Large Anomalous Hall Conductivity Research Articles

Crystalline electric field and large anomalous Hall effect in NdGaGe single crystals

We grew NdGaGe single crystals and investigated their magnetic and electrical transport properties. The magnetic susceptibility data revealed that NdGaGe orders magnetically at Tm≈ 8.8 K; also confirmed by heat capacity and electrical resistivity data. In ordered state, the heat capacity and electrical resistivity data exhibit a gapped-magnon behavior with an energy gap of ∼ 4.7 K. Our detailed crystalline electric field analysis of magnetic susceptibility, magnetization, and heat capacity data indicates that the (2J+1) degenerate energy levels of Nd3+ ion split into five doublets with an overall splitting of ∼ 123 K. We observe a large anomalous Hall conductivity (AHC) ∼530Ω−1 cm−1 at 2 K, which is close to the theoretical expected value due to intrinsic Berry-curvature. Moreover, the scaling parameter between anomalous Hall resistivity and magnetoresistivity together with the linear relationship between AHC and saturation magnetization suggests that the origin of large AHC in NdGaGe is due to the intrinsic Berry curvature.

Large anomalous Hall conductivity induced by spin chirality fluctuation in an ultraclean frustrated antiferromagnet PdCrO2

Magnetic frustration, realized in the special geometrical arrangement of localized spins, often promotes topologically nontrivial spin textures in the real space and induces significantly large unconventional Hall responses. This spin Berry curvature effect in itinerant frustrated magnets mainly works with a static spin order, limiting the effective temperature range below the magnetic transition temperature and yielding the typical anomalous Hall conductivity below ~ 103 Ω−1cm−1. Here we show that an ultraclean triangular-lattice antiferromagnet PdCrO2 exhibits a large anomalous Hall conductivity up to ~ 106 Ω−1cm−1 in the paramagnetic state, which is maintained far above the Neel temperature (TN) up to ~ 4TN. The reported enhancement of anomalous Hall response above TN is attributed to the skew scattering of highly mobile Pd electrons to fluctuating but locally-correlated Cr spins with a finite spin chirality. Our findings point at an alternative route to realizing high-temperature giant anomalous Hall responses, exploiting magnetic frustration in the ultraclean regime.

Large Anomalous Hall Effect at Room Temperature in a Fermi‐Level‐Tuned Kagome Antiferromagnet

AbstractThe recent discoveries of surprisingly large anomalous Hall effect (AHE) in antiferromagnets have attracted much attention due to their promising use in spintronics devices. However, such AHE‐hosting antiferromagnetic materials are rare in nature. Herein, it is demonstrated that Mn2.4Ga, a Fermi‐level‐tuned kagome antiferromagnet, has a large anomalous Hall conductivity of ≈150 Ω−1 cm−1 at room temperature that surpasses the usual high values (i.e., 20–50 Ω−1 cm−1) observed so far in two outstanding kagome antiferromagnets, Mn3Sn and Mn3Ge. Although the triangular spin structure of Mn2.4Ga shows a weak net magnetic moment of ≈0.05 µB per formula unit, it guarantees a nonzero Berry curvature in the kagome plane. Moreover, the anomalous Hall conductivity exhibits a sign reversal with the rotation of a small magnetic field that can be ascribed to the field‐controlled chirality of the spin triangular structure. This theoretical calculations further suggest that the large AHE in Mn2.4Ga originates from a significantly enhanced Berry curvature associated with the tuning of the Fermi level close to the Weyl points. These properties, together with the ability to manipulate moment orientations using a moderate external magnetic field, make Mn2.4Ga extremely exciting for future antiferromagnetic spintronics.

