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We report fabrication and characterization of double magnetic tunnel junction (DMTJ) magneto-resistive random access memory cells that exhibit characteristic about 2X reduction of switching current compared to single reference layer junctions, but maintain high tunneling magnetoresistance ratio exceeding 120 % , high coercive fields of the free layer of more than 2 kOe for 65 nm cells, and magnetically stable reference layers with pinning fields above 6 kOe. Switching analysis performed for two different relative magnetization orientations of the reference layers shows that the net switching current is the result of combined spin transfer torque effects of the individual reference layers, with tunneling and spin-valve-like contributions adding constructively. Our work shows that efficient reduction of switching current can be achieved in double magnetic tunnel junctions with dual MgO layers where one of the layers has significantly lower resistance-area product to enable high magnetoresistance ratio. [ABSTRACT FROM AUTHOR]

This paper presents the results of studies of the effects of magnetoresistance and magnetocapacitance in magnetic tunnel junctions Tb 2 2 − δ Co5 Fe 7 3 /Pr6 O 1 1 / Tb 1 9 − δ Co5 Fe 7 6 with perpendicular anisotropy of magnetic electrodes and a paramagnetic barrier layer. Experimentally measured values of tunnel magnetic resistance and tunnel magnetic capacitance in such contacts exceed 100% at room temperature. The paper analyzes the effect of magnetization reversal of one of the electrodes on the conductivity of magnetic tunnel junctions with electrodes that have perpendicular anisotropy. It is shown that significant changes in tunnel magnetic resistance and tunnel magnetic capacity in such contacts can be explained by the separation of electrons with major and minor spin polarization in the inverse nanolayer in the interface region. The separation of polarized electrons is caused by the magnetomotive force acting on the electron spin in a strongly gradient magnetic field. Such a magnetomotive force occurs with antiparallel magnetization of the magnetic electrodes and it has opposite directions for major and minor polarized electrons. As a result of the spatial separation of polarized electrons in the inversion layer, an inhomogeneous distribution of the electron density along the direction of magnetization of the magnetic contacts occurs. As a result, an additional Coulomb barrier between the magnetic electrodes and the dielectric nanolayer appears in the tunnel contacts and an additional spin capacitance appears. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ) is one of the cornerstones of modern information technologies. Bringing MTJ's operation beyond the conventional binary regime, enabled by tunneling magnetoresistance (TMR) effect, is highly promising for prospective memory technologies and neuromorphic hardware development. In this paper, we demonstrate multilevel magnetoresistance states in an all-perovskite-oxide La0.7Sr0.3MnO3 (LSMO)/BaTiO3/LSMO heterostructure grown on MgO substrates. Unlike traditional TMR, we observe four distinct regions of increased magnetoresistance, which result in three magnetic field-induced resistance states in total. We show that the observed phenomenon arises from the low-field magnetoresistance effect, which occurs in the two epitaxial LSMO layers, independently and at different values of the magnetic field. The effect is well simulated by a model based on the presence of structural defects and non-uniform deformations in the LSMO layers, induced by the large lattice mismatch of the LSMO with the MgO substrate. We believe that our findings contribute to the understanding of complex magnetoresistance effects in MTJs and can be taken into consideration for the design of multi-bit memory cells or neuromorphic devices. [ABSTRACT FROM AUTHOR]

The magnetic tunnel junctions (MTJs) based on van der Waals (vdW) materials possess atomically smooth interfaces with minimal element intermixing. This characteristic ensures that spin polarization is well maintained during transport, leading to the emergence of richer magnetoresistance behaviors. Here, using all 2D vdW MTJs based on magnetic metal Fe3GeTe2 and non-magnetic semiconductor MoSe2, we demonstrate that the magnitude and even sign of the magnetoresistance can be tuned by the applied voltage. The sign inversion of the magnetoresistance is observed in a wide temperature range below the Curie temperature. This tunable magnetoresistance sign may be attributed to the spin polarizations of the tunneling carriers and the band structure of the two ferromagnetic electrodes. Such robust electrical tunability of magnetoresistance extends the functionalities of low-dimensional spintronics and makes it more appealing for next-generation spintronics with all-vdW MTJs. [ABSTRACT FROM AUTHOR]

We report low-frequency electrically detected magnetic resonance (EDMR) and near-zero field magnetoresistance (NZFMR) measurements observed through spin-dependent trap-assisted tunneling on unpassivated 28Si/28SiO2 metal–insulator–semiconductor (MIS) capacitors. This study both experimentally and theoretically explores the effects of the low-frequency EDMR response and the mechanisms responsible for spin-mixing, which leads to the NZFMR response in the absence of electron–nuclear hyperfine interactions. Previous reports that utilized high-frequency EDMR and NZFMR on these devices indicated that the observed trap-assisted tunneling spectra are dominated by silicon dangling bonds back bonded to silicon at the Si/SiO2 interface, Pb0 and Pb1 centers. These previous results also suggest that the rate limiting step in trap-assisted tunneling is the interface to an oxide trapping event. In this work, we extend the theory to show the explicit connection of the defects observed between the NZFMR response and the EDMR, which has not yet been demonstrated. We also extend a theoretical approach to the analysis of both the EDMR and NZFMR spectra and match the theory to experimental observations made in 28Si/28SiO2 MIS capacitors. The method utilizes a least squares fitting algorithm of models developed from the stochastic quantum Liouville equation. We find that we can extract a dipolar coupling constant by fitting both the NZFMR and EDMR spectra. Our experimental results and resulting fitted spectra from our quantitative model suggest the mechanism responsible for spin-mixing, which leads to the NZFMR response in the absence of electron–nuclear hyperfine interactions, is predominately magnetic dipolar interactions between Pb centers at the interface. [ABSTRACT FROM AUTHOR]

