Anomalous Magnetoresistance Research Articles

Field‐Induced Butterfly‐Like Anisotropic Magnetoresistance in a Kagome Semimetal Co3In2S2

AbstractWith the interplay between magnetism and topological bands, magnetic kagome semimetals provide promising platforms for exploring exotic correlated electronic states and quantum phenomena such as anomalous Hall effect, quantum spin liquid, and unconventional magnetoresistance, as well as driving advances in electronic and spintronic applications. Here, a field‐induced butterfly‐like anomalous anisotropic magnetoresistance (AMR) effect in an intriguing kagome semimetal Co3In2S2 is reported. The kagome‐lattice Co3In2S2 single crystals are synthesized via a polycrystal‐source chemical vapor transport approach, possessing a high carrier mobility reaching 104 cm2V−1s−1. The Co3In2S2 single crystal exhibits a canted antiferromagnetic state below 5 K, but intriguingly, it is easily transformed into a ferromagnetic state under a small external magnetic field. Furthermore, the planar Hall effect (PHE) is detected, stemming from the complex contribution of field‐induced ferromagnetism and orbital magnetoresistance. Remarkably, as the magnetic field increases, the low‐temperature magnetoresistance behavior of the Co3In2S2 reveals a butterfly‐like AMR effect with a maximum value of 850%, exhibiting a superposition of the two‐, four‐, and six‐fold AMR terms. Band structure calculations suggest that such a field‐induced butterfly‐like AMR effect may originate from the modulations of the electronic structure near the Fermi level by the magnetic moment. The findings offer a valuable platform for understanding the anomalous AMR effect and for the development of advanced spintronic devices.

Weak localization and magnetoresistance phenomena of hydrogen-annealed WO3 films

We explore the electronic transport properties of hydrogenated epitaxial WO3 films. Ionized hydrogen not only generates an electron carrier but also acts as an impurity center, providing a useful approach to investigate a macroscopic quantum transport phenomenon of weak localization. Temperature dependent-resistivity and anomalous magnetoresistance results are analyzed based on Mott's variable range hopping and weak localization. From the model studies, the phase coherence length is estimated to have a temperature dependence of T −1.6 and is determined to vary from ∼22 nm at 80 K to ∼180 nm at 20 K. The length at 20 K is of a similar order of magnitude of film thickness, which requires a dimensional crossover between three-dimensional and two-dimensional localization.

Anomalous negative magnetoresistance in quantum dot Josephson junctions with Kondo correlations

Anomalous negative magnetoresistance in quantum dot Josephson junctions with Kondo correlations

Robust negative longitudinal magnetoresistance and spin–orbit torque in sputtered Pt3Sn and Pt3SnxFe1-x topological semimetal

Contrary to topological insulators, topological semimetals possess a nontrivial chiral anomaly that leads to negative magnetoresistance and are hosts to both conductive bulk states and topological surface states with intriguing transport properties for spintronics. Here, we fabricate highly-ordered metallic Pt3Sn and Pt3SnxFe1-x thin films via sputtering technology. Systematic angular dependence (both in-plane and out-of-plane) study of magnetoresistance presents surprisingly robust quadratic and linear negative longitudinal magnetoresistance features for Pt3Sn and Pt3SnxFe1-x, respectively. We attribute the anomalous negative longitudinal magnetoresistance to the type-II Dirac semimetal phase (pristine Pt3Sn) and/or the formation of tunable Weyl semimetal phases through symmetry breaking processes, such as magnetic-atom doping, as confirmed by first-principles calculations. Furthermore, Pt3Sn and Pt3SnxFe1-x show the promising performance for facilitating the development of advanced spin-orbit torque devices. These results extend our understanding of chiral anomaly of topological semimetals and can pave the way for exploring novel topological materials for spintronic devices.

