Two-dimensional van der Waals (vdW) magnetic materials hold promise for the development of high-density, energy-efficient spintronic devices for memory and computation. Recent breakthroughs in material discoveries and spin-orbit torque control of vdW ferromagnets have opened a path for integration of vdW magnets in commercial spintronic devices. However, a solution for field-free electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room temperatures, essential for building compact and thermally stable spintronic devices, is still missing. Here, we report a solution for the field-free, deterministic, and nonvolatile switching of a PMA vdW ferromagnet, Fe3GaTe2, above room temperature (up to 320 K). We use the unconventional out-of-plane anti-damping torque from an adjacent WTe2 layer to enable such switching with a low current density of 2.23 × 106 A cm−2. This study exemplifies the efficacy of low-symmetry vdW materials for spin-orbit torque control of vdW ferromagnets and provides an all-vdW solution for the next generation of scalable and energy-efficient spintronic devices.

pdf/field-free-deterministic-switching-of-all-van-der-waals-spin-1hs7twl9do.pdf

Field-free deterministic switching of all–van der Waals spin-orbit torque system above room temperature


 Artificial intelligence has become indispensable in modern life, but its energy consumption has become a significant concern due to its huge storage and computational demands. Artificial intelligence algorithms are mainly based on deep learning algorithms, relying on the backpropagation of convolutional neural networks or binary neural networks. While these algorithms aim to simulate the learning process of the human brain, their low bio-fidelity and the separation of storage and computing units lead to significant energy consumption. The human brain is a remarkable computing machine with extraordinary capabilities for recognizing and processing complex information while consuming very low power. Tunneling magnetoresistance (TMR)-based devices, namely magnetic tunnel junctions (MTJs), have great advantages in simulating the behavior of biological synapses and neurons. This is not only because MTJs can simulate biological behavior such as Spike-Timing Dependent Plasticity(STDP) and Leaky Integrate-Fire(LIF), but also because MTJs have intrinsic stochastic and oscillatory properties. These characteristics improve MTJs' bio-fidelity and reduce their power consumption. MTJs also possess advantages such as ultrafast dynamics and non-volatile properties, making them widely utilized in the field of neuromorphic computing in recent years. We conducted a comprehensive review of the development history and underlying principles of TMR, including a detailed introduction to the material and magnetic properties of MTJs and their temperature dependence. We also explored various writing methods of MTJs and their potential applications. Furthermore, we provided a thorough analysis of the characteristics and potential applications of different types of MTJs for neuromorphic computing. TMR-based devices have demonstrated promising potential for broad application in neuromorphic computing, particularly in the development of spiking neural networks. Their ability to perform on-chip learning with ultra-low power consumption makes them an exciting prospect for future advances in the era of the Internet of Things.

https://iopscience.iop.org/article/10.1088/2752-5724/ace3af/pdf

Tunneling Magnetoresistance Materials and Devices for Neuromorphic Computing

The field-free spin–orbit torque induced 180° reorientation of magnetization is beneficial for the high performance magnetic memory. The antiferromagnetic material (AFM) can provide a higher operation speed than the ferromagnetic counterpart. In this paper, we propose a trilayer AFM/insulator/heavy metal structure as the AFM memory device. We show that the field-free switching of the AFM with a perpendicular Néel vector can be achieved by using two orthogonal currents, which provide a uniform damping-like torque and uniform field-like torque, respectively. The reversible switching can be obtained by reversing either current. A current density of 1.79 × 1011 A/m2 is sufficient to induce the switching. In addition, the two magnetic moments become noncollinear during switching. This enables an ultrafast switching within 40 ps. The device and switching mechanism proposed in this work offer a promising approach to deterministically switch the AFM with the perpendicular Néel vector. It can also stimulate the development of an ultrafast AFM-based MRAM. 

pdf/field-free-spin-orbit-torque-switching-of-an-antiferromagnet-1dvhwiqv6r.pdf

Field-free spin–orbit torque switching of an antiferromagnet with perpendicular Néel vector

