Giant Tunneling Magnetoresistance Research Articles

Symmetry-controlled SrRuO3/SrTiO3/SrRuO3 magnetic tunnel junctions: spin polarization and its relevance to tunneling magnetoresistance

Magnetic tunnel junctions (MTJs), that consist of two ferromagnetic electrodes separated by an insulating barrier layer, have non-trivial fundamental properties associated with spin-dependent tunneling. Especially interesting are fully crystalline MTJs where spin-dependent tunneling is controlled by the symmetry group of wave vector. In this work, using first-principles quantum-transport calculations, we explore spin-dependent tunneling in fully crystalline SrRuO3/SrTiO3/SrRuO3(001) MTJs and predict tunneling magnetoresistance (TMR) of nearly 3000%. We demonstrate that this giant TMR effect is driven by symmetry matching (mismatching) of the incoming and outcoming Bloch states in the SrRuO3(001) electrodes and evanescent states in the SrTiO3(001) barrier. We argue that under the conditions of symmetry-controlled transport, spin polarization, whatever definition is used, is not a relevant measure of spin-dependent tunneling. In the presence of diffuse scattering, however, e.g. due to localized states in the band gap of the tunnel barrier, symmetry matching is no longer valid and TMR in SrRuO3/SrTiO3/SrRuO3(001) MTJs is strongly reduced. Under these conditions, the spin polarization of the interface transmission function becomes a valid measure of TMR. These results provide an important insight into understanding and optimizing TMR in all-oxide MTJs.

Giant tunnel magnetoresistance in in-plane magnetic tunnel junctions based on the heterointerface-induced half-metallic 2H-VS[formula omitted]

Magnetic tunnel junctions (MTJs) constructed from atomically thin two-dimensional (2D) magnetic materials have attracted great attention in recent years because it meets the requirements of miniaturization and high tunability of next-generation spintronic devices. In this work, we demonstrate that the ferromagnetic semiconductor VS2 is transformed into a half-metal in VS2/MoSSe vdW heterostructure. Based on the heterostructure, we design an in-plane MTJs that comprise a monolayer VS2 barrier sandwiched between two VS2/MoSSe heterostructure electrodes. Through density functional calculations combined with a nonequilibrium Green’s function technique, it is found that the tunnel magnetoresistance (TMR) ratio as high as 4.35 × 109% can be achieved. Moreover, the TMR ratio can be tuned by the barrier length, and the maximum value exceeds 1015%. These results not only provide a novel route for designing MTJs using 2D ferromagnetic semiconductor material, but also demonstrate the great importance of vdW heterostructures in the design of spintronic devices.

Voltage-Driven Fluorine Motion for Novel Organic Spintronic Memristor.

Integrating tunneling magnetoresistance (TMR) effect in memristors is a long-term aspiration because it allows to realize multifunctional devices, such as multi-state memory and tunable plasticity for synaptic function. However, the reported TMR in different multiferroic tunnel junctions is limited to 100%. This work demonstrates a giant TMR of -266% in La0.6Sr0.4MnO3(LSMO)/poly(vinylidene fluoride)(PVDF)/Co memristor with thin organic barrier. Different from the ferroelectricity-based memristors, this work discovers that the voltage-driven florine (F) motion in the junction generates a huge reversible resistivity change up to 106% with nanosecond (ns) timescale. Removing F from PVDF layer suppresses the dipole field in the tunneling barrier, thereby significantly enhances the TMR. Furthermore, the TMR can be tuned by different polarizing voltage due to the strong modification of spin-polarization at the LSMO/PVDF interface upon F doping. Combining of high TMR in the organic memristor paves the way to develop high-performance multifunctional devices for storage and neuromorphic applications.

