Hall Resistance Research Articles

Investigation of magnetic and transport properties of GdSbSe.

We report the detailed investigation of the magnetic, transport, and magnetocaloric effects (MCEs) of GdSbSe by magnetic susceptibilityχ(T), isothermal magnetizationM(H), resistivityρ(T,H), and heat capacityCp(T)measurements, crystallizing in the ZrSiS-type tetragonal crystal system with space group P4/nmm. Temperature-dependent magnetic susceptibility measurements revealed long-range antiferromagnetic ordering with two additional magnetic anomalies below Néel temperature (TN≈8.6K), corroborated through magnetocaloric and specific heat studies. Isothermal magnetization measurements unveil hidden metamagnetic signatures through a clear deviation from linearity. In addition, the enhanced value of the Sommerfeld coefficient (γ= 152(5) mJ mol-1K2) suggests strong electronic correlations in GdSbSe. The entropy of magnetization derived from magnetic isotherms unfolds the field-induced transition from Inverse MCE to Conventional MCE. The detailed transport properties indicate a semimetallic behavior, strongly coupled with magnetic order. Furthermore, the linear field dependence of MR in the high-field region anticipate the possibility of Dirac-like dispersion. Deviations from Kohler's rule and non-linear Hall resistivity suggest the multiband nature of GdSbSe.

Graphene quantum Hall resistance standard for realizing the unit of electrical resistance under relaxed experimental conditions

Graphene quantum Hall resistance standard for realizing the unit of electrical resistance under relaxed experimental conditions

Design of spike-timing-dependent plasticity synapses based on CoPt-SOT device and its application in all-spin spiking neural network

Spintronic could be used to simulate synapses or neurons due to its multistate storage characteristics. In this work, a reliable design of all-spin spiking neural networks (SNN) based on spin–orbit torque (SOT) devices has been proposed in A1 CoPt single layer. The CoPt-SOT devices exhibited field-free SOT switching, and the magnetization reversal mechanism was inferred to be a combination of domain nucleation and domain-wall propagation as observed through magneto-optical Kerr microscopy images. Moreover, the current-induced SOT switching process of the device exhibited stable multistate magnetic switching behavior, which can be controlled by varying the amplitude and pulse width of the current pulse. Meanwhile, the spike-timing-dependent plasticity (STDP) curve was inverted when the SOT switching polarity was reversed by different magnetic fields, and the change in anomalous Hall resistances (ΔRH) in the STDP curve was linearly related to the SOT switching ratio. In addition, at the zero magnetic field, we constructed an all-spin SNN using STDP synapses and leaky integrate-and-fire neurons of CoPt-SOT devices. The handwritten digits recognition rate of this all-spin SNN network was 89.9%. These results substantiate that the CoPt single layer represents a promising hardware solution for high-performance neuromorphic computing, with applicability in the domain of SNN.

Perpendicular magnetic anisotropy of Pd/Co2MnSi/Co/Pd multilayer

Abstract Pd/Co2MnSi(CMS)/Co/Pd multilayer films were designed based on the idea of combining highly spin-polarized materials with strong perpendicular magnetic anisotropy(PMA) films. The PMA of Pd/CMS/Co/Pd multilayer films were studied by optimizing the growth conditions and thickness of each film layer. The optimal structure of the multilayer films were Pd(6 nm)/CMS(5 nm)/Co(2 nm)/Pd(1 nm). Its Abnormal Hall resistance (R Hall), coercivity (H c) and effective magnetic anisotropy constant (K eff) are 0.08Ω, 284Oe and 1.36Merg/cm3, respectively, which are 100%, 492%, and 183% higher than the corresponding values (0.04Ω, 48Oe, and 0.48Merg/cm3) of the Pd (6 nm)/Co (1 nm)/Pd (3 nm) trilayer films. The analysis shows that the increase of the above values are the result of Pd/CMS interface effect and CMS/Co interface ferromagnetic coupling, and it is closely related to the thickness of each film layer in the multilayer films and the growth conditions of the multilayer films.