Magnons in a two-dimensional Weyl magnet

The discovery of topological states of matter has led to a revolution in condensed-matter science. While a non-trivial band topology in a material is often associated with intriguing transport properties, much less attention has been given to the impact on spin dynamics and non-equilibrium magnetization states. Here, we provide evidence that a chiral asymmetric magnon dispersion in the two-dimensional Weyl magnet Fe/W(110) is related to the presence of Weyl fermions close to the Fermi energy and surface Fermi arcs. We find that the large anomalous Hall conductivity and the Dzyaloshinskii–Moriya interaction are attributed to the non-trivial band topology in the composite momentum-magnetization space. Our results show the direct impact of Weyl fermions on both the charge and spin dynamics in a two-dimensional magnet. Unveiling these principles can promote innovative technologies in magnonics by utilizing topological materials, where magnons and non-trivial topological electronic states can be manipulated through magnetization.

Large anomalous transverse transport properties in atomically thin 2D Fe3GaTe2

Anomalous transverse conductivities, such as anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and anomalous thermal Hall conductivity (ATHC), play a crucial role in the emerging field of spintronics. Motivated by the recent fabrication of two-dimensional (2D) ferromagnetic thin film Fe3GaTe2, we investigate the thickness-dependent anomalous transverse conductivities of the 2D Fe3GaTe2 system (from one to four layers). The atomically ultrathin 2D Fe3GaTe2 system shows above-room-temperature ferromagnetism with a large perpendicular magnetic anisotropy energy. Furthermore, we obtain a large AHC of −485 S/cm in the four-layer thickness, and this is further enhanced to −550 S/cm with small electron doping. This AHC is seven times larger than the measured AHC in thicker 2D Fe3GaTe2 (178 nm). The ANC also reaches 0.55 A/K.m in the four-layer structure. Along with these, the four-layer system exhibits a large ATHC (−0.105 ~ −0.135 W/K.m). This ATHC is comparable to the large ATHC found in Weyl semimetal Co3Sn2S2. Based on our results, the atomically ultrathin 2D Fe3GaTe2 system shows outstanding anomalous transverse conductivities and can be utilized as a potential platform for future spintronics and spin caloritronic device applications.

Optical transparency in 2D ferromagnetic WSe2/1T-VSe2/WSe2 multilayer with strain induced large anomalous Nernst conductivity

Transparent two-dimensional (2D) magnetic materials may bring intriguing features and are indispensable for transparent electronics. However, it is rare to find both optical transparency and room-temperature ferromagnetism simultaneously in a single 2D material. Herein, we explore the possibility of both these features in 2D WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 heterostructures by taking one monolayer (1ML) and two monolayers (2ML) of 1T-VSe2 using first-principles calculations. Further, we investigate anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) using a maximally localized Wannier function. The WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 systems show Curie temperatures of 328 and 405 K. Under biaxial compressive strain, the magnetic anisotropy of both systems is switched from in-plane to out-of-plane. We find a large AHC of 1.51 e2/h and 3.10 e2/h in the electron-doped region for strained WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 systems. Furthermore, we obtain a giant ANC of 3.94 AK−1 m−1 in a hole-doped strained WSe2/1T-VSe2 (2ML)/WSe2 system at 100 K. Both WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 are optically transparent in the visible ranges with large refractive indices of 3.2–3.4. Our results may suggest that the WSe2/1T-VSe2/WSe2 structure possesses multifunctional physical properties and these features can be utilized for spintronics and optoelectronics device applications such as magnetic sensors, memory devices, and transparent magneto-optic devices at room temperature.

Colossal anomalous Hall effect in the layered antiferromagnetic EuAl2Si2 compound.

The anomalous Hall effect (AHE), significantly enhanced by the extrinsic mechanism, has attracted attention for its almost unlimited Hall response, which exceeds the upper limit of the Berry curvature mechanism. However, due to the high conductivity in the clean regime and weak skew scattering, it is a great challenge to obtain large anomalous Hall conductivities and large anomalous Hall angles at the same time. Here, we unveil a new magnetic metal system, EuAl2Si2, which hosts both colossal anomalous Hall conductivity (σAxy ≥ 104 Ω-1 cm-1) and large anomalous Hall angle (AHA >10%). The scaling relation suggests that the skew scattering mechanism is dominant in the colossal anomalous Hall response and gives rise to a large skew scattering constant. The large effective SOC and large magnetic moment may account for this anomaly. Our results indicate that EuAl2Si2 is a good platform to study the extrinsic AHE mechanism.

