Hall Effect Research Articles

Magneto-nonlinear Hall effect in time-reversal breaking system

Abstract Magneto-nonlinear Hall effect is known to be intrinsic and requires time-reversal symmetry. Here we show that a new type of magneto-nonlinear Hall effect can occur in the time-reversal breaking materials within the second-order response to in-plane electric and vertical magnetic fields. Such a Hall response is generated by the oscillation of the electromagnetic field and has a quantum origin arising from a geometric quantity associated with the Berry curvature and band velocity. We demonstrate that the massive Dirac model of LaAlO3/LaNiO3/LaAlO3 quantum well can be used to detect this Hall effect. Our work widens the theory of the Hall effect in the time-reversal breaking system by proposing a new kind of nonlinear electromagnetic response.

Electric Field-Induced Nonreciprocal Directional Dichroism in a Time-Reversal-Odd Antiferromagnet.

Antiferromagnets with broken time-reversal ( ) symmetry ( -odd antiferromagnets) have gained extensive attention, mainly due to their ferromagnet-like behavior despite the absence of net magnetization. However, certain types of -odd antiferromagnets remain inaccessible by the typical ferromagnet-like phenomena (e.g., anomalous Hall effect). One such system is characterized by a -odd scalar quantity, the magnetic toroidal monopole. To access the broken symmetry in such a system, a unique nonreciprocal optical phenomenon, electric field-induced nonreciprocal directional dichroism (E-induced NDD), is employed. Signals of E-induced NDD are successfully detected in a -odd antiferromagnet, Co₂SiO₄, whose magnetic structure is characterized by the magnetic toroidal monopole. Furthermore, by spatially resolving the E-induced NDD, spatial distributions of a pair of domain states related to one another by the operation are visualized. The domain imaging revealed the inversion of the domain pattern by applying a magnetic field, which is explained by trilinear coupling attributed to the piezomagnetic effect. The observation of E-induced NDD highlights unique functionalities of -odd antiferromagnets.

Direct observation of the enhanced photonic spin Hall effect in a subwavelength grating

Direct observation of the enhanced photonic spin Hall effect in a subwavelength grating

ENHANCING SOLAR CELL EFFICIENCY: A COMPREHENSIVE STUDY ON THE OPTO-ELECTRICAL PROPERTIES OF CUINALSE<sub>2</sub> THIN FILMS AS AN ABSORBER LAYER

CIAS (CuInAlSe2) thin films were prepared by 1-step electrodeposition on ITO coated glass substrate by varying deposition potential to obtain low cost, uniform and compact crystallinity at room temperature. The 200ml solution has been prepared and operated at 0.55V to 0.95V deposition potentials. CIAS solution has been prepared at different molarity ratios varying from 0.1M to 1.0M solution and optimum results obtained at 0.5M molar solution. The results obtained from cyclic voltammetry reveals that quaternary compound having different reduction potential can be deposited in potential range 0.5V to 0.95V. XRD technique were used to study the structural, morphological properties of thin films that shows the strong evident of its crystalline nature having tetragonal pure phase with preferred orientation at (400) plane. The result showed that single phase having good stoichiometry can be produced in this potential range. The optical properties studied by ellipsometry technique revealed that the films are highly absorbing in visible and visible-infrared region by increasing deposition potential. The band gap calculation form absorption spectra were maintained at 1.11 to 1.32 eV which was excellent for good absorbing solar materials. Hall effect application van der pauw method used for electrical properties which show promising results for production of electricity by solar cells. The variation of deposition potential offers very effective change in band gap. Structural, morphological, electrical and optical properties were carried out to establish the suitability of thin films for solar cells fabrication.

Altermagnetism in NiSi and Antiferromagnetic Candidate Materials with Non‐Collinear Spins

AbstractRecently, a new class of magnetic phenomenon, called altermagnetism, is proposed where the underlying spin configuration resembles antiferromagnetic structure, but the system violates PT (PT: Parity times Time reversal) symmetry due to the alternation of crystalline symmetry across magnetic ions. Although the original idea is proposed for the collinear spin structure, a recent report by Cheong et al. has suggested that antiferromagnetic materials with non‐collinear spin structure and local alternation of crystalline arrangement can also manifest altermagnetism. Besides breaking the PT symmetry, altermagnetic compounds are also expected to exhibit anomalous Hall effects of odd orders. Here, possible candidates are discussed in this regard. One example is nickel monosilicide, which is recently shown to exhibit high temperature antiferromagnetism with non‐collinear spin structure. It fulfills both criteria of breaking the PT symmetry and manifesting nonlinear anomalous Hall effect. In addition to NiSi, other potential antiferromagnetic materials are also discussed with non‐collinear spin configuration for the exploration of altermagnetic states.

