall Research Articles

Magnetothermoelectric properties of the bulk extruded samples of Bi85Sb15 solid solution with different grain sizes

Bulk extruded (including nanostructured) samples of Bi85Sb15 solid solutions consisting of particles with average sizes of 0.5 × 105, 380, 30, and 15 nm were obtained and their electrical conductivity (), thermo-e.m.f. (), Hall (R H), and thermal conductivity () coefficients in the temperature range ∼77–300 K and magnetic field strength (H) up to ∼74 × 104 A/m have been investigated. With decreasing powder sizes in the samples an increase in and a decrease in phonon thermal conductivity () and R H are observed; the dependences of these parameters of the samples on the size of the powders satisfactorily correlate in the studied temperature range. As the size of the crystals decreases, the concentration of the boundaries increases, this leads to increase of electron concentration in the samples. Effect of H on the electrical and thermal properties for annealed samples of Bi85Sb15 solid solutions was stronger than for the samples that have not undergone annealing.

Enhanced Spin Hall Effect in S‐Implanted Pt

AbstractHigh efficiency of charge–spin interconversion in spin Hall materials is a prime necessity to apprehend intriguing functionalities of spin–orbit torque for magnetization switching, auto‐oscillations, and domain wall motion in energy‐efficient and high‐speed spintronic devices. To this end, innovations in fabricating advanced materials that possess not only large charge–spin conversion efficiency but also viable electrical and spin Hall conductivity are of importance. Here, a new spin Hall material designed by implanting low energy 12 keV sulfur ions in heavy metal Pt, named as Pt(S), is reported that demonstrates eight times higher conversion efficiency as compared to pristine Pt. The figure of merit, spin Hall angle (θSH), up to of 0.502 together with considerable electrical conductivity of 1.65 × 106 Ω–1 m–1 is achieved. The spin Hall conductivity increases with increasing , as , implying an intrinsic mechanism in a dirty metal conduction regime. A comparatively large of 8.32 × 105 () Ω–1 m–1 among the reported heavy‐metals‐based alloys can be useful for developing next‐generation spintronic devices using spin–orbit torque.

Transport Properties of Ag‐doped ZnSb

The intermetallic compound ZnSb is a (II‐V) narrow gap semiconductor with interesting thermoelectric properties. Electrical resistivity, Hall coefficient, thermopower and thermal conductivity were measured up to 400 K on Ag‐doped samples with concentrations 0.2, 0.5, 1, 2, and 3 at.%, which were consolidated to densities in excess of 99.5 % by spark plasma sintering. The work confirms a huge improvement of the thermoelectric Figure‐of‐merit, ZT, upon Ag doping. The optimum doping level is near 0.5 at.% Ag and results in ZT values around 1.05 at 390 K. The improvement stems from a largely decreased resistivity, which in turn relates to an increase of the hole charge carrier concentration by two orders of magnitude. It is argued that Ag can replace minute concentrations of Zn (on the order of 0.2 at.%) in the crystal structure which enhances the intrinsic impurity band of ZnSb. Excess Ag was found to segregate in grain boundaries. So the best performing material may be considered as a composite Zn~0.998Ag~0.002Sb/Ag~0.003.

Nanoelectromagnetic of a highly conductive 2D transition metal carbide (MXene)/Graphene nanoplatelets composite in the EHF M-band frequency

Highly conductive materials, with minimal thickness and capable to afford electromagnetic interference (EMI) shielding, are highly advantageous, particularly if they are able to be easily processed into thin films. Here, we demonstrate the potential of a sandwich-like structure of a two-dimensional Ti3C2Tx MXene/Graphene nanoplatelets (GNPs) composites for EMI shielding in the extreme high frequency (EHF) M-band, ranging from 60 to 80 GHz. First, we investigated systematically the microstructural and electrical transport properties of these composites with respect to the GNP contents. After graphene integration, the composite-surface roughness has been found to decrease, while both electrical conductivity and Hall carrier mobility demonstrated a clear trend to increase, reaching the values of ∼105 S/cm and 55 cm2/V, respectively, for only 2.5 wt % of graphene content, reporting thereby one of the most electrically conductive MXene based composite to date. Furthermore, a 1.75 μm-thick Ti3C2Tx MXene/GNP film was found to exhibit an EM absorbance of about 64 dB, which is one of the highest values, normalized to the thickness, among tested materials so far. This remarkable performance could be associated to three key factors, namely the superior transport properties of the composite films, the dominant absorption mechanism, and the multiple internal reflections from Ti3C2Tx and graphene multilayers configuration. These reported results would lead to unprecedented applications in the fields of space, aeronautics, radars, air travels and mobile phones.

