Hall Signal Research Articles

Torque estimation in three-phase induction motors under broken bars and voltage variations using airgap flux measurement and a machine learning model

This paper proposes a new approach for load torque estimation in squirrel cage induction motors using airgap flux measurement, by means of a Hall effect sensor installed between two stator slots of the machine. The rotor speed was estimated from the Hall sensor signal using a previous method designed by the authors, and the root mean square and mean value were also computed from the Hall signal to serve as inputs to a multi-layer perceptron model.The positioning of the Hall sensor inside the machine was also investigated during different experiments for torque prediction and considered as an additional input for the regression task. The present methodology does not require motor parameters for torque prediction. This research has been validated using some simulated and experimental results for different motor operational conditions. The performance metrics disclosed a good torque prediction for the machine fed not only by a rated voltage, but also by overvoltage/undervoltage power supply and with broken rotor bars, even for low loads. Both experimental and simulation results showed a mean absolute percentage error lower than 4% for a 7.5 kW induction motor.

Field‐Free and Energy‐Efficient Switching of a Ferrimagnetic Insulator Through Orbital Currents of Copper

AbstractElectrically manipulating the magnetization of insulators presents exciting opportunities for fast and energy‐efficient spintronic devices. However, the existing approaches, which rely on spin‐orbit torque (SOT), invariably require an auxiliary field. Here field‐free current‐induced magnetization switching in perpendicularly magnetized Tm3Fe5O12 films is demonstrated. This is achieved through a magnetic hybrid structure, Tm3Fe5O12/Co40Fe40B20/Cu/SiO2, where the Cu layer acts as the source of orbital current, and the in‐plane magnetized Co40Fe40B20 layer functions as the converter of orbital‐to‐spin current. The interplay between the insulating and metallic magnetic layers not only yields a significant anomalous Hall signal for monitoring the Tm3Fe5O12 magnetization states, but also enables field‐free switching that is immune to the magnetic history of the structure. It also observes similar Tm3Fe5O12 switching in stacks with different spin/orbital current sources, with the SOT‐driven switching consuming substantially more power. This work establishes a pathway for achieving energetically efficient all‐electrical manipulation of insulator spins through orbital currents.

Decoupling topological antiskyrmion and non-topological magnetic phases in D2d symmetric Mn–Ni–Ga single crystalline device

Here, we present the finding of two types of distinct Hall signals in the single crystalline Hall devices of a D2d symmetric antiskyrmion host Mn–Ni–Ga sample. The out-of-plane device, where the magnetic field is applied along the [001] direction, exhibits a dip-like anomaly in the Hall resistivity data, signifying the presence of topological Hall signal originating from the antiskyrmion phase. Most importantly, we demonstrate the robustness of the antiskyrmion phase against an oblique field where the topological Hall signal survives up to a tilting angle of 75° with respect to the c-axis. In contrast, the Hall resistivity data for the in-plane device exhibit an aberrant hump-like feature that can be tuned with applying a rotating magnetic field. We show that this hump-like anomaly emerges from the existence of a two-component anomalous Hall effect arising due to the presence of twinning microstructure. The present study provides an important insight into the stability and evolution of the antiskyrmion phase under the oblique magnetic fields and helps in decoupling of anomalous Hall signals in the non-topological magnetic phases.

Orbital multiferroicity in pentalayer rhombohedral graphene.