Recent progress on quantum Hall effect in unconventional material systems

The quantum Hall effect (QHE) is an elegant macroscopic manifestation of quantum mechanical behavior on the microscopic scale, and its discovery is a major triumph in condensed matter physics. While QHE has been predominantly observed in two-dimensional electron gas (2DEG) systems, recently, many efforts have been devoted to searching for the QHE in unconventional materials platforms beyond the classical framework to extend the horizon of the QHE. In this Perspective, we highlight recent important experimental discoveries and progress on the QHE material platforms beyond 2DEG platforms, such as three-dimensional QHE, Weyl-orbit-based QHE, and QHE in two-dimensional insulators. In addition, novel phenomena arising from incorporating QHE with other exotic quantum states, such as topological band structures and superconductivity, will be discussed. We also present the emerging field-free version of QHE–quantum anomalous Hall effect on its transport characteristics, working principles as well as potential applications in quantum metrology and quantum computing. With the exploration of these unconventional QHE hosts and the development of the understanding of new physics arising from the interplay between QHE and other physical systems, QHE will continue to play a critical role in both advancing fundamental physics and developing next-generation quantum technologies.

Controllable z-Polarized Spin Current in Artificially Structured Ferromagnetic Oxide with Strong Spin-Orbit Coupling.

Realizing field-free switching of perpendicular magnetization by spin-orbit torques is crucial for developing advanced magnetic memory and logic devices. However, existing methods often involve complex designs or hybrid approaches, which complicate fabrication and affect device stability and scalability. Here, we propose a novel approach using z-polarized spin currents for deterministic switching of perpendicular magnetization through interfacial engineering. We fabricate La0.67Sr0.33MnO3-SrIrO3 (LSIMO) thin films with robust spin-orbit coupling and ferromagnetic order through orbital and lattice reconstruction, integrating SrIrO3 and La0.67Sr0.33MnO3 materials. Our investigation reveals that y- and z-polarized spin currents, driven by the spin Hall and spin-orbit precession effects, enable field-free switching of perpendicular magnetization. Notably, the z-polarized spin currents are tunable via the in-plane magnetization of LSIMO. These findings present a promising pathway for the development of energy-efficient spintronic devices, offering improved performance and scalability.

Strain manipulation of spin-polarized topological phase in WSe2/CrI3 heterostructure

Here, based on first-principles calculations and topological analysis, we show that the spin-polarized topological phase is present in a van der Waals (vdW) heterostructure WSe2/CrI3. We reveal that magnetism induced by proximity effects in the heterostructure breaks the time-reversal symmetry (TRS) and thus induces gapped topological edge states, exhibiting the TRS-breaking quantum spin Hall (QSH) effect. By applying a stress field, the WSe2/CrI3 heterostructure manifests enhanced spin polarization, Rashba splitting, and tunable bandgap. The TRS-breaking QSH effect observed in the WSe2/CrI3 heterostructure exhibits remarkable robustness against interlayer shearing. The distinct anisotropy associated with in-plane strain provides precise manipulation strategies for bandgap engineering. Notably, in-plane tensile strain can significantly increase the nontrivial bandgap by up to 98 meV, suggesting the magnetic WSe2/CrI3 heterostructure represents an outstanding platform for achieving the TRS-breaking QSH effect at room temperature. Our findings provide a theoretical foundation for the development of low-dissipation spintronic nanodevices.

High-performance, self-powered ZnO NWs-ZnSe heterojunction photodetectors for superior visible and near-infrared detection

Abstract We present the development of a type-II heterojunction photodetector (PD) comprising Ag/ZnO nanowires (NWs)/ZnSe/In, fabricated on a commercially available Si substrate. ZnO NWs were hydrothermally synthesized on thermally evaporated ZnSe thin films, with scanning electron microscopy (SEM) analysis revealing uniform, vertically aligned ZnO NWs on the ZnSe layer. Cross-sectional SEM imaging determined the thickness of the In/ZnSe thin film to be approximately 460 nm, with ZnO NWs exhibiting an average diameter of ∼161 nm. Structural analysis of the ZnSe thin film, annealed at 370 °C in an ambient environment, identified a prominent ZnSe peak at 27.48° alongside peaks at 30.98° and 33.21° corresponding to In2O3 and ZnSeO3, respectively. The ZnO NWs, under similar annealing conditions, displayed a strong (002) peak, confirming vertical growth. Hall effect measurements revealed a transition from p-type carriers in as-deposited ZnSe thin films to n-type in the annealed ZnSe and ZnO NWs, attributed to the formation of In2O3 as evidenced by XRD. The PD exhibited the highest photoresponse under IR illumination (950 nm), surpassing responses to green (515 nm) and blue (456 nm) LEDs, with a short-circuit current (I sc) of −26 μA and an open-circuit voltage (V oc) of +80 mV, characteristic of a self-powered device. In contrast, minimal photoresponse was observed in a Schottky-type Ag/ZnSe/In junction on the Si substrate. The photoresponse mechanism was elucidated using an energy band diagram, while density functional theory simulations using Vienna ab initio simulation package provided a strong correlation with the experimental data, validating the structural and electronic properties of the heterojunction.