Ferrielectricity controlled widely-tunable magnetoelectric coupling in van der Waals multiferroics

The discovery of various primary ferroic phases in atomically-thin van der Waals crystals have created a new two-dimensional wonderland for exploring and manipulating exotic quantum phases. It may also bring technical breakthroughs in device applications, as evident by prototypical functionalities of giant tunneling magnetoresistance, gate-tunable ferromagnetism and non-volatile ferroelectric memory etc. However, two-dimensional multiferroics with effective magnetoelectric coupling, which ultimately decides the future of multiferroic-based information technology, has not been realized yet. Here, we show that an unconventional magnetoelectric coupling mechanism interlocked with heterogeneous ferrielectric transitions emerges at the two-dimensional limit in van der Waals multiferroic CuCrP2S6 with inherent antiferromagnetism and antiferroelectricity. Distinct from the homogeneous antiferroelectric bulk, thin-layer CuCrP2S6 under external electric field makes layer-dependent heterogeneous ferrielectric transitions, minimizing the depolarization effect introduced by the rearrangements of Cu+ ions within the ferromagnetic van der Waals cages of CrS6 and P2S6 octahedrons. The resulting ferrielectric phases are characterized by substantially reduced interlayer magnetic coupling energy of nearly 50% with a moderate electric field of 0.3 V nm−1, producing widely-tunable magnetoelectric coupling which can be further engineered by asymmetrical electrode work functions.

Crystal-facet-oriented altermagnets for detecting ferromagnetic and antiferromagnetic states by giant tunneling magnetoresistance

Crystal-facet-oriented altermagnets for detecting ferromagnetic and antiferromagnetic states by giant tunneling magnetoresistance

Multilevel resistance states in van der Waals multiferroic tunnel junctions above room temperature

Multiferroic tunnel junctions (MFTJs) comprised of magnetic electrodes and a ferroelectric tunnel barrier have been emerging as promising candidates for nonvolatile memory applications. The recently discovered above room-temperature van der Waals (vdW) ferromagnet Fe3GaTe2 and ferroelectric α-In2Se3 provides possibilities for constructing room-temperature vdW MFTJs. In this work, by using first-principles calculations, we investigate the spin-dependent transport in vdW MFTJs with structure of Fe3GaTe2/bilayer α-In2Se3/Fe3GaTe2. We predict a giant tunneling magnetoresistance (TMR) high up to 10 000% by switching the magnetic alignments of Fe3GaTe2 and tunneling electroresistance (TER) exceeding 300% by controlling the ferroelectric configurations of bilayer α-In2Se3 in the proposed MFTJs. Furthermore, by introducing interface asymmetry and inserting monolayer of h-BN on one interface, the TMR and TER ratios of the MFTJs can be substantially enhanced. In consequence, the multi-level resistance states can be achieved by applying magnetic and electric field in asymmetric MFTJs. Our results highlight full vdW MFTJs for their potential applications in spintronic devices, particularly in the field of multilevel nonvolatile memories.

Giant tunnel magnetoresistance induced by thermal bias

We analyze the spin-resolved transport and, in particular, the tunnel magnetoresistance of an asymmetric ferromagnetic tunnel junction with an embedded quantum dot or molecule subject to thermal and voltage bias in the nonlinear response regime. We demonstrate that such system exhibits a giant tunnel magnetoresistance effect that can be tuned by gate and bias voltages. Large values of magnetoresistance are associated with the interplay between the Kondo correlations and the ferromagnetic-contact-induced exchange field. In particular, we show that the nonequilibrium current in the parallel and antiparallel magnetic configuration of the system changes sign at different values of the voltage and thermal bias. This gives rise to giant values of magnetoresistance, the sign of which can be controlled by the applied sources.

Enhanced sensitivity and thermal tolerance in tunnel magnetoresistance sensor using Ta-doped CoFeSiB soft magnetic layer

We developed a tunnel magnetoresistance (TMR) sensor consisting of a CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) and a CoFeSiB amorphous soft magnetic layer. This multilayer structure is promising for a high-sensitivity sensor because a giant TMR ratio of the MTJ and a small anisotropy field Hk of the free layer can be obtained simultaneously. However, the soft magnetic properties of the CoFeSiB layer disappear when it is annealed at above the crystallization temperature (around 300 °C), which determines the thermal tolerance of the TMR sensor and limits improvements to the sensor's sensitivity and applications. In this study, we doped the CoFeSiB layer with various amounts of Ta to raise its crystallization temperature. TMR sensors using the Ta-doped CoFeSiB layers showed thermal tolerance to annealing temperatures above 425 °C, whereas the sensor with the undoped CoFeSiB layer was tolerant to annealing temperatures up to 325 °C. As well, the Ta doping effectively reduced Hk of the CoFeSiB layer, which resulted in a sensitivity of 50%/Oe, over three times higher than the sensor with the undoped CoFeSiB layer. These results pave the way toward next-generation TMR sensors having higher sensitivity and wider applicability.

