Large Topological Hall Effect Research Articles

Spontaneous (Anti)meron Chains in the Domain Walls of van der Waals Ferromagnetic Fe5- x GeTe2.

The promise of topologically vortex-like magnetic spin textures hinges on the intriguing physical properties and theories in fundamental research and their distinguished roles as high-efficiency information units in future spintronics. The exploration of such magnetic states with unique spin configurations has never ceased. In this study, the emergence of unconventional (anti)meron chains from a domain wall pair is directly observed at zero field in 2D ferromagnetic Fe5- x GeTe2 , closely correlated with significant enhancement of the in-plane magnetization and weak van der Waals interactions. The simultaneous appearance of a large topological Hall effect is observed at the same temperature range as that of the abnormal magnetic transition. Moreover, the distinctive features of the (anti)meron chains and their collective dynamic behavior under external fields may provide concrete experimental evidence for the recent theoretical prediction of the magnetic-domain-wall topology and endorse a broader range of possibilities for electronics, spintronics, condensed matter physics, etc.

Magnetic transition behavior and large topological Hall effect in hexagonal Mn2−xFe1+xSn (x = 0.1) magnet

The magnetic transition, transport properties, and magnetic domain structures of the polycrystalline Mn1.9Fe1.1Sn compound with a hexagonal structure have been investigated. The result shows that ferromagnetic and antiferromagnetic phases coexist in this compound. A large topological Hall effect up to 3.5 μΩ·cm at 50 K has been found due to the formation of noncoplanar spin structures when the competition occurs among magnetocrystalline anisotropy, antiferromagnetic coupling, and ferromagnetic interaction at low temperature. The result of in situ Lorentz transmission electron microscopy cooling experiment at zero field indicates two shapes of domain walls containing vortexes coexisting simultaneously in the compound.

Large topological Hall effect in an easy-cone ferromagnet (Cr0.9B0.1)Te

The Berry phase understanding of electronic properties has attracted special interest in condensed matter physics, leading to phenomena such as the anomalous Hall effect and the topological Hall effect. A non-vanishing Berry phase, induced in momentum space by the band structure or in real space by a non-coplanar spin structure, is the origin of both effects. Here, we report a sign conversion of the anomalous Hall effect and a large topological Hall effect in (Cr0.9B0.1)Te single crystals. The spin reorientation from an easy-axis structure at high temperature to an easy-cone structure below 140 K leads to conversion of the Berry curvature, which influences both, anomalous and topological, Hall effects in the presence of an applied magnetic field and current. We compare and summarize the topological Hall effect in four categories with different mechanisms and have a discussion into the possible artificial fake effect of the topological Hall effect in polycrystalline samples, which provides a deep understanding of the relation between the spin structure and Hall properties.

Robust topological Hall effect driven by tunable noncoplanar magnetic state in Mn-Pt-In inverse tetragonal Heusler alloys

Manipulation of magnetic ground states by effective control of competing magnetic interactions has led to the finding of many exotic magnetic states. In this direction, the tetragonal Heusler compounds consisting of multiple magnetic sublattices and crystal symmetry favoring chiral Dzyaloshinskii-Moriya interaction (DMI) provide an ideal base to realize non-trivial magnetic structures. Here, we present the observation of a large robust topological Hall effect (THE) in the multi-sublattice Mn$_{2-x}$PtIn Heusler magnets. The topological Hall resistivity, which originates from the non-vanishing real space Berry curvature in the presence of non-zero scalar spin chirality, systematically decreases with decreasing the magnitude of the canting angle of the magnetic moments at different sublattices. With help of first principle calculations, magnetic and neutron diffraction measurements, we establish that the presence of a tunable non-coplanar magnetic structure arising from the competing Heisenberg exchanges and chiral DMI from the D$_{2d}$ symmetry structure is responsible for the observed THE. The robustness of the THE with respect to the degree of non-collinearity adds up a new degree of freedom for designing THE based spintronic devices.