Self-powered ultraviolet position-sensitive detectors based on PrNiO3/Nb-doped SrTiO3 p–n junctions

Position-sensitive detectors based on the lateral photovoltaic effect have been widely used in optical engineering for the measurement of position, distance, and angles. However, self-powered ultraviolet position-sensitive detectors with high sensitivity and fast response are still lacking due to the difficulty associated with the fabrication of p-type wide bandgap semiconductors, which hinders their further design and enhancement. Here, the influence of band structures and interfacial transport properties on the performance of self-powered ultraviolet position-sensitive detectors based on PrNiO3/Nb:SrTiO3p–n junctions is systematically investigated. Large position sensitivity and fast relaxation time of the lateral photovoltaic effect were observed up to 400 K in the perovskite-based ultraviolet position-sensitive detectors. Hall effect measurements revealed that the transport of photoexcited carriers occurs mainly through the interface of the PrNiO3/Nb:SrTiO3 junctions, resulting in a fast response and a stable photovoltaic effect. This study presents insights and avenues for designing self-powered perovskite oxide ultraviolet position-sensitive detectors with enhanced photoelectric performance.

Planar Hall Effect in Quasi-Two-Dimensional Materials

Planar Hall Effect in Quasi-Two-Dimensional Materials

Ferromagnetism and structural phase transition in monoclinic FeGe film

Binary compound FeGe hosts multiple structures, from cubic and hexagonal to monoclinic. Compared to the well-known skyrmion lattice in the cubic phase and the antiferromagnetic charge–density wave in the hexagonal phase, the monoclinic FeGe is less explored. Here, we synthesized the monoclinic FeGe films on Al2O3 (001) and studied their structural, magnetic, and transport properties. X-ray diffraction and transmission electron microscopy characterizations indicate that the FeGe films are epitaxial to the substrate. Unlike the antiferromagnetic bulk, the monoclinic FeGe films are ferromagnetic with Curie temperature as high as ∼800 K, contributing to the anomalous Hall effect in the transport measurements. Similar to the hexagonal FeGe, we captured a structural phase transition in the monoclinic FeGe films at ∼100 K in real and reciprocal spaces by transmission electron microscope. Our work enriches the phase diagram of the FeGe family and suggests that FeGe offers an ideal platform for studying multiphase transitions and related device applications.

Extreme Optical Chirality from Plasmonic Nanocrystals on a Mirror.

Metal nanocrystals synthesized in achiral environments usually exhibit no chiroptical effects. However, by placing nominally achiral nanocrystals 1.3 nm above gold films, we find giant chiroptical effects, reaching anisotropy factors as high as g ≈ 0.9 for single nanodecahedra placed on a gold mirror (NDoM). We show that this is a general phenomenon depending on the geometry, demonstrating it for various nanocrystal shapes. Theoretical modeling reveals that tiny chiral imperfections are strongly enhanced by edge modes in the gap, which coherently superpose with in-plane dipoles to generate strong chiroptical signatures. This phenomenon results in photonic spin Hall effects and distinctive chiral scattering patterns.

Nonvolatile Magnonics in Bilayer Magnetic Insulators.

Nonvolatile control of spin order or spin excitations offers a promising avenue for advancing spintronics; however, practical implementation remains challenging. In this Letter, we propose a general framework to realize electrical control of magnons in 2D magnetic insulators. We demonstrate that in bilayer ferromagnetic insulators with strong spin-layer coupling, the electric field Ez can effectively manipulate the spin exchange interactions between the layers, enabling nonvolatile control of the corresponding magnons. Notably, in this bilayer, Ez can induce nonzero Berry curvature and orbital moments of magnons, the chirality of which are coupled to the direction of Ez. This coupling facilitates Ez manipulation of the corresponding magnon valley and orbital Hall currents. Furthermore, such bilayers can be easily engineered, as demonstrated by our density-functional-theory calculations on Janus bilayer Cr-based ferromagnets. Our work provides an important step toward realizing nonvolatile magnonics and paves a promising way for future magnetoelectric coupling devices.