Heterostructure growth, electrical transport and electronic structure of crystalline Dirac nodal arc semimetal PtSn4

Topological semimetals have recently garnered widespread interest in the quantum materials research community due to their symmetry-protected surface states with dissipationless transport which have potential applications in next-generation low-power electronic devices. One such material, , exhibits Dirac nodal arcs and although the topological properties of single crystals have been investigated, there have been no reports in crystalline thin film geometry. We examined the growth of heterostructures on a range of single crystals by optimizing the electron beam evaporation of Pt and Sn and studied the effect of vacuum thermal annealing on phase and crystallinity. The electrical resistivity was fitted to a modified Bloch–Grüneisen model with a residual resistivity of 79.43(1) cm at 2K and a Debye temperature of 200K. Nonlinear Hall resistance indicated the presence of more than one carrier type with an effective carrier mobility of 33.6 and concentration of 1.41 at 300 K. X-ray photoemission spectra were in close agreement with convolved density of states and a work function of 4.7(2) eV was determined for the (010) surface. This study will facilitate measurements that require heterostructure geometry, such as spin and topological Hall effect, and will facilitate potential device incorporation in future quantum technologies.

In-Plane Anomalous Hall Effect Associated with Orbital Magnetization: Measurements of Low-Carrier Density Films of a Magnetic Weyl Semimetal.

For over a century, the Hall effect, a transverse effect under an out-of-plane magnetic field or magnetization, has been a cornerstone for magnetotransport studies and applications. Modern theoretical formulation based on the Berry curvature has revealed the potential that even an in-plane magnetic field can induce an anomalous Hall effect, but its experimental demonstration has remained difficult due to its potentially small magnitude and strict symmetry requirements. Here, we report observation of the in-plane anomalous Hall effect by measuring low-carrier density films of magnetic Weyl semimetal EuCd_{2}Sb_{2}. Anomalous Hall resistance exhibits distinct threefold rotational symmetry for changes in the in-plane field component, and this can be understood in terms of out-of-plane Weyl points splitting or orbital magnetization induced by the in-plane field, as also confirmed by model calculation. Our findings demonstrate the importance of the in-plane field to control the Hall effect, accelerating materials development and further exploration of various in-plane field-induced phenomena.

Observation of field-free spin–orbit torque switching in a single crystalline (Ga,Mn)(As,P) ferromagnetic film with perpendicular anisotropy

We report the observation of field-free spin–orbit torque (SOT) magnetization switching in a single layer of (Ga,Mn)(As,P) ferromagnetic film exhibiting perpendicular magnetic anisotropy. The SOT switching phenomenon is characterized by distinct transitions between two Hall resistance (HR) states during current scans. When subjected to an in-plane bias field, the observed switching chirality in the HR hysteresis loop consistently aligns with SOT induced by spin polarization arising from Rashba- and Dresselhaus-type spin–orbit fields within the tensile-strained crystalline structure of the (Ga,Mn)(As,P) film. Remarkably, in the present experiments, we observe SOT switching even in the absence of an external bias field, and with its chirality depending on the direction of initial magnetization. We attribute this field-free switching to symmetry breaking facilitated by an internal coupling field, the orientation of which is determined by the external field experienced as the magnetization is initialized. Further evidence supporting the presence of such a coupling field includes a shift in the field-scan HR hysteresis depending on the direction of initialized magnetization. Structural analysis reveals a surface layer enriched in Mn and O, indicating the presence of oxide-based magnetic structures that are magnetically coupled to the (Ga,Mn)(As,P) film. The temperature dependence of field-free SOT switching corroborates this explanation, as the internal coupling field disappears above 40 K, consistent with the expected magnetic transition of the Mn3O4 structure. Our discovery of field-free SOT magnetization switching in a single-layer film represents a significant advancement, offering a novel pathway for the development of simpler and more energy-efficient spintronic devices.

