Giant Topological Hall Effect Research Articles

Observation of Giant Topological Hall Effect in Room-Temperature Ferromagnet Cr0.82Te

Abstract Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years. Among them is the Cr x Te y family, the magnetism of which can persist above room temperature, thus providing an ideal system for potential spintronic applications. Here we report the synthesis of a new compound, Cr0.82Te, which demonstrates a record-high topological Hall effect at room temperature in this family. Cr0.82Te displays soft ferromagnetism below the Curie temperature of 340 K. The magnetic measurement shows an obvious magneto-crystalline anisotropy with the easy axis located in the ab plane. The anomalous Hall effect can be well explained by a dominating skew scattering mechanism. Intriguing, after removing the normal Hall effect and anomalous Hall effect, a topological Hall effect can be observed up to 300 K and reaches up to 1.14 μΩ⋅cm at 10 K, which is superior to most topological magnetic structural materials. This giant topological Hall effect possibly originates from the noncoplanar spin configuration during the spin flop process. Our work extends a new Cr x Te y system with topological non-trivial magnetic structure and broad prospects for spintronics applications in the future.

Interplay between Magnetism and Topology: Large Topological Hall Effect in an Antiferromagnetic Topological Insulator, EuCuAs.

Magnetic interactions in combination with nontrivial band structures can give rise to several exotic physical properties such as a large anomalous Hall effect, the anomalous Nernst effect, and the topological Hall effect (THE). Antiferromagnetic (AFM) materials exhibit the THE due to the presence of nontrivial spin structures. EuCuAs crystallizes in a hexagonal structure with an AFM ground state (Néel temperature ∼ 16 K). In this work, we observe a large topological Hall resistivity of ∼7.4 μΩ-cm at 13 K which is significantly higher than the giant topological Hall effect of Gd2PdSi3 (∼3 μΩ-cm). Neutron diffraction experiments reveal that the spins form a transverse conical structure during the metamagnetic transition, resulting in the large THE. In addition, by controlling the magnetic ordering structure of EuCuAs with an external magnetic field, several fascinating topological states such as Dirac and Weyl semimetals have been revealed. These results suggest the possibility of spintronic devices based on antiferromagnets with tailored noncoplanar spin configurations.

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO3 thin film

Electron-doped Ca0.96Ce0.04MnO3 (CCMO) possesses a unique band structure and exhibits a giant topological Hall effect contrary to other correlation-driven manganites known for insulator-to-metal transition, magnetoresistance, complex magnetic order, etc. The interaction mechanisms among the fundamental entities and their dynamical evolutions responsible for this unusual topological phase are yet to be understood. Here, we employ time-averaged and sub-picosecond time-resolved terahertz (THz) spectroscopy to explore the low-energy steady-state and ultrafast carrier dynamics, respectively, to unravel the complexity of charge carriers during their transition from a non-equilibrium state to the ground state in CCMO thin film. The THz optical conductivity confirms the presence of dichotomic charge carriers, i.e. heavy and light carriers throughout the temperature range of 15–300 K. A rare observation of both positive and negative photoconductivities along with a sharp crossover between the two resolved to a few picoseconds of illumination confirms the formation of polaron with a lifetime of a few nanoseconds. These optical evidences of dichotomic charge carriers, along with manipulation of the sign of photoconductivity induced by dynamics of related quasiparticles could facilitate a new mechanism for ultrafast optoelectronic switching devices.

A giant topological Hall effect in ferromagnetic compound CeMn2Ge2 with wide temperature range from 70 to 310 k

The transport properties of ferromagnetic compound CeMn2Ge2 have been systematically studied by magnetic resistivity measurements. Strikingly, it has been found that CeMn2Ge2 compound displays a giant topological Hall effect (THE) about 0.8 μΩ·cm with 0.45 T magnetic field under 220 k. THE appears in a wide temperature range between 70 and 310 K in a magnetic field region, and could even appear in a zero magnetic field at room temperature. The magnetoresistance curves present gradual change with kinks which have relation to magnetic transitions. Moreover, these results show that topologically protected spin texture may exist in CeMn2Ge2 ferromagnetic compound.

Giant Topological Hall Effect in the Noncollinear Phase of Two-Dimensional Antiferromagnetic Topological Insulator MnBi4Te7.

Magnetic topological insulators provide an important platform for realizing several exotic quantum phenomena, such as the axion insulating state and the quantum anomalous Hall effect, owing to the interplay between topology and magnetism. MnBi4Te7 is a two-dimensional Z2 antiferromagnetic (AFM) topological insulator with a Néel temperature of ∼13 K. In AFM materials, the topological Hall effect (THE) is observed owing to the existence of nontrivial spin structures. A material with noncollinearity that develops in the AFM phase rather than at the onset of the AFM order is particularly important. In this study, we observed that such an unanticipated THE starts to develop in a MnBi4Te7 single crystal when the magnetic field is rotated away from the easy axis (c-axis) of the system. Furthermore, the THE resistivity reaches a giant value of ∼7 μΩ-cm at 2 K when the angle between the magnetic field and the c-axis is 75°. This value is significantly higher than the values for previously reported systems with noncoplanar structures. The THE can be ascribed to the noncoplanar spin structure resulting from the canted state during the spin-flip transition in the ground AFM state of MnBi4Te7. The large THE at a relatively low applied field makes the MnBi4Te7 system a potential candidate for spintronic applications.