Anomalous anisotropic magnetoresistance in the topological semimetal HoPtBi

Discovering and understanding anomalous anisotropic magnetoresistance (AMR) effects are important aspects of studying the nature of modulated transport. The anisotropic transport coefficients of topological systems are often useful for mapping hidden phases and characterizing topological phase transitions and the evolution of topological electrons. Here, we report an unusual change in the AMR effect in HoPtBi. Remarkably, the AMR exhibits transitions from a quasi-twofold to fourfold symmetry and finally forms a stable rotated fourfold symmetry with increasing magnetic fields. The evolution analysis from the three-dimensional (3D) mapping experiments confirms that it is an intrinsic 3D effect. Fourier transformation analysis indicates that the superposition of C2, C4, and C6 signals with phase angle transitions leads to the novel AMR. All transitions are summarized as symmetry rotation or the inversion of peaks and valleys. By combining the features of band structures and AMR, we evaluate the possible origin of this symmetry rotation and attribute it to the topological band change. This work provides insight into the anomalous AMR effect of topological materials and is useful for understanding the evolution of topological bands in a magnetic field. We propose that other rare-earth half-Heusler alloys can potentially exhibit similar phenomena.

Temperature-induced anomalous magnetotransport in the Weyl semimetal Mn3Ge

The magnetic Weyl semimetallic state can lead to intriguing magnetotransport, such as chiral anomaly and the layered quantum Hall effect. Mn3X (X = Sn, Ge) is a noncollinear antiferromagnetic semimetal where a Weyl semimetallic state is stabilized by time-reversal symmetry breaking. Compared to the well-studied Mn3Sn, the Weyl fermion-induced magnetotransport in Mn3Ge has been merely studied. Here, we report an in-depth study on the magnetotransport in a microfabricated Mn3Ge single crystal from room temperature to 10 K. We reveal an anomalous anisotropic magnetoresistance with fourfold symmetry and a positive high-field longitudinal magnetoresistance below the critical temperature (160–170 K). The possible origin is the temperature-induced tilting of the Weyl nodes. Our study helps to understand the magnetotransport properties in the Weyl fermion system.

Anomalous magnetoresistance by breaking ice rule in Bi2Ir2O7/Dy2Ti2O7 heterostructure

While geometrically frustrated quantum magnets host rich exotic spin states with potentials for revolutionary quantum technologies, most of them are necessarily good insulators which are difficult to be integrated with modern electrical circuit. The grand challenge is to electrically detect the emergent fluctuations and excitations by introducing charge carriers that interact with the localized spins without destroying their collective spin states. Here, we show that, by designing a Bi2Ir2O7/Dy2Ti2O7 heterostructure, the breaking of the spin-ice rule in insulating Dy2Ti2O7 leads to a charge response in the conducting Bi2Ir2O7 measured as anomalous magnetoresistance during the field-induced Kagome ice-to-saturated ice transition. The magnetoresistive anomaly also captures the characteristic angular and temperature dependence of this ice-rule-breaking transition, which has been understood as magnetic monopole condensation. These results demonstrate a novel heteroepitaxial approach for electronically probing the transition between exotic insulating spin states, laying out a blueprint for the metallization of frustrated quantum magnets.

Topological states of thermoelectric Yb-filled skutterudites

The effects of topological states on the thermoelectric performance of a highly efficient thermoelectric Yb-filled ${\mathrm{CoSb}}_{3}$ skutterudite are investigated through combined ab initio calculations and electrical transport measurements. The nontrivial topological states are revealed by ab initio calculations and inferred from anomalous Hall conductivity and magnetoresistance. The linear bands associated with the topological states lead to low single-band effective mass and high carrier mobility, and consequently high power factor. Furthermore, the additional band minima due to filling the voids with Yb atoms raise the valley degeneracy, which favors the density-of-states effective mass and thus the Seebeck coefficient but scarcely changing the carrier mobility. These effects together contribute to the high power factor of Yb-filled ${\mathrm{CoSb}}_{3}$ skutterudite. Our results show that topological states play a crucial role in improving the performance of thermoelectric materials.