First principles methodology for studying magnetotransport in narrow gap semiconductors with ZrTe5 example

The origin of resistivity peak and sign reversal of Hall resistivity in ZrTe5 has long been debated. Despite various theories proposed to explain these unique transport properties, there’s a lack of comprehensive first principles studies. In this work, we employ first principles calculations and Boltzmann transport theory to explore transport properties of narrow-gap semiconductors across varying temperatures and doping levels within the relaxation time approximation. We simulate the temperature-sensitive chemical potential and relaxation time in semiconductors through proper approximations, then extensively analyze ZrTe5’s transport behaviors with and without an applied magnetic field. Our results reproduce crucial experimental observations such as the zero-field resistivity anomaly, nonlinear Hall resistivity with sign reversal, and non-saturating magnetoresistance at high temperatures, without introducing topological phases and/or correlation interactions. Our approach provides a systematic understanding based on multi-carrier contributions and Fermi surface geometry, and could be extended to other narrow-gap semiconductors to explore novel transport properties.

Giant Topological Hall Effect and Colossal Magnetoresistance in Heusler Ferromagnet near Room Temperature.

Colossal magnetoresistance (CMR) is an exotic phenomenon that allows for the efficient magnetic control of electrical resistivity and has attracted significant attention in condensed matter due to its potential for memory and spintronic applications. Heusler alloys are the subject of considerable interest in this context due to the electronic properties that result from the nontrivial band topology. Here, the observation of CMR near room temperature is reported in the shape memory Heusler alloy Ni2Mn1.4In0.6, which is attributed to the combined effects of magnetic field-induced martensite twin variant reorientation (MFIR) and magnetic field-induced structural phase transformation (MFIPT). This compound undergoes a structural phase transition from a cubic (austenite-L21) ferromagnetic (FM) to a monoclinic (martensite) antiferromagnetic (AFM), which leads to an effective increase in the size of the Fermi surface and consequently in CMR. Additionally, it exhibits significant anomalous Hall conductivity in both antiferromagnetic and ferromagnetic phases. Furthermore, it demonstrates a giant topological Hall resistivity (THR) ≈6µΩ.cm in the vicinity of martensite transition due to the enhanced spin chirality resulting from the formation of magnetic domains with Bloch-type domain walls. The findings contribute to the understanding of the magnetotransport of Ni-Mn-In Heusler alloys, which are prospective candidates for room-temperature spintronic applications.

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.

Combined first-principles and Boltzmann transport theory methodology for studying magnetotransport in magnetic materials

Unusual magnetotransport behaviors, such as temperature-dependent negative magnetoresistance (MR) and bowtie-shaped MR, have puzzled us for a long time. Although several mechanisms have been proposed to explain these phenomena, the absence of comprehensive quantitative calculations has made these explanations less convincing. In our work, we introduce a methodology to study magnetotransport behaviors in magnetic materials. This approach integrates the anomalous Hall conductivity induced by the Berry curvature, with a multiband ordinary conductivity tensor, employing a combination of first-principles calculations and semiclassical Boltzmann transport theory. Our method also incorporates the temperature dependence of the relaxation time and the anomalous Hall conductivity, as well as the field dependence of the anomalous Hall conductivity. We initially test this approach on models, obtaining distinct behaviors of magnetoresistance and Hall resistivity across several types of magnetic materials, and then apply it to a Weyl semimetal Co3Sn2S2. The results, which align well with experimental observations in terms of magnetic field and temperature dependencies, demonstrate the efficacy of our approach. This methodology provides a comprehensive and efficient means to understand the underlying mechanisms of the unusual complex behaviors observed in magnetotransport measurements in magnetic materials. Published by the American Physical Society 2024

A Quantitative Arrott Analysis Methodology for Magnetic Susceptibility of Microscale Ferromagnetic Nanoflakes.

Probing magnetic susceptibility of a microsized ferromagnet is a long-standing problem in condensed matter physics. Among various measuring methods for magnetic susceptibility including vibrating sample magnetometry and superconducting quantum interference device magnetometry, almost all require large-scale bulk samples or thick films. However, the quantitative measurement for magnetic susceptibility on a microscale nanoflake is a great challenge. Here, we demonstrate a new analysis method to quantitatively evaluate the magnetic susceptibility of a microscale ferromagnetic nanoflake. Based on the Arrott plot of magnetization isotherms obtained from anomalous Hall resistance, we achieve an in situ evaluation of the value of magnetic susceptibility of a microscale ferromagnetic Fe5GeTe2 nanoflake, identification of the out-of-plane and in-plane magnetization, and investigation of the magnetic anisotropy transition with quantifying critical exponents. Our method reveals critical information on magnetic phase transition in microscale ferromagnetic materials, providing deep insight into spin dynamics of correlated electron systems.