Giant topological Hall effect around room temperature in noncollinear ferromagnet NdMn2Ge2 single crystal

We report the observation of the giant topological Hall effect near room temperature in a complex noncollinear ferromagnet NdMn2Ge2 single crystal. Three successive magnetic transitions are observed below 400 K, including a spin reorientation transition at TSR = 215 K. The complex noncollinear magnetic structures give rise to anomalous transport behaviors. When the current flows along the a axis and the magnetic field is applied along the c axis, the anomalous Hall effect is observed, which is found to be dominated by the skew scattering mechanism. Strikingly, a giant topological Hall effect appears in a wide temperature range, which stems from the noncollinear spin configuration with finite scalar spin chirality. The topological Hall resistivity reaches the maximum of −1.35 μΩ cm at 300 K and drops slightly with temperature until below TSR. These results suggest that the NdMn2Ge2 single crystal would be a promising topological material for spintronic applications at room temperature.

Giant Topological Hall Effect and Superstable Spontaneous Skyrmions below 330 K in a Centrosymmetric Complex Noncollinear Ferromagnet NdMn2Ge2.

Skyrmions with topologically nontrivial spin textures are promising information carriers in next-generation ultralow power consumption and high-density spintronic devices. To promote their further development and utilization, the search for new room temperature skyrmion-hosting materials is crucial. Considering that most of the previous skyrmion-hosting materials are noncollinear magnets, here, the detection of the topological Hall effect (THE) and the discovery of skyrmions at room temperature are first reported in a centrosymmetric complex noncollinear ferromagnet NdMn2Ge2. Below 330 K, the compound can host stable Bloch-type skyrmions with about 75 nm diameter in a wide window of magnetic field and temperature, including zero magnetic field and room temperature. Moreover, the skyrmions can induce a giant topological Hall effect in a wide temperature range with a maximum value of -2.05 μΩ cm. These features make the compound attractive for both fundamental research and potential application in novel spintronic devices.

Giant topological Hall effect of ferromagnetic kagome metal Fe3Sn2**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0300504), the National Natural Science Foundation of China (Grant Nos. 11574394, 11774423, and 11822412), the Fundamental Research Funds for the Central Universities of China, and the Research Funds of Renmin University of China (RUC) (Grant Nos. 15XNLQ07, 18XNLG14, and 19XNLG17).

We present the experiment observation of a giant topological Hall effect (THE) in a frustrated kagome bilayer magnet Fe3Sn2. The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K. Its maximum absolute value reaches ∼ 2.01 µΩ·cm at 300 K and 0.76 T. The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration, possibly related to the magnetic frustration interaction in Fe3Sn2.

Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet.

Geometrically frustrated magnets can host complex spin textures, leading to unconventional electromagnetic responses. Magnetic frustration may also promote topologically nontrivial spin states such as magnetic skyrmions. Experimentally, however, skyrmions have largely been observed in noncentrosymmetric lattice structures or interfacial symmetry-breaking heterostructures. Here, we report the emergence of a Bloch-type skyrmion state in the frustrated centrosymmetric triangular-lattice magnet Gd2PdSi3 We observed a giant topological Hall response, indicating a field-induced skyrmion phase, which is further corroborated by the observation of in-plane spin modulation probed by resonant x-ray scattering. Our results may lead to further discoveries of emergent electrodynamics in magnetically frustrated centrosymmetric materials.

Emergent Topological Hall Effect in La0.7Sr0.3MnO3/SrIrO3 Heterostructures.

Recently, perovskite oxide heterostructures have drawn great attention because multiple and complex coupling at the heterointerface may produce novel magnetic and electric phenomena that are not expected in homogeneous materials either in the bulk or in films. In this work, we report for the first time that an emergent giant topological Hall effect (THE), associated with a noncoplanar (NC) spin texture, can be induced in ferromagnetic (FM) La0.7Sr0.3MnO3 thin films in a wide temperature range of up to 200 K by constructing La0.7Sr0.3MnO3/SrIrO3 epitaxial heterostructures on (001) SrTiO3 substrates. This THE is not observed in La0.7Sr0.3MnO3 single-layer films or La0.7Sr0.3MnO3/SrTiO3/SrIrO3 trilayer heterostructures, indicating the relevance of the La0.7Sr0.3MnO3/SrIrO3 interface, where the Dzyaloshinskii-Moriya interaction due to strong spin-orbital coupling in SrIrO3 may play a crucial role. The fictitious field associated with THE is independent of temperature in La0.7Sr0.3MnO3/SrIrO3 heterostructures, suggesting that the NC spin texture may be magnetic skyrmions. This work demonstrates the feasibility of using SrIrO3 to generate novel magnetic and transport characteristics by interfacing with other correlated oxides, which might be useful to novel spintronic applications.

Publisher Correction: Giant topological Hall effect in correlated oxide thin films

In the version of this Letter originally published, Hiroshi Kohno’s affiliation was incorrectly listed as Department of Earth and Space Science, Graduate School of Science, Osaka University, Osaka, Japan; it should have been Department of Physics, Nagoya University, Nagoya, Japan. This has been corrected in all versions of the Letter.

Giant topological Hall effect in correlated oxide thin films

Strong electronic correlations can produce remarkable phenomena such as metal-insulator transitions and greatly enhance superconductivity, thermoelectricity, or optical non-linearity. In correlated systems, spatially varying charge textures also amplify magnetoelectric effects or electroresistance in mesostructures. However, how spatially varying spin textures may influence electron transport in the presence of correlations remains unclear. Here we demonstrate a very large topological Hall effect (THE) in thin films of a lightly electron-doped charge-transfer insulator, (Ca, Ce)MnO3. Magnetic force microscopy reveals the presence of magnetic bubbles, whose density vs. magnetic field peaks near the THE maximum, as is expected to occur in skyrmion systems. The THE critically depends on carrier concentration and diverges at low doping, near the metal-insulator transition. We discuss the strong amplification of the THE by correlation effects and give perspectives for its non-volatile control by electric fields.