Слабая антилокализация в сильно разупорядоченном двумерном полуметалле в квантовой яме HgTe

Weak localization in a highly disordered quantum well CdxHg1−xTe/HgTe/CdxHg1−xTe with a thickness of d = 20 nm is experimentally investigated. An analysis is made of the anomalous positive magnetoresistance (APM) caused by the suppression of the interference correction to the conductivity by a magnetic field on both sides of the charge neutrality point: for a two-dimensional semimetal and for a two-dimensional electronic metal. For the same values of resistivity, the APM peak in a 2D semimetal has a much wider width than in a 2D electron gas. A quantitative comparison of the obtained results with the theory allows, in particular, to conclude that the intensity of carrier transitions between subsystems in the 2D semimetal binary system is maximum near the charge neutrality point, where the concentrations of electrons and holes are close, and decreases as the difference in concentrations increases.

Probing antiferromagnetism in exfoliated Fe3GeTe2 using magneto-transport measurements.

Among the material class of van der Waals magnets, Fe3GeTe2 (FGT) has emerged as one of the most studied owing to features such as its relatively high Curie temperature, metallic nature, and large spin polarization. Though most studies only investigate its explicitly ferromagnetic properties, FGT is also predicted to have an antiferromagnetic phase in the out-of-plane direction emerging at temperatures below 150 K, leading to a blend of ferromagnetic and antiferromagnetic ordering. Here, we explore the emergence of this phase and its effects in FGT/h-BN heterostructures using magneto-transport measurements. The devices' anomalous Hall and magnetoresistance responses exhibit a complex trend with temperature that is consistent with multiple magnetic phases. In addition to the usual out-of-plane sensing, we also rotate the applied field to the in-plane direction and observe behavior resembling the planar topological Hall effect. Intriguingly, this response follows a similar temperature trend to the out-of-plane response. We also use the out-of-plane anomalous Hall response to show that, at sufficiently low temperatures, both positive and negative field-cooling results in an increased saturation Hall resistance. Such a field-cooling divergence is consistent with antiferromagnetic ordering resulting in a spin-glass like state in the sample. In addition to providing insight into one of the most exciting candidate materials for 2D magnetic devices, our work demonstrates the power of magneto-transport measurements to probe complex behavior in vdW magnets where common magnetometry techniques used on bulk samples may not be viable.

Modulating saturation magnetization and topological Hall resistivity of flexible ferrimagnetic Mn4N films by bending strains

The ferrimagnetic rare-earth-free Mn4N films are considered as a good candidate in spintronics due to its low saturation magnetization (MS) and high Néel temperature. Here, Mn4N films are directly deposited on flexible mica to investigate strain-related magnetic and electronic transport properties. The MS variation of 11.0 nm Mn4N film reaches 453% at tensile strain of radius of curvature (ROC) = 2 mm. Bending strains cannot affect anomalous Hall resistivity and magnetoresistance. However, the topological Hall resistivity of 147.0 nm Mn4N film increases by 58% at tensile strain of ROC = 5 mm due to frustrated exchange interactions. The flexible Mn4N films have great potential applications in flexible magnetic sensor and strain gauge due to strain modulated MS, resistance, and stable magnetoresistance.

Anomalous magnetoresistance and Hall effect in amorphous Pt/TbFeCo thin films

Among the magnetic materials in technological usage, amorphous rare-earth transition metal (RE–TM) alloys are of great interest due to their adjustable magnetic properties and favorable perpendicular magnetic anisotropic (PMA) advantages. In this study, the properties of Tb25Fe61Co14 system with 2, 5, and 10 nm Pt underlayers have been systematically explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature and magnetic field dependence of Hall resistivity, magnetoresistivity, and magneto-optic Kerr Effect (MOKE) measurements. According to the results, whole thin films are amorphous in nature and display an out-of-plane magnetic anisotropy without annealing. Increasing the Pt underlayer thickness helps the TbFeCo layer to reach significantly enhanced perpendicular magnetic anisotropic values and visualize the appearance of anomalous magnetoresistance in the Hall effect measurements. The thin films with 5 and 10 nm Pt underlayer has a ratio of remanence magnetization/saturation magnetization (MR/MS) of around 1, which is the out of plane direction of MOKE signal. Besides, the present study also includes some pieces of evidence that might be related to the Berry phase trend.

