Topological Hall Effect Research Articles

Topological Hall effect in strongly correlated layered magnets: The effect of the spin of the magnetic atoms and of the polar and azimuthal angles subtended by the spin texture

Topological Hall effect in strongly correlated layered magnets: The effect of the spin of the magnetic atoms and of the polar and azimuthal angles subtended by the spin texture

Observation of skyrmion-induced topological Hall effects in Mn3.5Au0.5N films

The Mn4-xAuxN films were grown on MgO(001) substrates by plasma assisted molecular beam epitaxy. The magnetic characteristics and spin transport properties are systematically studied. A sign reversal of anomalous Hall coefficient is observed at 160 K in Mn3.5Au0.5N. This phenomenon can be attributed to the competition between electron-like and hole-like anomalous Hall effects (AHEs). The mutual eliminating of electron-like and hole-like AHEs gives rise to zero resistivity of 160 K at high field. A butterfly-like curve with two humps is observed at 160 K, which can be ascribed to the skyrmion-induced topological Hall effects (THEs). It is thus confirmed that the transverse resistivity in Mn3.5Au0.5N comprises of three components: electron-like AHEs, hole-like AHEs, and skyrmion-induced THEs. An effective method was employed to analyze THEs in the material systems that contain both electrons and holes. The THEs in Mn3.5Au0.5N can be observed after electron-like AHEs are subtracted down from transverse resistivity.

Thickness- and Field-Dependent Magnetic Domain Evolution in van der Waals Fe3GaTe2.

The discovery of room-temperature ferromagnetism in van der Waals (vdW) materials opens new avenues for exploring low-dimensional magnetism and its applications in spintronics. Recently, the observation of the room-temperature topological Hall effect in the vdW ferromagnet Fe3GaTe2 suggests the possible existence of room-temperature skyrmions, yet skyrmions have not been directly observed. In this study, real-space imaging was employed to investigate the domain evolution of the labyrinth and skyrmion structure. First, Néel-type skyrmions can be created at room temperature. In addition, the influence of flake thickness and external magnetic field (during field cooling) on both labyrinth domains and the skyrmion lattice is unveiled. Due to the competition between magnetic anisotropy and dipole interactions, the specimen thickness significantly influences the density of skyrmions. These findings demonstrate that Fe3GaTe2 can host room-temperature skyrmions of various sizes, opening up avenues for further study of magnetic topological textures at room temperature.

All-optical photonic switch via the higher-order topological spin Hall effect

All-optical photonic switch via the higher-order topological spin Hall effect

A correlated ferromagnetic polar metal by design.

Polar metals have recently garnered increasing interest because of their promising functionalities. Here we report the experimental realization of an intrinsic coexisting ferromagnetism, polar distortion and metallicity in quasi-two-dimensional Ca3Co3O8. This material crystallizes with alternating stacking of oxygen tetrahedral CoO4 monolayers and octahedral CoO6 bilayers. The ferromagnetic metallic state is confined within the quasi-two-dimensional CoO6 layers, and the broken inversion symmetry arises simultaneously from the Co displacements. The breaking of both spatial-inversion and time-reversal symmetries, along with their strong coupling, gives rise to an intrinsic magnetochiral anisotropy with exotic magnetic field-free non-reciprocal electrical resistivity. An extraordinarily robust topological Hall effect persists over a broad temperature-magnetic field phase space, arising from dipole-induced Rashba spin-orbit coupling. Our work not only provides a rich platform to explore the coupling between polarity and magnetism in a metallic system, with extensive potential applications, but also defines a novel design strategy to access exotic correlated electronic states.

Observation of topological hall effect and skyrmions in Pt/Co/Ir/Co/Pt system

Abstract The interlayer exchange coupling (IEC) between two ferromagnetic (FM) layers separated by a non-magnetic (NM) spacer layer gives rise to different types of coupling with the variation of spacer layer thickness. When the NM is metallic, the IEC is attributed to the well-known Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction which shows an oscillatory decaying nature with increasing thickness. Due to this, it is possible to tune the coupling between the two FM to be either ferromagnetic or antiferromagnetic. In this work we have studied a Pt/Co/Ir/Co/Pt system where the Co thickness has been taken in the strong perpendicular magnetic anisotropy regime which is much less than the spin reorientation transition thickness. By tuning the Ir thickness to 2.0 nm, a canted state of magnetization reversal in the system is observed which gives rise to a possibility of nucleating topologically non-trivial spin textures like skyrmions. Further, with the combination of transport and magnetic force microscopy (MFM) measurements, we have confirmed the presence of skyrmions in our system. These findings may be useful for potential applications in emerging spintronic and data storage technologies using skyrmions.

