Magnetic Tunnel Junctions Research Articles

Stability of ferromagnetism in diluted magnetic Sr1−xCrxX (X = S, Se and Te) semiconductor doped by Cr under Hubbard correction and strain effect

Abstract This study focuses on the electronic, magnetic, and elastic features of strontium chalcogenides SrX (X = S, Se, Te) doped with chromium (Cr) using ab-initio calculations, in the presence and absence of the Hubbard correction (U) and strain effect. The results show that adding Cr induces a half-metallic behavior and a stable ferromagnetic phase, with spin polarisation reaching 100% in the absolute majority of cases. The stability of this phase is confirmed by negative formation energies and high Curie temperatures, above room temperature, achieving its maximum values of 464K, 475 K, and 570 K for SrS, SrSe, and SrTe, respectively, at 24% of the chromium portion. The effect of applied strains (2% and 4%) reveals a modulation of the electronic properties, visualized by the shift in density of state (DOS) and the decrease of the band gap. A strengthening of the magnetic interactions while retaining the half-metallic character is also observed under strain. Since Cr-doped SrS has large elastic moduli and remarkable mechanical properties, it is a perfect choice for strong spintronic devices and spin filters that need mechanical stability. Its ability to blend mechanical strength and ductility makes Cr-doped SrSe a promising material for magnetic tunnel junctions (MTJs) in MRAM. For flexible spintronic devices, including SpinFETs, Cr-doped SrTe is an excellent choice due to its enhanced ductility (increased B / G ratio) and maximal deformability. These results highlight the potential of Cr-doped SrX compounds to improve device performance, efficiency, and functionality by relying on the interaction of ferromagnetism and elastic property tuning. The combination of all our findings makes our compound promising for spintronic applications.

Noise-based local learning using stochastic magnetic tunnel junctions

Noise-based local learning using stochastic magnetic tunnel junctions

Sign‐Tunable Magnetic Tunnel Junctions Engineered via Ferrimagnets for Efficient All‐Electrical and Thermal Switching

AbstractCoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) have revolutionized modern spintronics, driving extensive efforts to optimize their properties such as spin polarization, perpendicular magnetic anisotropy, and switching speed. Here, a novel MTJ architecture is demonstrated, integrating ferrimagnetic CoTb to the conventional CoFeB/MgO/CoFeB MTJ structure, achieving both superior device performance and unique functionalities. The key innovation lies in the realization of sign‐tunable tunneling magnetoresistance (TMR), where the TMR ratio undergoes a dramatic transition from +33% (300 K) to ‐58% (30 K). This sign reversal, occurring at the ferrimagnetic compensation temperature (TM = 212 K), stems from strong ferromagnetic (CoFeB‐Co sublattice) and antiferromagnetic (CoFeB‐Tb sublattice) couplings in the hybrid CoFeB/CoTb layers. Around TM, a distinctive spin‐flop mediated TMR sub‐loop is further observed at high field which provides additional resistance states. These resistance states can not only be switched by external magnetic field but also by thermal operations. Furthermore, energy‐efficient field‐free switching is demonstrated through synergistic spin‐orbit torque (SOT) and spin‐transfer torque (STT) effects, achieving all‐electrical switching of MTJ at JSOT = 5 MA cm−2 with a minimal 4.1% STT current incorporation. This innovative ferrimagnetic MTJ architecture establishes a new platform for developing next‐generation spintronic devices with superior functionality, operational versatility, and performance metrics.

Optoelectronic control of spin-valley dependent thermoelectric transport in a ferromagnetic monolayer WSe2 junction

Abstract We theoretically investigate the spin-valley dependent thermoelectric transport properties in the ferromagnetic WSe2 junction under the modulations of the off-resonance circularly polarized light (CPL) and gate voltage. It is found that the conductances strongly depend on the spin and valley degrees of freedom as well as the magnetic configuration, and the spin and valley filtering effect can be realized by adjusting the Fermi energy or CPL. The maximum values of the Seebeck coeffcients are robust against the ferromagnetic exchange field, and the peaks of the Seebeck coeffcients with different valleys can overlap under the suitable potential barrier and CPL. The charge (spin, valley) figure of merit is very sensitive to the Fermi energy and CPL, and a 100% tunneling magnetoresistance platform can be obtained. These findings provide an avenue to design the spin-valley caloritronics devices based on the monolayer WSe2.