Anisotropic physical properties and large critical current density in KCa2Fe4As4F2 single crystal

We present a systematic study of electrical resistivity, Hall coefficient, magneto-optical imaging, magnetization, and STEM analyses of KCa${_2}$Fe${_4}$As${_4}$F${_2}$ single crystals. Sharp diamagnetic transition and magneto-optical imaging reveal homogeneity of single crystal and prominent Bean-like penetrations of vortices. Large anisotropy of electrical resistivity, with ${\rho _c / \rho _{ab}}$ > 100, and semiconductor-like ${\rho _c}$ suggest that the electronic state is quasi two-dimensional. Hall effect measurements indicate that KCa${_2}$Fe${_4}$As${_4}$F${_2}$ is a multiband system with holes as main carriers. Magnetization measurements reveal significantly larger J$_c$ compared with that in other iron-based superconductors with different values of J$_c$ depending on the direction of magnetic field. Origin of these J$_c$ characteristics is discussed based on microstructural observations using STEM. In addition, further enhancement of J$_c$ in KCa${_2}$Fe${_4}$As${_4}$F${_2}$ for future application is demonstrated in terms of heavy-ion irradiation.

Electron transport in Dirac nodal-line semimetal ZrSiS

We report a study of magnetization and transport properties such as electrical resistivity, thermal conductivity, and thermal Hall conductivity in high fields and at low temperatures for ZrSiS single crystals. Here, we find that the thermal conductivity (κxx/T) is strongly suppressed in applied fields, having a good correlation with the large positive transverse magnetoresistance (TMR). The thermal Hall conductivity (κxy/T) displays a sharp peak at extremely low field which reveals the high mobility of the electrons. In addition, the TMR displays clear Shubnikov de Haas (SdH) oscillation at low temperatures. Although the Zeeman splitting is obviously appeared in de Haas-van Alphen (dHvA) oscillation of the magnetization measurements and distinguished easily from the SdH oscillation. Negative longitudinal magnetoresistance (LMR) is also observed in ZrSiS which may be related to the chiral anomaly.

Magnetospheric Multiscale Observations of Foreshock Transients at Their Very Early Stage

Abstract Foreshock transients are ion kinetic structures in the ion foreshock. Due to their dynamic pressure perturbations, they can disturb the bow shock and magnetosphere–ionosphere system. They can also accelerate particles contributing to shock acceleration. However, it is still unclear how exactly they form. Recent particle-in-cell simulations point out the important role of the electric field and Hall current in the formation process. To further examine this, we use data from the Magnetospheric Multiscale (MMS) mission to apply case studies on two small (1000–2000 km) foreshock transient events that just started to form. In event 1 where MMS was in a tetrahedral formation, we show that the current density configuration, which determined the magnetic field profile, was mainly driven by Hall currents generated by demagnetized foreshock ions. The resulting time variation of the magnetic field induced an electric field that drove cold plasma moving outward with magnetic field lines. In event 2 where MMS was in a string-of-pearls formation, we analyze the evolution of field and plasma parameters. We show that the magnetic flux and mass flux were transported outward from the core, resulting in the steepening of the boundary. The steepened boundary, which trapped more foreshock ions and caused stronger demagnetization of foreshock ions, nonlinearly further enhanced the Hall current. Based on our observations, we propose a physical formation process wherein the positive feedback of foreshock ions on the varying magnetic field caused by the foreshock ion Hall current enables an “instability” and the growth of the structure.

