Large Magnetoresistance Research Articles

Tunable High‐Temperature Tunneling Magnetoresistance in All‐van der Waals Antiferromagnet/Semiconductor/Ferromagnet Junctions

AbstractMagnetic tunnel junctions (MTJs) are widely applied in spintronic devices for efficient spin detection through the imbalance of spin polarization at the Fermi level. The van der Waals (vdW) property of 2D magnets with atomically flat surfaces and negligible surface roughness greatly facilitates the development of MTJs, primarily in ferromagnets. Here, A‐type antiferromagnetism in 2D vdW single‐crystal (Fe0.8Co0.2)3GaTe2 is reported with TN ≈ 203 K in bulk and ≈ 185 K in 9‐nm nanosheets. The metallic nature and out‐of‐plane magnetic anisotropy make it a suitable candidate for MTJ electrodes. By constructing heterostructures based on (Fe0.8Co0.2)3GaTe2/WSe2/Fe3GaTe2, a large tunneling magnetoresistance (TMR) ratio of 180% at low temperature is obtained, with the TMR signal persisting at near‐room temperature 280 K. Furthermore, the TMR is tunable by the electric field, and the MTJ device operates stably with a low applied bias down to 1 mV (≈0.6 nA), highlighting its potential for energy‐efficient spintronic devices. This work opens up new opportunities for 2D antiferromagnetic spintronics and quantum devices.

Unusual metallic state in superconducting A15-type La4H23

Abstract Hydride superconductors continue to fascinate the communities of condensed matter physics and material sciences because they host the promising room-temperature superconductivity. The current research has been concentrated on the new hydride superconductors with the enhancement of the superconducting transition temperature (Tc). The multiple extreme conditions (high pressure/temperature and magnetic field) will introduce new insights on the hydride superconductors. The study of transport properties under very high magnetic fields facilitates the understanding of the superconductivity in the conventional hydride superconductors. In the present work, we report experimental evidence of an unusual metal state in a newly synthesized cubic A15-type La4H23 that exhibits superconductivity with a Tc reaching 105 K at 118 GPa. A large negative magnetoresistance is observed for strong pulsed magnetic fields in the non-superconducting state below 40 K. Moreover, we construct the full magnetic phase diagram of La4H23 up to 68 T at high pressure. The present work reveals anomalous electronic structural properties of A15-La4H23 under high magnetic fields, therefore holding great importance for advancing the understanding of quantum transport behaviors in hydride superconductors.

Large unidirectional magnetoresistance from the dual functionality of copper oxide in naturally oxidized light-metal Al/Cu bilayer films

Large unidirectional magnetoresistance from the dual functionality of copper oxide in naturally oxidized light-metal Al/Cu bilayer films

Electrically Controlled All-Antiferromagnetic Tunnel Junctions on Silicon with Large Room-Temperature Magnetoresistance.

Antiferromagnetic (AFM) materials are a pathway to spintronic memory and computing devices with unprecedented speed, energy efficiency, and bit density. Realizing this potential requires AFM devices with simultaneous electrical writing and reading of information, which are also compatible with established silicon-based manufacturing. Recent experiments have shown tunneling magnetoresistance (TMR) readout in epitaxial AFM tunnel junctions. However, these TMR structures are not grown using a silicon-compatible deposition process, and controlling their AFM order required external magnetic fields. Here are shown three-terminal AFM tunnel junctions based on the noncollinear antiferromagnet PtMn3, sputter-deposited on silicon. The devices simultaneously exhibit electrical switching using electric currents, and electrical readout by a large room-temperature TMR effect. First-principles calculations explain the TMR in terms of the momentum-resolved spin-dependent tunneling conduction in tunnel junctions with noncollinear AFM electrodes.

Tunable anomalous resistance and large magnetoresistance in HfTe5 by atom doping

The Dirac layered material HfTe5 renews significant interest due to its exotic band structure, leading to abundant transport properties, such as the anomaly resistance peak and its large magnetoresistance. Here, we prepared single crystals HfTe5 and Cr-doped CrxHf1−xTe5 and carried out their electrical transport measurements to explore the underlying physical origin of the anomaly resistance behavior and the large magnetoresistance. An anomalous resistance peak was observed in both intrinsic HfTe5 and the Cr-doped ones. Specifically, the peak temperature in the doped ones experiences an obvious shift from 52 to 34 K as the doping concentration x increases from 0 to 0.15, as well as the magnitude of the peak resistance is significantly enhanced. Furthermore, the magnetoresistance of CrxHf1−xTe5 is reduced by more than one order of magnitude compared with the intrinsic one. The significant reduction in magnetoresistance after Cr doping is attributed to the breaking of the balance between electron and hole carriers, which is confirmed by Kohler's plots. Meanwhile, in the sample where the magnetoresistance was minimized, we observed Shubnikov–de Haas oscillations. These observations illustrate that the large magnetoresistance is primarily contributed by the compensation of electrons and holes rather than the high mobility. Our findings provide valuable insight into how to engineer HfTe5 to achieve large magnetoresistance and its further applications in magnetic sensors and spintronics.