L10 FePd is increasingly recognized as a potential candidate for magnetic tunnel junctions (MTJs), yet there remains room for enhancing device performance. In this work, we fabricated fully-integrated L10 FePd-based perpendicular MTJ devices and achieved a significant increase in tunnel magnetoresistance, reaching ∼65%, compared to the previous record of 25%. Notably, we observed bi-directional switching with a low switching current density of about 1.4 × 105 A/cm2, which outperforms the typical spin-transfer torque (STT) MTJ by about one order of magnitude. We propose two possible mechanisms to elucidate the switching process and associated device performance: (1) The voltage-controlled exchange coupling-driven switching of the bottom CoFeB layer; (2) The STT-driven switching of the exchange-coupled L10 FePd–CoFeB composite. While additional research is necessary, these findings may further advance the integration of L10 FePd into spintronic devices, potentially enabling low-energy memory and logic technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] In recent years, enormous efforts have been made to identify and manipulate the exotic electrical and magnetic properties at a two-dimensional (2D) limit of various exciting materials. The spin–orbit coupling (SOC) in 2D van der Waals (vdW) heterostructures opens a fascinating and versatile platform to implement the intriguing quantum-engineered spintronic devices for practical applications. This review comprehensively outlines the modern-era progress of investigating the inherent magnetism of atomically thin 2D materials. Firstly, in this review, the most recent developments of synthesis, characterizations, functionalities, and spin textures in 2D magnetic materials are summarized in detail. Secondly, we conferred the well-known phenomena related to the proximity effect, spin–orbit torque (SOT), spin valve magnetic tunnel junction (MTJ), spin field effect transistor (FET) and magneto memristive-based applications. In addition, we also explored the possible interplay between 2D magnetic materials and associated band topology for spin caloritronics. Finally, we provided our perspective on the recent and upcoming challenges and goals of this promising research area, which leads the 2D magnetic materials to the modern era of energy-efficient quantum computing. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) and memristors are two key emerging nanotechnologies that attracted significant interest for potential applications at the forefront of the digital revolution, including sensing, data storage, and non‐conventional computation. The co‐integration of these phenomena into a single multifunctional device is an important step toward harnessing the re‐programmability of memristive systems with the high yield and varied functionality of MTJs. This study demonstrates the co‐existence of magnetoresistance and memristive properties on MgO‐based MTJs. These devices show a magnetoresistance with a linear response as a function of a magnetic field and no hysteresis, which are the requirements for good magnetic field sensors, as well as demonstrating a non‐volatile and quasi‐analogue memristive behavior as a function of an applied electrical field down to nanosecond pulses. Furthermore, by doping the oxide barrier, the memristive power consumption is lowered by 20% giving the multi‐functionality of the devices a promising scalability potential. This study also shows that, memristive switching can be reversibly used to completely suppress and recover the spintronic functionalities. These results can pave the way for a seamless co‐integration of memristors and spintronic devices in complex reprogrammable circuits addressing applications such as reprogrammable multifunctional field sensor arrays and neuromorphic computing. [ABSTRACT FROM AUTHOR]

This document discusses the global energy crisis caused by the exponential increase in fossil fuel consumption and the resulting environmental and health impacts. To address this crisis, researchers have been exploring renewable energy sources and the use of nanomaterials in energy conversion and storage. Nanomaterials, with their unique properties, have shown promise in applications such as thermoelectric devices, photovoltaic devices, supercapacitors, batteries, and sensors. The document highlights recent research breakthroughs in the development of innovative electrode materials for supercapacitors, as well as advancements in the use of nanomaterials in phase-change materials and magnetic tunnel junctions. These findings contribute to the advancement of energy storage technologies and offer insights for future developments in the field. [Extracted from the article]

This article discusses the current state of development, open research opportunities, and application perspectives of electric‐field‐controlled magnetic tunnel junctions that use the voltage‐controlled magnetic anisotropy effect to control their magnetization. The integration of embedded magnetic random‐access memory (MRAM) into mainstream semiconductor foundry manufacturing opens new possibilities for the development of energy‐efficient, high‐performance, and intelligent computing systems. The current generation of MRAM, which uses the current‐controlled spin‐transfer torque (STT) effect to write information, has gained traction due to its nonvolatile data retention and lower integration cost compared to embedded Flash. However, scaling MRAM to high bit densities will likely require a transition from current‐controlled to voltage‐controlled operation. In this perspective, an overview of voltage‐controlled magnetic anisotropy (VCMA) as a promising beyond‐STT write mechanism for MRAM devices is provided and recent advancements in developing VCMA‐MRAM devices with perpendicular magnetization are highlighted. Starting from the fundamental mechanisms, the key remaining challenges of VCMA‐MRAM, such as increasing the VCMA coefficient, controlling the write error rate, and achieving field‐free VCMA switching are discussed. Then potential solutions are discussed and open research questions are highlighted. Lastly, prospective applications of voltage‐controlled magnetic tunnel junctions (VC‐MTJs) in security applications, extending beyond their traditional role as memory devices are explored. [ABSTRACT FROM AUTHOR]