Tunable long-range spin transport in a van der Waals Fe3GeTe2/WSe2/Fe3GeTe2 spin valve.

The seamless integration of two-dimensional (2D) ferromagnetic materials with similar or dissimilar materials can widen the scope of low-power spintronics. In this regard, a vertical van der Waals (vdW) heterostructure of 2D ferromagnets with semiconducting transition metal dichalcogenides (TMDCs) forms magnetic junctions with exceptional stability and electrical control. Interestingly, 2D metallic Fe3GeTe2 (FGT) reveals above room temperature Curie temperatures and has large magneto anisotropy due to spin-orbit coupling. In addition, it also possesses topological states and a large Berry curvature. Herein, we designed the FGT/WSe2/FGT vdW heterostructure with a uniform and sharp interface so that FGT could maintain its inherent electronic properties. Also, the uniform thickness of the barrier provides a smooth flow of spins through the junctions as tunneling exponentially decays with an increasing barrier thickness. However, strong energy-dependent spin polarization is crucial for achieving optimum spin valve properties, such as large tunneling magnetoresistance (TMR) along with the manipulation of the magnitude and sign reversal. We have observed a shifting of high-energy localized minority spin states toward low-energy regions, which causes spin polarization fluctuation between -42.5% and 41% over a wide range of bias voltage. This leads to a negative TMR% of ∼-100% at 0.1 V Å-1 and also a large positive TMR% at 0.2 V Å-1 and -0.4 V Å-1. Besides, the system exhibits a highly tunable large anomalous Hall conductivity (AHC) of 626 S cm-1. Interestingly, such unprecedented electronic behaviour with large and switchable spin polarization, anomalous Hall conductivity and TMR can be incorporated into MTJ devices, which provide electrical control and long-range spin transport. Additionally, the system emerges as a standout candidate in low-power spintronic devices (e.g., MRAM and magnetic sensors) owing to its distinctive energy-dependent electronic structure with a wide range of external bias.

Amplification of ferromagnetic and transverse transport properties during monolayer-to-bilayer transition in MnSe2: A first-principle study

Transverse anomalous transport properties are highly beneficial for spintronics applications compared with conventional longitudinal transport properties behaviors. Thus, we explore the thickness-dependent anomalous transverse transport properties of mono- and bilayer two-dimensional MnSe2. Both structures have ferromagnetic ground states with half metallicity. The monolayer structure has a perpendicular magnetic anisotropy of 2.51 meV, and this is increased to 3.57 meV in the bilayer. We find a Curie temperature of 221 K in monolayer MnSe2, and it reaches 286 K in the bilayer MnSe2. Despite a relatively small anomalous Hall conductivity (AHC) in the monolayer (−30 S/cm), it is substantially enhanced to −402 S/cm in the bilayer. Due to this enhancement of the AHC, the bilayer MnSe2 displays a large anomalous thermal Hall conductivity −0.10 W/K.m at 100 K and is further enhanced to −0.2 W/K.m at 200 K. Overall, our study may suggest that the 2D MnSe2 can be utilized for potential spintronics applications.

First-principles prediction of intrinsic piezoelectricity, spin-valley splitting and magneto-crystal anisotropy in 2H-VS2 magnetic semiconductor

