Hall Effect Research Articles

Impacts of Hall and Ion Slip Currents with Cattaneo { Christov Features on the Peristaltic Blood Flow of Sisko Micropolar Nano uid inside an Annulus through a Porous Medium

Impacts of Hall and Ion Slip Currents with Cattaneo { Christov Features on the Peristaltic Blood Flow of Sisko Micropolar Nano uid inside an Annulus through a Porous Medium

Predictions of spin-valley properties in ferromagnetic Janus 2H-CeXY (X, Y = Cl, Br, I, X ≠ Y) monolayers: Merger of valleytronics with spintronics

In this work, the Janus 2H-CeXY monolayers are predicted as 2D intrinsic ferrovalley materials with bipolar ferromagnetic (FM) semiconductor characters, high Tc of 511–540 K, robust in-plane/perpendicular magnetic anisotropy (IMA/PMA) and spontaneous valley polarization through first-principles calculations. The d-p-d indirect exchange interaction between the Ce atom and X(Y) atoms is responsible for the observed FM ordering. Applying the biaxial strain ε from −6 % to 6 %, the Janus 2H-CeXY monolayers keep energy bandgap and large magnetic anisotropy. While a transition from PMA to IMA character is observed for the 2H-CeBrCl monolayer, which is due to the competition between Ce-p/d and Br/Cl-p orbitals. The intrinsic magnetic interaction and strong SOC effect induce a large spontaneous valley polarization of 29.1–78.7 meV for the Janus 2H-CeXY monolayers, which is also robust under various ε. Besides, the anomalous valley Hall effect (AVHE) can be observed due to the nonzero Ωz(k) induced by the broken space/time-reversal symmetry. Overall, the Janus 2H-CeXY monolayers provides a new candidate for the spintronic and valleytronic devices.

Noncoplanar magnetic structures in Mn4N epitaxial films evaluated by alternating magnetic force microscopy

Abstract Noncoplanar magnetic structures in the Mn4N epitaxial thin films grown on the 001-oriented MgO and SrTiO3 (STO) substrates were studied, based on the measurements of topological Hall effect (THE) and the observation of magnetic domain nucleation. The typical nucleation diameter of domain was determined using an alternating magnetic force microscope, which proved advantageous for the visualization of the domain with an out-of-plane magnetic component. The nucleation diameter of the domains on the MgO substrate were ∼150 nm for the thickness of 30 nm and ∼110 nm for 10 nm, while ∼130 nm for 30 nm on the STO substrate. The value of THE was one or two orders of magnitude larger than that estimated based on the nucleation diameter, indicating that the existence of a noncoplanar magnetic structure is the primary factor contributing to the THE in the Mn4N films, comparing to the effect from domain nucleation. The noncoplanar magnetic structure was more pronounced with decreasing thickness and substrate-induced strain.

Solution‐Processed Zinc‐Tin‐Based Ternary Oxide Electron Transport Layers for Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have acquired popularity owing to their high efficiency, ease of fabrication, and affordability. In this context, the development of electron transport layers (ETLs) for highly efficient planar photovoltaic devices has received considerable attention. This study investigates the potential of zinc‐tin‐based ternary metal oxide ETLs for application in planar PSCs. Solution‐processed methods are used to fabricate crystalline zinc stannate (Zn2SnO4), amorphous zinc‐tin oxide (ZTO), and Zn2SnO4/ZTO‐based bilayer films, and their structural, morphological, and optoelectronic properties are thoroughly studied. X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) images show enhanced crystallite size and better surface morphology of perovskite films deposited on bilayer ETL. Photoluminescence (PL) studies and Hall effect measurements reveal superior charge extraction, improved charge carrier mobility (21.84 cm2 V−1 s−1) and enhanced n‐type conductivity in the bilayer ETL. Moreover, contact angle analysis of perovskite layer deposited on bilayer ETL shows increased resistance to moisture erosion (52.20°), which is particularly significant given the detrimental effects moisture can have on the performance of PSCs.