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. Van der Waals materials are composed of layers held weakly by van der Waals forces. This feature allows different materials to be combined into heterostructures, with fewer restrictions on growth and lattice matching. Here, Zhu et al make use of this feature to create a van der Waals magnetic tunnel junction with a semiconducting spacer, allowing for improved tunability and reduced device thickness. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ) based on van der Waals (vdW) magnetic layers has been found to present excellent tunneling magnetoresistance (TMR) property, which has great potential applications in field sensing, nonvolatile magnetic random access memories, and spin logics. Although MTJs composed of multilayer vdW magnetic homojunction have been extensively investigated, the ones composed of vdW magnetic heterojunction are still to be explored. Here, we use first-principles approaches to reveal that the magnetic heterojunction MTJs have much more distinguishable TMR values than the homojunction ones. In the MTJ composed of bilayer CrI3/bilayer Cr2Ge2Te6 heterojunction, we find there are eight stable magnetic states, leading to six distinguishable electronic resistances. As a result, five sizable TMRs larger than 300% can be obtained (the maximum TMR is up to 620 000%). Six distinguishable memories are obtained, which is two times larger than that of a four-layered homojunction MTJ. The underlying relationships among magnetic state, spin-polarized band structures, and transmission spectra are further revealed to explain the multiple TMR values. We also find that the magnetic states, and thus TMRs, can be efficiently modulated by an external electric field. This study opens an avenue to the design of high-performance MTJ devices based on vdW heterojunctions. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs), a prominent type of spintronic device based on the spin valve effect, have facilitated the development of numerous spintronic applications. The technical appeal for the next‐generation MTJ devices has been proposed in two directions: improving device performance by utilizing advanced two‐dimensional (2D) ferromagnetic materials or extending device functionalities by exploring the gate‐tunable magnetic properties of ferromagnets. Based on the recent development of 2D magnets with the ease of external stimuli, such as electric field, due to their reduced dimensions, reliable prospects for gate‐tunable MTJ devices can be achieved, shedding light on the great potential of next‐generation MTJs with multiple functionalities for various application environments. While the electrical gate‐tunable MTJ device is highly desirable for practical spintronic devices, it has not yet been demonstrated. Here, we demonstrate the experimental realization of a spin valve device by combining a vertical Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ with an electrolyte gate. The magnetoresistance ratio (MR ratio) of 36% for the intrinsic MTJ confirms the good performance of the device. By electrolyte gating, the tunneling MR ratio of Fe3GeTe2/h‐BN/Fe3GeTe2 MTJ can be elevated 2.5 times, from 26% to 65%. Importantly, the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating, providing a promising method to control the magnetization configuration of the MTJ. Our work demonstrates a gate‐tunable MTJ device toward the possibility for gate‐controlled spintronic devices, paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications. [ABSTRACT FROM AUTHOR]

Magnetoresistive sensors have been enthusiastically selected for applications requiring magnetic field detection with small footprint sensors. The optimisation of the sensor response includes using soft magnetic free layers, based on CoFeB and NiFe alloys. Here we report the TMR and noise performance of magnetically saturated in-plane MTJ sensors including CoFeBTa and CoFeSiB soft magnetic films as free layers (FL). Assessing magneto-crystalline anisotropy μ0Hk values of 2.1 and 0.7 mT in CoFeB 2.5 (nm)/Ru 0.2/CoFeBTa 4 and CoFeB 3/Ru 0.2/CoFeSiB 4 compared to 1.7 mT in CoFeB 2.5/Ru 0.2/NiFe 4, together with an improved magnetoresistance of 230% in CoFeBSi comparing with 170% (NiFe) with superior noise characteristics, with Hooge parameter of αH = 7 × 10−11 μm2. [ABSTRACT FROM AUTHOR]

We fabricated magnetic tunnel junctions (MTJs) with FeAlSi free layers and investigated the tunnel magnetoresistance (TMR) properties at low temperature. We observed TMR ratio increase with temperature decrease, and confirmed the TMR ratio of 179.9% at 10 K. The conductance dependence on bias voltage was measured, and a clear peak at low bias voltage similar to Fe/MgO/Fe MTJs was observed. This behavior can be explained by considering the majority band of Fe(001), and Δ5 electrons tunneling in FeAlSi/MgO/CoFeB MTJs at low bias voltage. We also investigated tunnel anisotropic magneto-resistance (TAMR) and clearly observed a TAMR peak similar to Fe/MgO/Fe MTJs, where the TAMR ratio of FeAlSi/MgO/CoFeB MTJs was 1.0% comparable to 1.1% in Fe/MgO/Fe MTJs. We concluded that electron tunneling was caused by the interfacial resonance states originating from spin orbit coupling in the FeAlSi/MgO/CoFeB MTJs. [ABSTRACT FROM AUTHOR]

We report on first-principles spin-polarised quantum transport calculations (from NEGF + DFT) in MgO-spaced magnetic tunnel junctions (MTJs) based on two different Mn-based Heusler ferrimagnetic metals, namely Mn3Al and Mn3Ga in their tetragonal DO22 phase. The former is a fully compensated half-metallic ferrimagnet, while the latter is a low-moment high-spin-polarisation ferrimagnet, both with a small lattice mismatch from MgO. In identical symmetric and asymmetric interface reconstructions across a 3-monolayer thick MgO barrier for both ferrimagets, the linear response (low-voltage) spin-transfer torque (STT) and tunneling magneto-resistance (TMR) effects are evaluated. A larger staggered in-plane STT is found in the Mn3Ga case, while the STT in Mn3Al vanishes quickly away from the interface (similarly to STT in ferromagnetic MTJs). The roles are reversed for the TMR, which is practically 100% in the half-metallic Mn3Al-based MTJs (using the conservative definition) as opposed to 60% in the Mn3Ga case. The weak dependence on the exact interface reconstruction would suggest Mn3Ga–Mn3Al solid solutions as a possible route towards optimal trade-off of STT and TMR in the low-bias, low-temperature transport regime. [ABSTRACT FROM AUTHOR]