The piezoelectricity, valley character and magnetic properties of intrinsic ferrovalley 2H-VS2 monolayer are studied using density functional theory. The results suggest that 2H-VS2 monolayer exhibits obvious bipolar magnetic semiconductor characters with Curie temperature (TC) of 278 K, large piezoelectric coefficient d11 of 3.925 pm/V, in-plane magneto-crystal anisotropy (MA) and large valley splitting (ΔKK′) of 75.1 meV. Applying in-plane strain (-6% to 6 %) can well adjust the ΔKK′ and TC from 72 meV to 76.7 meV and from 98 K to 397 K, respectively, resulting an obvious change of electronic structures from bipolar magnetic semiconductor to spin gapless semiconductor phase. The magnetic anisotropy energy (MAE) of 2H-VS2 monolayer firstly increases and then decreases as the strain increases from −6% to 6 %, which mainly originates from the contribution of V dx2-y2 and dxy orbitals. In addition, 2H-VS2 monolayer retains a large valley-contrasting Berry curvature and non-zero anomalous Hall conductivity, indicating that the transverse velocity of carriers is opposite to the effect of in-plane longitudinal electric field. These results suggest that the 2H-VS2 monolayer can become good candidates for the spintronic and valleytronic applications.

Modulating intrinsic anomalous Hall effect in Fe3GeTe2 monolayer via strain engineering

The Fe3GeTe2 monolayer, a ferromagnetic topological candidate with a high Curie temperature of 130 K, has recently garnered considerable interest. We investigated the impact of strain on the electronic, magnetic, and topological properties of the Fe3GeTe2 monolayer using density functional theory calculations. Our results showed that the Fe3GeTe2 monolayer was an itinerant ferromagnet with a high spin polarization of 69.93% and out-of-plane easy magnetization. Tensile strain had no profound impact on the anomalous Hall conductivity (AHC). However, when applying a compressive biaxial strain of −3%, the AHC at the Fermi level was dramatically enhanced to 1.62 e2/h, which is much larger than that of the bulk (0.7 e2/h) and bilayer (1.5 e2/h) material. The large AHC nearly coincided with the singularity of the energy bands near the M point. Our results highlight the potential of using strain engineering to control and optimize the properties of two-dimensional topological materials.

Interplay between altermagnetism and nonsymmorphic symmetries generating large anomalous Hall conductivity by semi-Dirac points induced anticrossings

Interplay between altermagnetism and nonsymmorphic symmetries generating large anomalous Hall conductivity by semi-Dirac points induced anticrossings

Giant anomalous Hall and Nernst conductivities in cubic Fe3Pt and Ni3In

The topological anomalous Hall effect and the anomalous Nernst effect are of great interest for the development of spintronic devices for energy-efficient data storage and energy harvesting. Using first-principles calculations, we have studied the anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) of six ferromagnetic compounds Co3Al, Fe3Ge, Fe3Pt, Ni3Ga, Ni3In, and Rh3Cr belonging to the cubic Cu3Au structure. A large AHC of 1973 S cm−1 is obtained for Fe3Pt. Parallel to the large AHC, a giant ANC of −5.41 A mK−1 and −4.18 A mK−1 is observed for Ni3In and Co3Al, respectively. Finally, we found that AHC and ANC can be adjusted by switching the magnetization direction.

The anomalous Hall effect controlled by residual epitaxial strain in antiferromagnetic Weyl semimetal Mn3Sn thin films grown by molecular beam epitaxy

The large anomalous Hall effect (AHE) in antiferromagnetic(AFM) Weyl semimetal Mn3Sn attracts intensive attentions in spintronics. Here, we report the structural property of high quality Mn3Sn thin film on insulator substrate MgO(110) by molecular beam epitaxy (MBE), and AHE in control of residual mismatch strain between Mn3Sn film and substrate. We are able to grow strain-free Mn3Sn(10 1¯ 0) films or alternatively strained Mn3Sn(11 2¯ 0) films via a three-step process. The strain-free Mn3Sn film has large anomalous Hall conductivity up to 30 Ω-1cm−1 at room temperature, which is comparable to bulk Mn3Sn. In contrast, AHE is switched off in strained Mn3Sn film due to piezomagnetic effect under a uniaxial compress strain of ∼2.0%. These findings provide a deeper understanding on AFM spintronic applications.