Involvement of the quantum radiative effect on Jeans instability with electrical resistance and Hall current

The influence of quantum radiative effect and electrical resistivity incorporating the Hall current is studied on the Jeans instability of magnetized plasma. The basic equation of the problem is constructed and linearized by using the QMHD model. The general dispersion relation is derived using a normal mode technique and discussed in the parallel and perpendicular propagation. In the case of longitudinal propagation, the Jeans instability is modified due to quantum radiative impact but is unaffected by electrical resistivity and Hall current. While in transverse propagation the electrical resistivity is modifying the growth rate of instability. In the graphical presentation, we found that the electrical resistivity has destabilizing influence but the presence of a quantum parameter is reduced the destabilizing effect of electrical resistivity in the system. The result is relevant to understanding many astrophysical problems.

Growth of Large Single Crystals of n-Type SnS from Halogen-Added Sn Flux

We report the growth of large Cl-doped and Br-doped SnS single crystals from a molten Sn-based flux. Compared with the small and lamellar undoped SnS crystals, the addition of SnCl2 or SnBr2 halogen sources in the flux substantially enhanced lateral growth along the (100)-plane and vertical growth. The maximum size of the obtained single crystals reached a diameter and thickness of 16 mm and 0.7 mm for the Cl-doped SnS and 24 mm and 1.0 mm for the Br-doped SnS, respectively. The X-ray rocking curves and the X-ray back-reflection Laue patterns indicated a high crystal quality. The obtained crystals were further characterized via electrical measurements, including electrical conductivity and Hall measurements, optical absorption spectroscopy, and X-ray and ultraviolet photoelectron spectroscopies. Both the Cl-doped and Br-doped SnS single crystals exhibited degenerate n-type conductivity with a high electrical conductivity of 11.1 S cm–1 for Cl-doped SnS and 18.9 S cm–1 for Br-doped SnS along the (100)-plane at 300 K. Furthermore, the photoelectron spectroscopy results also indicated n-type conductivity. The large single crystals of n-type SnS obtained in this work would enable the fabrication of p-n homojunction SnS solar cells via the deposition of p-type SnS thin films.

Electrical Properties of Compact Drop-Casted Cu2SnS3 Films

We investigated temperature-dependent electrical conduction of Cu2SnS3 (CTS) thin films in the range of 77–500 K synthesized by drop-casting molecular ink. The films were directly formed by drop-casted molecular ink, consisting of a Cu+2-Sn+2-thiourea complex dissolved in a mixture of ethylene glycol–isopropyl alcohol and annealed. The CTS films have a smooth layer with a compact structure, as revealed by cross-sectional scanning electron microscopy. The films are p-type and show a band gap of 1.18 eV. The electrical conductivity and Hall mobility of the films were found to be 1.1 S/cm and 6.72 cm2 V−1 s−1, respectively. Data from temperature-dependent measurements show hopping and thermally activated conduction below and above 300 K, with an activation energy of ∼ 10 and 90 meV, respectively. Our results suggest that the drop-casted CTS films can be used as an absorber layer in thin film solar cells at an affordable cost.

Electrical transport properties of Weyl semimetal WTe2 under high pressure

Tungsten ditelluride (WTe2) has recently become one of the most extensively investigated materials as a Weyl semimetal with an orthorhombic Td phase due to its unique properties, including its pressure-induced superconductivity and unsaturated giant magnetoresistance. The electrical resistivity, photoconductivity, and Hall effect under high pressures are considered in WTe2 using in situ measurements up to 40 GPa. The structural phase transition is reflected from the Td to 1T′ phase at approximately 11 GPa based on the discontinuous electrical parameters. The abrupt increase of resistivity is caused by a joint decrease in the carrier concentration and mobility. The semimetal-to-semiconductor transition is apparent at around 11 GPa based on the resistivity measurements under different temperatures, and the transition is reversible due to the structural phase transition. The photoconductivity is much higher than the conductivity, and the phase transition pressure is lower at approximately 9.6 GPa. Electrical transport properties of Weyl Semimetal WTe2 are investigated under high pressure, and pressure-induced semiconductor transition is confirmed.

