Large Tunneling 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.

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 it is 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.

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.

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.

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

Tunneling conductance regulated by the electrostatic barrier in monolayer black phosphorene

We investigate the tunneling conductance of monolayer black phosphorene through double magnetic barriers modulated by the electrostatic barrier. This magnetic barrier is generated by two ferromagnetic strips deposited on monolayer phosphorene and can form parallel (P) and antiparallel (AP) structures. Applying a voltage to a ferromagnetic strip will create an electrostatic barrier. The transmission of P and AP magnetic structures is calculated using the transfer matrix. Tunneling conductance is given by Landauer–Büttiker theory. Our results show that under double electrostatic barriers modulation, the AP conductance of the system is zero except for sharp peaks, while the P conductance has a certain value, which implies a large tunneling magnetoresistance. However, in the case of single electrostatic barrier modulation, the conductance becomes flat. For the Fermi level in the valence band, the movement of the Fermi level leads to the severe mismatching of transmitted wave vectors in the barrier region, resulting a positive and negative oscillation magnetoresistance. This may be useful for designing memory using a two-dimensional electron gas system.

Large and tunable magnetoresistance in van der Waals ferromagnet/semiconductor junctions

Magnetic tunnel junctions (MTJs) with conventional bulk ferromagnets separated by a nonmagnetic insulating layer are key building blocks in spintronics for magnetic sensors and memory. A radically different approach of using atomically-thin van der Waals (vdW) materials in MTJs is expected to boost their figure of merit, the tunneling magnetoresistance (TMR), while relaxing the lattice-matching requirements from the epitaxial growth and supporting high-quality integration of dissimilar materials with atomically-sharp interfaces. We report TMR up to 192% at 10 K in all-vdW Fe3GeTe2/GaSe/Fe3GeTe2 MTJs. Remarkably, instead of the usual insulating spacer, this large TMR is realized with a vdW semiconductor GaSe. Integration of semiconductors into the MTJs offers energy-band-tunability, bias dependence, magnetic proximity effects, and spin-dependent optical-selection rules. We demonstrate that not only the magnitude of the TMR is tuned by the semiconductor thickness but also the TMR sign can be reversed by varying the bias voltages, enabling modulation of highly spin-polarized carriers in vdW semiconductors.

Layer-Dependent Magnetism and Spin Fluctuations in Atomically Thin van der Waals Magnet CrPS4.

van der Waals (vdW) magnets, an emerging family of two-dimensional (2D) materials, have received tremendous attention due to their rich fundamental physics and significant potential for cutting-edge technological applications. In contrast to the conventional bulk counterparts, vdW magnets exhibit significant tunability of local material properties, such as stacking engineered interlayer coupling and layer-number dependent magnetic and electronic interactions, which promise to deliver previously unavailable merits to develop multifunctional microelectronic devices. As a further ingredient of this emerging topic, here we report nanoscale quantum sensing and imaging of the atomically thin vdW magnet chromium thiophosphate CrPS4, revealing its characteristic layer-dependent 2D static magnetism and dynamic spin fluctuations. We also show a large tunneling magnetoresistance in CrPS4-based spin filter vdW heterostructures. The excellent material stability and robust strategy against environmental degradation in combination with tailored magnetic properties highlight the potential of CrPS4 in developing state-of-the-art 2D spintronic devices for next-generation information technologies.

Effect of spin-orbit coupling within the spin-filter layer on the tunnel magneto-resistance in spin-filter magnetic tunnel junctions

The tunnel magneto-resistance ratio is investigated for spin-filter magnetic tunnel junctions in the presence of spin–orbit coupling within a spin-filter layer. The non-equilibrium Green’s function formalism is utilized to calculate the transmission function in the linear-response limit. The results show that a larger tunnel magneto-resistance is achieved for spin-filter magnetic tunnel junctions compared to that for conventional magnetic tunnel junctions due to the existence of a spin-filter layer. Therefore, the current findings can be introduced new routes to improve the field of spintronics.