Multi- k magnetic structure and large anomalous Hall effect in candidate magnetic Weyl semimetal NdAlGe

The magnetic structure, magnetoresistance (MR), and Hall effect of the noncentrosymmetric magnetic semimetal NdAlGe are investigated, revealing an unusual magnetic state and anomalous transport properties that are associated with the electronic structure of this compound. The magnetization and MR measurements are both highly anisotropic and indicate an Ising-like magnetic system. The magnetic structure is complex in that it involves two magnetic ordering vectors, including an incommensurate spin density wave and commensurate ferrimagnetic state in zero field. We have discovered a large anomalous Hall conductivity that reaches $\ensuremath{\approx}430\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.28em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$, implying that it originates from an intrinsic Berry curvature effect stemming from Weyl nodes found in the electronic structure. These electronic structure calculations indicate the presence of nested Fermi surface pockets with nesting wave vectors like the measured magnetic ordering wave vector and the presence of Weyl nodes in proximity to the Fermi surface. We associate the incommensurate magnetic structure with the large anomalous Hall response to be the result of the combination of Fermi surface nesting and the Berry curvature associated with Weyl nodes.

Large anomalous Hall effect and intrinsic Berry curvature in magnetic Weyl semimetal NdAlGe

Weyl semimetals driven by both time-reversal (TRS) and inversion symmetries (IS) are rare and be a good platform to investigate the relationship between chiral current and magnetic order. NdAlGe compound, grown in a single crystalline form by the flux method, has a noncentrosymmetric I41md crystal structure, which breaks inversion symmetry. The magnetic susceptibility χ(T) shows anisotropic behavior; ferromagnetic with divergence of field cooling (FC) and zero field cooling (ZFC) in H∥c, and antiferromagnetic transition for magnetic field H⊥c. The band structure calculation has revealed that NdAlGe is the type-II Weyl semimetal with four types of Weyl nodes in the ab-plane with a probable Fermi surface nesting vector. The ferromagnetic spin alignment gives a significant anomalous Hall coefficient Rs and large anomalous Hall conductivity σxyA, for H∥c. The giant anomalous Hall conductivity σxyA, constant SH=σxyA/M (H = 50 kOe) value, and their Karplus and Luttinger (KL) analysis support that the giant AHE is associated with the intrinsic Berry curvature in NdAlGe compound. The intrinsic Berry curvature is also confirmed by the planar Hall effect over a wide temperature range, implying that the Weyl semimetallic property is not relevant with the magnetic order.

Magnetization-direction-tunable spin coupling in kagome magnet LiMn6Sn6

The LiMn6Sn6-type of RMn6Sn6 kagome magnet, a room temperature intrinsic ferromagnet with a large anomalous Hall conductivity, has recently been shown to have magnetic-field-direction-dependent electronic structure due to the possible interplay between magnetism and band topology. In this work, we demonstrate magnetic moment direction tunable spin coupling from 3D-Ising type in in-plane spin orientation to 3D-Heisenberg type in out-of-plane spin orientation in kagome magnet LiMn6Sn6, which will further enhance the physics and functionality of LiMn6Sn6. Magnetization measurement of LiMn6Sn6 single crystal revealed paramagnetic to ferromagnetic (PM-FM) phase transition at around 381 K and an easy magnetization axis along the ab-plane (H‖ab). The comprehensive analysis of magnetization isotherms measured in the vicinity of Tc yields the asymptotic critical exponents β, γ, and δ as 0.323, 1.169 and 4.72 for H‖ ab, and 0.350, 1.37, and 4.77 for (H‖ c). These critical exponents satisfy the scaling relation and scaling equation of the magnetic state predicted by scaling theory. The critical exponents obtained are consistent with those found using the renormalization group theory approach for a three-dimensional Ising spin system with spin ordered in an easy in-plane axis (H ⊥ c). However, when the H is applied parallel to the c-axis (H‖ c), the spin coupling changes to a three-dimensional Heisenberg type. Consequently, the origin of ferromagnetism and long-range spin interaction are investigated by DFT first-principles calculations. The calculating result reveals that the Mn3-Mn3 interlayer FM coupling mediated by the super-exchange interaction via Sn2 honeycomb layers sandwiched between the two Mn3 layers is responsible for the macroscopic magnetization in LiMn6Sn6. At the same time, the magnetic couplings between Sn2Li and Mn3 layers play an important role in stabilizing the long-range ferromagnetic ordering.

