Magnetic Tunnel Junctions Research Articles

Thermally-Stable Temperature-Independent Tunneling Magnetoresistance in all van der Waals Fe3GaTe2/GaSe/Fe3GaTe2 Magnetic Tunnel Junctions.

Thermal stability is of great significance for the next-generation two-dimensional (2D) non-volatile spintronic devices. Typically, as the temperature increases, the spin polarization of materials decreases rapidly following the Bloch 𝑇3/2 law in low-temperature regions, resulting in a rapid decrease in the tunneling magnetoresistance (TMR) of the magnetic tunnel junction (MTJ). Owing to the thermal effects induced by current during the writing processes, even small temperature fluctuations can result in significant variations in the TMR of MTJs, hindering their practical applications. In this paper, all-van der Waals Fe3GaTe2/GaSe/Fe3GaTe2 (FGaT/GaSe/FGaT) MTJ devices are constructed, achieving a TMR ratio of 47% at low temperatures and 17% at room temperature. Importantly, the TMR ratio remains stable within a temperature range from 2 to 160 K, breaking the Bloch 𝑇3/2 law. The temperature-independent TMR is highly related to the enhanced perpendicular magnetic anisotropy (PMA) with reduced dimensionality is demonstrated. This work paves a promising path to achieve high-performance, thermally stable 2D spintronic memory chips.

Solving combinatorial optimization problems through stochastic Landau-Lifshitz-Gilbert dynamical systems

We present a method to approximately solve general instances of combinatorial optimization problems using the physical dynamics of three-dimensional (3D) rotors obeying Landau-Lifshitz-Gilbert dynamics. Conventional techniques to solve discrete optimization problems that use simple continuous relaxation of the objective function followed by gradient-descent minimization are inherently unable to avoid local optima, thus producing poor-quality solutions. Our method considers the physical dynamics of macrospins capable of escaping from local minima, thus facilitating the discovery of high-quality, nearly optimal solutions, as supported by extensive numerical simulations on a prototypical quadratic unconstrained binary optimization (QUBO) problem. Our method produces solutions that compare favorably with those obtained using state-of-the-art minimization algorithms (such as simulated annealing) while offering the advantage of being physically realizable by means of arrays of stochastic magnetic tunnel-junction devices. Published by the American Physical Society 2025

Bipolar Random Signal Generation With Electrical Operation Based on Two Magnetic Tunnel Junctions

Bipolar Random Signal Generation With Electrical Operation Based on Two Magnetic Tunnel Junctions

Design of Area-Efficient and Low-Power Magnetic Full Adder

Complementary metal oxide semiconductor (CMOS) is an extensively used promising technology for developing integrated circuits, such as memory chips, microprocessors and microcontrollers with high noise immunity. However, deep scaling of CMOS technology ([Formula: see text] [Formula: see text]nm) suffers from various impediments at the device and architectural level, namely high leakage current, increased radiation sensitivity, more die area and dynamic power dissipation. To overcome these limitations of CMOS devices, logic-in-memory (LIM) structures have been developed with spin-based devices like Magnetic Tunnel Junctions (MTJs). MTJs are not affected by external particles and feature zero standby power. The MTJs in magnetic logic circuit and magnetic random-access memory (MRAM) applications are robust against radiation, high speed, low leakage power, nonvolatility and easily compatible with the back end. Existing magnetic full adder (MFA) techniques require augmented circuits for seamless operation. A major drawback in the existing MFA structure is the data loss due to single event upset (SEU) and poor sensitivity of pre-charge sense amplifiers (PCSAs) to input arrival timing. This paper proposes an MTJ-based nonvolatile magnetic full adder (NV-MFA) using 10T logic to address the above issues. The output buffer circuit is designed with a read-write parallel switching (RWPS) writing circuit based on spin orbit torque (SOT). The proposed circuit is more immune to the fault occurrence compared with the existing pass transistor and PCSA-based MFA logic. It leads to reduced power dissipation, die area and delay. Perpendicular anisotropy MTJ (CoFeB/MgO/CoFeB) model is chosen for the MTJ structure. It is suitable for efficient MRAM structure. The transient response is verified on Cadence virtuoso using 45[Formula: see text]nm gpdk CMOS technology. The simulation analysis shows the performance is enhanced with fault-free data output and improved reliability compared with previous MFAs.