Giant Tunneling Magnetoresistance in Spin-Filter Magnetic Tunnel Junctions Based on van der Waals A-Type Antiferromagnet CrSBr

Two-dimensional van der Waals magnetic materials have demonstrated great potential for new-generation high-performance and versatile spintronic devices. Among them, magnetic tunnel junctions (MTJs) based on A-type antiferromagnets, such as CrI3, possess record-high tunneling magnetoresistance (TMR) because of the spin filter effect of each insulating unit ferromagnetic layer. However, the relatively low working temperature and the instability of the chromium halides hinder applications of this system. Using a different technical scheme, we fabricated the MTJs based on an air-stable A-type antiferromagnet, CrSBr, and observed a giant TMR of up to 47000% at 5 K. Meanwhile, because of a relatively high Néel temperature of CrSBr, a sizable TMR of about 50% was observed at 130 K, which makes a big step towards spintronic devices at room temperature. Our results reveal the potential of realizing magnetic information storage in CrSBr-based spin-filter MTJs.

Electrical-gate-controlled giant tunneling magnetoresistance and its quasi-periodic oscillation in an interlaced magnetic-electric silicene superlattice.

In this work, we propose a silicene-based lateral resonant tunneling device by placing silicene under the superlattices interlaced, arranged by ferromagnetic gates and electric gates. Its ballistic transport properties are calculated by the transfer matrix method. Combined with the unique electrically tuned energy gap of silicene, its magnetoresistance (MR) can be exaggeratedly modulated over a wide range by applying electrostatic potential and the on-site potential difference. It is interestingly found that there is a quasi-periodic oscillation of the MR in silicene-based superlattice devices from the quantum resonant confinement of the band splitting by the electrostatic field. Moreover, the peak of the MR in a single-period structure can reach more than 104, while the peak of the MR in an interlaced alternating magnetic-electric silicene superlattice can reach more than 1017, which is one of the best-reported values. This may originate from the enhancement effect of the wave vector filtering by the controlled field. Our studies indicate that the silicene superlattices alternately arranged by the ferromagnetic gate and electric gate not only have giant MR (GMR) properties, but also exhibit the periodic oscillation characteristics of MR in which electric gates can be modulated. Therefore, this work provides a more flexible strategy for the construction of silicene-based nanoelectronic devices.

Giant tunneling magnetoresistance in in-plane double-barrier magnetic tunnel junctions based on MXene Cr2C.

The discovery of two-dimensional (2D) magnetic materials makes it possible to realize in-plane magnetic tunnel junctions. In this study, the transport characteristics of an in-plane double barrier magnetic tunnel junction (IDB-MTJ) based on Cr2C have been studied by density functional theory combined with the nonequilibrium Green's function method. The results showed its maximum tunneling magnetoresistance ratio (TMR) value reached 6.58 × 1010. Its minimum TMR value (3.86 × 106) was also comparable to those of conventional field effect transistors (FETs). Due to its giant TMR and unique structural characteristics, the IDB-MTJ based on Cr2C has great potential applications in magnetic random access memory (MRAM) and logic computing.

Electric field induced tunable half-metallicity in an A -type antiferromagnetic bilayer LaBr2

How to achieve half-metallicity is always a central topic in spintronics and the polarity-tunable half-metallicity is particularly interesting for spin manipulation. In this work, motivated by the intrinsic ferromagnetism in the monolayer electride ${\mathrm{LaBr}}_{2}$, based on density functional theory calculations, we investigate the electronic and magnetic properties of bilayer ${\mathrm{LaBr}}_{2}$, with an aim to search for polarity-tunable half-metallicity. We first find that the antiferromagnetic interlayer coupling state is the ground state and the band structure is spin degenerate, with an indirect band gap of 0.454 eV. By applying a vertical electric field, spin splitting occurs and when the electric field is strong enough ($\ensuremath{\ge}0.33$ V/\AA{}), half-metallicity can be achieved. More interestingly, the spin polarity of the half-metallicity can be tuned by reversing the electric field direction. It originates from the spatial separation of the two spin channels in both the valence band and conduction band and their localization at different layers. Based on the polarity-tunable half-metallicity under vertical electric field, a magnetic tunnel junction based on bilayer ${\mathrm{LaBr}}_{2}$ is designed and the ON/OFF switching can be achived by applying parallel or anti-parallel vertical electric fields in the two leads, which leads to giant tunnel magnetoresistance up to $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The findings suggest new potential of ${\mathrm{LaBr}}_{2}$, and more generally, $A$-type antiferromagnets of application in spintronic devices.

Origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface

The Fe/MgO interface is an essential ingredient in spintronics as it shows giant tunneling magnetoresistance and strong perpendicular magnetic anisotropy (PMA). A recent study demonstrated that the insertion of an ultra-thin LiF layer between the Fe and MgO layers enhances PMA significantly. In this study, we perform x-ray magnetic circular dichroism measurements on Fe/LiF/MgO multilayers to reveal the origin of the PMA enhancement. We find that the LiF insertion increases the orbital-magnetic-moment anisotropy and thus the magnetic anisotropy energy. We attribute the origin of this orbital-magnetic-moment-anisotropy enhancement to the stronger electron localization and electron-electron correlation or the better interface quality with fewer defects.

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.

Giant tunnel magnetoresistance in two-dimensional van der Waals magnetic tunnel junctions: Ag/CrI3/MoSi2N4/CrI3/Ag

With intrinsic magnetism, two-dimensional (2D) $\mathrm{Cr}{\mathrm{I}}_{3}$ has attracted tremendous interest because of the potential application in magnetic devices of smaller size. We propose to use 2D $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ material, which has remarkable stability, excellent electronic properties, and high mobility, as tunnel barrier in vertical magnetic tunnel junction (MTJ), and demonstrate that it is able to generate a giant tunnel magnetoresistance (TMR) over ${10}^{5}%$ when integrated with $\mathrm{Cr}{\mathrm{I}}_{3}$ ferromagnetic layers and Ag electrodes. Combining with density-functional theory and nonequilibrium Green's function approach, we systematically investigate the electron transmission, band structures, and projected local density of states and elaborate the transmission mechanism. The TMR and spin injection efficiency maintain high values below 0.25 V. These results indicate that $\mathrm{Mo}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ is a promising barrier material in future 2D vertical MTJs and provide important guidance for designing devices.

Spin-Filter Magnetic Tunnel Junctions Based on A-Type Antiferromagnetic CrSBr with Giant Tunnel Magnetoresistance

CrSBr is a stable two-dimensional (2D) van der Waals (vdW) magnet with intralayer ferromagnetic and interlayer antiferromagnetic couplings. Here, we propose to use CrSBr as the barrier in spin-filter (sf) MTJ and establish the devices based on graphene/CrSBr/graphene structures. Employing density functional theory (DFT) combined with the nonequilibrium Green’s function approach, we investigated the transmission details, and the results show TMR values above 330%, 2 × 107% and 105% with two-, four- and six-layer CrSBr at zero bias, respectively. Subsequently, we systematically analyze the transmission spectra, transmission eigenstates, electrostatic potentials, band structures and local density of states to elaborate the underlying mechanism of the TMR effect in the sf-MTJs. Our results indicate the great prospect of CrSBr-based sf-MTJs in applications, and provide guidance for futural experiments.

Spin-thermoelectric properties and giant tunneling magnetoresistance of boron-substituted graphene nanoribbon: a first principle study

In this study we have designed a spin caloritronic device based on boron doped armchair graphene nanoribbons (B2-7AGNR). In presence of ferromagnetic (FM) graphitic-carbon nitride (g-C4N3) electrodes the spin-thermoelectric features of the device, both for FM and antiferromagnetic (AFM) states, are studied using first principle calculations. The spin polarized transmission peaks and the presence of density of states near the Fermi level indicate that the system have large spin-thermoelectric figure of merit. In addition, it is observed that the system has a large tunneling magnetoresistance due to the difference in total current between FM and AFM configurations. Further studies reveal that the spin component of the Seebeck coefficient of the device is much higher than the other zigzag and armchair nanoribbons. When the spin magnetic moments of the electrodes are aligned in parallel manner, spin-thermoelectric figure of merit of the system becomes significantly high. It has also been found that on decreasing temperature the efficiency of the device increases. As a whole, the numerical results show that g-C4N3-B2-7AGNR-g-C4N3 system in FM configuration is an efficient low temperature thermoelectric device.