In this work, IrMn-based perpendicular magnetic tunnel junctions (MTJs) are investigated. By inserting a thin W layer at an antiferromagnet/ferromagnet (AFM/FM) interface, we enhance the annealing temperature to 355 °C and obtain a high tunnel magnetoresistance ratio of 127%. Subsequently, field-free spin–orbit torque (SOT) switching of perpendicular MTJ is realized thanks to the in-plane exchange bias generated at the AFM/FM interface. Moreover, by applying a gate voltage, a coercive field is effectively decreased due to the voltage-controlled magnetic anisotropy (VCMA) effect. Finally, through the interplay of the SOT and VCMA effects, the critical switching current density is dramatically reduced by 73% (to 2.4 MA/cm2) and the total writing power consumption is decreased by 84% when a gate voltage of 0.76 V is applied. These findings pave the way for the practical applications of the IrMn-based perpendicular MTJs in low-power magnetic random-access memory. [ABSTRACT FROM AUTHOR]

The magnetic tunnel junction (MTJ) is an important spintronic device and widely used in storage and sensor applications due to its large tunnel magnetoresistance. Here, we demonstrate that MTJs with an MgO barrier can be used in a straightforward way for accurate and quantitative temperature measurements in buried nanostructures. For this purpose, three intrinsic properties of the MTJ are employed: (i) the temperature dependence of the tunnel resistance, (ii) the temperature dependence of the coercivity of the free layer, and (iii) the temperature dependence of the coercivity of the synthetic antiferromagnet. We compare the three methods for the case in which a metal layer above the MTJ is heated by femtosecond laser pulses and find a good agreement between the different techniques. Our results might contribute to a better understanding of nanoscale thermal transport in multilayer structures for which corresponding simulations are very complicated. Additionally, the developed techniques, which have a high spatial resolution, will be suitable for the study of new physical phenomena where quantitative information about temperature and temperature gradients is required. [ABSTRACT FROM AUTHOR]

Perpendicular magnetic tunnel junctions (pMTJs) with a CoFeB/W/CoFeB/MgO composite free layer are experimentally investigated. Magnetic anisotropy and tunneling magnetoresistance (TMR) are determined as functions of ferromagnetic (CoFeB) and capping (MgO) layer thicknesses using the ferromagnetic resonance technique. In pMTJs fabricated into 130 and 150-nm diameters, the TMR ratio > 160% and the thermal stability factor Δ > 60 are measured for the MgO capping layer thickness of tMgO ≥ 1 nm. The voltage vs. magnetic field stability diagram indicates field-free current induced switching with voltages | V S | < 0.5 V. [ABSTRACT FROM AUTHOR]

The popularity gained by magnetic tunnel junction (MTJ) devices in recent years has made the analysis of various effects on MTJs necessary. This paper describes a comparative analysis of the addition of high-K dielectrics (HfO2 or ZrO2 or TiO2 or h-BN or Ta2O5) along with the MgO dielectric layer as MgO–HfO2/ZrO2/TiO2/h-BN/Ta2O5–MgO to form a composite dielectric layer (CDL). Utilizing these CDL, we have presented a double-barrier penta-layer MTJ device by introducing CDL between CoFeB ferromagnetic layers and Fe ferromagnetic layers. First, the crystallographic analysis of the materials has been performed using the first-principles computation in density functional theory for predicting material behavior. Furthermore, the simulations were executed using a non-equilibrium Green's function (NEGF)-based simulator. This NEGF-based quantum transport simulator has been used for calculating the various critical transport characteristics of an MTJ such as tunneling magnetoresistance (TMR), differential tunneling magnetoresistance, and spin-transfer torque (STT, both in-plane and out-of-plane) along with other properties such as resistance and differential resistance ∂ V ∂ I for both parallel and antiparallel states by giving material parameters and geometric dimensions of an MTJ as inputs. When compared to the traditional tri-layer MTJ devices (CoFeB–MgO–CoFeB and Fe–MgO–Fe), CoFeB–CDL–CoFeB, and Fe–CDL–Fe are found to be superior in terms of both high TMR ratio and low switching current. We have also included the temperature-related analysis for all the MTJ devices. Among all the MTJ models investigated, the highest TMR ratio found at 13 K is for Ta2O5 and TiO2-based CDL MTJ for Fe-based MTJ models, with 1218% and 1246%, respectively. [ABSTRACT FROM AUTHOR]

Because of the wide selectivity of ferromagnetic and ferroelectric (FE) components, electric-field (E-field) control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures. Here, an MgO-based magnetic tunnel junction (MTJ) is chosen rationally as the ferromagnetic constitution and a high-activity (001)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-0.3PT) single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure. The shape of tunneling magnetoresistance (TMR) versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias. The E-field-controlled change in the TMR ratio is up to â€"0.27% without magnetic-field bias. Moreover, when a typical magnetic field (∼ ±10 Oe) is applied along the minor axis of the MTJ, the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias. This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ. In addition, based on such a multiferroic heterostructure, a strain-gauge factor up to approximately 40 is achieved, which decreases further with a sign change from positive to negative with increasing magnetic fields. This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature. [ABSTRACT FROM AUTHOR]

Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted great interest. In this paper, we examine the tunnel magnetoresistance of Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions dependent on the capping layer, i.e., Hf or Ta. In these stacks, perpendicular exchange bias fields of 500 Oe along with perpendicular magnetic anisotropy are combined. A tunnel magnetoresistance of (47.2 ± 1.4)% for the Hf-capped sample was determined compared to the Ta one (42.6 ± 0.7)% at room temperature. Interestingly, this observation is correlated with the higher boron absorption of Hf compared to Ta, which prevents the suppression of the △1 channel and leads to higher tunnel magnetoresistance values. Furthermore, the temperature dependent coercivities of the soft electrodes of both samples are mainly described by the Stoner-Wohlfarth model including thermal fluctuations. Slight deviations at low temperatures can be attributed to a torque on the soft electrode which is generated by the pinned magnetic layer system. [ABSTRACT FROM AUTHOR]