Ferroic orders describe spontaneous polarization of spin, charge and lattice degrees of freedom in materials. Materials exhibiting multiple ferroic orders, known as multiferroics, have important parts in multifunctional electrical and magnetic device applications1-4. Two-dimensional materials with honeycomb lattices offer opportunities to engineer unconventional multiferroicity, in which the ferroic orders are driven purely by the orbital degrees of freedom and not by electron spin. These include ferro-valleytricity corresponding to the electron valley5 and ferro-orbital-magnetism6 supported by quantum geometric effects. These orbital multiferroics could offer strong valley-magnetic couplings and large responses to external fields-enabling device applications such as multiple-state memory elements and electric control of the valley and magnetic states. Here we report orbital multiferroicity in pentalayer rhombohedral graphene using low-temperature magneto-transport measurements. We observed anomalous Hall signals Rxy with an exceptionally large Hall angle (tanΘH > 0.6) and orbital magnetic hysteresis at hole doping. There are four such states with different valley polarizations and orbital magnetizations, forming a valley-magnetic quartet. By sweeping the gate electric field E, we observed a butterfly-shaped hysteresis of Rxy connecting the quartet. This hysteresis indicates a ferro-valleytronic order that couples to the composite fieldE·B(where Bis the magnetic field), but not to the individual fields. Tuning E would switch each ferroic order independently and achieve non-volatile switching of them together. Our observations demonstrate a previously unknown type of multiferroics and point to electrically tunable ultralow-power valleytronic and magnetic devices.

Berry curvature induced spontaneous and topological-like Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) thin films

We report a study of longitudinal resistivity, anisotropic magnetoresistance (MR), and Hall effect on epitaxial Nd2Ir2O7 (111) thin films grown by the solid phase epitaxy technique, in which spin–orbit coupling, electronic correlation, magnetic frustration, and f-d exchange interaction are present. Temperature-dependent longitudinal resistivity (ρxx) data indicate semimetallic charge transport in the low-temperature region. Field-cooled longitudinal resistivity measurements detect negligible domain-wall conductance compared to the polycrystal or single-crystal samples. Angle-dependent MR measurement shows that the magnetic structure of Ir4+ 5d moments can be finely tuned by applying a magnetic field along different crystallographic directions. MR measurements show a field-induced modification of the Nd3+ 4f spin structure from all-in-all-out/all-out-all-in (AIAO/AOAI) (4-in-0-out) to 1-in-3-out for the applied field (H) along the [111] direction, resulting in field-induced plastic deformation of the Ir4+ domain distribution. In contrast, the application of field (H) along the [001] and [011] directions could not modify any domain distribution. A large spontaneous Hall effect (SHE) signal has been observed on Nd2Ir2O7 (111) thin film with AIAO/AOAI antiferromagnetic ordering for the application of field (H) along [001], [1̄1̄0], and [111] directions. The appearance of a large spontaneous Hall signal for the applied field along [001] and [1̄1̄0] directions rules out domain switching as the origin of the Hall effect and confirms the presence of the Weyl semimetallic phase in Nd2Ir2O7 (111) thin films. In addition to SHE, a large topological-like Hall signal is also observed, possibly due to the presence of multiple Weyl nodes in the electronic band structure.

A Hybrid Magnetic Current Sensor With a Multiplexed Ripple-Reduction Loop

This article presents a hybrid magnetic current sensor for galvanically isolated measurements. It consists of a CMOS chip that senses the magnetic field generated by current flowing through a lead-frame-based current rail. Hall plates and coils are used to sense low-frequency (dc to 10 kHz) and high-frequency (10 kHz to 5 MHz) magnetic fields, respectively. With the help of on-chip calibration coils, the biasing current of the Hall plates is trimmed to match the sensitivity of the Hall and coil signal paths. The sensitivity drift of the coil path with temperature is compensated by using temperature-dependent gain-setting resistors, while the drift of the Hall path is compensated by biasing the Hall plates with a proportional-to-absolute-temperature (PTAT) current. The resulting sensitivity drift is less than 9% from –40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C to 80 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C. The offset of the Hall plates is reduced by the current spinning technique, and the resulting ripple is suppressed by a multiplexed ripple-reduction loop (MMRL). Fabricated in a standard 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m CMOS process, the current sensor occupies 4.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> and draws 7.8 mA from a 1.8-V supply. It achieves a gain variation of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 2% in a 5-MHz BW. It also achieves high energy efficiency, with an figure of merit (FoM) of 1.6 fW/Hz.