Room-temperature valleytronic transistor

Valleytronics, based on the valley degree of freedom rather than charge, is a promising candidate for next-generation information devices beyond complementary metal-oxide-semiconductor (CMOS) technology1-4. Although many intriguing valleytronic properties have been explored based on excitonic injection or the non-local response of transverse current schemes at low temperature4-7, demonstrations of valleytronic building blocks similar to transistors in electronics, especially at room temperature, remain elusive. Here, we report a solid-state device that enables a full sequence of generating, propagating, detecting and manipulating valley information at room temperature. Chiral nanocrescent plasmonic antennae8 are used to selectively generate valley-polarized carriers in MoS2 through hot-electron injection under linearly polarized infrared excitation. These long-lived valley-polarized free carriers can be detected in a valley Hall configuration9-11 even without charge current, and can propagate over 18 μm by means of drift. In addition, electrostatic gating allows us to modulate the magnitude of the valley Hall voltage. The electrical valley Hall output could drive the valley manipulation of a cascaded stage, rendering the device able to serve as a transistor free of charge current with pure valleytronic input/output. Our results demonstrate the possibility of encoding and processing information by valley degree of freedom, and provide a universal strategy to study the Berry curvature dipole in quantum materials.

Numerical Computing Paradigm for Investigation of Micropolar Nanofluid Flow Between Parallel Plates System with Impact of Electrical MHD and Hall Current

The current study develops a novel application of numerical computing paradigm to inspect the cumulative effects of both electric and magnetic field on a micropolar nanofluid bounded by two parallel plates in a rotating system by using Adams and Explicit Runge–Kutta (RK) solvers. The steady state micropolar nanofluidics flow has been considered between parallel plates under the Hall current effect. The conventional expressions for the governing flow in terms of system of ODEs are engaged. Adams and Explicit RK-based numerical solvers have been exploited for approximate solution of the system dynamics. Accuracy, convergence and stability analyses of both numerical schemes established their correctness. The impact of the Sherwood number on the concentration profile, Nusselt number and coefficient of skin friction on temperature and velocity profiles, respectively, have been analyzed numerically along with thermophoresis investigation, rotation, Hall current and Brownian motion of micropolar nanofluid. The effect of physical quantities including viscosity, magnetic, rotating, coupling, Brownian motion, thermophoretic and micropolar fluid parameters as well as Prandtl and Schmidt numbers has been presented.

On the preparation and electrical properties of thallium bismuth diselenide crystals

Thallium bismuth diselenide (TlBiSe2) crystals were grown by an optimized process based on Bridgman technique. The material has been characterized by X-ray powder diffraction. An investigation was done on the influence of temperature on the electrical conductivity and Hall effect. The energy gap as well as the ionization energy was calculated. The electrical conductivity temperature dependence was tested to determine the dominant mechanism of conductivity in a temperature range of 203 K and 338 K. Our outcomes show an n-type semiconducting behaviour due to a degenerate state. The scattering character of the free carriers was defined by determination Hall mobilities, the concentration of carriers, activation energies of donors, the diffusion coefficient, and diffusion length of majority carriers. The performed characterization confirms that the grown TlBiSe2 crystals are narrow gap semiconductors with promising properties for practical application.

Observation of domain wall segment jump among disorders

In creep regime, a magnetic domain wall (DW) is regarded as a one-dimensional object that consists of many small segments. However, observation of such a specific segment motion has remained a challenge due to its small size. Here we present direct evidence of individual DW segment motion by employing electrical Hall measurement. When the DW is moved by a weak magnetic field, we find that the anomalous Hall effect (AHE) resistance, RAHE, exhibits random jumps between two resistance states. We confirm that the RAHE jump appears in various samples but the RAHE jump is absent when the width of sample is narrower than DW jump size. These results imply the existence of a specific segment length that governs the DW creep motion.

Temperature Dependence of the Electrical Resistivity and Hall Effect of Disordered Au$${}_{x}$$Pd$${}_{1-x}$$ Alloys

Within the framework of the coherent potential approximation for the s-d model, we compute the electrical resistivity $$\rho$$ and Hall coefficient $$R_{o}$$ of disordered paramagnetic Au $${}_{x}$$ Pd $${}_{1-x}$$ alloys, taking the electron–phonon interaction into account. Based on the example of these alloys, the mechanisms responsible for the correlation between the resistivity and its temperature coefficient (Mooij rule) and the correlation between temperature dependencies of $$\rho$$ and $$R_{o}$$ are discussed. The results are in good agreement with the experimental data.