Effect of disorder on anomalous Hall effect and spin Hall magnetoresistance in the ferrimagnetic film

Ferrimagnets have attracted increasing attention in spintronics due to the possibility of easy manipulation by magnetic or electric fields. We report the anomalous Hall effect (AHE) and spin Hall magnetoresistance (SMR) in ferrimagnetic Mn1.77Co0.44V0.83Al0.96 (MCVA) films, which are sensitive to the disorder of the film. As the thickness of the film increases, the film gradually transitions from the disordered to the ordered state, resulting in the anomalous Hall resistivity changes from negative to positive. By separating their distinct the contributions to the AHE, we demonstrate that the thickness dependence originates from the competition between the skew scattering contribution and the sum of the side jump and intrinsic contributions. Moreover, under the effect of disorder, the dependence of the SMR ratio on thickness is more complex, and a critical level of disorder may lead to a sharp decrease in the SMR ratio. Our research reveals the impact of disorder on spin transport and provides a pathway for the design of ferrimagnetic Heusler alloy-based spintronic devices.

PECULIARITIES OF MAGNETOTRANSPORT PROPERTIES OF MOXW1-XTE2 (X = 0; 0.7) SINGLE CRYSTALS

The magnetotransport properties of Mo0.7W0.3Te2 and WTe2 single crystals were studied at temperatures from 4.2 to 80 K and in magnetic fields up to 10 T. The concentrations and mobilities of electron and hole current carriers were estimated in the studied samples at a temperature of 4.2 K. It was found that the carrier mobility in the WTe2 single crystal is an order of magnitude higher than the values obtained for Mo0.7W0.3Te2, which is associated with its higher “electrical” purity. A minimum of the temperature dependence of the resistivity of WTe2 was found in a magnetic field of 10 T at a temperature of 60 K, which can be explained by the transition from effectively high magnetic fields to weak ones. The absence of such a minimum for the Mo0.7W0.3Te2 single crystal is due to the fact that the region of effectively high magnetic fields is not reached for it. The Hall resistivity of WTe2 was shown to depend quadratically on the magnetic field at a temperature of 4.2 K, which is associated with the decompensation of electrons and holes, as well as with the scattering of charge carriers on the surface of the sample. Whereas for Mo0.7W0.3Te2, along with the quadratic contribution, a linear contribution to the Hall resistivity was observed, the cause of which may be the presence of a large number of defects and impurities in the crystal, which leads to a decrease in the mean free path of carriers and, consequently, to a decrease in the contribution of electron-surface scattering.

Observation of planar Hall effect in the topological insulator NaCd4As3

The observation of the planar Hall effect (PHE) illuminates the spin textures and topological properties of materials, indicating potential applications in quantum computing and electronic devices. Here, we present a study on the planar Hall transport of topological insulator NaCd4As3 single crystals. When the magnetic field is rotated within the sample plane relative to the current direction, we observe remarkable planar Hall resistivity and giant planar anisotropic magnetoresistance (AMR), both consistent with the theoretical expression of the PHE. Further analysis reveals that the orbital magnetoresistance effect, unrelated to surface electrons from topological surface states or bulk electrons from nontrivial Berry phases, lays a dominant role in the PHE in NaCd4As3. Additionally, the AMR ratio reaches −43% at 3 K under 14 T and remains −9% at room temperature, markedly exceeding that of traditional ferromagnetic metals. These findings provide a platform for understanding the PHE mechanism in topological insulators and highlight the potential of NaCd4As3 for angle and magnetic field detection applications.

The Hall Effect in Single Crystals of Topological Semimetals WTe<sub>2</sub> and MoTe<sub>2</sub>

The Hall effect in single crystals of topological semimetals WTe2 and MoTe2 is studied in the temperature range from 2 to 100 K and in magnetic fields up to 9 T. It is established that the Hall resistivity of WTe2 shows a nonlinearly dependence on the magnetic field at temperatures below 100 K. At the same time, the Hall resistivity of MoTe2 depends linearly with the magnetic field at temperatures range from 2 to 25 K and a nonlinear contribution appears at 50 K. Along with the known mechanism of compensation/decompensation of electron and hole charge carriers, the nonlinear dependence of the Hall resistivity of WTe2 and MoTe2 single crystals on the magnetic field is associated with the scattering of charge carriers on the surface.

