arXiv subjects

Xuekui Xi

Publications and source records attributed to Xuekui Xi.

At least 19 recordsLinked to original sources

arXiv2026

Large Exchange Magnetostriction in a Kagome Antiferromagnet at Room Temperature

The pursuit of high-performance magnetostrictive materials is crucial for advancing technologies in sensing, actuation, and microelectromechanical systems. Although pronounced magnetostrictive effects have been observed in a few ferromagnets, a systematic exploration of magnetostriction across a broader range of antiferromagnets remains limited. Here, we report the observation of large magnetostriction in the kagome antiferromagnet YMn6Sn6. Under a magnetic field, the system undergoes a field-induced evolution from a helical magnetic ground state toward a collinear field-polarized state, accompanied by a large anisotropic lattice strain and a substantial volume magnetostriction exceeding 400 ppm at room temperature. Remarkably, the magnetostrictive response remains nearly fully reversible up to 9 T with nearly hysteresis-free behavior, effectively minimizing the energy dissipation commonly associated with domain-wall pinning. Combined experimental measurements and theoretical calculations reveal that the large, nearly hysteresis-free magnetostriction originates from the competition between intralayer ferromagnetic and interlayer exchange interactions. This exchange-driven magnetoelastic coupling further gives rise to a strongly direction-dependent lattice distortion pathway. This work establishes kagome helimagnets as a tunable platform for low-dissipation magnetoelastic functionalities and responsive magnetomechanical applications.

cond-mat.mtrl-sci↗

arXiv2026

Magnetoelastic instabilities in kagome antiferromagnet Mn3-xGa

We present a systematic study of the structural, magnetic, and transport properties of hexagonal Mn3-xGa alloys, revealing a series of composition-controlled emergent phenomena. By tuning the Mn concentration, we uncover distinct lattice responses, including a zero thermal expansion-like volume compensation behavior in Mn-poor compositions and a magnetoelastic-driven, field-assisted structural phase transition in Mn-rich samples. These lattice instabilities are accompanied by correlated magnetic and transport anomalies, including metamagnetic transitions, negative magnetoresistance, and anomalous Hall sign reversal. First-principles calculations demonstrate that the Hall sign reversal originates from crystal-symmetry breaking rather than magnetic reorientation alone. Our results establish composition as the key control parameter governing magnetoelastic coupling in Mn3-xGa, providing a unified framework to tailor structural, magnetic, and topological transport properties in kagome antiferromagnets and reconcile previously disparate experimental observations.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic signal scan imaging system based on giant magnetoimpedance (GMI) differential sensor

This paper presents the design and implementation of a magnetic signal scanning and imaging system based on the giant magnetoimpedance (GMI) effect. The system employs a pair of performance-matched GMI sensing elements configured as a differential probe structure. Through co-optimized low-noise electronic and probe design, the system effectively suppresses both intrinsic sensor common-mode drift and external environmental magnetic noise, enabling high signal-to-noise ratio detection of nono-tesla to micro-tesla-level magnetic signals without magnetic shielding. Experimental results demonstrate that the differential system achieves significantly lower noise spectral density in unshielded environments compared to conventional GMI sensors (\SI{46}{pT}/$\sqrt{\text{Hz}}$ versus \SI{286}{pT}/$\sqrt{\text{Hz}}$ at \SI{1}{Hz}), with a sensitivity of 186,790 V/T and spatial resolution better than 200 micrometers. The system's excellent performance in weak magnetic field detection and spatial resolution was verified through scanning experiments of magnetic ink on US banknotes and magnetic reference samples. Compared to SQUID scanning systems, which requiring liquid helium cooling, this system based on the GMI effect offers advantages of room-temperature operation, compact structure, and low cost. Relative to conventional single-element GMI microscopes, it achieves significant improvements in signal-to-noise ratio and environmental adaptability. This research provides a practical solution for high-resolution magnetic field imaging at room temperature with broad application potential in materials magnetism, biomagnetic imaging, and nanomagnetic detection.

physics.ins-det↗

arXiv2025

Giant magneto-cubic in-plane Hall effect in a nonmagnetic material

In-plane Hall effect (IPHE) triggered by an external magnetic field applied in the transport plane has attracted significant experimental attentions in recent few years 1-6. However, most experiments focus on magnetic materials, where the existence of magnetic ordering may complicate understanding the physics behind, and the relatively small signal magnitudes limit the application of the effect. Here, we report a giant IPHE in a nonmagnetic half-Heusler compound LuAuSn, with a magnitude exceeding all the previously reported values. A -period of IPHE and the consistent cubic dependence on the magnetic field are observed, realizing the long-sought theoretical prediction of magneto-cubic IPHE under threefold rotational symmetry7-9 in an unexpected material. The scaling law analysis and first-principles calculations indicate that extrinsic side jump and skew scattering processes from both impurity and phonon scatterings dominate the observed effect. These findings unravel a new type of magneto-nonlinear IPHE, and its large magnitude and wide-temperature operation may open the door to practical applications of IPHE.