Ultra-low Gilbert damping and self-induced inverse spin Hall effect in GdFeCo thin films

Ferrimagnetic materials have garnered significant attention due to their broad range of tunabilities and functionalities in spintronics applications. Among these materials, rare earth-transition metal GdFeCo alloy films have been the subject of intensive investigation due to their spin-dependent transport properties and strong spin–orbit coupling. In this report, we present self-induced spin-to-charge conversion in single-layer GdFeCo films of different thicknesses via an inverse spin Hall effect. A detailed investigation of spin dynamics was carried out using broadband ferromagnetic resonance measurements. The anisotropy constant and the effective g-factor are found to decrease with thickness, and they become nearly constant for thicknesses beyond 25 nm. A remarkably low damping constant of 0.0029 ± 0.0003 is obtained in the 43 nm-thick film, which is the lowest among all previous reports on GdFeCo thin films. Furthermore, we have demonstrated a self-induced inverse spin Hall effect, which has not been reported so far in a single-layer of GdFeCo thin films. Our analysis shows that the inverse spin Hall effect becomes increasingly dominant over the spin rectification effect with increasing film thickness. The in-plane angular-dependent voltage measurement of the 43 nm-thick film reveals a spin pumping voltage of 1.64 μV. The observation of spin-to-charge current conversion could be due to the high spin–orbit coupling element Gd in the film as well as the interface between GeFeCo/Ti and substrate/GdFeCo of the films. Our findings underscore the potential of GdFeCo as a prime ferrimagnetic material for emerging spintronic technologies.

Impact of Cr doping on Hall resistivity and magnetic anisotropy in SrRuO3 thin films

Hall effects, including anomalous and topological types, in correlated ferromagnetic oxides provide an intriguing framework to investigate emergent phenomena arising from the interaction between spin-orbit coupling and magnetic fields. SrRuO3is a widely studied itinerant ferromagnetic system with intriguing electronic and magnetic characteristics. The electronic transport of SrRuO3is highly susceptible to the defects (O/Ru vacancy, chemical doping, ion implantation), and interfacial strain. In this regard, we investigate the impact of Cr doping on the magnetic anisotropy and the Hall effect in SrRuO3thin films. The work encompasses a comprehensive analysis of the structural, spectroscopic, magnetic, and magnetotransport properties of Cr-doped SrRuO3films grown on SrTiO3(001) substrates. Cross-sectional transmission electron microscopy reveals a sharp and coherent interface between the layers. Notably, perpendicular magnetic anisotropy is preserved in doped films with thicknesses up to 113 nm. The resistivity exhibits aT2dependence below the Curie temperature, reflecting the influence of disorder and correlation-induced localization effects. Interestingly, in contrast to the undoped parent compound SrRuO3, an anomaly in the Hall signal has been observed up to a large thickness (56 nm) attributed to the random Cr doping and Ru vacancy. Based on our measurements, a field-temperature (H - T) phase diagram of anomalous Hall resistivity is constructed.

Unconventional Anomalous Hall Effect Driven by Self-Intercalation in Covalent 2D Magnet Cr2Te3.

Covalent 2D magnets such as Cr2Te3, which feature self-intercalated magnetic cations located between monolayers of transition-metal dichalcogenide material, offer a unique platform for controlling magnetic order and spin texture, enabling new potential applications for spintronic devices. Here, it is demonstrated that the unconventional anomalous Hall effect (AHE) in Cr2Te3, characterized by additional humps and dips near the coercive field in AHE hysteresis, originates from an intrinsic mechanism dictated by the self-intercalation. This mechanism is distinctly different from previously proposed mechanisms such as topological Hall effect, or two-channel AHE arising from spatial inhomogeneities. Crucially, multiple Weyl-like nodes emerge in the electronic band structure due to strong spin-orbit coupling, whose positions relative to the Fermi level is sensitively modulated by the canting angles of the self-intercalated Cr cations. These nodes contribute strongly to the Berry curvature and AHE conductivity.This component competes with the contribution from bands that are less affected by the self-intercalation, resulting in a sign change in AHE with temperature and the emergence of additional humps and dips. The findings provide compelling evidence for the intrinsic origin of the unconventional AHE in Cr2Te3and further establish self-intercalation as a control knob for engineering AHE in complex magnets.