Room-temperature skyrmions in the van der Waals ferromagnet Fe3GaTe2

The recently emerged van der Waals ferromagnet Fe3GaTe2 has an above-room-temperature TC of ∼350 K. By measuring the magneto-optical Kerr effect microscopy and Lorentz transmission electron microscopy on high quality Fe3GaTe2 crystals at room temperature, we visualized that the magnetic field applied perpendicularly to the (001) plane of the bulk crystal below TC can turn the ground-state labyrinth-stripe magnetic domain into Néel-type skyrmions. The result is also supported by the measured topological Hall effect. Furthermore, we identified that the reduction in crystal thickness can influence the density of skyrmions. The observation paves the way to use this van der Waals ferromagnet in next-generation low-power magnetoelectronic and spintronic devices that can work at room temperature.

The Topological Hall Effect in CoGd Films Controlled by Hydrogen Migration under Gate Voltage

AbstractThe topological Hall effect (THE) presents hump signals in the Hall resistance versus magnetic field hysteresis loop, showing promise for future spintronics due to its robust chiral magnetic textures. Here, it is shown that solid‐state protonic gating can control possible topological magnetic structures in CoGd thin films. Injecting H+ leads to sizable hump signals in the film. Magneto‐optical Kerr microscopy shows that induced hump signals in transporting measurements do not scale with magnetization, supporting topological magnetism. Successive hydrogen ion extraction completely erases the effect. Thus, topological magnetism manipulations are reversible, nonvolatile, and effective. Ab inito calculations and effective chiral spin models demonstrate that hydrogen injection remarkably enhances the Dzyaloshinskii–Moriya interaction over fourfold, stabilizing chiral structures contributing to the large THE. These findings reveal the vital role of hydrogen ions in topological magnetism and suggest that amorphous ferrimagnetic CoGd thin films are outstanding platforms for realizing controllable topological spintronics at room temperature.

Proximity effect of emergent field from spin ice in an oxide heterostructure.

Geometrical frustration endows magnets with degenerate ground states, resulting in exotic spin structures and quantum phenomena. Such magnets, called quantum magnets, can display non-coplanar spin textures and be a viable platform for the topological Hall effect driven by "emergent field." However, most quantum magnets are insulators, making it challenging to electrically detect associated fluctuations and excitations. Here, we probe magnetic transitions in the spin ice insulator Dy2Ti2O7, a prototypical quantum magnet, as emergent magnetotransport phenomena at the heterointerface with the nonmagnetic metal Bi2Rh2O7. Angle-dependent longitudinal resistivity exhibits peaks at the magnetic phase boundaries of spin ice due to domain boundary scattering. In addition, the anomalous Hall resistivity undergoes a sign change with the magnetic transition in Dy2Ti2O7, reflecting the inversion of the emergent field. These findings, on the basis of epitaxial techniques, connect the fundamental research on insulating quantum magnets to their potential electronic applications, possibly leading to transformative innovations in quantum technologies.

Distinct Composition‐Dependent Topological Hall Effect in Mn2‐xZnxSb

AbstractSpintronics, an evolving interdisciplinary field at the intersection of magnetism and electronics, explores innovative applications of electron charge and spin properties for advanced electronic devices. The topological Hall effect (THE), a key component in spintronics, has gained significance due to emerging theories surrounding noncoplanar chiral spin textures. This study focuses on Mn2‐xZnxSb, a material crystalizing in centrosymmetric space group with rich magnetic phases tunable by Zn contents. Through comprehensive magnetic and transport characterizations, we found that the high‐Zn (x > 0.6) samples display THE which is enhanced with decreasing temperature, while THE in the low‐Zn (x < 0.6) samples show an opposite trend. The coexistence of those distinct temperature dependencies for THE suggests very different magnetic interactions/structures for different compositions and underscores the strong coupling between magnetism and transport in Mn2‐xZnxSb. The findings contribute to understanding topological magnetism in centrosymmetric tetragonal lattices, establishing Mn2‐xZnxSb as a unique platform for exploring tunable transport effects and opening avenues for further exploration in the realm of spintronics.