Large tunnel magnetoresistance in magnetic tunnel junctions with magnetic electrodes of metastable body-centered cubic CoMnFe alloys

A magnetic tunnel junction (MTJ) is a key device in spintronics applications, such as magnetoresistive random access memory (MRAM). Current standard magnetic material for MTJs is a body-centered cubic (bcc) FeCo(B), which shows large tunnel magnetoresistance (TMR) and high perpendicular magnetic anisotropy (PMA), both are crucial for high-memory capacities MRAM. It is demanded that magnetic materials showing TMR as well as PMA higher than FeCo(B) for further advance. One of alternative magnetic materials may be bcc Co since past ab-initio studies predict that bcc Co show large TMR effect in MgO-barrier MTJs and large PMA due to magneto-elastic effect for those strained state. However, bcc Co is thermodynamically unstable; thus, it is aimed to explore metastable bcc Co based alloys with high stability. Here, we propose metastable bcc Co based alloy with adding both Mn and Fe as a candidate. We study in-plane magnetized MTJs utilizing metastable bcc CoMnFe films as electrodes and demonstrate large TMR effect of 350% at 300 K and of 1002% at 5 K. This experimental finding will open a route to advanced bcc Co based magnetic material for MRAM applications.

Giant intrinsic magnetoresistance in spin-filtered tunnel junctions with ferrimagnetic electrode

In recent years, magnetic tunnel junctions (MTJs) have attracted strong research interest due to their potential use in nonvolatile memory technologies, such as magnetoresistive random access memory and magnetic logic applications. Half-metallic materials have been proposed as ideal electrode materials for MTJs to achieve large tunnel magnetoresistance (TMR) effects. Here, we design and investigate a spin-filter MTJ (sf-MTJ) consisting of a ferrimagnetic inverse Heusler alloy, ${\mathrm{Mn}}_{2}\mathrm{CoSi}$ as the electrode and CaS as the insulating tunnel barrier using ab initio quantum transport calculations. Our results demonstrate a high zero-bias voltage TMR ratio that initially oscillated before decreasing as the bias voltage increased. Despite the oscillatory TMR under bias voltage, the spin injection remains high and stable, highlighting the potential of sf-MTJs formed by ${\mathrm{Mn}}_{2}\mathrm{CoSi}$ electrodes for practical applications.

631% room temperature tunnel magnetoresistance with large oscillation effect in CoFe/MgO/CoFe(001) junctions

We demonstrate tunnel magnetoresistance (TMR) ratios of up to 631% at room temperature (RT) using CoFe/MgO/CoFe(001) epitaxial magnetic tunnel junctions (MTJs). The TMR ratio increased up to 1143% at 10 K. The large TMR ratios resulted from fine-tuning of atomic-scale structures of the MTJs, such as crystallographic orientations and MgO interface oxidation by interface insertion of ultrathin CoFe and Mg layers, which are expected to enhance the well-known Δ1 coherent tunneling transport. Interestingly, the TMR oscillation effect, which is not covered by the standard coherent tunneling theory, also became significant. A 0.32-nm period TMR oscillation with increasing MgO thickness dominates the transport in a wide range of MgO thicknesses; the peak-to-valley difference of the TMR oscillation exceeds 140% at RT, which is attributed to the appearance of large oscillatory components in the resistance area product.

Ab-initio predictions of mechanical, electronic, magnetic, and transport properties of bulk and heterostructure of a novel Fe-Cr based full Heusler chalcogenide

According to electronic structure calculations based on density functional theory, we predicted and studied the structural, mechanical, electronic, magnetic, and transport properties of a new full Heusler chalcogenide called Fe2CrTe in both its bulk and heterostructure forms. This system exhibits ferromagnetic and half-metallic (HM)-like behavior, with very high (about 95%) spin polarization at the Fermi level in its cubic phase. Interestingly, under tetragonal distortion, a clear minimum (with almost the same energy as the cubic phase) was found at a c/a value of ∼1.26, but it exhibits ferrimagnetic and fully metallic characteristics. The compound was found to be dynamically stable against lattice vibration in both phases. The elastic properties indicate that the compound is mechanically stable in both phases according to the stability criteria for the cubic and tetragonal phases. The elastic parameters demonstrate the mechanically anisotropic and ductile nature of the alloy system. Due to the HM-like behavior of the cubic phase and considering practical aspects, we probed the effect of strain and the substrate on various physical properties of the alloy. The transmission profile was calculated for the Fe2CrTe/MgO/Fe2CrTe heterojunction to investigate its possible use as a magnetic tunneling junction material in both the cubic and tetragonal phases. A large tunneling magnetoresistance ratio of ≈103 % was determined for the tetragonal phase and it was one order of magnitude larger than that for the cubic phase.