We present a study on perpendicular magnetic tunnel junctions with W as buffer and capping layers. A tunneling magnetoresistance of 138% and an interfacial magnetic anisotropy of 1.67 erg/cm² were obtained in optimally annealed samples. However, after extended annealing at 420 °C, junctions with W layers showed extremely small resistance due to interdiffusion of W into the MgO barrier. In contrast, in Ta-based junctions, the MgO barrier remained structurally stable despite disappearance of magnetoresistance after extended annealing due to loss of perpendicular magnetic anisotropy. Compared with conventional tunnel junctions with in-plane magnetic anisotropy, the evolution of tunneling conductance suggests that the relatively low magnetoresistance in perpendicular tunnel junctions is related to the lack of highly polarized Δ1 conducting channel developed in the initial stage of annealing. [ABSTRACT FROM AUTHOR]

The Fe/MgO/Fe magnetic tunnel junction with B and N modified interfaces has been studied based on the first-principle density function theory method. For junctions with thin (five layers) and thick (ten layers) MgO barriers, positive and negative tunneling magnetic resistance (TMR) ratios are obtained as a function of the interface structure under finite bias voltage. The junctions with B modified interface have Δ1 channel conductance perfectly preserved. But the spin filtering effect is reduced and thus very low TMR value is resulted. N modified interface has obvious influence to the interfacial state and drastically changes the bias dependence of the TMR output, which is promising for multifunction spintronic device applications with high TMR output and optimized bias dependence. Also, the formation energy of N insertion at the interface is lower than that of B. It will be very effective to prevent B staying at the interface with N insertion. [ABSTRACT FROM AUTHOR]

The low‐field magnetoresistance properties in double‐perovskite strontium ferromolybdate core–shell structures arise from spin‐dependent tunneling through a barrier formed by the shell. It is strongly dependent on synthesis conditions. In this work, first, the resistivity behavior of granular strontium ferromolybdate ceramics comprising intergrain tunnel barriers is reviewed. Based on this generalization, the modification of the tunneling process with barrier thickness and interface conditions is demonstrated. For the first time, equations for the magnetoresistance in each special case are derived. [ABSTRACT FROM AUTHOR]

The emergence of two-dimensional van der Waals (vdW) intrinsic magnets offers exciting opportunities to explore high-performance vdW magnetic tunnel junctions (vdW MTJs) and miniaturization of devices beyond Moore's law for future energy efficient nano-electronic devices. In this work, using first principles calculations, we investigate the spin-dependent transport of vdW MTJs formed by two vdW ferromagnetic (FM) CrSe2 electrodes and an interlayer antiferromagnetic bilayer NiCl2 barrier (CrSe2/NiCl2/CrSe2 vdW MTJ). We find that in contrast to the large resistance-area (RA) products higher than several kilohms square micrometer in crystalline MgO based MTJs with high tunneling magnetoresistance (TMR) ratios, the large TMR ratio of about 5200% and the low RA products ranging from 0.11 to 6 Ω μm2 are simultaneously achieved in the CrSe2/NiCl2/CrSe2 vdW MTJ at zero bias due to the spin-dependent tunnel transport associated with the FM CrSe2 electrode and the significant spin filtering effect associated with the half-metallic bilayer NiCl2 barrier. Moreover, the TMR ratio of the CrSe2/NiCl2/CrSe2 vdW MTJ increases first with increasing bias voltage and then decreases with the further increase in the bias voltage after reaching the highest value, and the optimized bias voltage can significantly promote the TMR ratio up to 12 000%. Our results pave the way to develop high-performance vdW MTJs with both large TMR ratios and low RA products for future spintronic applications. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions have been widely used in various applications, such as magnetic sensors and magnetic random-access memories. In the practical application of MTJs, they are usually used in series toward high sensitivity and high stability, especially for sensor applications. In this paper, serial MTJs devices on 8 in. wafers were fabricated. The temperature dependence of the tunnel magnetoresistance ratio, resistances in parallel and antiparallel configurations, and dynamic conductance were systematically investigated. The results of serial MTJs devices are consistent with a single MTJ device. This research suggests that serial MTJs can be directly used to investigate the magnetic tunneling properties of MTJ stacks. [ABSTRACT FROM AUTHOR]

Thin-film strontium ferromolybdate is a promising material for applications in room-temperature magnetic tunnel junction devices. These are spin-based, low-power-consuming alternatives to CMOS in non-volatile memories, comparators, analog-to-digital converters, and magnetic sensors. In this work, we consider the main tasks to be solved when creating such devices based on strontium ferromolybdate: (i) selecting an appropriate tunnel barrier material, (ii) determining the role of the interface roughness and its quantification, (iii) determining the influence of the interface dead layer, (iv) establishing appropriate models of the tunnel magnetoresistance, and (v) promoting the low-field magnetoresistance in (111)-oriented thin films. We demonstrate that (i) barrier materials with a lower effective electronegativity than strontium ferromolybdate are beneficial, (ii) diminution of the magnetic offset field (the latter caused by magnetic coupling) requires a wavy surface rather than solely a surface with small roughness, (iii) the interface dead-layer thickness is of the order of 10 nm, (iv) the tunnel magnetoresistance deteriorates due to spin-independent tunneling and magnetically disordered interface layers, and (v) antiphase boundaries along the growth direction promote the negative low-field magnetoresistance by reducing charge carrier scattering in the absence of the field. [ABSTRACT FROM AUTHOR]