cond-mat.mtrl-sci↗

arXiv2024

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

The recent discoveries of surperisingly large anomalous Hall effect in chiral antiderromagnets have triggered extensive research efforts in various fields, ranging from topological condensed-matter physics to antiferromagnetic spintronics, and energy harvesting technology. However, such AHE-hosting antiferromagnetic materials are rare in nature. Herein, we demonstrate that Mn2.4Ga, a Fermi-level-tuned kagome antiferromagnet, has a large anomalous Hall conductivity of about 150 {\Omega}-1cm-1 at room temperature that surpasses the usual high values (i.e.,20-50 {\Omega}-1cm-1) observed so far in two outstanding kagome antiferromagnets, Mn3Sn and Mn3Ge. The spin triangular structure of Mn2.4Ga guarantees a nonzero Berry curvature while generates only a weak net moment in the kagome plane.Moreover, the anomalous Hall conductivity exhibits a sign reversal with the rotation of a small magnetic field, which can be ascribed to the field-controlled chirality of the spin triangular structure. Our theoretical calculation indicate that the large AHE in Mn2.4Ga originates from a significantly enhanced Berry curvature associated wiht 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.

cond-mat.mtrl-sci↗

arXiv2022

Observation of short-period helical spin order and magnetic transition in a non-chiral centrosymmetric helimagnet

The search for materials exhibiting nanoscale spiral order continues to be fuelled by the promise of emergent inductors. Although such spin textures have been reported in many materials, most of them exhibit long periods or are limited to operate far below room temperature. Here, we present the real-space observation of an ordered helical spin order with a period of 3.2 nm in a non-chiral centrosymmetric helimagnet MnCoSi at room temperature via multi-angle and multi-azimuth approach of Lorentz transmission electron microscopy (TEM). A magnetic transition from the ordered helical spin order to a cycloidal spin order below 228 K is clearly revealed by in situ neutron powder diffraction and Lorentz TEM, which is closely correlated with temperature-induced variation in magneto-crystalline anisotropy. These results reveal the origin of spiral ordered spin textures in non-chiral centrosymmetric helimagnet, which can serve as a new strategy for searching materials with nanoscale spin order with potential applications in emergent electromagnetism.

cond-mat.mtrl-sci↗

arXiv2021

Coherent spin rotation-induced zero thermal expansion in MnCoSi-based spiral magnets

Materials exhibiting zero thermal expansion (ZTE), namely, volume invariance during temperature change, can resist thermal shock and are highly desired in modern industries as high-precision components. However, pure ZTE materials are rare, especially those that are metallic. Here, we report the discovery of a pure metallic ZTE material: an orthorhombic Mn1-xNixCoSi spiral magnet. The introduction of Ni can efficiently enhance the ferromagnetic exchange interaction and construct the transition from a spiral magnetic state to a ferromagnetic-like state in MnCoSi-based alloys. Systematic in situ neutron powder diffraction revealed a new cycloidal spiral magnetic structure in bc plane at ground state which would transform to the helical spiral in the ab plane with increasing temperature. Combined with Lorentz transmission electron microscopy techniques, the cycloidal and helical spin order coherently rotated at varying periods along the c axis during the magnetic transition. This spin rotation drove the continuous movement of the coupled crystalline lattice and induced a large negative thermal expansion along the a axis, eventually leading to a wide-temperature ZTE effect. Our work not only introduces a new ZTE alloy but also presents a new mechanism by which to discover or design ZTE magnets.

cond-mat.mtrl-sci↗

arXiv2021

Magnetic anisotropy and critical behavior of the quaternary van der Waals ferromagnetic material $\bf CrGe_δSi_{1-δ}Te_3$

Recently, two-dimensional ferromagnetism in the family of Chromium compounds $\rm CrXTe_3 (X=Si, Ge)$ has attracted a broad research interest. Despite the structural similarity in $\rm CrTe_6$ octahedra, the size effect of inserted Ge or Si dimer contributes to significant differences in magnetism. Here, we report a new quaternary van der Waals ferromagnetic material $\rm CrGe_δSi_{1-δ}Te_3$ synthesized by flux method. Ge substitution in Si site results in the lattice expansion, further increasing the Curie temperature and reducing the magnetic anisotropy. The critical behavior of $\rm Cr_{0.96}Ge_{0.17}Si_{0.82}Te_3$ has been studied by specific heat as well as magnetization measurements. And the extracted critical exponents are self-consistent and well-obeying the scaling laws, which are closer to the 2D Ising model with interaction decaying as $J(r)\approx r^{-3.44}$.