Giant tunneling magnetoresistance and electroresistance in α−In2Se3 -based van der Waals multiferroic tunnel junctions

In the multiferroic tunnel junction (MFTJ) composed of ferromagnetic and ferroelectric materials, the tunneling electroresistance (TER) coexists with the tunneling magnetoresistance (TMR), making it an ideal platform for designing multifunctional electronic devices. Recently, the rapid development of van der Waals (vdW) materials opened up a new avenue of MFTJ due to their atomic thickness and significance in miniaturizing device sizes. Here by employing the nonequilibrium Green's function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ (FGT)/bilayer $\ensuremath{\alpha}\ensuremath{-}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (BIS)/FGT vdW MFTJs. We find that the MFTJ can form multiple nonvolatile resistance states by altering the polarization orientation of the ferroelectric barrier BIS and the magnetization alignment of the two ferromagnetic FGT electrodes, with a maximum TMR (TER) ratio up to $1.1\ifmmode\times\else\texttimes\fi{}{10}^{7}$% (744%). The TER ratio can be further increased to 1868% by using left and right symmetrical copper electrodes. More interestingly, the perfect spin filtering effect can be realized in our MFTJs and the spin current can be controlled by the sign of bias voltages, suggesting a promising route for spin valves that can flexibly manipulate spin currents. Our results demonstrate that giant TMR, large TER, as well as a tunable spin filter can coexist in one system, and that the feasible tunability of such kind of vdW MFTJs is beneficial in designing next-generation logic and memory devices.

Demonstration of reconfigurable magnetic tunnel diode and giant tunnel magnetoresistance in magnetic tunnel junctions made with spin gapless semiconductor and half-metallic Heusler alloy

Here, we report fabrication of a high quality exchanged biased trilayer magnetic tunnel junction (MTJ) utilizing a magnetron sputtering system. The MTJ is composed of a type-II spin gapless semiconductor (SGS) Ti2CoSi inverse Heusler alloy (used as a lower electrode), a thin MgO layer (used as a tunnel barrier), and a half-metallic ferromagnet (HMF) Co2MnSi Heusler alloy (used as an upper electrode). Spin dependent transport properties reveal that the micro-fabricated MTJ can act as a reconfigurable magnetic tunnel diode, which lets the electric current to flow in either the forward or reverse path relying on the relative alignment of the magnetization direction of the upper and lower magnetic electrodes. A considerably high on/off current ratio (∼103) and a significantly low turn on voltage (VT) of 0.09 V have been achieved at 5 K for both parallel and antiparallel configurations. Another important characteristic shown by our fabricated MTJ is that it exhibits extremely large tunnel magnetoresistance ratios of 892% at 5 K and 197% at room temperature, which brings to light the utmost importance of using the combination of HMF and SGS materials as magnetic electrodes in a tunnel junction for potential applications in modern spintronic devices. All these exceptional features can undoubtedly nominate CMS/MgO/TCS MTJs as a promising candidate to serve as memory or logic elements in next generation ultra-high density magnetoresistive random access memories together with contemporary spin based electronic devices.

Giant tunneling magnetoresistance in atomically thin VSi2N4/MoSi2N4/VSi2N4 magnetic tunnel junction

With rich electrical and magnetic properties and environmental stability, layered MSi2N4 (M = transition metal) has recently attracted much attention. By using a ferromagnetic VSi2N4 monolayer as an electrode and a semiconducting MoSi2N4 monolayer as a tunneling barrier, an atomically thin VSi2N4/MoSi2N4/VSi2N4 magnetic tunnel junction (MTJ) is theoretically proposed. Our calculated results suggest that the MTJ has a giant tunneling magnetoresistance (TMR) as large as 1010% and a near perfect (100%) spin injection efficiency (SIE). Our nonequilibrium Green's functions calculations indicate that the TMR and SIE are robust under a finite bias voltage of −100 mV to 100 mV. These results show that layered MSi2N4 can be promising materials for designing atomically thin MTJ with a giant TMR for future spintronic applications.