Large Tunneling Magnetoresistance in Perpendicularly Magnetized Magnetic Tunnel Junctions Using Co75Mn25 / Mo/Co20Fe60B20 Multilayers

We study the magnetic and electrical transport properties of magnetic tunnel junctions (MTJs) consisting of a ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}{/\mathrm{Mo}/\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ multilayer prepared using a mass-production-compatible magnetron sputtering system. The ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}{/\mathrm{Mo}/\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ multilayer sandwiched between two MgO layers exhibits remarkable perpendicular magnetic anisotropy, and a uniaxial magnetic anisotropy constant as large as $0.2\phantom{\rule{0.2em}{0ex}}{\mathrm{MJ}/\mathrm{m}}^{3}$ is achieved by optimizing the ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}$ layer thickness as well as the annealing temperature. The current-in-plane tunneling measurement reveals a large tunneling magnetoresistance of over 100% in perpendicularly magnetized MTJs. These experimental results indicate the applicability of ${\mathrm{Co}}_{75}{\mathrm{Mn}}_{25}$ alloy for magnetic random access memory devices.

Octupole-driven magnetoresistance in an antiferromagnetic tunnel junction

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices1–5. Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface1 and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn3Sn/MgO/Mn3Sn (ref. 6). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn3Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet7 can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets8–10.

Large tunneling magnetoresistance in van der Waals magnetic tunnel junctions based on FeCl2 films with interlayer antiferromagnetic couplings.

Antiferromagnets (AFMs) are some of the most promising candidates for next-generation magnetic memory technology owing to their advantages over conventional ferromagnets (FMs), such as zero stray field and THz-range magnetic resonance frequency. Motivated by the recent synthesis of FeCl2 films with interlayer AFM and intralayer FM couplings, we investigated the magnetic properties of few-layer FeCl2 and the spin-dependent transmissions of graphite/bilayer FeCl2/graphite and Au/n-layer FeCl2/Au magnetic tunnel junctions (MTJs) using first-principles calculations combined with the nonequilibrium Green's function. The interlayer AFM coupling of FeCl2 is certified to be stable and independent of the stacking orders and relative displacement between layers. Furthermore, based on the Au electrode with better conductive performance than the graphite electrode and monolayer 1T-FeCl2 with complete spin polarization, high Curie temperature and large magnetic anisotropic energy, a high tunnel magnetoresistance (TMR) ratio of 2.7 × 103% is achieved in Au/bilayer FeCl2/Au MTJs at zero bias and it increases with different layers of FeCl2 (n = 2-10). These excellent spin transport properties of Au/n-layer FeCl2/Au MTJs based on two-dimensional (2D) AFM barriers with out-of-plane magnetization directions suggest their great potential for application in high-reliability, high-speed and high-density spintronic devices.

Excellent spin-filtering and giant tunneling magnetoresistance in a dual-electrode van der Waals magnetic tunnel junction based on ferromagnetic CrSe2

Magnetic tunnel junctions (MTJs) both with efficient spin-filtering effect and large tunneling magnetoresistance (TMR) ratio are extremely attractive and highly desirable in the field of spintronics. Inspired by recent successful preparation of a stable two-dimensional (2D) layered ferromagnet 1T-CrSe2 on a 2H-WSe2 substrate via chemical vapor deposition (CVD) synthesis, herein, employing first-principles calculations, we investigate the spin-dependent transport properties of van der Waals (vdW) MTJs built with a monolayer 2H-WSe2 tunnel barrier and a 1T-CrSe2 single-electrode or a 1T-MoSe2/1T-CrSe2 dual-electrode. Compared to low TMR (67.3%) in single-electrode MTJ, dual-electrode MTJ exhibits excellent spin-filtering effect (with 99.96% spin polarization) and a giant TMR ratio (up to 2.29 × 105%), which mainly originates from the half-metallicity of CrSe2 induced by charge transfer at MoSe2/CrSe2 interface. Relatively high TMR values (over 1 × 103%) are always maintained at small bias voltages (|Vb| ≤ 0.35 V). Our work have for the first time theoretically verified feasibility of realizing the transition of 2D CrSe2 from metallicity to half-metallicity in the vdW MTJ and yielding excellent spin-filtering and giant magnetoresistance via electrode interface engineering, thereby providing important theoretical guidance for the experimental design of high-performance vdW MTJs in spintronic devices.