Saturation of the anomalous Hall effect at high magnetic fields in altermagnetic RuO2

Observations of the anomalous Hall effect in RuO2 and MnTe have demonstrated unconventional time-reversal symmetry breaking in the electronic structure of a recently identified new class of compensated collinear magnets, dubbed altermagnets. While in MnTe, the unconventional anomalous Hall signal accompanied by a vanishing magnetization is observable at remanence, the anomalous Hall effect in RuO2 is excluded by symmetry for the Néel vector pointing along the zero-field [001] easy-axis. Guided by a symmetry analysis and ab initio calculations, a field-induced reorientation of the Néel vector from the easy-axis toward the [110] hard-axis was used to demonstrate the anomalous Hall signal in this altermagnet. We confirm the existence of an anomalous Hall effect in our RuO2 thin-film samples, whose set of magnetic and magneto-transport characteristics is consistent with the earlier report. By performing our measurements at extreme magnetic fields up to 68 T, we reach saturation of the anomalous Hall signal at a field Hc ≃ 55 T that was inaccessible in earlier studies but is consistent with the expected Néel-vector reorientation field.

Quantized valley Hall response from local bulk density variations

The application of a mechanical strain to a 2D material can create pseudo-magnetic fields and lead to a quantized valley Hall effect. However, measuring valley-resolved effects remains a challenging task due to their inherent fragility and dependence on the sample’s proper design. Additionally, non-local transport probes based on multiterminal devices have often proven to be inadequate in yielding conclusive evidence of the valley Hall signal. Here, we introduce an alternative way of detecting the quantized valley Hall effect, which entirely relies on local density measurements, performed deep in the bulk of the sample. The resulting quantized signal is a genuine Fermi sea response, independent of the edge physics, and reflects the underlying valley Hall effect through the Widom-Středa formula. Specifically, our approach is based on measuring the variation of the particle density, locally in the bulk, upon varying the strength of the applied strain. This approach to the quantized valley Hall effect is particularly well suited for experiments based on synthetic lattices, where the particle density (or integrated density of states) can be spatially resolved.

Crossover from Positive to Negative Spin Hall Signal in a Ferromagnetic Metal Induced by the Magnetization Modulated Interface Effect (Adv. Phys. Res. 9/2023)

Crossover from Positive to Negative Spin Hall Signal in a Ferromagnetic Metal Induced by the Magnetization Modulated Interface Effect (Adv. Phys. Res. 9/2023)

Detection of Nontrivial Topology Driven by Charge Density Wave in a Semi‐Dirac Metal

AbstractThe presence of electron correlations in a system with topological order can lead to exotic ground states. Considering single crystals of LaAgSb2 which has a square net crystal structure, one finds multiple charge density wave transitions (CDW) as the temperature is lowered. Large planar Hall (PHE) signals are found in the CDW phase, which are still finite in the high‐temperature phase though they change sign. Optimizing the structure within first‐principles calculations, one finds an unusual chiral metallic phase. This is because as the temperature is lowered, the separation between the Ag/Sb atoms on different layers decreases, leading to stronger repulsions between electrons associated with atoms on different layers. This leads to successive layers sliding with respect to each other, thereby stabilizing a chiral structure in which inversion symmetry is also broken. The large Berry curvature associated with the low‐temperature structure explains the low‐temperature PHE. At high temperature, the PHE arises from the changes induced in the anisotropic Dirac cone in presence of a magnetic field. This work represents a route toward detecting and understanding the mechanism in a correlation‐driven topological transition through electron transport measurements, complemented by ab‐initio electronic structure calculations.