We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, and model the frequencies to deduce the exchange stiffness of this material in the ultrathin limit. For this, we embody the layers in magnetic tunnel junctions patterned into circular nanopillars of diameters ranging from 100 to 300 nm, and we use magneto-resistance to determine which rf-current frequencies are efficient in populating the spin wave modes. Micromagnetic calculations indicate that the ultrathin nature of the layer and the large wave vectors used ensure that the spin wave frequencies are predominantly determined by the exchange stiffness, such that the number of modes in a given frequency window can be used to estimate the exchange stiffness. For 1 nm layers, the experimental data are consistent with an exchange stiffness A ≐ 20±2 pJ/m, which is slightly lower than its bulk counterpart. The thickness dependence of the exchange stiffness has strong implications for the numerous situations that involve ultrathin films hosting strong magnetization gradients, and the micromagnetic description thereof. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The recent discovery of 2D magnetic materials, which are compounds of transition metals (TM) with other elements, has opened new avenues for basic research on low‐dimensional magnetism and potential applications in spintronics. To further explore new 2D magnets of pure TM is an interesting topic. Based on the first‐principles calculations, here a strategy of obtaining monolayer TM magnets, i.e., depositing TM atoms on graphyne (Gy), which has proper hexagonal hollow geometry, is proposed. It is found that a TM monolayer with perfect hexagonal geometry can be formed on Gy. The TM monolayer exhibits a wealth of physical properties in dependence of TM species, such as ferromagnetic and anti‐ferromagnetic ground states, as well as intriguing semimetal and half‐metal characteristics. It is also found that the half‐metal characteristics make the monolayer TM have great potential applications in horizontal magnetic tunnel junction (MTJ) devices, where the tunneling magnetoresistance can reach as high as 850 000%. These results provide a new framework for obtaining 2D magnets with outstanding spintronic properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Spintronic rf detectors are efficient nanoscale counterparts to conventional semiconductor-based components for energy harvesting and wireless communication at low input power. Here, we report on the optimization of the rectified output dc voltage using magnetic tunnel junctions (MTJs) with strong perpendicular anisotropy of both the polarizing and free layers. The magnetization of the polarizing layer is fixed out-of-plane, while the free layer thickness is adjusted so that its magnetization orientation changes from in-plane to out-of-plane. Rectification dc output voltages in the mV range are obtained for moderate rf source powers with a signal-to-noise ratio of 26–39 dB for Prf = −25 dBm and a sensitivity ε of 300 mV/mW. The rectified signal shows a strong dependence on MTJ dimensions: it increases by a factor of 5–6 when reducing the diameter from 180 to 50 nm. Furthermore, this enhancement can be doubled when reducing the free layer thickness from 1.8 to 1.6 nm. This size-related enhancement is attributed to several jointly acting effects: the amplitude of the spin transfer torque that depends inversely on the diameter, the effective anisotropy that depends on the thickness of the excited layer, and the tunneling magneto-resistance ratio that for the devices studied here depends on diameter. The obtained results indicate that the geometry of the MTJ can be used to design spintronic based rf detectors with optimized sensitivity. [ABSTRACT FROM AUTHOR]

Spin‐resolved electron symmetry filtering is a key mechanism behind giant tunneling magnetoresistance (TMR) in Fe/MgO/Fe and similar magnetic tunnel junctions (MTJs), providing room temperature functionality in spin electronics. However, the electron symmetry filtering breaks down under applied bias, dramatically reducing the TMR above 0.5 V. This strongly hampers the application range of MTJs. To circumvent the problem, resonant tunneling through quantum well states in thin layers has been used so far. This mechanism, however, is mainly effective at low temperatures. Here, a fundamentally different approach is demonstrated, providing a strong TMR boost under applied bias in V/MgO/Fe/MgO/Fe/Co hybrids. This pathway uses spin orbit coupling (SOC) controlled interfacial states in vanadium, which contrary to the V(001) bulk states are allowed to tunnel to Fe(001) at low biases. The experimentally observed strong increase of TMR with bias is modeled using two nonlinear resistances in series, with the low bias conductance of the first (V/MgO/Fe) element being boosted by the SOC‐controlled interfacial states, while the conductance of the second (Fe/MgO/Fe) junctions are controlled by the relative alignment of the ferromagnetic layers. These results pave a way to unexplored and fundamentally different spintronic device schemes, with tunneling magnetoresistance uplifted under applied electric bias. [ABSTRACT FROM AUTHOR]

Future generations of magnetic random access memory demand magnetic tunnel junctions that can provide simultaneously high magnetoresistance, strong retention, low switching energy, and small cell size below 10 nm. Here, we study perpendicular magnetic tunnel junctions with composite free layers, where multiple ferromagnet/nonmagnet interfaces can contribute to the thermal stability. Different nonmagnetic materials (MgO, Ta, and Mo) have been employed as the coupling layers in these multi-interface free layers. The evolution of junction properties under different annealing conditions is investigated. A strong dependence of the tunneling magnetoresistance on the thickness of the first CoFeB layer has been observed. In junctions where Mo and MgO are used as coupling layers, a large tunneling magnetoresistance above 200% has been achieved after 400 °C annealing. [ABSTRACT FROM AUTHOR]

