Non-saturating Magnetoresistance Research Articles

Extreme magnetoresistance at high-mobility oxide heterointerfaces with dynamic defect tunability

Magnetic field-induced changes in the electrical resistance of materials reveal insights into the fundamental properties governing their electronic and magnetic behavior. Various classes of magnetoresistance have been realized, including giant, colossal, and extraordinary magnetoresistance, each with distinct physical origins. In recent years, extreme magnetoresistance (XMR) has been observed in topological and non-topological materials displaying a non-saturating magnetoresistance reaching 103−108% in magnetic fields up to 60 T. XMR is often intimately linked to a gapless band structure with steep bands and charge compensation. Here, we show that a linear XMR of 80,000% at 15 T and 2 K emerges at the high-mobility interface between the large band-gap oxides γ-Al2O3 and SrTiO3. Despite the chemically and electronically very dissimilar environment, the temperature/field phase diagrams of γ-Al2O3/SrTiO3 bear a striking resemblance to XMR semimetals. By comparing magnetotransport, microscopic current imaging, and momentum-resolved band structures, we conclude that the XMR in γ-Al2O3/SrTiO3 is not strongly linked to the band structure, but arises from weak disorder enforcing a squeezed guiding center motion of electrons. We also present a dynamic XMR self-enhancement through an autonomous redistribution of quasi-mobile oxygen vacancies. Our findings shed new light on XMR and introduce tunability using dynamic defect engineering.

IrGe4: A Predicted Weyl-Metal with a Chiral Crystal Structure.

Polycrystalline IrGe4 was synthesized by annealing elements at 800 °C for 240 h, and the composition was confirmed by energy-dispersive X-ray spectroscopy. IrGe4 adopts a chiral crystal structure (space group P3121) instead of a polar crystal structure (P31), which was corroborated by the convergent-beam electron diffraction and Rietveld refinements using synchrotron powder X-ray diffraction data. The crystal structure features layers of IrGe8 polyhedra along the b axis, and the layers are connected by edge- and corner-sharing. Each layer consists of corner-shared [Ir3Ge20] trimers, which are formed by three IrGe8 polyhedra connected by edge-sharing. Temperature-dependent resistivity indicates metallic behavior. The magnetoresistance increases with increasing applied magnetic field, and the nonsaturating magnetoresistance reaches 11.5% at 9 T and 10 K. The Hall resistivity suggests that holes are the majority carrier type, with a carrier concentration of 4.02 × 1021 cm-3 at 300 K. Electronic band structures calculated by density functional theory reveal a Weyl point with a chiral charge of +3 above the Fermi level.

Colossal anomalous Hall conductivity and topological Hall effect in ferromagnetic kagome metal Nd3Al

We report a polycrystalline kagome metallic ferromagnet Nd3Al with a large unconventional positive magnetoresistance (∼80%) and a colossal anomalous Hall conductivity of 3 × 104 S/cm. We find that, though it is predominantly ferromagnetic, the low temperature phase is rather complex. The reduction in the effective moment, thermomagnetic irreversibility, anomalous temperature dependence of magnetization, large and non-saturating positive magnetoresistance, and existence of the finite topological Hall effect make this compound quite interesting. Various experimental proofs point toward topological band structure and topological spin texture in the frustrated kagome lattice. Ab initio calculations broadly confirm the presence of flatbands and Weyl points originating from the itinerant Nd-moments. The non-trivial band structure, enhanced skew scattering, and topological spin texture in a frustrated kagome lattice are found to be responsible for the colossal Hall conductivity and the topological Hall effect.

Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa4

Magnetic topological semimetals allow for an effective control of the topological electronic states by tuning the spin configuration. Among them, Weyl nodal line semimetals are thought to have the greatest tunability, yet they are the least studied experimentally due to the scarcity of material candidates. Here, using a combination of angle-resolved photoemission spectroscopy and quantum oscillation measurements, together with density functional theory calculations, we identify the square-net compound EuGa4 as a magnetic Weyl nodal ring semimetal, in which the line nodes form closed rings near the Fermi level. The Weyl nodal ring states show distinct Landau quantization with clear spin splitting upon application of a magnetic field. At 2 K in a field of 14 T, the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than two orders of magnitude larger than that of other known magnetic topological semimetals. Our theoretical model suggests that the non-saturating magnetoresistance up to 40 T arises as a consequence of the nodal ring state.