A peculiar topological Hall effect in noncentrosymmetric ternary carbide GdCoC2

A peculiar topological Hall effect (THE) is reported in a noncentrosymmetric ternary carbide GdCoC2. The GdCoC2 reveals a magnetic ordering transition from paramagnetic to ferromagnetic state at the Curie temperature TC = 15.6 K, followed by a commensurate-incommensurate phase transition at Tt = 14.1 K. Below Tt, the competition between an external magnetic field and magnetic interactions, including the Dzyaloshinskii–Moriya interaction, would give rise to characteristic spin textures with non-zero scalar spin chirality χijk, or even topologically protected spin configurations like skyrmions, for which the exotic spin-charge coupled phenomena are induced. Besides a large negative magnetoresistance (MR) up to ∼−52% at 14 K, a remarkably sharp topological Hall signal is observed with almost no anomalous Hall resistivity below 10 K. The topological Hall resistivity (ρxyT) of GdCoC2 reaches a maximum value of ∼0.23 μΩ cm at 3 K under μ0H = 0.6 T. The mechanism underlying the exceptional THE with relatively large ρxyT value in GdCoC2 is discussed in detail.

Intrinsic Nonlinear Hall Effect and Gate-Switchable Berry Curvature Sliding in Twisted Bilayer Graphene.

Though the observation of the quantum anomalous Hall effect and nonlocal transport response reveals nontrivial band topology governed by the Berry curvature in twisted bilayer graphene, some recent works reported nonlinear Hall signals in graphene superlattices that are caused by the extrinsic disorder scattering rather than the intrinsic Berry curvature dipole moment. In this Letter, we report a Berry curvature dipole induced intrinsic nonlinear Hall effect in high-quality twisted bilayer graphene devices. We also find that the application of the displacement field substantially changes the direction and amplitude of the nonlinear Hall voltages, as a result of a field-induced sliding of the Berry curvature hotspots. Our Letter not only proves that the Berry curvature dipole could play a dominant role in generating the intrinsic nonlinear Hall signal in graphene superlattices with low disorder densities, but also demonstrates twisted bilayer graphene to be a sensitive and fine-tunable platform for second harmonic generation and rectification.

High field magnetic transport measurements of FeGe thin plates

Magnetic skyrmions have garnered considerable attention due to their topological properties and potential applications in information storage. These unique structures can be found in chiral magnets, including well-known compounds like MnSi and FeGe with a B20-type crystal structure. In this study, we utilized Lorentz transmission electron microscopy to investigate the influence of magnetic skyrmions on the Hall effect in FeGe under low magnetic fields. Additionally, we examined the magnetoresistance (MR) and Hall effect of FeGe under a high magnetic field of 28 T. Our findings reveal distinct mechanisms governing the MR at low and high temperatures. Notably, the anomalous Hall effect plays a significant role in the Hall resistivity observed at low magnetic fields. Meanwhile, the contribution of the skyrmion-induced topological Hall signal in the FeGe is ignorable. Furthermore, by employing a two-carrier model and fitting the carrier concentration of FeGe under high magnetic fields, we demonstrate a transition in the dominant carrier type from electrons to holes as the temperature increases. These results contribute to a deeper understanding of the intrinsic magnetic properties of FeGe.

A Sage-Husa Prediction Algorithm-Based Approach for Correcting the Hall Sensor Position in DC Brushless Motors.

Accurate knowledge of the rotor position is essential for the control of brushless DC motors (BLDCM). Any deviation in this identification can cause fluctuations in motor current and torque, increase noise, and lead to reduced motor efficiency. This paper focused on a BLDCM equipped with a three-phase binary Hall sensor. Based on the principle of minimum deviation, this paper estimated the relative installation offset between the Hall sensors. It also provided a clear method for ideal phase commutation position recognition and eliminated the Hall sensor installation position deviation. The proposed pre-calibration method identified and eliminated the offset of the permanent magnet poles, the delay time caused by the Hall signal conditioning circuit, and the offset of the sensor signal identification due to armature response under different loads. Based on the pre-calibration results, a correction strategy for correcting the rotor position information of BLDCMs was proposed. This paper presented a self-adaptive position information prediction algorithm based on the Sage-Husa method. This filters out rotor position information deviations that are not eliminated in pre-calibration. Experimental results on a hydrogen circulation pump motor showed that, after the pre-calibration method was adopted, the Mean Square Error (MSE) of motor speed fluctuations decreased by 92.0%, motor vibration was significantly reduced, average phase current decreased by 62.8%, and the efficiency of the hydrogen circulation pump system was significantly improved. Compared to the traditional KF prediction algorithm, the Sage-Husa adaptive position information prediction algorithm reduced the speed fluctuation during the uniform speed operation stage and speed adjustment stage, the speed curve overshoot, and the commutation time deviation throughout the process by 44.8%, 56.0%, 54.9%, and 14.7%, respectively. This indicates a higher disturbance rejection ability and a more accurate and stable prediction of the commutation moment.