We studied the CoFeB thickness and composition dependence of tunneling magnetoresistance (TMR) and resistance-area product (RA) in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction (MTJ), in which the bottom CoFeB is coupled to an in-plane exchange biased magnetic layer. This stack structure allows us to measure TMR and RA of the MTJs in sheet film format without patterning them, using current-in-plane-tunneling (CIPT) technique. The thickness ranges for both top and bottom CoFeB to exhibit perpendicular magnetic anisotropy are similar to what are seen in each single magnetic film stack. However, CIPT measurement revealed that there exists an optimal thickness for both top and bottom CoFeB to achieve the highest TMR value. Magnetic hysteresis loops also suggest the thickness-dependent coupling between the top and bottom CoFeB layers. We studied MTJs with two CoFeB compositions (Co40Fe40B20 and Co20Fe60B20) and found that Co20Fe60B20 MTJs give higher TMR and also wider perpendicular thickness range when used at the top layer. [ABSTRACT FROM AUTHOR]

Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3×106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application. [ABSTRACT FROM AUTHOR]

The magnetic and magneto-transport properties of the multilayered MgO/CoFeB/Mo/CoFeB/MgO films have been investigated. Perpendicular magnetic anisotropy and alternating ferromagnetic and antiferromagnetic interlayer coupling along the perpendicular direction as well as giant magnetoresistance have been observed in this Mo separated CoFeB/MgO structure. More importantly, the antiferromagnetic interlayer coupling of perpendicular layers is thermally stable against annealing temperature up to 400 °C, showing that the present perpendicular synthetic antiferromagnetic structure is promising for the magnetic engineering of nanodevices based on the perpendicular CoFeB/MgO system. The largest antiferromagnetic exchange coupling is obtained for Mo thickness of 0.8 nm, the corresponding exchange coupling energy density is 0.036 erg/cm2. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ) is an important device element for many practical spintronic systems. In this paper, we propose and theoretically investigate a very attractive MTJ Fe(001)/O/ NaCl(001)/O/Fe(001) as a two-terminal transport junction. By density functional theory total energy methods, we establish two viable device models: one with and the other without mirror symmetry across the center plane of the structure. Large tunnel magnetoresistance ratio (TMR) is predicted from first principles, at over 1800% and 3600% depending on the symmetry. Microscopically, a spin filtering effect is responsible for the large TMR. This effect essentially filters out all the minority spin channels (spin-down) from contributing to the tunnelling current. On the other hand, transport of the majority spin channel (spin-up) having D1 and D5 symmetry is enhanced by the FeO buffer layer in the MTJ. VC 2015 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

In order to recover the patterning damage and improve the electric and magnetic properties of the patterned magnetic tunnel junctions (MTJs), the novel post-treatment process using oxygen ions has been studied. Generally, the oxygen is known as an unsuitable gas for the MTJs patterning because it causes degradation of the patterned MTJs by over-oxidation of MgO. By the way, if the damaged layer could be oxidized selectively without over-oxidation of the damage-less area, oxygen can be the most effective gas to recover the patterning damage of the MTJs. In this study, for the selective oxidation, we proposed the non-reactive oxygen treatment scheme called the oxygen showering post-treatment process (OSP) using an ozone diffusion chamber. By the specific OSP conditions, 8 l/min of the flow rate, 250 °C of the temperature, and 30 s of the time, the magneto-resistance (MR) was increased from 103% to 110%, and the switching current was decreased from 41.1 μA to 31.6 μA when compared with reference data at the same resistance level. These results show that the electric and magnetic properties of the patterned MTJs by the OSP treatment have been improved compared to the reference sample. The improvement in electric and magnetic properties by the OSP treatment is assumed because the reference sample already contains slight patterning damages at the edge of the MTJs despite the optimized patterning process, and these damages have been oxidized by the OSP treatment. Moreover, by the OSP treatment, the proportion of the electric short fail was dramatically decreased from 1.51% to 0%, which is a remarkable improvement in terms of a successful commercialization of spintronic devices. [ABSTRACT FROM AUTHOR]

The state‐of‐the‐art magnetic tunnel junction, a cornerstone of spintronic devices and circuits, uses a magnesium oxide tunnel barrier that provides a uniquely large tunnel magnetoresistance at room temperature. However, the wide bandgap and band alignment of magnesium oxide‐iron systems increases the resistance‐area product and creates variability and breakdown challenges. Here, the authors study using first principles narrower‐bandgap scandium nitride (ScN) transport properties in magnetoresistive junctions in comparison to magnesium oxide. The results show a high magnetoresistance in Fe/ScN/Fe via Δ1 and Δ2′ symmetry filtering with low wave function decay rates, suggesting scandium nitride could be a new barrier material for spintronic devices. [ABSTRACT FROM AUTHOR]

This letter presents a magnetic gain cell structure that consists of a new kind of voltage-controlled magnetic tunnel junction (MTJ) and two transistors for a large separation in the output current for the two memory states while retaining the low power advantages of a voltage-controlled write mechanism. The voltage-controlled MTJ utilizes the interlayer exchange coupling and the resonant tunneling phenomena to enable a resonant-exchange-controlled (REC) magnetization switching, leading to a substantially low write energy and delay, in the order of 29.5 fJ/bit and 1.6 ns, respectively. Two transistors in a gain cell configuration can provide a 103 times change in the output current between the 0 and 1 states from a ~25% magnetoresistance of the REC MTJ with a high baseline resistance in the order of a few $\text{M}\Omega $. Such a magnetic gain-cell also exhibits low read energy and delay, in the range of 7.6~39 fJ/bit and 0.6~1 ns, thus promising for low energy, fast, and high-density memory technologies. [ABSTRACT FROM AUTHOR]