Numerical Simulation of One-Sided Normal Zone Propagation in Large Helical Device Conductors

The large helical device (LHD) at the National Institute for Fusion Science (NIFS) is the world's largest heliotron-type superconducting magnetic device for nuclear fusion. At the start of the LHD experiment, a phenomenon in which a finite length of the normal zone propagates only to one side, is observed in the region below the rated operating point. The LHD conductor comprises a NbTi/Cu Rutherford conductor, pure aluminum stabilizer, and copper sheath. The aluminum-stabilized conductor is known to exhibit anomalous magnetoresistance due to Hall currents flowing in its cross-section. To simulate the one-sided propagation phenomenon, a quench simulation is performed, considering the Hall effect. A difference is observed in the current-transfer length from the Rutherford conductor to the aluminum stabilizer and copper sheath between the left front and the right front of the normal zone, and the Joule heat in the Rutherford conductor immediately after the normal transition is asymmetric. Under He II cooling (2 K) and a magnetic flux density of 6 T, the one-sided propagation phenomenon is numerically simulated in the transport current range of 15–17 kA. These results are in good agreement with the experimental results.

Low-temperature quantum correction to anisotropic magnetoresistance in Tm3Fe5O12/Pt heterostructures

Spin transport in ferromagnetic insulator/heavy metal heterojunctions has attracted much attention because of its rich physics and potential applications. Here, we report an anomalous anisotropic magnetoresistance (AMR) at low temperature in a ${\mathrm{Tm}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}\text{/Pt}$ bilayer, which has often been neglected for its weak signal compared with spin Hall magnetoresistance. In our study, the magnetic proximity effect is weak above 50 K so that the AMR signal is mainly caused by ordinary magnetoresistance and spin-related scattering. However, at low temperatures, the AMR changes dramatically due to the weak localization (WL) and weak anti-localization (WAL) related to the quantum diffusion mechanism. Moreover, the dominated mechanism changes from WL to WAL in a Cu-inserted structure of TmIG/Cu/Pt without the magnetic proximity exchange coupling at the interfaces, accompanied by an AMR variation from negative to positive. Our study reveals the quantum correction effect on the AMR, which provides a possible explanation of the complex resistive behavior at low temperatures.

Mosaic growth induced magnetic anisotropy in double perovskite PrBaCo2O5+δ thin films

Controlling crystal structure is one of the most crucial steps for tuning the physical properties in layered perovskite oxides. The growth of mosaic-patterned double perovskite PrBaCo2O5+δ (PBCO) thin films was achieved to study the growth dynamics and the effect on the magnetic anisotropy (MA). High-resolution X-ray diffraction and scanning transmission electron microscopy studies indicate the crystal structures of PBCO thin films are highly oriented with three variants, i.e., <100>(013) grains tilted around ±18° away from [00l] direction along a or b axis, <110>(001) domains rotated 45° along c axis, and common cube-on-cube <100>(001) epitaxy. The MA transformation to isotropic and an anomalous anisotropic magnetoresistance were observed in the films with the mosaic-patterned nanostructures. These evidences not only highlight the correlation between nanostructures and physical properties in perovskite systems, but also lay out the new avenues to manipulate the MA through controlling the preferred oriented nanostructures, which paves the way to create future nanoelectronics and spintronic devices via nanostructure design.

Antisymmetric Magnetoresistance due to Domain-Wall Tilting in Perpendicularly Magnetized Films

Electrical currents flowing through magnetic domain walls tend to encounter additional extraordinary resistance. At the thin-wall limit, the occurrence of anomalous-field antisymmetric magnetoresistance breaks Onsager symmetry, which seems to be determined by the combination of single-wall and perpendicular-current-injection geometry. However, the delicate magnetic structure and measurement configuration are hard to implement, and the abnormal transport properties observed in multidomain structures are not fully understood. Here, we report the observation of antisymmetric magnetoresistance due to domain-wall tilting in a multidomain structure controlled by a magnetic field gradient. We demonstrate, both experimentally and theoretically, that the anomalous magnetoresistance arises from the nonequilibrium current in the vicinity of tilting domain walls, which are basically governed by the geometry factor of the tilting walls.