Magnetoresistance in 2D Magnetic Materials: From Fundamentals to Applications

AbstractMagnetoresistance effects, such as tunnel magnetoresistance and giant magnetoresistance, play pivotal roles in spintronics, where the coupling between spin and current affects the electrical resistance. These effects are fundamental for various applications, including high‐density information storage, signal transmission, and processing. With the growing demand for magnetoresistance‐based modern devices in the post‐Moore era, researchers are now focusing on developing such devices using 2D magnetic materials. These materials offer several advantages, including a unique layered structure, high integration density, tunable room‐temperature ferromagnetism, and intriguing magnetoresistive properties. This review starts with a brief introduction to 2D magnetic materials and their typical synthesis routes, followed by a preview of some classifications of magnetic materials. In particular, different magnetoresistance effects in 2D magnetic materials and their unique applications in spintronics are critically discussed. Finally, current challenges and prospects of this emerging field are suggested. This work highlights the importance of the pivotal magnetoresistance effect in advancing modern technology, offering vital applications in many fields ranging from magnetic memory to neuromorphic computing.

Aluminium foil micro-defect detection method based on motion-induced eddy current using differential TMR sensor spatial position compensation

ABSTRACT Lithium-ion batteries are a key technology in the energy storage field, and aluminum foil, a common cathode current collector, can develop micro-defects that significantly affect battery performance, especially during high-speed manufacturing. Motion-induced eddy current (MIEC) sensing is effective for detecting defects in conductive materials. However, lift-off fluctuations degrade the signal-to-noise ratio (SNR), making it challenging to detect small or shallow defects. Traditional methods, such as differential sensor outputs, help reduce these fluctuations, but baseline signal deviations caused by varying relative positions between the sensor and the permanent magnet limit their effectiveness. To address this, this study proposes a spatial compensation method for differential tunnel magnetoresistance (TMR) sensors, which reduces baseline deviations caused by position differences, mitigating lift-off fluctuations and improving the SNR for micro-defect detection.

High-Precision Tunneling Magnetoresistance (TMR) Current Sensor for Weak Current Measurement in Smart Grid Applications

To meet the demand for high-precision, high-resolution measurement of weak currents in smart grids, this article presents the design of a current sensor based on the tunneling magnetoresistance (TMR) effect. To improve the detection accuracy of the sensor, this design adopts a low-noise, high-sensitivity TMR chip as its chip selection; in the sensor circuit, a high-linearity interface circuit is used to eliminate fixed bias; and a magnetic flux concentrator is used to improve sensitivity and anti-interference capability. Experimental results indicate that the sensor achieves a sensitivity of 29.4 mV/V/mA, a linearity of 0.19%, and an accuracy of 0.045% within a ±100 mA range, supporting current measurement from DC up to 10.5 kHz. The proposed sensor demonstrates several advantages, including a wide measurement range, high accuracy, high resolution, and non-invasive measurement capability, making it well suited for weak current detection in smart grid applications.

Write error ballooning due to anisotropy variation within the free layer in perpendicular magnetic tunnel junctions

Abstract A finite-temperature micromagnetic investigation is conducted to analyze magnetization switching and write error rates in perpendicular spin-transfer torque random access memory (STT-RAM), including the influence of domain wall (DW) pinning arising from variations within the free layer (FL) magnet and stray field from reference layer assembly in the magnetic tunnel junction. The study reveals that uneven perpendicular magnetic anisotropy within the FL could lead to the formation of pinning sites that give rise to metastable states during switching. Such metastable states could result in a significant increase in the write error rates as compared to the ideal situation. Unlike the case with stray fields arising from reference layer assembly, where the DW propagation is hindered only for one switching direction, inhomogeneity within the FL causes the DW pinning to occur in both switching directions. Combined effects of FL inhomogeneity and stray field from the reference layer result in write error ballooning similar to those reported in recent experiments. The impact of free layer inhomogeneity could be further exacerbated by the stray field for one of the switching directions. Surprisingly, the impact of inhomogeneity is also observed to persist at smaller FL dimensions where quasi-coherent switching is expected. These findings provide deeper insights into the potential factors contributing to anomalous write errors in perpendicular STT-RAM.