physics.app-ph↗

arXiv2021

On the anomalous low-resistance state and exceptional Hall component in hard-magnetic Weyl nanoflakes

Magnetic topological materials, which combine magnetism and topology, are expected to host emerging topological states and exotic quantum phenomena. In this study, with the aid of greatly enhanced coercive fields in high-quality nanoflakes of the magnetic Weyl semimetal Co3Sn2S2, we investigate anomalous electronic transport properties that are difficult to reveal in bulk Co3Sn2S2 or other magnetic materials. When the magnetization is antiparallel to the applied magnetic field, the low longitudinal resistance state occurs, which is in sharp contrast to the high resistance state for the parallel case. Meanwhile, an exceptional Hall component that can be up to three times larger than conventional anomalous Hall resistivity is also observed for transverse transport. These anomalous transport behaviors can be further understood by considering nonlinear magnetic textures and the chiral magnetic field associated with Weyl fermions, extending the longitudinal and transverse transport physics and providing novel degrees of freedom in the spintronic applications of emerging topological magnets.

cond-mat.mtrl-sci↗

arXiv2021

Large barocaloric effect with high pressure-driving efficiency in hexagonal MnNi0.77Fe0.23Ge alloy

The hydrostatic pressure is expected to be an effective knob to tune the magnetostructural phase transitions of hexagonal MMX alloy. In this study, magnetization measurements under hydrostatic pressure were performed on a MMX martensitic MnNi0.77Fe0.23Ge alloy. The magnetostructural transition temperature can be efficiently tuned to lower temperatures by applying moderate pressures, with a giant shift rate of -151 K GPa-1. A temperature span of 30 K is obtained under the pressure, within which a large magnetic entropy change of -23 J kg-1 K-1 in a field change of 5 T is induced by the mechanical energy gain due to the large volume change. Meanwhile, a decoupling of structural and magnetic transitions is observed at low temperatures when the martensitic transition temperature is lower than the Curie temperature. These results show a multi-parameter tunable caloric effect that benefits the solid-state cooling.

cond-mat.mtrl-sci↗

arXiv2021

Planar topological Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal

The planar topological Hall effect (PTHE), appeared when the magnetic field tended to be along the current, is believed to result from the real-space Berry curvature of the spin spiral structure and has been experimentally observed in skyrmion-hosting materials. In this paper, we report an experimental observation of the PTHE in a hexagonal ferromagnetic Fe5Sn3 single crystal. With a current along the c axis of Fe5Sn3, the transverse resistivity curves exhibited obvious peaks near the saturation field as the magnetic field rotated to the current and appeared more obvious with increasing temperature, which was related to the noncoplanar spin structure in Fe5Sn3. This spin structure induced nonzero scalar spin chirality, which acted as fictitious magnetic fields to conduction electrons and contributed the additional transverse signal. These findings deepen the understanding of the interaction between conduction electrons and complex magnetic structures and are instructive for the design of next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Abnormal Critical Fluctuations Revealed by Magnetic Resonance in the Two-Dimensional Ferromagnetic Insulators

Phase transitions and critical phenomena, which are dominated by fluctuations and correlations, are one of the fields replete with physical paradigms and unexpected discoveries. Especially for two-dimensional magnetism, the limitation of the Ginzburg criterion leads to enhanced fluctuations breaking down the mean-field theory near a critical point. Here, by means of magnetic resonance, we investigate the behavior of critical fluctuations in the two-dimensional ferromagnetic insulators $\rm CrXTe_3 (X=Si, Ge)$. After deriving the classical and quantum models of magnetic resonance, we deem the dramatic anisotropic shift of the measured $g$ factor to originate from fluctuations with anisotropic interactions. The deduction of the $g$ factor behind the fluctuations is consistent with the spin-only state (${g\approx}$ 2.050(10) for $\rm CrSiTe_3$ and 2.039(10) for $\rm CrGeTe_3$). Furthermore, the abnormal enhancement of $g$ shift, supplemented by specific heat and magnetometry measurements, suggests that $\rm CrSiTe_3$ exhibits a more typical two-dimensional nature than $\rm CrGeTe_3$ and may be closer to the quantum critical point.

cond-mat.mes-hall↗

arXiv2020

33% Giant Anomalous Hall Current Driven by both Intrinsic and Extrinsic Contributions in Magnetic Weyl Semimetal Co3Sn2S2