A novel non-contact torque measurement method for ultrasonic micromotors based on Tunnel Magnetoresistance angle sensor

A novel non-contact torque measurement method for ultrasonic micromotors based on Tunnel Magnetoresistance angle sensor

First-principles investigation of magnetic exchange force microscopy on adatoms adsorbed on an antiferromagnetic surface

Using density functional theory (DFT), we calculate the magnetic short-ranged exchange forces between a magnetic tip and an adatom adsorbed on the antiferromagnetic Mn monolayer on the W(110) surface [Mn/W(110)]. These exchange forces can be measured in magnetic exchange force microscopy allowing atomic-scale imaging of spin structures on insulating and conducting surfaces. We consider two types of 3d transition-metal atoms with intrinsic magnetic moments: Co and Mn and Ir as an example of a 5d transition-metal atom exhibiting an induced magnetic moment on Mn/W(110). The tips are modeled by Fe pyramids and terminated either with an Fe or a Mn apex atom. From our total energy DFT calculations for a parallel and antiparallel alignment between tip and adatom magnetic moments we obtain the exchange energy Eex(d) as a function of tip-adatom distance d. The exchange forces, Fex(d), are calculated based on the Hellmann-Feynman theorem. We show that structural relaxations of tip and sample due to their interaction need to be taken into account. Due to the exchange interaction the relaxations depend on the alignment between tip and adatom magnetization—an effect which will affect the tunneling magnetoresistance that can be measured by a spin-polarized scanning tunneling microscope. A maximum in the exchange energy and force curves is obtained for magnetic adatoms at tip-adatom separations of about 3 to 4 Å. The exchange forces with an Fe terminated tip reach a maximum value of up to 0.2 and 0.6 nN for Co and Mn adatoms, respectively, and prefer an antiferromagnetic coupling. Surprisingly, we also find an exchange force of up to 0.2 nN for Ir adatoms. We analyze the exchange interaction between tip and adatom based on the spin-polarized electronic structure of the coupled system. A competition occurs between long-range Zener-type indirect double exchange favoring ferromagnetic coupling and short-range direct d−d antiferromagnetic exchange. For the Ir adatom the interaction can be explained from the spin-dependent hybridization with the tip apex atom. Our results show that magnetic adatoms on Mn/W(110) are a promising system to study exchange forces at the single-atom level via magnetic exchange force microscopy. Published by the American Physical Society 2025

Ultralow Electrical Current Driven Field‐Free Spin‐Orbit Torque Switching of Magnetic Tunnel Junctions by Topological Insulators

AbstractSpin‐orbit torque‐driven magnetic random‐access memory (SOT‐MRAM) is one of the promising candidates for next‐generation memory technologies beyond Moore's law. Due to its separation of writing and reading channels, the 3‐terminal device design significantly improves the device endurance of SOT‐MRAM. However, two major challenges still exist for the perpendicular SOT‐MRAM: the ultrahigh writing current density and the need for an external magnetic field to achieve deterministic switching. In this work, a 3‐terminal SOT‐MRAM device is demonstrated that integrates topological insulators (TIs) by perpendicular magnetic tunnel junction (pMTJ). The giant spin‐orbit torque generated by spin‐momentum‐locked topological surface states significantly reduces the switching current density to as low as 3.0 × 105 A cm−2. The double magnetic layers with different saturation magnetizations are employed as the recording layer of TIs‐pMTJ. Therefore, non‐collinear canted magnetic states are generated during the current‐driven SOT. By breaking the chiral symmetry of these states through interlayer Dzyaloshinskii–Moriya interaction (DMI), the field‐free deterministic SOT switching is achieved. This work demonstrates the topological insulator‐driven magnetic field‐free SOT‐MRAM with ultralow writing density, inspiring the revolution of SOT‐MRAM technology from classical to quantum materials.