Observation of Topological Hall Effect in a Chemically Complex Alloy.

The topological Hall effect (THE) is the transport response of chiral spin textures and thus can serve as a powerful probe for detecting and understanding these unconventional magnetic orders. So far, the THE is only observed in either noncentrosymmetric systems where spin chirality is stabilized by Dzyaloshinskii-Moriya interactions, or triangular-lattice magnets with Ruderman-Kittel-Kasuya-Yosida-type interactions. Here, a pronounced THE is observed in a Fe-Co-Ni-Mn chemically complex alloy with a simple face-centered cubic (fcc) structure across a wide range of temperatures and magnetic fields. The alloy is shown to have a strong magnetic frustration owing to the random occupation of magnetic atoms on the close-packed fcc lattice and the direct Heisenberg exchange interaction among atoms, as evidenced by the appearance of a reentrant spin glass state in the low-temperature regime and the first principles calculations. Consequently, THE is attributed to the nonvanishing spin chirality created by strong spin frustration under the external magnetic field, which is distinct from the mechanism responsible for the skyrmion systems, as well as geometrically frustrated magnets.

Dual-component anomalous Hall effect in a helical spin-spiral metamagnet

We report a dual-component anomalous Hall effect (AHE) in polycrystalline Fe3Ga4 thin films grown on STO (001) and Al2O3 substrates. Systematic magnetic and magnetotransport measurements reveal an AHE consisting of positive and negative contributions that coexist across a wide range of temperatures and magnetic phases. We find that both magnitudes are nearly equal in the low-temperature ferromagnetic (FM) phase, but that their relative ratio is reduced upon heating through the antiferromagnetic helical spin-spiral state where they compete with metamagnetism and topological Hall effects, maintaining finite values at least up to the high-temperature FM phase.

Interface-induced transverse resistivity anomaly in AgNbO3/SrRuO3 heterostructures

The transverse resistivity anomaly with a hump feature, associated with topological magnetic textures, is of paramount importance for the applications of next-generation chiral spintronic devices. However, the origin of the hump feature still remains debated due to the complicated mechanism, not merely assigned to the intrinsic topological Hall effect (THE). In this work, we observe the apparent transverse resistivity hump characteristic superimposed on the Hall signals in AgNbO3/SrRuO3 (ANO/SRO) heterostructures. The intrinsic THE is ruled out by minor-loop and current density measurements. Combining the microscopic characterization and the two-channel anomalous Hall effect fitting, the hump feature is unambiguously attributed to the synergetic contribution from the SRO layer and the interfacial intermixing thin layer of ANO and SRO.

Bloch Point Quadrupole Constituting Hybrid Topological Strings Revealed with Electron Holographic Vector Field Tomography.

Topological magnetic (anti)skyrmions are robust string-like objects heralded as potential components in next-generation topological spintronics devices due to their low-energy manipulability via stimuli such as magnetic fields, heat, and electric/thermal current. While these 2D topological objects are widely studied, intrinsically 3D electron-spin real-space topology remains less explored despite its prevalence in bulky magnets. 2D-imaging studies reveal peculiar vortex-like contrast in the core regions of spin textures present in antiskyrmion-hosting thin plate magnets with S4 crystal symmetry, suggesting a more complex 3D real-space structure than the 2D model suggests. Here, holographic vector field electron tomography captures the 3D structure of antiskyrmions in a single-crystal, precision-doped (Fe0.63Ni0.3Pd0.07)3P (FNPP) lamellae at room temperature and zero field. These measurements reveal hybrid string-like solitons composed of skyrmions with topological number W = -1 on the lamellae's surfaces and an antiskyrmion (W = + 1) connecting them. High-resolution images uncover a Bloch point quadrupole (four magnetic (anti)monopoles that are undetectable in 2D imaging) which enables the observed lengthwise topological transitions. Numerical calculations corroborate the stability of hybrid strings over their conventional (anti)skyrmion counterparts. Hybrid strings result in topological tuning, a tunable topological Hall effect, and the suppression of skyrmion Hall motion, disrupting existing paradigms within spintronics.