Anisotropic transport properties and high-mobility of charge carriers of antiferromagnetic GdAgSb2

We report detailed magnetic and magnetotransport properties of single-crystalline GdAgSb2 antiferromagnet. The electronic transport properties show metallic behavior along with large, anisotropic, and non-saturating magnetoresistance (MR) in transverse experimental configuration. At 2 K and 9 T, the value of MR reaches as high as ∼1.8×103%. The anisotropic MR along with additional features for applied magnetic field along some specific crystallographic directions reveal the quasi-two-dimensional nature of the Fermi surface of GdAgSb2. Hall resistivity confirms the presence of two types of charge carriers. The high carrier mobilities (∼1.2×104 cm2 V−1 s−1) and nearly-compensated electron and hole-density (∼1019 cm−3) could be responsible for the large transverse MR in GdAgSb2. We have also observed the de Haas–van Alphen oscillations in the magnetization measurements below 7 K. Furthermore, the robust planar Hall effect, which persists up to high temperatures, could indicate the nontrivial nature of the electronic band structure for GdAgSb2.

Double-Layer Kagome Metals Pt3Tl2 and Pt3In2

The connectivity and inherent frustration of the kagome lattice can produce interesting electronic structures and behaviors in compounds containing this structural motif. Here we report the properties of Pt3X2 (X = In and Tl) that adopt a double-layer kagome net structure related to that of the topologically nontrivial high-temperature ferromagnet Fe3Sn2 and the density wave hosting compound V3Sb2. We examined the structural and physical properties of single crystal Pt3Tl2 and polycrystalline Pt3In2 using X-ray and neutron diffraction, magnetic susceptibility, heat capacity, and electrical transport measurements, along with density functional theory calculations of the electronic structure. Our calculations show that Fermi levels lie in pseudogaps in the densities of states with several bands contributing to transport, and this is consistent with our Hall effect, magnetic susceptibility, and heat capacity measurements. Although electronic dispersions, characteristic of simple kagome nets with nearest-neighbor hopping, are not clearly seen, likely due to the extended nature of the Pt 5d states, we do observe moderately large and non-saturating magnetoresistance values and quantum oscillations in the magnetoresistance and magnetization associated with the kagome nets of Pt.

Effect of thickness on the superconducting properties of the thin films of FeTe0.55Se0.45 deposited on YSZ substrates using Pulsed laser deposition (PLD) technique

We report the successful fabrication of thin films of thickness ∼26 nm, 59 nm, 76 nm, and 158 nm of the composition FeTe0.55Se0.45 on the (100)-oriented Yttria-stabilized zirconia (YSZ) substrate using the pulsed laser deposition (PLD) technique. The effect of thickness on the structure and superconducting properties of the thin films has been investigated. X-ray diffraction study reveals the growth of thin films along the c-axis. The temperature-dependent resistivity measurements confirm superconductivity in all the fabricated thin films, and the highest ∼ 16.2 K has been observed for the thin film of thickness ∼59 nm, which is higher than the corresponding value of the polycrystalline target sample. The superconducting parameters such as upper critical magnetic field coherence length thermally activated energy (TAE) U0, and vortex phase state have been measured by magnetotransport measurements near in the different applied magnetic fields up to 12 T. The TAE values determined from the conventional and modified thermally activated flux flow (TAFF) models are discussed and compared. A crossover from 2-dimensional (2D) vortex to 3-dimensional (3D) vortex behaviour has been observed. The vortex phase diagrams are used to observe the transition from the vortex liquid to the vortex glass state in the grown thin films. Moreover, magnetoresistance (MR) measurements show non-saturating linear magnetoresistance (LMR) in the high field region, indicating the presence of the possible topological state in the grown thin films. The values of magnetic field dependent transport critical current density, have been evaluated from the current-voltage (I-V) curves. Furthermore, the normalised pinning force density has been used to characterize the pinning processes using the Dew Hughes’ scaling rule which reveals that the grown thin films contain δl-surface pinning centers.