High-mobility spin-polarized quasi-two-dimensional electron gas and large low-field magnetoresistance at the interface of EuTiO3/SrTiO3 (110) heterostructures

High-mobility spin-polarized two-dimensional electron gas (2DEG) at the interfaces of complex oxide heterostructures provide great potential for spintronic device applications. Unfortunately, the interfacial ferromagnetism and its associated spin polarization of mobile electrons and negative magnetoresistance (MR) are too weak. As of now, obtaining enhanced interfacial ferromagnetism and MR and strong spin-polarized 2DEG is still a great challenge. In this paper, we report on the realization of strong spin-polarized 2DEG at the interface of EuTiO3/SrTiO3 (110) heterostructures, which were prepared by directly depositing 39-nm EuTiO3 films onto as-received SrTiO3 (110) substrates. Hall and Kondo effects, low-field MR, Shubnikov–de Haas (SdH) oscillation, and magnetic hysteresis loop measurements demonstrate that high mobility electrons (1.4 × 104 cm2 V−1 s−1) accumulate at the interface of the heterostructures, which are not only highly conducting and show SdH oscillations with a non-zero Berry phase but also show a large out-of-plane and in-plane butterfly-like negative low-field MR whose magnitude is unprecedentedly large (46%–59% at 500 Oe and 1.8 K), approximately one to two orders higher than those of previously reported spin-polarized 2DEG systems. The strong spin polarization of the interfacial 2DEG is attributed to the presence of interfacial Eu2+ 4f (3.6–4 μB/f.u.) and Ti3+ 3d moments. Our results may provide guidance for exploring strong spin-polarized 2DEG at the interface of rare-earth titanate–strontium titanate heterostructures.

Large tunneling magnetoresistance and its high bias stability in Weyl half-semimetal based lateral magnetic tunnel junctions

Magnetic tunnel junctions (MTJs) based on novel states of two-dimensional (2D) magnetic materials will significantly improve the value of the tunneling magnetoresistance (TMR) ratio. However, most 2D magnetic materials exhibit low critical temperatures, limiting their functionality to lower temperatures rather than room temperature. Moreover, most MTJs experience the decay of TMR ratio at large bias voltages within a low spin injection efficiency (SIE). Here, we construct a series of MTJs with Weyl half-semimetal (WHSM, e.g. MnSiS3, MnSiSe3, and MnGeSe3 monolayers) as the electrodes and investigate the spin-dependent transport properties in these kind of lateral heterojunctions by employing density functional theory combined with non-equilibrium Green’s function method. We find that an ultrahigh TMR (∼109%) can be obtained firmly at a small bias voltage and maintains a high SIE even at a large bias voltage, and MnSiSe3 monolayer is predicted to exhibit a high critical temperature. Additionally, we reveal that the same structure allows for the generation of fully spin-polarized photocurrent, irrespective of the polarization angle. These findings underscore the potential of WHSMs as candidate materials for high-performance spintronic devices.

Origin of linear magnetoresistance in Bi2Te3 topological insulator: Role of surface state and defects

Connection between topological surface states (TSS) and large linear magnetoresistance (LMR) is established in tetradymite Bi2Te3 through tuning of native defects. Thorough analysis of temperature dependent synchrotron X-ray diffraction data quantifies 0-D, 1-D and 2-D defect concentrations. Plausible variation of antisite defects is explained via carrier concentration data. Resistivity data divulge contribution of mixed bulk and surface states in the synthesized samples. High Fermi velocity (∼106 ms−1) and low Fermi energy (∼14 meV) of carriers are obtained. Lower defect concentration sample emerges with high magnetoresistance (MR) and higher mobility. Weak antilocalization (WAL) effect, signature of TSS, is revealed from MR. Large (80%), non-saturating LMR along with ultrahigh mobility (∼1 m2V−1s−1) in Bi2Te3 supports the presence of TSS. Magnetoconductance data are fitted with Hikami-Larkin-Nagaoka equation, obtaining further insight on WAL effect. In addition, extracted parameters like disorder correlation length and coherence length explicate the role of defect density on LMR.

Mechanism for Electrostatically Generated Magnetoresistance in Chiral Systems without Spin-Dependent Transport.