Quantum description of Fermi arcs in Weyl semimetals in a magnetic field

For a Weyl semimetal (WSM) in a magnetic field, a semiclassical description of the Fermi-arc surface state dynamics is usually employed for explaining various unconventional magnetotransport phenomena, e.g., Weyl orbits, the three-dimensional quantum Hall effect, and the high transmission through twisted WSM interfaces. For a half-space geometry, we determine the low-energy quantum eigenstates for a four-band model of a WSM in a magnetic field perpendicular to the surface. The eigenstates correspond to in- and out-going chiral Landau level (LL) states, propagating (anti)parallel to the field direction near different Weyl nodes, which are coupled by evanescent surface-state contributions generated by all other LLs. These replace the Fermi arc in a magnetic field. Computing the phase shift accumulated between in- and out-going chiral LL states, we compare our quantum-mechanical results to semiclassical predictions. We find quantitative agreement between both approaches. Published by the American Physical Society 2024

Yb5Rh6Sn18: a valence fluctuating system with ultra-low thermal conductivity.

Yb5Rh6Sn18 crystallizes with a unique structural arrangement [space group P42/nmc, a = 9.6997(4) Å, c = 13.7710(7) Å], which is related with primitive cubic Yb3Rh4Sn13 and body-centered tetragonal (Sn1-xTbx)Tb4Rh6Sn18 types. X-ray absorption spectroscopy showed that Yb atoms exhibit temperature-dependent valence fluctuations (VF) (i.e., intermediate valence state). Its complex mechanism is corroborated by the fact that the well-pronounced maximum in magnetic susceptibility can only be fairly described by the Bickers-Cox-Wilkins model developed for a J = 3/2 multiplet, atypical for Yb ions. Both Hall and Seebeck coefficients revealed a switch of the sign, indicating the change of charge carrier type from electrons to holes between 120 and 220 K. Both these effects together with electrical resistivity and theoretical DFT calculations confirm Yb5Rh6Sn18 to be a metal, which disobeys the free electron gas theory. 'Rattling' motion of Sn1 atoms within the enlarged 16-vertices distorted Frank-Kasper polyhedra, concluded from the specific heat measurements, is argued to be the main reason for the appearance of a phonon resonance behavior, resulting in an ultra-low thermal conductivity in the studied stannide.

Topological Fermiology of gate-tunable Rashba electron gases.

By introducing first-order quantum phases as topological invariants, recent symmetry analysis-based theories have reinvigorated magnetic quantum oscillations as a versatile quantum probe for unfolding the Fermi surface topology along with the geometry information, i.e., topo-Fermiology. Here, we demonstrate the comprehensive topo-Fermiology of high-mobility Rashba two-dimensional electron gases with ultragate tunability of spin-orbit coupling parameter in few-layer black arsenic. The remarkable consistencies with the key theoretical predictions of period doubling in quantum oscillations, gate-tunable aperiodic beating patterns, and the symmetry-enforced Landau level crossing phenomena controlled by the competition between Rashba coupling and the Zeeman interaction, which ultimately manifests as all odd-filling factor integer quantum Hall effect with superb sensitivity to quantum phases, establish topo-Fermiology as an indispensable methodology for studying topological quantum matters.

Confined Magnetization at the Sublattice-Matched Ruthenium Oxide Heterointerface.

Creating a heterostructure by combining two magnetically and structurally distinct ruthenium oxides is a crucial approach for investigating their emergent magnetic states and interactions. Previously, research has predominantly concentrated on the intrinsic properties of the ferromagnet SrRuO3 and recently discovered altermagnet RuO2 solely. Here, the study engineers an ultrasharp sublattice-matched heterointerface using pseudo-cubic SrRuO3 and rutile RuO2, conducting an in-depth analysis of their spin interactions. Structurally, to accommodate the lattice symmetry mismatch, the inverted RuO2 layer undergoes an in-plane rotation of 18 degrees during epitaxial growth on SrRuO3 layer, resulting in an interesting and rotational interface with perfect crystallinity and negligible chemical intermixing. Performance-wise, the interfacial layer of 6 nm in RuO2 adjacent to SrRuO3 exhibits a nonzero magnetic moment, contributing to an enhanced anomalous Hall effect (AHE) at low temperatures. Furthermore, the observations indicate that in contrast to SrRuO3 single layers, the AHE of [(RuO2)15/(SrRuO3)n] heterostructures show nonlinear behavior and reaches its maximum when the SrRuO3 thickness reaches tens of nm. These results suggest that the interfacial magnetic interaction surpasses that of all-perovskite oxides (≈5-unit cells). This study underscores the significance and potential applications of magnetic interactions based on the crystallographic asymmetric interfaces in the design of spintronic devices.