Type‐II Dirac Nodal Lines in a Double‐Kagome‐Layered Semimetal

AbstractLorentz‐violating type‐II Dirac nodal line semimetals (DNLSs), hosting curves of band degeneracy formed by two dispersion branches with the same sign of slope, represent a novel state of matter. While being studied extensively in theory, convincing experimental evidence of type‐II DNLSs remain elusive. Recently, vanadium‐based kagome materials have emerged as a fertile ground to study the interplay between lattice symmetry and band topology. This work studies the low‐energy band structure of double‐kagome‐layered CsV8Sb12 and identifies it as a scarce type‐II DNLS protected by mirror symmetry. This work observes multiple DNLs consisting of type‐II Dirac cones close to or almost at the Fermi level via angle‐resolved photoemission spectroscopy (ARPES), which provides an electronic explanation for the nonsaturating magnetoresistance effect as observed. First‐principles theory analyses show that spin‐orbit coupling only opens a small gap, resulting in effectively gapless ARPES spectra, yet generating large spin Berry curvature. These type‐II DNLs, together with the interaction between a low‐energy van Hove singularity and quasi‐one‐dimensional band as observed in the same material, suggest CsV8Sb12 as an ideal platform for exploring novel transport properties.

Engineering of Advanced Materials for High Magnetic Field Sensing: A Review

Advanced scientific and industrial equipment requires magnetic field sensors with decreased dimensions while keeping high sensitivity in a wide range of magnetic fields and temperatures. However, there is a lack of commercial sensors for measurements of high magnetic fields, from ∼1 T up to megagauss. Therefore, the search for advanced materials and the engineering of nanostructures exhibiting extraordinary properties or new phenomena for high magnetic field sensing applications is of great importance. The main focus of this review is the investigation of thin films, nanostructures and two-dimensional (2D) materials exhibiting non-saturating magnetoresistance up to high magnetic fields. Results of the review showed how tuning of the nanostructure and chemical composition of thin polycrystalline ferromagnetic oxide films (manganites) can result in a remarkable colossal magnetoresistance up to megagauss. Moreover, by introducing some structural disorder in different classes of materials, such as non-stoichiometric silver chalcogenides, narrow band gap semiconductors, and 2D materials such as graphene and transition metal dichalcogenides, the possibility to increase the linear magnetoresistive response range up to very strong magnetic fields (50 T and more) and over a large range of temperatures was demonstrated. Approaches for the tailoring of the magnetoresistive properties of these materials and nanostructures for high magnetic field sensor applications were discussed and future perspectives were outlined.

Evidence of the Coulomb gap in the density of states of MoS2

${\mathrm{MoS}}_{2}$ is an emergent van der Waals material that shows promising prospects in semiconductor industry and optoelectronic applications. However, its electronic properties are not yet fully understood. In particular, the nature of the insulating state at low carrier density deserves further investigation, as it is important for fundamental research and applications. In this study we investigate the insulating state of a dual-gated exfoliated bilayer ${\mathrm{MoS}}_{2}$ field-effect transistor by performing magnetotransport experiments. We observe a positive and nonsaturating magnetoresistance, in a regime where only one band contributes to electron transport. At low electron density ($\ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$) and a perpendicular magnetic field of 7 Tesla the resistance exceeds by more than one order of magnitude the zero field resistance and exponentially drops with increasing temperature. We attribute this observation to strong electron localization. Both temperature and magnetic field dependence can, at least qualitatively, be described by the Efros-Shklovskii law, predicting the formation of a Coulomb gap in the density of states due to Coulomb interactions. However, the localization length obtained from fitting the temperature dependence exceeds by more than one order of magnitude the one obtained from the magnetic field dependence. We attribute this discrepancy to the presence of a nearby metallic gate, which provides electrostatic screening and thus reduces long-range Coulomb interactions. The result of our study suggests that the insulating state of ${\mathrm{MoS}}_{2}$ originates from a combination of disorder-driven electron localization and Coulomb interactions.

Exploring the Dirac nature of RbBi2

Characteristics of topological semimetals such as a nonsaturating magnetoresistance (MR), a field-induced metal to semiconducting crossover and a robust resistivity plateau are observed under a magnetic field in type-I ${\mathrm{RbBi}}_{2}$ bulk superconductor with ${T}_{\mathrm{c}}=4.15$ K. The MR exhibits a notable 3500% increase at 2 K and 9 T and the resistivity follows a power law temperature dependence, while the MR $\ensuremath{\propto}\phantom{\rule{4pt}{0ex}}{H}^{1.26}$, indicating weak carrier compensation. First principles calculations provided insights into the dynamical stability of the cubic structure at 0 K. Both hole and electron pockets are observed at the Fermi surface. The electron-phonon interaction constant indicates weak coupling strength ($<1$) that leads to a maximum predicted ${T}_{\mathrm{c}}$ of 2.852 K. Just below the Fermi level, ${\mathrm{E}}_{F}$, the electronic band structure consists of linear band crossings at the $X$ points in the Brillouin zone (BZ) corresponding to massless, symmetry-protected Dirac fermions.