Spontaneous magnetic bubbles and large topological Hall effect in Mn3-xFexSn compound

Magnetic and transport properties as well as magnetic domain structures have been investigated in a hexagonal polycrystalline Mn2.1Fe0.9Sn compound. The in-situ observation of Lorentz transmission electron microscopy shows that spontaneous magnetic bubbles owing a pair of Bloch lines and biskyrmions consisting of two skyrmions of opposite spin helicities coexist in this compound at low temperature. A large topological Hall resistivity up to about 9 µΩ·cm at 50 K has been found owing to the formation of noncoplanar spin textures deriving from the competition among magnetocrystalline anisotropy, antiferromagnetic coupling, and ferromagnetic interaction.

Large anisotropic topological Hall effect in a hexagonal non-collinear magnet Fe5Sn3

We report the observation of a large anisotropic topological Hall effect (THE) in the hexagonal non-collinear magnet Fe5Sn3 single crystals. It is found that the sign of the topological Hall resistivity ρTH is negative when a magnetic field H is perpendicular to the bc-plane (H ⊥ bc-plane); however, it changes form negative to positive when H is parallel to the c-axis (H ∥ c-axis). The value of ρTH increased with the increasing temperature and reached approximately −2.12 μΩ cm (H ⊥ bc-plane) and 0.5 μΩ cm (H ∥c-axis) at 350 K, respectively. Quantitative analyses of the measured data suggest that the observed anisotropic THE may originate from the opposite scalar spin chirality induced by the magnetic fields perpendicular and parallel to the c-axis, respectively.

Skyrmion phase and competing magnetic orders on a breathing kagom\xe9 lattice

Magnetic skyrmion textures are realized mainly in non-centrosymmetric, e.g. chiral or polar, magnets. Extending the field to centrosymmetric bulk materials is a rewarding challenge, where the released helicity/vorticity degree of freedom and higher skyrmion density result in intriguing new properties and enhanced functionality. We report here on the experimental observation of a skyrmion lattice (SkL) phase with large topological Hall effect and an incommensurate helical pitch as small as 2.8 nm in metallic Gd3Ru4Al12, which materializes a breathing kagomé lattice of Gadolinium moments. The magnetic structure of several ordered phases, including the SkL, is determined by resonant x-ray diffraction as well as small angle neutron scattering. The SkL and helical phases are also observed directly using Lorentz-transmission electron microscopy. Among several competing phases, the SkL is promoted over a low-temperature transverse conical state by thermal fluctuations in an intermediate range of magnetic fields.

Large topological Hall effect in a geometrically frustrated kagome magnet Fe3Sn2

We report on the observation of a large topological Hall effect (THE) over a wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a kagome-bilayer structure. We found that the magnitude of the THE resistivity increases with temperature and reaches −0.875 μΩ cm at 380 K. Moreover, the critical magnetic fields with the change of THE are consistent with the magnetic structure transformation, which indicates that the real-space fictitious magnetic field is proportional to the formation of magnetic skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates from the topological magnetic spin textures and may open up further research opportunities in exploring emergent phenomena in kagome materials.

Observation of the topological Hall effect and signature of room-temperature antiskyrmions in Mn-Ni-Ga D2d Heusler magnets

Topologically stable nontrivial spin structures, such as skyrmions and antiskyrmions, display a large topological Hall effect owing to their quantized topological charge. Here, we present the finding of a large topological Hall effect beyond room temperature in the tetragonal phase of a Mn-Ni-Ga based ferrimagnetic Heusler shape memory alloy system. The origin of the field induced topological phase, which is also evidenced by the appearance of dips in the ac-susceptibility measurements, is attributed to the presence of magnetic antiskyrmions driven by D2d symmetry of the inverse Heusler tetragonal phase. Detailed micromagnetic simulations asserts that the antiskyrmionic phase is stabilized as a result of interplay among inhomogeneous Dzyaloshinskii-Moriya interaction, the Heisenberg exchange, and the magnetic anisotropy energy. The robustness of the present result is demonstrated by stabilizing the antiskyrmion hosting tetragonal phase up to a temperature as high as 550 K by marginally varying the chemical composition, thereby driving us a step closer to the realization of ferrimagnetic antiskyrmion based racetrack memory.