Electrical control on interfaces is one of the key approaches to harvest advanced functionalities in modern electronic devices. In this work, it is proposed and demonstrated that a "battery‐like" tunnel junction structure can be embedded with added control and functionalities via reversible lithium‐ion motion. In a model system of FeCo/FeCoOx/LiF/FeCo magnetic tunnel junctions, the ultrathin LiF barrier makes strong electric fields possible under moderate applied voltages, and can therefore electrically drive reversible lithium‐ion migration within the barrier. The ion motion subsequently leads to reversible interfacial modifications that generates over a thousand percent resistance change across the devices. Meanwhile, sizable tunneling magnetoresistance persists and even reverses the sign of spin polarization as a function of the interfacial control. The devices are therefore responsive to both electric and magnetic field manipulations, giving rise to diverse and nonvolatile functionalities. [ABSTRACT FROM AUTHOR]

A new series of double half-Heusler (DHH) alloy Cr 2 FeCoZ 2 (Z = As, Ge, S, P) are investigated by using the non-equilibrium Green's function in combination with the first-principles calculations. The calculations on magnetism reveal that these Cr-based DHH alloys are ferrimagnets due to the antiparallel magnetic coupling between Cr and Fe (Co). The electronic structure calculations of the Cr-based DHH alloys reveal half-metallicity, and Cr 2 FeCoAs 2 possesses the largest spin-down gap of 1.181 eV. Within the c/a ranges from 1.60 to 2.52, Cr 2 FeCoAs 2 maintains its 100 % spin-polarization, and the changes in total and spin-resovled atomic magnetic moment are negligible, showing a stable half metallicity and magnetism against the tetragonal distortion. Futhermore, the transport properties are investigated by constructing the Cr 2 FeCoZ 2 /GaAs/Cr 2 FeCoZ 2 magnetic tunnel junction (MTJ) model. By changing the magnetic arrangement of the left and right electrodes into antiparallel configuration, the capability of transportation in both spin channels is significantly limited. Conversely, by modulating the magnetic arrangement of the left and right electrodes into parallel configuration, the transportation of electrons in spin-up channel is exceptionally strong while that of the spin-down channel is severely impeded. The Cr 2 FeCoAs 2 /GaAs/Cr 2 FeCoAs 2 MTJ owns the highest tunneling magnetoresistance (TMR) ratio of ∼7.42 × 108 %, indicating that Cr 2 FeCoAs 2 is the most promising candidate for high performance spintronic devices. • A series of Cr-based double half-Heusler alloy is confirmed to possess stable half-metallicity. • The calculated TMR ratio of the Cr 2 FeCoAs 2 /GaAs/Cr 2 FeCoAs 2 MTJ is up to ∼7.42 × 108 %. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction with a large tunneling magnetoresistance has attracted great attention due to its importance in the spintronics applications. By performing extensive density functional theory calculations combined with the nonequilibrium Green's function method, we explore the spin-dependent transport properties of a magnetic tunnel junction, in which a non-polar SrTiO3 barrier layer is sandwiched between two Heusler alloy Co2MnSi electrodes. Theoretical results clearly reveal that the near perfect spin-filtering effect appears in the parallel magnetization configuration. The transmission coefficient in the parallel magnetization configuration at the Fermi level is several orders of magnitude larger than that in the antiparallel magnetization configuration, resulting in a huge tunneling magnetoresistance (i.e. > 106), which originates from the coherent spin-polarized tunneling, due to the half-metallic nature of Co2MnSi electrodes and the significant spin-polarization of the interfacial Ti 3d orbital. [ABSTRACT FROM AUTHOR]

Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L10-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions. [ABSTRACT FROM AUTHOR]

Magnetic and magneto-transport properties of amorphous Al2O3-based magnetic tunnel junctions (MTJ) having two Co/Ni multilayer electrodes exhibiting perpendicular magnetic anisotropy (PMA) are presented. An additional Co/Pt multilayer is required to maintain PMA in the top Co/Ni electrode. Slight stacking variations lead to dramatic magnetic changes due to dipolar interactions between the top and bottom electrodes. Tunnel magneto-resistance (TMR) of up to 8% at 300K is measured for the MTJ with two PMA electrodes. The TMR value increases when the top PMA electrode is replaced by an in-plane magnetized Co layer. These observations can be attributed to significant intermixing in the top Co/Ni electrode. [ABSTRACT FROM AUTHOR]

The interface magnetism between Co2FeGe Heusler alloy layers and MgO layers was investigated using 57Fe Mössbauer spectroscopy. Interface-sensitive samples, where the 57Fe isotope was used only for the interfacial atomic layer of the Co2FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The 57Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co2FeGe films in which the 57Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co2FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers. [ABSTRACT FROM AUTHOR]

Spin‐torque memristors are proposed in 2009, and can provide fast, low‐power, and infinite memristive behavior for neuromorphic computing and large‐density non‐volatile memory. However, the strict requirements of combining high magnetoresistance, stable domain wall pinning and current‐induced switching in a single device pose difficulties in physical implementation. Here, a nanoscale spin‐torque memristor based on a perpendicular‐anisotropy magnetic tunnel junction with a CoFeB/W/CoFeB composite free layer structure is experimentally demonstrated. Its tunneling magnetoresistance is higher than 200%, and memristive behavior can be realized by spin‐transfer torque switching. Memristive states are retained by strong domain wall pinning effects in the free layer. Experiments and simulations suggest that nanoscale vertical chiral spin textures can form around clusters of W atoms under the combined effect of opposite Dzyaloshinskii–Moriya interactions and the Ruderman–Kittel–Kasuya–Yosida interaction between the two CoFeB free layers. Energy fluctuation caused by these textures may be the main reason for the strong pinning effect. With the experimentally demonstrated memristive behavior and spike‐timing‐dependent plasticity, a spiking neural network to perform handwritten pattern recognition in an unsupervised manner is simulated. Due to advantages such as long endurance and high speed, the spin‐torque memristors are competitive in the future applications for neuromorphic computing. [ABSTRACT FROM AUTHOR]