Tunnel-magnetoresistance sensors with sub-pT detectivity for detecting bio-magnetic fields

Tunnel-magnetoresistance (TMR) sensors based on magnetic tunnel junctions are emerging spintronic devices that are promising for applications to wearable bio-magnetic-field monitoring systems. Targeting bio-magnetic fields from the human heart and brain requires TMR sensors with sub-pT detectivity at frequencies of 1–1000 Hz. In this article, technical strategies for achieving such detectivity from the viewpoints of thin-film materials and sensor configurations are reviewed. Recent demonstrations of magnetocardiography and magnetoencephalography using our TMR sensors are also reviewed, and potentially effective techniques to further optimize detectivity are proposed.

Magnetic phase transition, enhanced magnetic anisotropy, and anomalous Hall effect in bilayer FeCl2 with different stacking orders

The controllability of magnetic order and magnetic anisotropy in van der Waals magnets is crucial for 2D spintronic applications. Based on the recent experimental few-layer FeCl2 [Zhou et al., ACS Nano 18, 10912 (2024) and Jiang et al., ACS Nano 17, 1363 (2023)], in this Letter, we use first-principles to systemically explore the effects of electric field and strain on magnetic order, magnetic anisotropy, and electronic structure of bilayer FeCl2 with different stacking orders. We demonstrate that for both AA- and AB-stacked bilayer FeCl2, the perpendicular electric field induces the change in orbital overlap between nearest-neighbor interlayer Fe atoms, resulting in the interesting transition from interlayer antiferromagnetic to ferromagnetic coupling, and the critical electric field is only 0.10 V/Å for the AB-stacking order. Simultaneously, the electric field can induce the transition of magnetic easy axis from out-of-plane to in-plane to out-of-plane due to the change in Fe-3d intraorbital hybridizations. In contrast, the in-plane strain does not trigger the phase transitions of magnetic order and magnetic easy axis, but the −5% compressive strain significantly increases the out-of-plane magnetic anisotropic energy by 69% and 124% for AA- and AB-stacking orders, respectively. Additionally, the anomalous Hall effect is predicted in AB-stacked bilayer FeCl2 without and with electric field. The present work indicates the promising applications for bilayer FeCl2 in low-energy-consumption spintronic devices such as electrical control magnetic tunnel junctions and magnetic storage devices, and will stimulate broad study on electric field and strain tuned van der Waals magnets.

Investigation of Electronic and Transport Properties of Zigzag Aluminium Nitride Nanoribbon for Magnetoresistive Devices using Selective Edge Chlorination

AbstractIn this work, the utility of Zigzag Aluminium Nitride Nanoribbons (ZAlNNR) for voltage‐controlled magnetoresistive devices is investigated using the DFT‐NEGF approach. Based on energy calculations and magnetic moment analysis, it is proposed that selective edge chlorination of ZAlNNR leads to the magnetic ground state (AFM). To examine the impact of electrode magnetization on transport properties, the curve is calculated for parallel and antiparallel spin orientation of the electrodes. For parallel cases, spin‐filtering efficiency (SFE) is calculated, which is at various voltages, and also observe negative differential resistance (NDR) behavior. In the antiparallel case, it is observed that both finite transmission and zero transmission regions for variable bias voltage. Hence, an oscillatory current behavior is observed in this case. Finally, magnetoresistance (MR) is calculated in both spin‐up and spin‐down cases, which is of the order of at (for spin‐up configuration). Such large values of SFE and MR make it an appropriate choice for spin filter/voltage‐controlled magnetic tunnel junctions (MTJs).

Spin-current drift–diffusion transport in common spin–orbit-torque structures

We summarize and simplify the drift–diffusion transport of spin-currents in s-band dominant transition metal systems for a few well-studied one dimensional solutions for technology-relevant measurements. They highlight the importance of the spin-current “loading” effect and interface spin resistance-area products (spin-RAs). Main conclusions from this study are (1) For a nonmagnetic conduction metal, there is a material-specific spin-RA that is defined by (ρ×λsf), i.e., the resistivity-spin flip diffusion length product. This spin-RA sets the scale for other interface-related spin-RA quantities for effective spin-current transport. (2) Any spin-Hall coefficient (ΘSH) measurements needs to have a full spin-conductance analysis to ensure the proper deduction of material specific metrics, such as ΘSH and λsf from observations, while including the role of interface spin-RAs. (3) Such interface-related spin-RA consideration exists also for common ferromagnetic transition metal/alloys, which combines spin-flip scattering with that of transverse spin-dephasing (mixing-conductance) related spin-currents and generally making an interface spin-conductance that is non-isotropic against spin-current’s polarization direction. Finally, these spin-RAs present a very low impedance environment of the order of 1mΩ μm2, in contrast with common structures in CMOS technology where RAs are usually above 1Ω μm2, such as a magnetic tunnel junction in CMOS-integrated magnetic memory. The low impedance nature of spin-current drift–diffusion transport is important to consider for accurate measurements and for technology integration.