Designing giant Hall response in layered topological semimetals

Noncoplanar magnets are excellent candidates for spintronics. However, such materials are difficult to find, and even more so to intentionally design. Here, we report a chemical design strategy that allows us to find a series of noncoplanar magnets—Ln3Sn7 (Ln = Dy, Tb)—by targeting layered materials that have decoupled magnetic sublattices with dissimilar single-ion anisotropies and combining those with a square-net topological semimetal sublattice. Ln3Sn7 shows high carrier mobilities upwards of 17,000 cm2 ⋅ V−1 ⋅ s−1, and hosts noncoplanar magnetic order. This results in a giant Hall response with an anomalous Hall angle of 0.17 and Hall conductivity of over 42,000 Ω−1 ⋅ cm−1—a value over an order of magnitude larger than the established benchmarks in Co3Sn2S2 and Fe thin films.

Modulation of the Nernst Thermoelectrics by Regulating the Anomalous Hall and Nernst Angles.

The large anomalous Nernst effect in magnetic Weyl semimetals is one of the most intriguing transport phenomena, which draws significant attention for its potential applications in topological thermoelectrics. Despite frequent reports of substantial anomalous Nernst conductivity (ANC), methods to optimize Nernst thermoelectrics remain limited. The research reveals that the magnitude of the ANC is directly related to the sum of the anomalous Nernst and Hall angles. While the sign of the anomalous Hall angle is relatively stable in a certain material, the sign of the anomalous Nernst angle can be intrinsically tuned. Therefore, the ANC can be effectively optimized by regulating these angles to work in concert. This finding is verified by experimental modulation from iron-doped magnetic topological material Co3Sn2S2. Additionally, a robust TlnT scaling law of the ANC over the temperature range of 40 to 140 K is observed in all studied samples, suggesting an intrinsic origin of the ANC. Considering the common opposite sign of the anomalous Nernst and Hall angles in many magnetic topological materials, the research offers an applicable scheme for optimizing the Nernst thermoelectrics.

Proposal for bulk measurement of braid statistics in the fractional quantum Hall effect

Proposal for bulk measurement of braid statistics in the fractional quantum Hall effect

The quantum anomalous Hall effect and strong robustness in two-dimensional p-state Dirac half-metals Y3X2 (Y = Li, Na; X = Se, Te).

Based on first-principles calculations, we have predicted a novel group of 2D p-state Dirac half-metal (DHM) materials, Y3X2 (Y = Li, Na; X = Se, Te) monolayers. All the monolayers exhibit intrinsic ferromagnetism. Among them, Li3Te2 and Na3Se2 open topologically nontrivial band gaps of 4.0 meV and 5.0 meV considering spin-orbit coupling (SOC), respectively. The Curie temperature of Li3Te2 is 355 K. The non-zero Chern number and the presence of edge states further confirm that the Li3Te2 monolayer is a room-temperature ferromagnetic material and a quantum anomalous Hall (QAH) insulator. Additionally, it is found that Y3X2 (Y = Li, Na; X = Se, Te) monolayers exhibit strong robustness against strain and electric fields. Finally, we have proposed the growth of Y3X2 (Y = Li, Na; X = Se, Te) monolayers on h-BN substrates, which shows promise for experimental synthesis. Our research indicates that Y3X2 (Y = Li, Na; X = Se, Te) monolayers exhibit strong robustness as DHMs, showcasing significant potential for realizing the intrinsic quantum anomalous Hall effect (QAHE).