Observation of the Time-Reversal Symmetric Hall Effect in Graphene-WSe2 Heterostructures at Room Temperature.

In this Letter, we provide experimental evidence of the time-reversal symmetric Hall effect in a mesoscopic system, namely, high-mobility graphene-WSe2 heterostructures. This linear, dissipative Hall effect, whose sign depends on the sign of the charge carriers, persists up to room temperature. The magnitude and the sign of the Hall signal can be tuned using an external perpendicular electric field. Our joint experimental and theoretical study establishes that the strain induced by lattice mismatch, or alignment angle inhomogeneity, produces anisotropic bands in graphene while simultaneously breaking the inversion symmetry. The band anisotropy and reduced spatial symmetry lead to the appearance of a time-reversal symmetric Hall effect. Our study establishes graphene-transition metal dichalcogenide-based heterostructures as an excellent platform for studying the effects of broken symmetry on the physical properties of band-engineered two-dimensional systems.

Improving the Accuracy of Multipole Magnetic Encoder by Three-Phase Hall

Magnetic encoders have widespread applications in various fields such as aerospace, automotive, robot joint control and machine tool turntables. For instance, obtaining accurate rotation angles of motors is crucial for servo motor control. Herein, we propose an angle-solving algorithm based on a dual-multipair pole magnetic encoder. First, we analyze the nonlinearity issue caused by installation error of the Hall signal and devise a self-adjustment algorithm for the analog signal. Second, we improve the high speed and robustness of the encoder in identifying eigenvalue intervals while solving for angles. Finally, through the big data analysis, the calibration compensation of curve fitting error was performed, and experiments were conducted to verify the effectiveness of the real-time angle-solving algorithm in a high-precision encoder.

Macroscopic Quantum Tunneling of a Topological Ferromagnet.

The recent advent of topological states of matter spawned many significant discoveries. The quantum anomalous Hall (QAH) effectis a prime example due to its potential for applications in quantum metrology, as well as its influence on fundamental research into the underlying topological and magnetic states and into axion electrodynamics. Here, electronic transport studies on a (V,Bi,Sb)2 Te3 ferromagnetic topological insulator nanostructure in the QAH regime are presented. This allows access to the dynamics of an individual ferromagnetic domain. The domain size is estimated to be in the 50-100 nm range. Telegraph noise resulting from the magnetization fluctuations of this domain is observed in the Hall signal. Careful analysis of the influence of temperature and external magnetic field on the domain switching statistics provides evidence for quantum tunneling (QT) of magnetization in a macrospin state. This ferromagnetic macrospin is not only the largest magnetic object in which QT is observed, but also the first observation of the effect in a topological state ofmatter.

Excitonic topological order in imbalanced electron-hole bilayers.