Single-shot all-optical magnetization switching in in-plane magnetized magnetic tunnel junction

Single pulse All Optical Helicity-Independent Switching is demonstrated in an in-plane magnetized magnetic tunnel junction. A toggle switching of the 2 nm thick Co40Fe40B20 soft layer could be achieved by exchange coupling the Co40Fe40B20 with a 10 nm thick Co85Gd15 layer monitored by measuring the Tunnel magneto resistance of the device. The use of in plane magnetized electrodes relaxes the constrains linked to perpendicular magnetic anisotropy systems while achieving a tunneling magnetoresistance ratio exceeding 100%. The influence of the upper electrical electrode, which is opaque to the laser beam in this study, is also discussed.

Evaluation of intermediate states during switching in MgO-based magnetic tunnel junctions

Abstract This study investigates the switching characteristics of magnetic tunnel junctions (MTJs) used in spin-transfer-torque magnetoresistive random-access memory. MTJs are expected to exhibit parallel (P) and antiparallel (AP) states, but some MTJs exhibit an intermediate (IM) state between the P and AP states at switching. Here we analyze in detail the size dependence and write error rates (WERs) of MTJs with IM states. The number of IM states increases with increasing MTJ size. The WER is independent of MTJ size and the number of IM state but the occurrence of the IM state itself causes a writing error.

Reconfigurable diode effect and giant tunnel magnetoresistance ratio in magnetic tunnel junctions based on spin gapless semiconductor and half metallic Heusler alloy

Reconfigurable diode effect and giant tunnel magnetoresistance ratio in magnetic tunnel junctions based on spin gapless semiconductor and half metallic Heusler alloy

A novel field-free SOT magnetic tunnel junction with local VCMA-induced switching

A novel field-free SOT magnetic tunnel junction with local VCMA-induced switching

Fully Electrically Controlled Low Resistance‐Area Product and Enhanced Tunneling Magnetoresistance in the Van Der Waals Multiferroic Tunnel Junction

AbstractThe development of next‐generation spin nanomemory systems faces the challenge of achieving nonvolatile electrical control of magnetic states in magnetic tunnel junctions. Here, a strategy is proposed using trilayer van der Waals heterostructures combining an A‐type antiferromagnetic YBr2 bilayer and a ferroelectric Al2Se3 monolayer. Nonvolatile modulation of the ferroelectric polarization direction of Al2Se3 can flip the interlayer magnetic coupling of YBr2 between ferromagnetic and antiferromagnetic states. The interlayer magnetic phase transition is caused by the band structure shift and interfacial charge transfer induced by the polarization field. The TiTe2/2L‐YBr2/Al2Se3/TiTe2 multiferroic devices achieve a fully electrically controlled tunneling magnetoresistance with a ratio of up to 11550% and an exceptionally low resistance‐area product of 0.28 Ω µm2 by establishing a good P‐type Ohmic contact between the TiTe2 electrode and the central heterojunction. There is also a perfect spin filtering effect. This work provides new perspectives for the development of low‐power, fast‐response, nonvolatile and fully electrically controlled spintronic memory devices.