Significant attention has been drawn to electronic transport in chiral materials coupled to ferromagnets in the chirality-induced spin selectivity (CISS) effect. A large magnetoresistance (MR) is usually observed, which is widely interpreted to originate from spin (dependent) transport. However, there are severe discrepancies between the experimental results and the theoretical interpretations, most notably the apparent failure of the Onsager reciprocity relations in the linear response regime. We provide an alternative mechanism for the two terminal MR in chiral systems coupled to a ferromagnet. For this, we point out that it was observed experimentally that the electrostatic contact potential of chiral materials on a ferromagnet depends on the magnetization direction and chirality. The mechanism that we provide causes the transport barrier to be modified by the magnetization direction, already in equilibrium, in the absence of a bias current. This strongly alters the charge transport through and over the barrier, not requiring spin transport. This provides a mechanism that allows the linear response resistance to be sensitive to the magnetization direction and also explains the failure of the Onsager reciprocity relations. We propose experimental configurations to confirm our alternative mechanism for MR.

Proposal for All-Electrical Skyrmion Detection in van der Waals Tunnel Junctions.

A major challenge for magnetic skyrmions in atomically thin van der Waals (vdW) materials is reliable skyrmion detection. Here, based on rigorous first-principles calculations, we show that all-electrical skyrmion detection is feasible in two-dimensional vdW magnets via scanning tunneling microscopy (STM) and in planar tunnel junctions. We use the nonequilibrium Green's function method for quantum transport in planar junctions, including self-energy due to electrodes and working conditions, going beyond the standard Tersoff-Hamann approximation. We obtain a very large tunneling anisotropic magnetoresistance (TAMR) around the Fermi energy for a graphite/Fe3GeTe2/germanene/graphite vdW tunnel junction. For atomic-scale skyrmions, the noncollinear magnetoresistance (NCMR) reaches giant values. We trace the origin of the NCMR to spin mixing between spin-up and -down states of pz and dz2 character at the surface atoms. Both TAMR and NCMR are drastically enhanced in tunnel junctions with respect to STM geometry due to orbital symmetry matching at the interface.

Chiral anomaly and Weyl orbit in three-dimensional Dirac semimetal Cd3As2 grown on Si

Preparing Cd3As2, which is a three-dimensional (3D) Dirac semimetal in certain crystal orientation, on Si is highly desirable as such a sample may well be fully compatible with existing Si CMOS technology. However, there is a dearth of such a study regarding Cd3As2 films grown on Si showing the chiral anomaly. Here, for the first time, we report the novel preparation and fabrication technique of a Cd3As2 (112) film on a Si (111) substrate with a ZnTe (111) buffer layer which explicitly shows the chiral anomaly with a nontrivial Berry’s phase of π. Despite the Hall carrier density ( n3D≈ 9.42×1017 cm−3) of our Cd3As2 film, which is almost beyond the limit for the portents of a 3D Dirac semimetal to emerge, we observe large linear magnetoresistance in a perpendicular magnetic field and negative magnetoresistance in a parallel magnetic field. These results clearly demonstrate the chiral magnetic effect and 3D Dirac semimetallic behavior in our silicon-based Cd3As2 film. Our tailoring growth of Cd3As2 on a conventional substrate such as Si keeps the sample quality, while also achieving a low carrier concentration.

Extremely large magnetoresistance and anisotropic transport in the multipolar Kondo system PrTi2Al20

Multipolar Kondo systems offer unprecedented opportunities to design astonishing quantum phases and functionalities beyond spin-only descriptions. A model material platform of this kind is the cubic heavy fermion system PrT2Al20 (T=Ti, V), which hosts a nonmagnetic crystal-electric-field ground state and substantial Kondo entanglement of the local quadrupolar and octopolar moments with the conduction electron sea. Here, we explore the magnetoresistance (MR) and Hall effect of PrTi2Al20, which develops ferroquadrupolar (FQ) order below TQ∼2 K, and compare their behavior with that of the MR and Hall effect of the non-4f analog, LaTi2Al20. In the FQ ordered phase, PrTi2Al20 displays extremely large magnetoresistance (XMR) of ∼103%. The unsaturated, quasilinear field (B) dependence of the XMR violates Kohler's scaling and defies description based on carrier compensation alone. By comparing the MR and the Hall effect observed in PrTi2Al20 and LaTi2Al20, we conclude that the open-orbit topology on the electron-type Fermi surface sheet is key for the observed XMR. The low-temperature MR and the Hall resistivity in PrTi2Al20 display pronounced anisotropy in the [111] and [001] magnetic fields, which is absent in LaTi2Al20, suggesting that the transport anisotropy ties in with the anisotropic magnetic field response of the quadrupolar order parameter. Published by the American Physical Society 2024

Excellent temperature dependence of retention energy and large tunnel magnetoresistance of MTJs with strain-induced magnetic anisotropy for SOT-MRAMs with high write efficiency

Excellent temperature dependence of retention energy and large tunnel magnetoresistance of MTJs with strain-induced magnetic anisotropy for SOT-MRAMs with high write efficiency

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.