Detailed structural and topological analysis of SnBi2Te4 single crystal

We report herein the successful synthesis of the topological material SnBi2Te4 in single-crystal form. Phase purity and unidirectional growth are evident from X-ray diffraction (XRD) patterns acquired from a powdered sample and a crystal flake. The crystalline morphology has also been visualized by acquiring a field-emission scanning electron microscope (FESEM) image. The crystal has been thoroughly characterized by means of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. The topological properties of SnBi2Te4 have been probed through magneto-transport measurements. SnBi2Te4 has been found to exhibit a small but non-saturating magneto-resistance (MR) up to ±12 T. The low-field magnetoconductivity (MC) of SnBi2Te4 at 2 K can be well explained through the Hikami–Larkin–Nagaoka (HLN) formalism, which confirms the presence of a weak anti-localization (WAL) effect in its crystal. Moreover, the non-trivial topological character has been evidenced through first-principles calculations using density functional theory (DFT), with and without spin-orbit coupling (SOC) protocols. A significant change in the bulk electronic band structure is observed upon the inclusion of SOC parameters, signifying topological properties of SnBi2Te4. Its topological non-trivial character has also been verified through calculation of Z2 invariants and the surface states spectrum in the (111) plane.

Possible origin of extremely large magnetoresistance in the topological insulator CaBi2 single crystal

CaBi2 has been experimentally found to be a superconductor with a transition temperature of 2 K and identified as a topological insulator via spin- and angle-resolved photoemission spectroscopy, which makes it a possible platform to study the interplay between superconductivity and topology. But the detailed transport properties for CaBi2 single crystal remain unexplored in experiments. Here, we systematically studied the magneto-transport properties of CaBi2 single crystal grown by a flux method. CaBi2 shows a magnetic-field-induced upturn behavior with a plateau in resistivity at low temperature. An extremely large and non-saturating magnetoresistance up to ∼15000% at 3 K and 12 T was achieved. The possible reason for the magnetic field and temperature dependence of resistivity and extremely large magnetoresistance at low temperature was discussed by adopting the Kohler’s scaling law, which can be understood by the compensation effect confirmed by the Hall Effect measurement.

Linear nonsaturating magnetoresistance in kagome superconductor CsV3Sb5 thin flakes

Linear nonsaturating magnetoresistance (LMR) represents a class of anomalous resistivity response to external magnetic field that has been observed in a variety of materials including but not limited to topological semi-metals, high-T c superconductors and materials with charge density wave (CDW)/spin density wave orders. Here we report the observation of LMR in layered kagome superconductor and CDW material CsV3Sb5 thin flakes, as well as the dimensional crossover and temperature (T) crossover of such LMR. Specifically, in ultrathin CsV3Sb5 crystals, the magnetoresistance (MR) exhibits a crossover from LMR at low T to quadratic B dependence above the CDW transition temperature; the MR also exhibits a crossover from LMR to sublinear MR for sample thickness at around ∼20 nm at low T. We discuss several possible origins of the LMR and attribute the effect to two-dimensional CDW fluctuations. Our results may provide a new perspective for understanding the interactions between competing orders in kagome superconductors.

Dispenser Printed Bismuth‐Based Magnetic Field Sensors with Non‐Saturating Large Magnetoresistance for Touchless Interactive Surfaces (Adv. Mater. Technol. 10/2022)

Printed Magnetic Field Sensors In article number 2200227, Mykola Vinnichenk, Denys Makarov, and co-workers present dispenser printing of magnetic field sensors based on bismuth powder. Benefiting from the non-saturating large magnetoresistance effect, this technology enables scalable large-area printing of sensors with broad detection range on flexible and rigid substrates. Touchless interactive surfaces based on dispenser-printed magnetically sensitive devices are demonstrated.