Magnon Hall effect

Hall effect is an ancient but highly potential subfield in condensed matter physics, and its origin can be traced back hundreds of years. In 1879, Hall made a momentous discovery that when a current-carrying conductor is placed in a magnetic field, the Lorentz force pushes its electrons to one side of the conductor. This intriguing phenomenon was dubbed Hall effect. Since then, a series of novel Hall effects have been discovered, including anomalous Hall effect, quantum Hall effect, spin Hall effect, topological Hall effect, and planar Hall effec. Notably, Hall effects play an important role in realizing the information transport, since it can realize the mutual conversion of current in different directions. In bosonic systems such as magnons, a series of magnon Hall effects have been found, jointly driving the development of the magnon-based spintronics. In this perspective, we review the researches of the Hall effect in magnonic system in recent years, and briefly introduce its modern semi-classical theories, including virtual electromagnetic field theory and scattering theory. Furthermore, we introduce the different magnon Hall effects and clarify the physics behind them. Finally, the prospect of magnon Hall effect is discussed.

Universal skyrmion logic gates and circuits based on antiferromagnetically coupled skyrmions without a topological Hall effect

Nanoscale skyrmions are spin-based quasiparticles that are promising for nonvolatile logic applications.

Tunable Spin Textures in a Kagome Antiferromagnetic Semimetal via Symmetry Design.

Kagome antiferromagnetic semimetals such as Mn3Sn have attracted extensive attention for their potential application in antiferromagnetic spintronics. Realizing high manipulation of kagome antiferromagnetic spin states at room temperature can reveal rich emergent phenomena resulting from the quantum interactions between topology, spin, and correlation. Here, we achieved tunable spin textures of Mn3Sn through symmetry design by controlling alternate Mn3Sn and heavy-metal Pt thicknesses. The various topological spin textures were predicted with theoretical simulations, and the skyrmion-induced topological Hall effect, strong spin-dependent scattering, and vertical gradient of spin states were obtained by magnetotransport and magnetic circular dichroism (MCD) spectroscopy measurements in Mn3Sn/Pt heterostructures. Our work provides an effective strategy for the innovative design of topological antiferromagnetic spintronic devices.

Tetrahedral triple-Q magnetic ordering and large spontaneous Hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2

The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120° structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q magnetic ordering with the associated topological Hall effect (non-zero σxy(H = 0)). We also present a theoretical framework that describes the emergence of this magnetic ground state, which is further supported by the electronic structure measured by angle-resolved photoemission spectroscopy. Additionally, our measurements of the inelastic neutron scattering cross section are consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state.

Mapping of Spin‐Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy

AbstractSpin waves, collective dynamic magnetic excitations, offer crucial insights into magnetic material properties. Rare‐earth iron garnets offer an ideal spin‐wave (SW) platform with long propagation length, short wavelength, gigahertz frequency, and applicability to magnon spintronic platforms. Of particular interest, thulium iron garnet (TmIG) has attracted huge interest recently due to its successful growth down to a few nanometers, observed topological Hall effect, and spin‐orbit torque‐induced switching effects. However, there is no direct spatial measurement of its SW properties. This work uses diamond nitrogen‐vacancy (NV) magnetometry in combination with SW electrical transmission spectroscopy to study SW transport properties in TmIG thin films. NV magnetometry allows probing spin waves at the sub‐micrometer scale, seen by the amplification of the local microwave magnetic field due to the coupling of NV spin qubits with the stray magnetic field produced by the microwave‐excited spin waves. By monitoring the NV spin resonances, the SW properties in TmIG thin films are measured as a function of the applied magnetic field, including their amplitude, decay length (≈50 µm), and wavelength (0.8–2 µm). These results pave the way for studying spin qubit‐magnon interactions in rare‐earth magnetic insulators, relevant to quantum magnonics applications.

Quadrupole anomalous Hall effect in magnetically induced electron nematic state

Berry phases in both momentum and real space cause transverse motion in itinerant electrons, manifesting various off-diagonal transport effect such anomalous and topological Hall effects. Although these Hall effects are isotropic within the plane perpendicular to the fictitious magnetic field, here, we report the manifestation of the anisotropic linear anomalous Hall effect (AHE) in the spinel oxide NiCo2O4 epitaxial film. The unconventional Hall effect indicates a quadrupole dependence on the in-plane current direction being added to the uniform AHE. Moreover, its sign can be manipulated just by magnetic-field cooling. The anisotropic effect is attributed to an electron nematic state originating from a deformed electronic state owing to an extended magnetic toroidal quadrupole and ferrimagnetic order.