Effect of oxygen flow rate on physical properties of Al-doped ZnO transparent conducting films prepared by reactive dc magnetron sputtering using metallic Zn:Al target

In this work, Al-doped ZnO transparent conducting thin films were prepared by a reactive dc magnetron sputtering method on slide glass substrate using single metallic Zn:Al (2 wt.% Al) target with the oxygen flow rate 1, 3, 5, 7 and 9 sccm, respectively. From XRD patterns, the films prepared at R(O2) of 1 sccm showed amorphous characteristics. In contrast, the films prepared at R(O2) of 3, 5, 7 and 9 sccm showed the preferred orientation (002) plane of hexagonal structure. Surface morphology and diameter of nanocolumns of the films were observed by AFM and FESEM. From transmittance spectra, energy gap value was found to vary between 3.24 and 3.32 eV. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The temperature-dependent conductivity was performed in the range 20-300 K. Three types of conduction mechanisms were expected. Thermally activated band conduction at the high temperature range (250-300 K), Mott variable-range hopping (Mott-VRH) at the low temperature range (100-210 K) and Efros-Shklovskii variable-range hopping (ES-VRH) at the very low temperature range (<100 K) can be found in the films prepared with different oxygen flow rate conditions. Except for the oxygen flow rate at 5 sccm, the behavior of weakly localized electrons was observed. Then, the sets of parameters explaining the properties of localized electrons in each conduction regime were determined. The results indicated that the reactive dc magnetron sputtering using a single metallic Zn:Al (2 wt.% Al) target is suitable for TCO films since it can be easily obtained at low temperatures with good physical properties.

Electrical conductivity and Hall conductivity of a hot and dense quark gluon plasma in a magnetic field: A quasiparticle approach

We estimate here the electrical and Hall conductivity using a quasiparticle approach for quark matter. We use a Boltzmann kinetic approach in presence of external magnetic field. We confront the results of model calculations with Lattice QCD simulations for vanishing magnetic field. In general electrical conductivity decreases with magnetic field. The Hall conductivity on the other hand can show a non monotonic behaviour with magnetic field due to an intricate interplay of behaviour of relaxation time and strength of the magnetic field. We argue for vanishing quark chemical potential Hall conductivity vanishes and quark gluon plasma with finite quark chemical potential can show Hall effect. Both electrical conductivity and Hall conductivity increases with increasing quark chemical potential.

Thermal Hall conductance and a relative topological invariant of gapped two-dimensional systems

We derive a Kubo-like formula for the thermal Hall conductance of a 2d lattice systems which is free from ambiguities associated with the definition of energy magnetization. We use it to define a relative topological invariant of gapped 2d lattice systems at zero temperature. Up to a numerical factor, it can be identified with the difference of chiral central charges for the corresponding edge modes. This establishes the bulk-boundary correspondence for the chiral central charge. We also show that for any Local Commuting Projector Hamiltonian the relative chiral central charge vanishes, while for free fermionic systems it is related to the zero-temperature electric Hall conductance via the Wiedemann-Franz law.

Electron and phonon transport anisotropy of ZnO at and above room temperature

Due to the lack of experimental evidence, it is not clearly known if the charge and heat transport of ZnO exhibit noticeable anisotropy at and above room temperature. Here, we measure the charge and heat transport properties of strongly crystallographically textured ZnO polycrystals at and above room temperature, up to 750 K. Our observations reveal a remarkable difference of the electrical conductivity, Hall coefficient, Seebeck coefficient, and electron mobility between the ZnO c-axis and ab-plane directions. The origin of electron transport anisotropy is discussed. We experimentally show that the lattice thermal conductivity for the c-axis direction can be at least 20% larger than that for the ab-plane direction, and the anisotropy ratio is only weakly dependent on temperature, which qualitatively agrees well with our first-principles density functional theory (DFT) calculations. Our DFT calculations also reveal that the heat transport difference between the c-axis and ab-plane directions is due to the anisotropy in phonon group velocities and Umklapp phonon scattering rates. The present work fills in the knowledge gap about ZnO. These findings can provide important implications for designing ZnO crystals to optimize the material or device performance in numerous applications where charge and/or heat transport properties are important.