Magnetic and transport properties of Fe-doped Weyl semimetal Co3Sn2S2

Ferromagnetic Weyl semimetal Co3Sn2S2 has recently attracted a lot of interest on account of its large non-saturating magnetoresistance and the high carrier mobility common to topological semimetals. Moreover, the material also provides a platform for studying the interplay between the intrinsic magnetism and topological band structures, which generates a significant anomalous Hall effect. Chemical doping is the usual approach to adjust materials’ properties, and it can lead to fascinating results. Here, we present the influence of Fe-doping on the magnetic and transport properties of polycrystalline Co3Sn2S2. The Fe-doping suppresses the sample’s magnetic order, increases the electrical resistivity, results in a skew-scattering contribution to the anomalous Hall effect and Fe impurities cause the Kondo effect. In addition, we report on the impact of Fe-doping on the magnetoresistance of Co3Sn2S2, where Fe-doping leads to a dramatic decline in magnetoresistance. Furthermore, the hysteresis behavior in the low magnetic field region, detected previously in nanoflake samples only, is observed in both pure and Fe-doped Co3Sn2S2 bulk samples. Our findings serve as a reference and source of inspiration for future chemical doping research on topological semimetals.

Resistance anomaly and linear magnetoresistance in thin flakes of itinerant ferromagnet Fe3GeTe2

Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations, topological effects, and dimensional crossovers. Fe3GeTe2 represents such a two-dimensional van der Waals platform exhibiting itinerant ferromagnetism with many intriguing properties. Up to date, most electronic transport studies on Fe3GeTe2 have been limited to its anomalous Hall responses while the longitudinal counterpart (such as magnetoresistance) remains largely unexplored. Here, we report a few unusual transport behaviors on thin flakes of Fe3GeTe2. Upon cooling to the base temperature, the sample develops a resistivity upturn that shows a crossover from a marginally –ln T to a –T 1/2 dependence, followed by a lower-temperature deviation. Moreover, we observe a negative and non-saturating linear magnetoresistance when the magnetization is parallel or antiparallel to the external magnetic field. The slope of the linear magnetoresistance also shows a nonmonotonic temperature dependence. We deduce an anomalous contribution to the magnetoresistance at low temperatures with a scaling function proportional –HT 1/2, as well as a temperature-independent linear term. Possible mechanisms that could account for our observations are discussed.

Surface states induced weak anti-localization effect in Bi0.85Sb0.15 topological single crystal

We report, an experimental evidence of surface states (SS) driven magneto-transport in a Bi0.85Sb0.15 single crystal. Detailed high field (up to 12T) and low temperature (down to 2 K) magneto-transport measurements are been carried out on the studied Bi0.85Sb0.15 single crystal. The phase, composition and Raman modes are studied through x-ray diffraction, Energy dispersive x-ray, and Raman spectroscopy. The obtained crystal shows non-saturating magnetoresistance (≈ 4250%) at 2 K and 12T, along with the existence of weak-anti localization (WAL) effect at around zero magnetic field. Further, the Hikami-Larkin-Nagaoka (HLN) analysis is performed to analyse the WAL effect. The prefactor (α) and phase coherence length (L φ) are deduced at various temperatures, which signified the presence of more than one conduction channel in the studied Bi0.85Sb0.15 single crystal. The effect of quantum scattering, bulk contribution from underneath the surface states and defects are been studied by adding various field dependent quadratic, linear and constant terms to the SS driven HLN equation. Various possible scattering mechanism are studied by analysing the temperature dependence of the phase coherence length. Angle dependent magneto-conductivity of the studied Bi0.85Sb0.15 single crystal clearly confirmed the surface states dominated transport in present crystal.

Large positive magnetoresistance in photocarrier-doped potassium tantalites

We report on the high-field magnetotransport of KTaO3 single crystals, which are a promising candidate for study in the extreme quantum limit. By photocarrier doping with 360 nm light, we observe a significant positive, non-saturating, and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient. When cooling down to 10 K, the magnetoresistance value of KTaO3 (100) reaches ∼ 433% at a magnetic field of 12 T. Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit. Light inhomogeneity may also contribute to large linear magnetoresistance. These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.

Analytical formula describing the non-saturating linear magnetoresistance in inhomogeneous conductors

The effective-medium theory (EMT) has proved successful in modeling the non-saturating linear magnetoresistance induced by inhomogeneity. However, calculating magnetoresistance using the EMT usually involves solving coupled integral equations which have no analytical solutions, and therefore, it is still difficult to directly compare the predictions of EMT with experimental data. Here we demonstrate that the linear magnetoresistance predicted by the EMT can be either exactly formulated or well approximated by a simple analytical equation in a number of known situations. The relations between the EMT parameters and the phenomenological parameters k and a are evaluated. Our results provide a convenient and effective method for extracting the EMT parameters from experimental data.