Multilayer magnetic skyrmion devices for spiking neural networks

Abstract Spintronic devices -based on magnetic solitons, such as the domain wall motion and
the skyrmions, have shown a significant potential for applications in energy-efficient
data storage and beyond CMOS computing architectures. Based on the magnetic multilayer
hetero-structures, we propose a magnetic skyrmion-magnetic tunnel junction
device structure, mimicking leaky integrate and fire LIF neuron characteristics. The
device is controlled by spin-orbit torque-SOT driven skyrmion motion in the ferromagnetic
thin film. The modified leaky integrate and fire LIF neuron-like characteristics
are shown using the combination of SOT and the skyrmion position dependence of the
demagnetization energy. The device characteristics are modeled as the modified LIF
neuron. The LIF neuron is one of the fundamental spiking neuron models; we integrate
the model in the 3-layer spiking neural network (SNN) and convolutional CSNN
framework to test these spiking neuron models to classify the MNIST and FMNIST
datasets. In both architectures, the network achieves classification accuracy above
97.10%. Additionally, the LIF neuron latency is in ns; thus, when integrated with
the CMOS, the proposed device structures and associated systems exhibit an excellent
future for energy-efficient neuromorphic computing.

Switching of a magnetic tunnel junction by voltage-controlled magnetic anisotropy

Switching of a magnetic tunnel junction by voltage-controlled magnetic anisotropy

Effect of dynamical electron correlations on the tunnelling magnetoresistance of Fe/MgO/Fe(001) junctions

Effect of dynamical electron correlations on the tunnelling magnetoresistance of Fe/MgO/Fe(001) junctions

Shape Anisotropy-Dependent Leaking in Magnetic Neurons for Bio-Mimetic Neuromorphic Computing.

Spiking neural networks seek to emulate biological computation through interconnected artificial neuron and synapse devices. Spintronic neurons can leverage magnetization physics to mimic biological neuron functions, such as integration tied to magnetic domain wall (DW) propagation in a patterned nanotrack and firing tied to the resistance change of a magnetic tunnel junction (MTJ), captured in the domain wall-magnetic tunnel junction (DW-MTJ) device. Leaking, relaxation of a neuron when it is not under stimulation, is also predicted to be implemented based on DW drift as a DW relaxes to a low energy position, but it has not been well explored or demonstrated in device prototypes. Here, we study DW-MTJ artificial neurons capable of leaky integrate-and-fire (LIF) behavior and demonstrate geometry-dependent leaking dynamics that results in repeatable, tunable LIF operation. Studying the behavior of five different device designs, we show tuning the geometry, stimulating fields and currents, and location of electrical contacts results in a wide range of neuron behavior. Additionally, implementation of an asymmetric notch allows for nonlinear pinning which increased expressivity without sacrificing leaking. The measured behavior is implemented in a simulated spiking neural network that outperforms a 1D model of continuous DW motion and approaches the performance of an ideal LIF activation function. The results show that the analog LIF capability of DW-MTJ neurons combines many desirable neuron functions into a single device, which can result in varied forms of multifunctional neuromorphic computing.

Enhanced tunnel magnetoresistance of Fe/MgGa2O4/Fe(001) magnetic tunnel junctions by interface-tuning with atomic-scale MgO insertion layers

We demonstrate a significant effect of atomic-scale MgO insertion layers on the tunnel magnetoresistance (TMR) in epitaxial magnetic tunnel junctions (MTJs) using a small bandgap oxide MgGa2O4. An enhanced TMR ratio of 151% at room temperature (resistance area product, RA: 23 kΩ ⋅ μm2) and 291% at 5 K (RA: 26 kΩ ⋅ μm2) were observed using 0.3 nm MgO insertion layers at the bottom and top barrier interfaces in Fe/MgGa2O4/Fe(001) MTJs with a total barrier thickness of 2.3 nm. The TMR showed a strong MgO thickness dependence. Microstructure analyses revealed that after MgO insertion, a homogeneous rock-salt structured Mg0.55Ga0.45O(001) barrier is formed, which differs from the nominal spinel crystal MgGa2O4. Elemental mapping of the MTJ showed that Ga diffusion into the adjacent Fe can be effectively suppressed while maintaining perfect lattice-matching at the Fe/barrier interfaces, thereby improving effective tunneling spin polarization through the barrier. The RA of the Mg0.55Ga0.45O (2.3 nm) MTJ is smaller than that of a comparable MgAl2O4 barrier (2.3 nm), thanks to the lower barrier height of the Mg0.55Ga0.45O as confirmed by the current–voltage characteristics.