Correlation and frustration play essential roles in physics, giving rise to novel quantum phases1-6. A typical frustrated system is correlated bosons on moat bands, which could host topological orders with long-range quantum entanglement4. However, the realization of moat-band physics is still challenging. Here, we explore moat-band phenomena in shallowly inverted InAs/GaSb quantum wells, where we observe an unconventional time-reversal-symmetry breaking excitonic ground state under imbalanced electron and hole densities. We find that a large bulk gap exists, encompassing a broad range of density imbalances at zero magnetic field (B), accompanied by edge channels that resemble helical transport. Under an increasing perpendicular B, the bulk gap persists, and an anomalous plateau of Hall signals appears, which demonstrates an evolution from helical-like to chiral-like edge transport with a Hall conductance approximately equal to e2/h at 35 tesla,where e is the elementarycharge and h is Planck's constant. Theoretically, we show that strong frustration from density imbalance leads to a moat band for excitons, resulting in a time-reversal-symmetry breaking excitonic topological order, which explains all our experimental observations. Our work opens up a new direction for research on topological and correlated bosonic systems in solid states beyond the framework of symmetry-protected topological phases, including but not limited to the bosonic fractional quantum Hall effect.

Symmetry-based requirement for the measurement of electrical and thermal Hall conductivity under an in-plane magnetic field

The in-plane (thermal) Hall effect is an unconventional transverse response when the applied magnetic field is in the (heat) current plane. In contrast to the normal Hall effect, the in-plane Hall effect requires the absence of certain crystal symmetries, and possibly manifests a non-trivial topology of quantum materials. An accurate estimation of the intrinsic in-plane (thermal) Hall conductivity is crucial to identify the underlying mechanisms as in the case of the Kitaev spin-liquid candidate alpha-RuCl3. Here, we give the symmetry conditions for the in-plane Hall effect and discuss the implications that may impede the experimental evaluation of the in-plane (thermal) Hall conductivity within the single-device measurement. First, the lack of symmetry in crystals can create merohedral twin domains that cancel the total Hall signal. Second, even in a twin-free crystal, the intrinsic response is potentially contaminated by the out-of-plane conduction in three-dimensional systems, which is systematically unavoidable in the in-plane Hall systems. Third, even in a quasi-two-dimensional system, the conversion of (thermal) resistivity, rho (lambda), to (thermal) conductivity, sigma (kappa) requires protocols beyond the widely-used simplified formula due to the lack of in-plane-rotational symmetry. In principle, two independent sample devices are necessary to accurately estimate the s_xy (k_xy). As a case study, we discuss the half-integer quantization of the in-plane thermal Hall effect in the spin-disordered state of alpha-RuCl3. For an accurate measurement of the thermal Hall effect, it is necessary to avoid crystals with the merohedral twins contributing oppositely to k_xy, while the out-of-plane transport may have a negligible effect. To deal with the field-induced rotational-symmetry breaking, we propose two symmetry-based protocols, improved single-device and two-device methods.

Crossover from Positive to Negative Spin Hall Signal in a Ferromagnetic Metal Induced by the Magnetization Modulated Interface Effect

AbstractThe spin Hall effect and its inverse (SHE/ISHE), describing the charge‐to‐spin interconversion, are of critical importance to the fundamental physics involving spin‐orbit coupling and the application of spintronic devices. These phenomena in nonmagnetic materials are reasonably understood after extensive studies. In ferromagnetic metals, however, the fundamental issue of generation and transport of pure spin current, especially the interplay of charge‐to‐spin interconversion and magnetization, is as‐yet poorly understood. Here, direct experimental evidence for the sign change in ISHE by injecting a spin current from Y3Fe5O12 into a Fe film via a Cu spacer is reported. The sizable negative ISHE signal (VISHE) in nanometer‐thick Fe films reverses its sign with a comparable magnitude when Fe magnetization is varied from a longitudinal to transverse orientation with respect to spin current polarization. With decreasing Fe thickness, this negative longitudinal VISHE increases rapidly to a larger positive value in magnitude. The opposite spin Hall angles for longitudinally and transversely polarized spin currents are reproduced by first‐principles transport calculations and the sign change is attributed to the anisotropic contribution at the ferromagnetic interface. This work lays a firm foundation for manipulating spin‐to‐charge interconversion with an extra degree of freedom of magnetization orientation through ferromagnetic metals.