VTaNbAl: A class of spin gapless semiconductors with topological nontrivial features

We report a class of spin gapless semiconductors (SGSs) hosting topological nontrivial features along with a fully compensated ferrimagnetic behavior in VTaNbAl, a quaternary Heusler alloy. Unlike conventional SGSs, this class of compounds acquires a unique band structure with opposite spin characters in the valence and conduction band edges, making them potential candidates for spin valves and a large anomalous Nernst effect. Interestingly, despite compensated ferrimagnetic (CF) behavior, VTaNbAl shows a reasonably large anomalous Hall effect possibly arising from the intrinsic nonvanishing Berry curvature. The CF state breaks the time-reversal symmetry and hence opens the possibility of Weyl nodes. We found four pairs of Weyl nodes located near the Fermi level leading to the nonvanishing Berry curvature, and hence a large anomalous Hall conductivity ($\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$). Our experimental synthesis confirms VTaNbAl to crystallize in a cubic Heusler structure with $A2$-type disorder. A magnetization measurement shows a very small saturation moment ($\ensuremath{\sim}{10}^{\ensuremath{-}3}{\textmu{}}_{B}/\text{f.u.}$), which agrees fairly well with our theoretical findings of fully compensated ferrimagnetism in the alloy. Resistivity shows a metalliclike nature, with the signature of disorder-induced weak localization in the low-temperature limit. The overall variation with varying temperature, however, is extremely weak.

Ab initio prediction of anomalous Hall effect in antiferromagnetic CaCrO3

While the anomalous Hall effect takes place typically in ferromagnets with finite magnetization, large anomalous Hall conductivity in noncollinear antiferromagnetic systems has been recently observed and attracted much attention. In this paper, we predict the anomalous Hall effect in perovskite ${\mathrm{CaCrO}}_{3}$ as a representative of collinear antiferromagnetic materials. Our result shows that the $C$-type antiferromagnetic ordering generates the sizable anomalous Hall conductivity. Based on symmetry analyses, we show that the antiferromagnetic order parameter belongs to the same irreducible representation as the ferromagnetic order parameter in the nonsymmorphic space group, allowing the nonvanishing Berry curvatures in $k$ space. By performing first-principles density-functional theory calculations, we find that the Berry-curvature ``hot spots'' lie along the gapped nodal lines where spin-orbit coupling induces the spin splitting of Cr-$3d$ bands near the Fermi energy and enhances the anomalous Hall effect in ${\mathrm{CaCrO}}_{3}$.

Exotic Weyl semimetal, emergent Fermi surface, and Lifshitz phase transition

Weyl semimetals (WSMs) with paired Weyl points in momentum space have attracted much attention in the past decade, and materials for this phase and the exotic Fermi arcs at their surface have been realized, in which the topology can be found in a finite momentum interval. Here we suggest a four-band model for WSM with two Weyl points in the ${k}_{z}$ axis, yet with totally different Fermi arcs at the surfaces. It exhibits a large anomalous Hall conductivity in the bulk, and large density of state on their surface. We analytically and numerically demonstrate the topological properties of this model from the dispersion, ${k}_{z}$-dependent Chern number, Fermi arc states, and dual topological phase. Furthermore, we investigate the effects of the magnetic field on the unusual Fermi arcs and find two emergent Fermi surfaces. Their combination can lead to diverse Lifshitz phase transitions when the thickness of the slab is decreased. The change of Fermi surfaces can be detected by the quantum oscillation, in which the contributions from a different number of closed Fermi surfaces can lead to different magnetotransport behaviors. We expect this model can stimulate the search for its realization in condensed matter physics and quantum simulating platforms.