Topological Hall effect instigated in kagome Mn3–xSn due to Mn-deficit induced noncoplanar spin structure

Magnetic topological semimetals are manifestations of the interplay between electronic and magnetic phases of matter, leading to peculiar characteristics such as the anomalous Hall effect (AHE) and the topological Hall effect (THE). Mn3Sn is a time-reversal symmetry-broken magnetic Weyl semimetal showing topological characteristics within the Kagome lattice network. This study reveals a large THE in Mn2.8Sn (6% Mn deficit Mn3Sn) at room temperature in thexy-plane, despite being an antiferromagnet. We argue that the magnetocrystalline anisotropy induced noncoplanar spin structure is responsible for the observed THE in these systems. Further, the topological properties of these systems are highly anisotropic, as we observe a large AHE in thezx-plane. We find that Fe doping at the Mn site, Mn3-xFexSn (x= 0.2, 0.25, & 0.35), tunes the topological properties of these systems. These findings promise the realization of potential topotronic applications at room temperature.

Quantum Hall effect in a CVD-grown oxide

Two-dimensional (2D) electron systems are promising for investigating correlated quantum phenomena. In particular, 2D oxides provide a platform that can host various quantum phases such as quantized Hall effect, superconductivity, or magnetism. The realization of such quantum phases in 2D oxides heavily relies on dedicated heterostructure growths. Here we show the integer quantum Hall effect achieved in chemical vapor deposition grown Bi2O2Se - a representative member of a more accessible oxide family. A single or few subband 2D electron system can be prepared in thin films of Bi2O2Se, where the film thickness acts as the key subband design parameter and the occupation is determined by the electric field effect. This oxide platform exhibits characteristic advantages in structural flexibility due to its layered nature, making it suitable for scalable growth. The unique small mass distinguishes Bi2O2Se from other high-mobility oxides, providing a new platform for exploring quantum Hall physics in 2D oxides.

Handedness manipulation of propagating antiferromagnetic magnons

Antiferromagnetic magnons possess a distinctive feature absent in their ferromagnetic counterparts: the presence of two distinct handedness modes, the right-handed (RH) and left-handed (LH) precession modes. The magnon handedness determines the sign of spin polarization carried by the propagating magnon, which is indispensable for harnessing the diverse functionalities in magnonic devices, such as data encoding, magnon polarization-based logic systems, and quantum applications involving magnons. However, the control of coherently propagating magnon handedness in antiferromagnets has remained elusive. Here we demonstrate the manipulation and electrical readout of propagating magnon handedness in perpendicularly magnetized synthetic antiferromagnets (SAF). We find that the antiferromagnetic magnon handedness can be directly identified by measuring the inverse spin Hall effect (ISHE) voltage, which arises from the spin pumping effect caused by the propagating antiferromagnetic magnons in the SAF structure. The RH and LH modes of the magnon can be distinguishable when the SAF structure is sandwiched by heavy metals with the same sign of spin Hall angle. This work unveils promising avenues for harnessing the unique properties of antiferromagnetic magnons.

Spin-Orbit Coupling Driven Magnetic Response in Altermagnetic RuO2.

The recent prediction of the new magnetic class, altermagnetism, has drawn considerable interest, fueled by its potential to host novel phenomena and to be utilized in next-generation spintronics devices. Among many promising candidates, rutile RuO2 is a prototypical candidate for realizing the prospects of altermagnetism. However, the experimental studies on RuO2 are still in the early stages. In this study, the magnetic responses in RuO2 film are investigated by the Planar Hall effect (PHE). By rotating the external field (Hext), the PHE exhibits twofold behaviors. Moreover, the planar Hall conductivity shows a nonlinear response to the Hext. These observed features in PHE resemble those in ferromagnet and topologically nontrivial systems, suggesting the field-induced magnetic response in rutile antiferromagnet. The work provides a strategy for detecting intriguing magnetic responses in altermagnetic materials, promoting further research in altermagnet-based spintronics and novel phenomena.

Semimetallization induced Hall anomaly in doped polymers

Hall anomaly related to deviations in Hall carrier concentrations have always been recognized as signs of charge incoherence in organic semiconductors, which lack ordered lattices. In this paper, we show that the Hall carrier concentration anomaly in doped polymers might be a result of semimetallization. Based on the observation of semimetal-like states, a dual-channel model, in which electrons and holes compensate the Hall voltages of each other, is employed to account for the anomaly. Observations of possible nonlinear Hall effect and temperature dependent Hall signs further support the origin of Hall anomaly from semimetal states. Published by the American Physical Society 2024