Compact Modeling and Exploration of the Light Metal Insertion Effect for a Voltage-Controlled Spin–Orbit Torque Magnetic Tunnel Junction

Magnetic random-access memory, recognized as a breakthrough in spintronics, demonstrates substantial potential for next-generation nonvolatile memory and logic devices due to its unique magnetization-switching mechanism. However, realizing reliable perpendicular magnetization switching via spin–orbit torque necessitates an externally applied in-plane magnetic bias, a requirement that complicates integration in high-density device architectures. This study proposes a novel device architecture where geometric asymmetry engineering in an interlayer design generates an intrinsic equivalent in-plane magnetic field. By strategically introducing a non-symmetrical spacer between the heavy metal and ferromagnetic layers, we establish deterministic magnetization reversal while eliminating external field dependency. Furthermore, the energy barrier during magnetization switching is dynamically adjusted by applying a voltage across a perpendicular-anisotropy magnetic tunnel junction, leveraging the voltage-controlled magnetic anisotropy effect. We established a physics-driven compact model to assess the design and performance of voltage-controlled spin–orbit torque magnetic tunnel junction (VCSOT-MTJ) devices. Simulations reveal that the introduction of a minimally asymmetric light metal layer effectively resolves the issue of incomplete switching in field-free spin-orbit torque systems.

2D Spintronics for Neuromorphic Computing with Scalability and Energy Efficiency

The demand for computing power has been growing exponentially with the rise of artificial intelligence (AI), machine learning, and the Internet of Things (IoT). This growth requires unconventional computing primitives that prioritize energy efficiency, while also addressing the critical need for scalability. Neuromorphic computing, inspired by the biological brain, offers a transformative paradigm for addressing these challenges. This review paper provides an overview of advancements in 2D spintronics and device architectures designed for neuromorphic applications, with a focus on techniques such as spin-orbit torque, magnetic tunnel junctions, and skyrmions. Emerging van der Waals materials like CrI3, Fe3GaTe2, and graphene-based heterostructures have demonstrated unparalleled potential for integrating memory and logic at the atomic scale. This work highlights technologies with ultra-low energy consumption (0.14 fJ/operation), high switching speeds (sub-nanosecond), and scalability to sub-20 nm footprints. It covers key material innovations and the role of spintronic effects in enabling compact, energy-efficient neuromorphic systems, providing a foundation for advancing scalable, next-generation computing architectures.

Electrical Control of Spin Polarization in a Multiferroic Heterojunction Based on One-Dimensional Chiral Hybrid Metal Halide.

Hybrid metal halide materials have been demonstrated to show potential in spintronic applications. In the field of spintronics, controlling the spin degree of freedom by electrical means represents a significant advancement. In this work, we present a spintronic device with a ferromagnet/ferroelectric/ferromagnet heterostructure, in which a one-dimensional (1D) chiral hybrid metal halide serves as an interlayer. The ferroelectricity of the material has been confirmed through both experimental and theoretical approaches. Unlike conventional magnetic tunnel junctions, this multiferroic device exhibits four distinct resistance states, which can be tuned by magnetic and electric fields. Notably, the sign of magnetoresistance can be modulated by an applied bias voltage, demonstrating that the spin polarization of carriers injected from ferromagnetic electrodes can be controlled by an external electric field. Our study not only provides a feasible pathway for electrically controlled spin but also highlights the potential of chiral hybrid metal halides in spintronic applications.

Magneto-Ionic Engineering of Antiferromagnetically RKKY-Coupled Multilayers.

Voltage-driven ion motion offers a powerful means to modulate magnetism and spin phenomena in solids, a process known as magneto-ionics, which holds great promise for developing energy-efficient next-generation micro- and nano-electronic devices. Synthetic antiferromagnets (SAFs), consisting of two ferromagnetic layers coupled antiferromagnetically via a thin non-magnetic spacer, offer advantages such as enhanced thermal stability, robustness against external magnetic fields, and reduced magnetostatic interactions in magnetic tunnel junctions. Despite its technological potential, magneto-ionic control of antiferromagnetic coupling in multilayers (MLs) has only recently been explored and remains poorly understood, particularly in systems free of platinum-group metals. In this work, room-temperature voltage control of Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions in Co/Ni-based SAFs is achieved. Transitions between ferrimagnetic (uncompensated) and antiferromagnetic (fully compensated) states is observed, as well as significant modulation of the RKKY bias field offset, emergence of additional switching events, and formation of skyrmion-like or pinned domain bubbles under relatively low gating voltages. These phenomena are attributed to voltage-driven oxygen migration in the MLs, as confirmed through microscopic and spectroscopic analyses. This study underscores the potential of voltage-triggered ion migration as a versatile tool for post-synthesis tuning of magnetic multilayers, with potential applications in magnetic-field sensing, energy-efficient memories and spintronics.