Large Room-Temperature Magnetoresistance in van der Waals Ferromagnet/Semiconductor Junctions

A magnetic tunnel junction (MTJ) is the core component in memory technologies, such as the magnetic random-access memory, magnetic sensors and programmable logic devices. In particular, MTJs based on two-dimensional van der Waals (vdW) heterostructures offer unprecedented opportunities for low power consumption and miniaturization of spintronic devices. However, their operation at room temperature remains a challenge. Here, we report a large tunnel magnetoresistance (TMR) of up to 85% at room temperature (T = 300 K) in vdW MTJs based on a thin (< 10 nm) semiconductor spacer WSe2 layer embedded between two Fe3GaTe2 electrodes with intrinsic above-room-temperature ferromagnetism. The TMR in the MTJ increases with decreasing temperature up to 164% at T = 10 K. The demonstration of TMR in ultra-thin MTJs at room temperature opens a realistic and promising route for next-generation spintronic applications beyond the current state of the art.

Enhanced magnetoresistance in perpendicular magnetic tunneling junctions with MgAl2O4 barrier

Perpendicular magnetic tunnel junction with MgAl2O4 barrier is investigated. It is found that reactive RF sputtering with O2 is essential to obtain strong perpendicular magnetic anisotropy and large tunneling magnetoresistance in MgAl2O4-based junctions. An interfacial perpendicular magnetic anisotropy energy density of 2.25 mJ/m2 is obtained for the samples annealed at 400 °C. An enhanced magnetoresistance of 60% has also been achieved. The Vhalf, bias voltage at which tunneling magnetoresistance drops to half of the zero-bias value, is found to be about 1 V, which is substantially higher than that of MgO-based junctions.

Ab Initio Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect

Magnetic tunnel junctions (MTJs) have attracted strong research interest within the last decades due to their potential use as nonvolatile memory such as magnetoresistive random access memory as well as for magnetic logic applications. Half-metallic magnets (HMMs) have been suggested as ideal electrode materials for MTJs to achieve an extremely large tunnel-magnetoresistance (TMR) effect. Despite their high TMR ratios, MTJs based on HMMs do not exhibit current rectification, i.e., a diode effect, which was achieved in a magnetic tunnel junction concept [E. \ifmmode \mbox{\c{S}}\else \c{S}\fi{}a\ifmmode \mbox{\c{s}}\else \c{s}\fi{}\ifmmode \imath \else \i \fi{}o\ifmmode \breve{g}\else \u{g}\fi{}lu et al., ACS Appl. Electron. Mater. 1, 1552--9 (2019)] based on HMMs and type-II spin-gapless semiconductors (SGSs). The proposed concept has recently been experimentally demonstrated using Heusler compounds. In the present work, we investigate from first-principles MTJs based on type-II SGS and HMM quaternary Heusler compounds $\mathrm{Fe}\mathrm{V}\mathrm{Ta}\mathrm{Al}$, $\mathrm{Fe}\mathrm{V}\mathrm{Ti}\mathrm{Si}$, $\mathrm{Mn}\mathrm{V}\mathrm{Ti}\mathrm{Al}$, and $\mathrm{Co}\mathrm{V}\mathrm{Ti}\mathrm{Sb}$. Our ab initio quantum transport calculations based on a nonequilibrium Green's function method have demonstrated that the MTJs under consideration exhibit current rectification with relatively high on:off ratios. We show that, in contrast to conventional semiconductor diodes, the rectification bias voltage window (or breakdown voltage) of the MTJs is limited by the spin gap of the HMM and SGS Heusler compounds. A unique feature of the present MTJs is that the diode effect can be configured dynamically, i.e., depending on the relative orientation of the magnetization of the electrodes, the MTJ allows the electrical current to pass either in one or the other direction, which leads to an inverse TMR effect. The combination of nonvolatility, reconfigurable diode functionality, tunable rectification voltage window, and high Curie temperature of the electrode materials makes the proposed MTJs very promising for room-temperature spintronic applications and opens ways to magnetic memory and logic concepts as well as logic-in-memory computing.