Write error reduction in magnetic tunnel junctions for voltage-controlled magnetoresistive random access memory by using exchange coupled free layer

Voltage-controlled magnetoresistive random access memory (VC-MRAM) is an emerging nonvolatile memory based on the voltage-controlled magnetic anisotropy (VCMA) effect. It has been garnering considerable attention because of its fast and low-power operation. However, two major issues must be addressed for practical applications. First, the voltage-induced switching of the free layer magnetization is sensitive to ultrashort voltage pulse duration. Second, the write error rate (WER) of the voltage-induced switching is high. To address these issues, a magnetic tunnel junction (MTJ) structure with an exchange coupled free layer, consisting of a precession layer with the VCMA effect and an anchor layer without the VCMA effect, is proposed. The anchor layer prevents the precession layer from returning to its initial direction, thereby reducing the WER without requiring the voltage pulse duration to be precisely controlled. The write operation of the proposed MTJ with an exchange coupled free layer was analyzed using the macrospin model. Using optimized MTJ parameters, a low WER of approximately 10−6 was obtained for an 80 nm MTJ without requiring the pulse duration to be precisely controlled. These results facilitate the reduction of the WER for VC-MRAM and improve its usability, thereby expanding its range of applications.

Spin transfer torque switching in double magnetic tunnel junctions based on dual MgO layers

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.

Bias voltage controlled inversions of tunneling magnetoresistance in van der Waals heterostructures Fe3GaTe2/hBN/Fe3GaTe2

Abstract We report the bias voltage-controlled inversions of tunnel magnetoresistance (TMR) in magnetic tunneling junctions composed of Fe3GaTe2 electrodes and hBN tunneling barrier, observed at room temperature. The polarity reversal of TMR occurs consistently at around 0.625 V across multiple devices and temperatures, highlighting the robustness of the effect. To understand this behavior, we developed a theoretical model incorporating spin-resolved density of states (DOS) at high energy levels. By adjusting the DOS weighting at different k-points to account for misalignment between the crystal structure of electrodes in experimental devices, we improved agreement between experimental and theoretical inversion voltages. Our results provide valuable insight into the voltage-controlled spin injection and detection in two-dimensional magnetic tunnel junctions, with implications for the development of energy-efficient spintronic devices.

Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization

AbstractMagnetic random-access memory that uses magnetic tunnel junction memory cells is a high-performance, non-volatile memory technology that goes beyond traditional charge-based memories. Today, its speed is limited by the high magnetization of the memory storage layer. Here we prepare magnetic tunnel junction memory devices with a low magnetization ferrimagnetic Heusler alloy Mn3Ge as the memory storage layer on technologically relevant amorphous substrates using a combination of a nitride seed layer and a chemical templating layer. We switch the magnetic state of the storage layer with nanosecond long write pulses at a reliable write error rate of 10−7 and detect a tunnelling magnetoresistance of 87% at ambient temperature. These results provide a strategy towards lower write switching currents using ferrimagnetic Heusler materials and, therefore, to the scaling of high-performance magnetic random-access memories beyond those nodes possible with ferromagnetic memory layers.

Tunnel barriers for Fe-based spin valves providing high spin-polarized current.

Employing density functional theory for ground state quantum mechanical calculations and the non-equilibrium Green's function method for transport calculations, we investigate the potential of CdS, ZnS, Cd3ZnS4, and Zn3CdS4 as tunnel barriers in magnetic tunnel junctions for spintronics. Based on the finding that the valence band edges of these semiconductors are dominated by pz orbitals and the conduction band edges by s orbitals, we show that Δ1 symmetry filtering of the Bloch states in magnetic tunnel junctions with Fe electrodes results in high tunneling magnetoresistances and high spin-polarized current (up to two orders of magnitude higher than in the case of the Fe/MgO/Fe magnetic tunnel junction).

Gate-controllable two-dimensional transition metal dichalcogenides for spintronic memory

Rapid technological advancement has increased the demand for high-speed, low-power devices, particularly applied in artificial intelligence (AI) and the Internet of Things (IoT). Limitations of traditional memory devices underscore the urgency for high-performance, energy-efficient memory technologies. On the other hand, developing two-dimensional (2D) material-based devices is indispensable for next-generation memory and three-dimensional integration circuit (3D-IC) systems. Here, we propose a gate-controllable spin valve utilizing transition metal dichalcogenides (TMDs) to meet the urgent need. A high tunneling magnetoresistance (TMR) of over 4000% can be reached in reading with the help of the controlled gate. Moreover, under ungated conditions, a giant spin current density with an ultralow power consumption of 80 μW and a high spin-polarized ratio of 0.9 can be achieved, enabling high-speed and energy-efficient switching during writing. According to our design, the gate-controllable system can prevent undesired mixed reading and writing operations. Our results highlight TMDs as a promising material in spintronic memory devices.

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