Unusual Anomalous Hall Effect in Two-Dimensional Ferromagnetic Cr7Te8.

Two-dimensional (2D) materials with inherent magnetism have attracted considerable attention in the fields of spintronics and condensed matter physics. The anomalous Hall effect (AHE) offers a theoretical foundation for understanding the origins of 2D ferromagnetism (2D-FM) and offers a valuable opportunity for applications in topological electronics. Here, we present uniform and large-size 2D Cr7Te8 nanosheets with varying thicknesses grown using the chemical vapor deposition (CVD) method. The 2D Cr7Te8 nanosheets with robust perpendicular magnetic anisotropy, even a few layers deep, exhibit a Curie temperature (TC) ranging from 180 to 270 K according to the varying thickness of Cr7Te8. Moreover, we observed a temperature-induced reversal in the sign of the anomalous Hall resistance, correlating with changes in the intrinsic Berry curvature. Additionally, the topological Hall effect (THE) observed at low temperatures suggests the presence of non-trivial spin chirality. Our findings about topologically non-trivial magnetic spin states in 2D ferromagnets provide a promising opportunity for new designs in magnetic memory spintronics.

Giant and negative magnetoresistances in conical magnets in the nonequilibrium Boltzmann equation approach

We study magnetotransport in conical helimagnet crystals using the nonequilibriun Boltzmann equation approach. Spin dependent magnetoresistance exhibits dramatic properties for high and low electron concentrations at different temperatures. For spin up electrons we find negative magnetoresistance despite only considering a single carrier type. For spin down electrons we observe giant magnetoresistance due to depletion of spin down electrons with an applied magnetic field. For spin up carriers, the magnetoresistance is negative, due to the increase in charge carriers with a magnetic field. In addition, we investigate the spin dependent Hall effect. If a magnetic field reaches some critical value for spin down electrons, giant Hall resistance occurs, i.e. Hall current vanishes. This effect is explained by the absence of spin down carriers. For spin up carriers, the Hall constant dramatically decreases with field, due to the increase in spin up electron density. Because of the giant spin dependent magnetoresistance and Hall resistivity, conical helimagnets could be useful in spin switching devices.

Orbital Hall Effect Accompanying Quantum Hall Effect: Landau Levels Cause Orbital Polarized Edge Currents.

The quantum Hall effect emerges when two-dimensional samples are subjected to strong magnetic fields at low temperatures: Topologically protected edge states cause a quantized Hall conductivity in multiples of e^{2}/h. Here we show that the quantum Hall effect is accompanied by an orbital Hall effect. Our quantum mechanical calculations fit well the semiclassical interpretation in terms of "skipping orbits." The chiral edge states of a quantum Hall system are orbital polarized akin to a hypothetical orbital version of the quantum anomalous Hall effect in magnetic systems. The orbital Hall resistivity scales quadratically with the magnetic field, making it the dominant effect at high fields.

Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator.

Topological insulators (TI) and magnetic topological insulators (MTI) can apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization with their unique topological surface states (TSS) with ultrahigh efficiency. Here, efficient SOT switching of a hard MTI, V-doped (Bi,Sb)2Te3 (VBST), with a large coercive field that can prevent the influence of an external magnetic field, is demonstrated. A giant switched anomalous Hall resistance of 9.2 kΩ is realized, among the largest of all SOT systems, which makes the Hall channel a good readout and eliminates the need to fabricate complicated magnetic tunnel junction (MTJ) structures. The SOT switching current density can be reduced to 2.8×105Acm-2, indicating its high efficiency. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge-state-mediated to surface-state-mediated transport, thus enhancing the SOT effective field to (1.56±0.12)×10-6TA-1cm2 and the interfacial charge-to-spin conversion efficiency to 3.9±0.3 nm-1. The findings establish VBST as an extraordinary candidate for energy-efficient magnetic memory devices.