Tungsten Ditelluride: Synthesis, Structure, and Magnetoresistance Property

AbstractTungsten ditelluride (WTe2) is arising as an attractive material in magnetoresistance (MR) properties filed. The magnetoresistance properties of WTe2 makes it an ideal material for its magnetoresistive heads of computer and magnetic sensor device applications. So far, people have developed various controlled synthesis methods to produce large‐quantity uniform flat WTe2 crystals. Nevertheless, none of the methods are sustainable, some methods use reducing gases, and some use very long heat preservation, and the process is very complicated. Here, a mild and fast self‐flux method is described for WTe2 synthesis that can avoid producing reducing gases. After conducting structural and physical tests, it is found that annealing time is critical for WTe2 structure formation. Long annealing time improves the crystallinity of WTe2 and makes its texture more obvious, increasing the conductivity of WTe2. Therefore, it will lead to the anomalous nonsaturating positive magnetoresistance with different field dependent behaviors, reaching the ultrastrong magnetoresistive value of 1040% at 5 K and 14 T. The results provide a sustainable approach for uniform WTe2 crystal synthesis, which will benefit the large‐quantity production of WTe2 magnetoresistive materials.

Magnetotransport properties of chiral helimagnet Cr1/3NbS2 near phase transition

Many interesting physical phenomena emerge in the vicinity of phase transition temperature (Tc) for magnetic materials. However, it remains a big challenge to elucidate the near-Tc behaviors of chiral helimagnets, owing to their diversified magnetic interactions and complicated phase transitions. Here, we have systematically studied the near-Tc properties of a chiral helimagnet Cr1/3NbS2 by magnetotransport measurements with fine tuning of temperature and magnetic field. An anomalous positive magnetoresistance (MR) appears around the critical field (Hc) in a narrow temperature range (~ 128–132 K), which can be attributed to the competing scattering effects on electrons between the chiral magnetic order and thermal fluctuation near critical point. Moreover, the negative MR continues to increase even above Hc, and this behavior becomes more pronounced near Tc. Based on the MR results, a near-Tc magnetic phase diagram of Cr1/3NbS2 is presented, with a particular emphasis on the determination of internal phase boundary of chiral soliton lattice (CSL). This work gains an insight on the near-Tc behaviors of chiral magnetic materials and sheds light on the related electronic and spintronic applications.

Tunable Berry curvature and transport crossover in topological Dirac semimetal KZnBi

Topological Dirac semimetals have emerged as a platform to engineer Berry curvature with time-reversal symmetry breaking, which allows to access diverse quantum states in a single material system. It is of interest to realize such diversity in Dirac semimetals that provides insight on correlation between Berry curvature and quantum transport phenomena. Here, we report the transition between anomalous Hall and chiral fermion states in three-dimensional topological Dirac semimetal KZnBi, which is demonstrated by tuning the direction and flux of Berry curvature. Angle-dependent magneto-transport measurements show that both anomalous Hall resistance and positive magnetoresistance are maximized at 0° between net Berry curvature and rotational axis. We find that the unexpected crossover of anomalous Hall resistance and negative magnetoresistance suddenly occurs when the angle reaches to ~70°, indicating that Berry curvature strongly correlates with quantum transports of Dirac and chiral fermions. It would be interesting to tune Berry curvature within other quantum phases such as topological superconductivity.

Normal-state negative longitudinal magnetoresistance and Dirac-cone-like dispersion in PtPb4 single crystals: a potential Weyl-semimetal superconductor candidate

Magnetotransport measurements of PtPb4 single crystals with the T c of ∼2.80 K reveal pronounced exotic topological nature. An anomalous negative longitudinal magnetoresistance (MR) related to the chiral anomaly and a linear-like transverse MR examined within the framework of quantum MR theory were studied. Results indicate the presence of chiral-anomaly-induced quantum transport associated with the Weyl states and show a Dirac-cone-like band dispersion in PtPb4. This work reveals the drastic impact of the concept that the surface electrons in a Weyl fermion state may dominate the normal-state magnetotransport in PtPb4, leading to the conclusion that PtPb4 can be a Weyl-semimetal superconductor candidate.