Topological Hall effect in thin films of Mn1.5PtSn

Spin chirality in metallic materials with non-coplanar magnetic order can give rise to a Berry phase induced topological Hall effect. Here, we report the observation of a large topological Hall effect in high-quality films of Mn$_{1.5}$PtSn that were grown by means of magnetron sputtering on MgO(001). The topological Hall resistivity is present up to $\mu_{0}H \approx 4~$T below the spin reorientation transition temperature, $T_{s}=185$~K. We find, that the maximum topological Hall resistivity is of comparable magnitude as the anomalous Hall resistivity. Owing to the size, the topological Hall effect is directly evident prior to the customarily performed subtraction of magnetometry data. Further, we underline the robustness of the topological Hall effect in Mn\textsubscript{2-x}PtSn by extracting the effect for multiple stoichiometries (x~=~0.5, 0.25, 0.1) and film thicknesses (t = 104, 52, 35~nm) with maximum topological Hall resistivities between $0.76~\mu\Omega$cm and $1.55~\mu\Omega$cm at 150~K.

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.

Large topological hall effect observed in tetragonal Mn2PtSn Heusler thin film

Tetragonal Mn-Pt-Sn Heusler compounds have been of interest because they enable magnetic antiskyrmion phases, which can potentially lead to low energy cost spintronic device applications. We report the synthesis and systematic study of the magnetic and transport properties of magnetron sputtered tetragonal Mn2PtSn thin films on the thermally oxidized Si substrates. We have observed a large topological Hall resistivity up to 0.57 μΩ cm around 150 K, which is the largest value among the Mn-based metallic materials so far. Moreover, the large topological Hall effect (THE) appears in a very wide temperature range of 10 K–300 K in a magnetic field region where the field-dependent Hall resistivity largely deviates from the magnetization. The large THE indicated here may also provide pathways towards realizing the magnetic antiskyrmions in tetragonal Mn2PtSn thin films.

Observation of large exchange bias and topological Hall effect in manganese nitride films

The magnetic and magneto-transport properties of manganese nitride films grown by molecular beam epitaxy have been investigated. Due to the mixed ferrimagnetic (FI) phase (ε-phase with TFI ∼ 738 K) and the antiferromagnetic phase (ζ-phase with TN ∼ 273 K), we observe magnetization hysteresis loops with non-zero exchange bias below TN, reaching ∼0.22 T at 5 K. This indicates that noncollinear spins exist at the interfaces of two phases, creating competition between interfacial Dzyaloshinskii-Moriya and exchange interactions. Strikingly, in addition to the normal Hall effect by the Lorentz force and the anomalous Hall effect by magnetizatism, we observe another contribution, namely, topological Hall effect below 75 K. This verifies the existence of topological spin texture, which is the consequence of competing interactions controlled by both applied field and temperature. Our work demonstrates that spintronic devices may be fabricated, exploiting rich magnetic properties of different phases.

Large topological Hall effect in nonchiral hexagonal MnNiGa films

We report a systematic study of the magnetic and transport properties of magnetron sputtered nonchiral hexagonal MnNiGa films on the thermally oxidized Si substrates as a function of film thickness. A large topological Hall effect (THE) is observed, and its magnitude increases correspondingly with increasing the film thickness. The large THE appears in a very wide temperature range of 10 K–300 K in a magnetic field region where the field-dependent Hall resistivity largely deviates from the magnetization. Moreover, the measurements on the cubic MnNiGa films do not show any evidence of the existence of THE. These results indicate that the non-collinear spin configurations from geometrical frustration of Mn moments are the likely origin of the observed large THE in hexagonal MnNiGa films.

Large topological Hall effect in the non-collinear phase of an antiferromagnet

Non-trivial spin arrangements in magnetic materials give rise to the topological Hall effect observed in compounds with a non-centrosymmetric cubic structure hosting a skyrmion lattice, in double-exchange ferromagnets and magnetically frustrated systems. The topological Hall effect has been proposed to appear also in presence of non-coplanar spin configurations and thus might occur in an antiferromagnetic material with a highly non-collinear and non-coplanar spin structure. Particularly interesting is a material where the non-collinearity develops not immediately at the onset of antiferromagnetic order but deep in the antiferromagnetic phase. This unusual situation arises in non-cubic antiferromagnetic Mn5Si3. Here we show that a large topological Hall effect develops well below the Néel temperature as soon as the spin arrangement changes from collinear to non-collinear with decreasing temperature. We further demonstrate that the effect is not observed when the material is turned ferromagnetic by carbon doping without changing its crystal structure.