Resonant tunneling induced large magnetoresistance in vertical van der Waals magnetic tunneling junctions based on type-II spin-gapless semiconductor VSi2P4

Schematics (a and b) and eigenstates (c and d) of 1H (a and c) and 3H (b and d) devices.

Extremely large magnetoresistance with coexistence of a nontrivial Berry phase in Nb0.5Ta0.5P: an experimental and theoretical study

We synthesized Nb0.5Ta0.5P, exhibiting XMR at low temperatures with charge carrier compensation up to 50 K. SdH oscillations reveal multiple Fermi pockets and non-zero Berry phase. SOC effects were analyzed via band structure calculations.

Temperature-dependent Fermi surface probed by Shubnikov–de Haas oscillations in topological semimetal candidates DyBi and HoBi

Rare earth-based monopnictides are among the most intensively studied groups of materials in which extremely large magnetoresistance has been observed. This study explores magnetotransport properties of two representatives of this group, DyBi and HoBi. The extreme magnetoresistance is discovered in DyBi and confirmed in HoBi. At T=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T=2$$\\end{document} K and in B=14\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B=14$$\\end{document} T for both compounds, magnetoresistance reaches the order of magnitude of 104%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^4\\%$$\\end{document}. For both materials, standard Kohler’s rule is obeyed only in the temperature range from 50 to 300 K. At lower temperatures, extended Kohler’s rule has to be invoked because carrier concentrations and mobilities strongly change with temperature and magnetic field. This is further proven by the observation of a quite rare temperature-dependence of oscillation frequencies in Shubnikov–de Haas effect. Rate of this dependence clearly changes at Néel temperature, reminiscent of a novel magnetic band splitting. Multi-frequency character of the observed Shubnikov–de Haas oscillations points to the coexistence of electron- and hole-type Fermi pockets in both studied materials. Overall, our results highlight correlation of temperature dependence of the Fermi surface with the magnetotransport properties of DyBi and HoBi.

Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene

Recently, magic-angle twisted bilayer graphene (MATBLG) has emerged with various interaction-driven novel quantum phases at the commensurate fillings of the moiré superlattice, while the charge neutrality point (CNP) remains mostly a trivial insulator. Here, we show an emerging phase of compensated semimetallicity at the CNP of twisted double bilayer graphene (TDBLG), a close cousin of MATBLG, with signatures of electronic correlation. Using electrical and thermal transport, we find two orders of magnitude enhancement of the thermopower at magnetic fields much smaller than the extreme quantum limit, accompanied by large magnetoresistance ( ~ 2500%) at CNP, providing strong experimental evidence of compensated semimetallicity at CNP of TDBLG. Moreover, at low temperatures, we observe unusual sublinear temperature dependence of resistance. A recent theory1 predicts the formation of an excitonic metal near CNP, where small electron and hole pockets co-exist. We understand this sublinear temperature dependence in terms of critical fluctuations in this theory.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance (MR) effect in a low static magnetic field environment at room temperature. However, how to obtain a large room-temperature negative MR effect in them remains to be studied. In this paper, by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side, we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment, but not in a static low magnetic field environment. Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory, we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field. This theoretical analytical model is further confirmed by regulating the geometry size of the device. Our work sheds light on the development of novel magnetic sensing, magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

Extremely large magnetoresistance and quantum oscillations in semimetal Ni3In2S2

In this work, we present magnetotransport properties and quantum oscillations in single-crystalline shandite compound Ni3In2S2, which is a recently identified semimetal with endless Dirac-nodal lines. Ni3In2S2 displays a giant transverse magnetoresistance of ∼24 000 % at 2 K and 14 T and a magnetic field-induced resistivity upturn behavior at low temperatures. Below 50 K, the magnetoresistance curves show a linear magnetic field dependence under high magnetic fields. The computation results indicate that Ni3In2S2 is a semimetal with linear crossings near the Fermi level. The small effective mass, deduced from de Haas–van Alphen quantum oscillations, suggests the high carrier mobility in Ni3In2S2. The high mobility and quantum linear magnetoresistance resulting from the linear dispersive bands jointly lead to the extreme transverse magnetoresistance in our Ni3In2S2 crystal. Our findings can be a reference to understand and search for semimetals with extreme magnetoresistance.