Topological orbital Hall effect caused by skyrmions and antiferromagnetic skyrmions

The topological Hall effect is a hallmark of topologically non-trivial magnetic textures such as magnetic skyrmions. It quantifies the transverse electric current that is generated once an electric field is applied and occurs as a consequence of the emergent magnetic field of the skyrmion. Likewise, an orbital magnetization is generated. Here we show that the charge currents are orbital polarized even though the conduction electrons couple to the skyrmion texture via their spin. The topological Hall effect is accompanied by a topological orbital Hall effect even for s electrons without spin-orbit coupling. As we show, antiferromagnetic skyrmions and antiferromagnetic bimerons that have a compensated emergent field, exhibit a topological orbital Hall conductivity that is not accompanied by charge transport and can be orders of magnitude larger than the topological spin Hall conductivity. Skyrmionic textures serve as generators of orbital currents that can transport information and give rise to considerable orbital torques.

Topochemical Synthesis and Electronic Structure of High-Crystallinity Infinite-Layer Nickelates on an Orthorhombic Substrate.

Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the "parent" phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO2. This is achieved through the growth of a perovskite precursor phase (NdNiO3) of superior crystallinity on the NdGaO3 substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this "non-doped" phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5d and Ni 3d orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.

Effect of growth temperature on the physical properties of kesterite Cu2ZnSnS4 (CZTS) thin films

Spray pyrolysis technique was used to deposit Cu2ZnSnS4 (CZTS) thin films onto SLG substrates. The effect of substrate temperature (Tsub), ranging from 300°C to 390°C on their structure and optoelectronic properties. The structural properties reveal that all the prepared CZTS films have a kesterite structure, with a preferential orientation along (112) plane, and presence of secondary phases. XRD data indicated an improvement in crystallinity with an increase in average crystallites size, from 12.29 to 24.73 nm, while Tsub rise up to 390 °C. Raman spectra reveal CZTS formation, with two vibrational modes observed at 335 and 373 cm−1 along with a small Raman peak at 472 cm−1 associated to the Cu2S phase. Transmittance spectra show low values in the visible range with an absorption coefficient of 105 cm−2, The band gap energy (Eg) of the sprayed-CZTS films was consistently found to decrease from 1.6 to 1.38 eV as Tsub is increased from 300 to 390 °C. Hall effect measurements revealed p-type conductivity for all the samples, and the electrical conductivity increased from 1.8 to 150 (Ω.cm)−1 with substrate temperature (Tsub). Overall, experimental results demonstrate that grown CZTS thin films can be considered as a promising absorber material in solar cell devices.

Magnetic topological Weyl fermions in half-metallic In2CoSe4

Magnetic Weyl semimetals (WSMs) have recently attracted much attention due to their potential in realizing strong anomalous Hall effects. Yet, how to design such systems remains unclear. Based on first-principles calculations, we show here that the ferromagnetic half-metallic compound In2CoSe4has several pairs of Weyl points and is hence a good candidate for magnetic WSM. These Weyl points would approach the Fermi level gradually as the HubbardUincreases, and finally disappear after a critical valueUc. The range of the HubbardUthat can realize the magnetic WSM state can be expanded by pressure, manifesting the practical utility of the present prediction. Moreover, by generating two surface terminations at Co or In atom after cleaving the compound at the Co-Se bonds, the nontrivial Fermi arcs connecting one pair of Weyl points with opposite chirality are discovered in surface states. Furthermore, it is possible to observe the nontrivial surface state experimentally, e.g. angle-resolved photoemission spectroscopy measurements. As such, the present findings imply strongly a new magnetic WSM which may host a large anomalous Hall conductivity.

Two-carrier model-fitting of Hall effect in semiconductors with dual-band occupation: A case study in GaN two-dimensional hole gas

Two-carrier model-fitting of Hall effect in semiconductors with dual-band occupation: A case study in GaN two-dimensional hole gas

Magnetic-proximity-induced anomalous Hall effect at the EuO/Sb2Te3 interface

Time-reversal symmetry breaking of a topological insulator phase generates zero-field edge modes which are the hallmark of the quantum anomalous Hall effect (QAHE) and of possible value for dissipation-free switching or non-reciprocal microwave devices. But present material systems exhibiting the QAHE, such as magnetically doped bismuth telluride and twisted bilayer graphene, are intrinsically unstable, limiting their scalability. A pristine magnetic oxide at the surface of a TI would leave the TI structure intact and stabilize the TI surface, but epitaxy of an oxide on the lower-melting-point chalcogenide presents a particular challenge. Here we utilize pulsed laser deposition to grow (111)-oriented EuO on vacuum cleaved and annealed Sb2Te3(0001) surfaces. Under suitable growth conditions, we obtain a pristine interface and surface, as evidenced by x-ray reflectivity and scanning tunneling microscopy, respectively. Despite bulk transport in the thick (2 mm) Sb2Te3layers, devices prepared for transport studies show a strong AHE, the necessary precursor to the QAHE. Our demonstration of EuO-Sb2Te3epitaxy presents a scalable thin film approach to realize QAHE devices with radically improved chemical stability as compared to competing approaches.