Anomalous Hall effect (AHE) can be induced by intrinsic mechanism due to the band Berry phase and extrinsic one arising from the impurity scattering. The recently discovered magnetic Weyl semimetal Co3Sn2S2 exhibits a large intrinsic anomalous Hall conductivity (AHC) and a giant anomalous Hall angle (AHA). The predicted energy dependence of the AHC in this material exhibits a plateau at 1000 Ω-1 cm-1 and an energy width of 100 meV just below EF, thereby implying that the large intrinsic AHC will not significantly change against small-scale energy disturbances such as slight p-doping. Here, we successfully trigger the extrinsic contribution from alien-atom scattering in addition to the intrinsic one of the pristine material by introducing a small amount of Fe dopant to substitute Co in Co3Sn2S2. Our experimental results show that the AHC and AHA can be prominently enhanced up to 1850 Ω-1 cm-1 and 33%, respectively, owing to the synergistic contributions from the intrinsic and extrinsic mechanisms as distinguished by the TYJ model. In particular, the tuned AHA holds a record value in low fields among known magnetic materials. This study opens up a pathway to engineer giant AHE in magnetic Weyl semimetals, thereby potentially advancing the topological spintronics/Weyltronics.

cond-mat.mtrl-sci↗

arXiv2020

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 is negative when a magnetic field H perpendicular to the bc-plane (H\perp bc-plane), however, it changes form negative to positive when H parallel to the c-axis (H\parallel c-axis). The value of topological Hall resistivity increased with the increasing temperature and reached approximately -2.12 μΩcm (H\perp bc-plane) and 0.5 μΩcm (H\parallel 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.

cond-mat.mtrl-sci↗

arXiv2020

Large anomalous Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal

In this paper, we report an experimental observation of the large anomalous Hall effect (AHE) in a hexagonal ferromagnetic Fe5Sn3 single crystal with current along the b axis and a magnetic field normal to the bc plane. The intrinsic contribution of the anomalous Hall conductance sigma_AH^int was approximately 613 Ω-1 cm-1, which was more than 3 times the maximum value in the frustrated kagome magnet Fe3Sn2 and nearly independent of the temperature over a wide range between 5 and 350 K. The analysis results revealed that the large AHE was dominated by a common, intrinsic term, while the extrinsic contribution, i.e., the skew scattering and side jump, turned out to be small. In addition to the large AHE, it was found the types of majority carriers changed at approximately 275 and 30 K, consistent with the critical temperatures of the spin reorientation. These findings suggest that the hexagonal ferromagnetic Fe5Sn3 single crystal is an excellent candidate to use for the study of the topological features in ferromagnets.

cond-mat.mtrl-sci↗

arXiv2020

Disorder-Induced Elevation of Intrinsic Anomalous Hall Conductance in an Electron-Doped Magnetic Weyl Semimetal

Topological materials are expected to show distinct transport signatures due to their unique band-inversion character and band-crossing points. However, the intentional modulation of such topological responses by experimentally feasible means is less explored. Here, an unusual elevation of anomalous Hall effect (AHE) is obtained in electron(Ni)-doped magnetic Weyl semimetal Co3-xNixSn2S2, showing peak values of anomalous Hall-conductivity, Hall-angle and Hall-factor at a relatively low doping level of x = 0.11. The separation of intrinsic and extrinsic contributions to total AHE using TYJ scaling model indicates that such significant enhancement is dominated by the intrinsic mechanism of electronic Berry curvature. Theoretical calculations reveal that compared with the Fermi-level shifting from electron filling, a usually overlooked effect of doping, i.e., local disorder, imposes a striking effect on broadening the bands and narrowing the inverted gap, and thus results in an elevation of the integrated Berry curvature. Our results not only realize the enhancement of AHE in a magnetic Weyl semimetal, but also provide a practical design principle to modulate the bands and transport properties in topological materials, by exploiting the disorder effect of doping.

cond-mat.mtrl-sci↗

arXiv2019

Observation of Magnetic Skyrmion Bubbles in a van der Waals ferromagnet Fe3GeTe2

Two-dimensional (2D) van der Waals (vdW) magnetic materials have recently been introduced as a new horizon in materials science and enable the potential applications for next-generation spintronic devices. Here, in this communication, the observations of stable Bloch-type magnetic skyrmions in single crystals of 2D vdW Fe3GeTe2 (FGT) are reported by using in-situ Lorentz transmission electron microscopy (TEM). We find the ground-state magnetic stripe domains in FGT transform into skyrmion bubbles when an external magnetic field is applied perpendicularly to the (001) thin plate with temperatures below the Curie-temperature TC. Most interestingly, a hexagonal lattice of skyrmion bubbles is obtained via field cooling manipulation with magnetic field applied along the [001] direction. Owing to their topological stability, the skyrmion bubble lattices are stable to large field-cooling tilted angles and further reproduced by utilizing the micromagnetic simulations. These observations directly demonstrate that the 2D vdW FGT possesses a rich variety of topological spin textures, being of a great promise candidate for future applications in the field of spintronics.

cond-mat.mtrl-sci↗

arXiv2019

Large topological Hall effect in a geometrically frustrated kagome magnet Fe$_3$Sn$_2$

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.

cond-mat.mtrl-sci↗