The field-free spin-orbit torque induced 180° reorientation of perpendicular magnetization is beneficial for the high performance magnetic memory. The antiferromagnetic material (AFM) can provide higher operation speed than the ferromagnetic counterpart. In this paper, we propose a trilayer AFM/Insulator/Heavy Metal structure as the AFM memory device. We show that the field-free switching of the AFM with perpendicular Néel vector can be achieved by using two orthogonal currents, which provide the uniform damping-like torque and stagger field-like torque, respectively. The reversible switching can be obtained by reversing either current. A current density of 1.79×10 11 A/m 2 is sufficient to induce the switching. In addition, the two magnetic moments become noncollinear during the switching. This enables an ultrafast switching within 40 picoseconds. The device and switching mechanism proposed in this work offer a promising approach to deterministically switch the AFM with perpendicular Néel vector. It can also stimulate

Field-free spin-orbit torque switching of an antiferromagnet with perpendicular N\'eel vector

The emerging all-van der Waals (vdW) magnetic heterostructure provides a new platform to control the magnetization by the electric field beyond the traditional spintronics devices. One promising strategy is using unconventional spin-orbit torque (SOT) exerted by the out-of-plane polarized spin current to enable deterministic magnetization switching and enhance the switching efficiency. However, in all-vdW heterostructures, large unconventional SOT remains elusive and the robustness of the field-free switching against external magnetic field has not been examined, which hinders further applications. Here, the study demonstrates the field-free switching in an all-vdW heterostructure combining a type-II Weyl semimetal TaIrTe 

Robust Field‐Free Switching Using Large Unconventional Spin‐Orbit Torque in an All‐Van der Waals Heterostructure

Spin-orbit-torque (SOT)-driven perpendicular magnetization switching has attracted great attention for designing energy-efficient, high-density, and thermal-stable storage devices. As field-free deterministic switching of perpendicular magnetization is not allowed in conventional heavy metals or topological insulators where spin polarization is limited to the in-plane direction, transition metal dichalcogenides (TMDs) emerge as current spin platforms due to their low-crystal symmetries. However, present studies using TMDs are restricted to mechanically exfoliated samples with micron sizes and to low-temperature operation, which impede their practical applications. Here, based on large-scale, chemical vapor deposition (CVD)-grown, few-layer WTe2 thin films, the field-free switching at room temperature of the CoFeB/MgO heterostructure with perpendicular magnetic anisotropy is experimentally realized owing to unconventional SOTs in WTe2. Furthermore, we employ micromagnetic simulations to explore magnetization dynamics in the out-of-plane polarized spin’s presence. This work paves the way for constructing all-electrical, low-power spintronic devices based on two-dimensional TMDs. 

Room temperature field-free switching of CoFeB/MgO heterostructure based on large-scale few-layer WTe2

The writing performance of the easy-cone magnetic tunnel junction (MTJ) and perpendicularly magnetized MTJ (pMTJ) under various temperatures was investigated based on the macrospin model. When the temperature is changed from 273 K to 373 K, the switching current density of the pMTJ changes by 56%, whereas this value is only 8% in the easy-cone MTJ. Similarly, the temperature-induced variation of the switching delay is more significant in the pMTJ. This indicates that the easy-cone MTJ has a more stable writing performance under temperature variations, resulting in a wider operating temperature range. In addition, these two types of MTJs exhibit opposite temperature dependence in the current overdrive and write error rate. In the easy cone MTJ, these two performance metrics will reduce as temperature is increased. The results shown in this work demonstrate that the easy-cone MTJ is more suitable to work at high temperatures compared with the pMTJ. Our work provides a guidance for the design of STT-MRAM that is required to operate at high temperatures.

/pdf/comparative-study-of-temperature-impact-in-spin-torque-22ls6jtc.pdf

Comparative Study of Temperature Impact in Spin-Torque Switched Perpendicular and Easy-Cone MTJs

Magnetodynamic properties on square patterned of FeGaB and Al2O3/FeGaB thin films

Fast domain wall motion in systems with perpendicular magnetization is necessary for many novel applications such as the racetrack memory, domain wall logic devices and artificial synapses. The domain wall speed has been greatly improved after the demonstration of current driven domain wall motion using the spin transfer torque, and later achieved another leap due to the combined effect of spin-Hall effect and Dzyaloshinskii-Moriya interaction (DMI). However, only Neel wall can be effectively driven in the latter system. In this paper, we show that both Bloch and Neel domain walls can be effectively moved by exploiting the field-like torque with the out-of-plane spin polarization, which can be generated in materials with reduced symmetry. In addition, we find that the Neel wall and Bloch walls stabilized by the magnetostatic energy are easily distorted by the spin-orbit torque and they then enter the Walker breakdown region. External magnetic field and DMI are introduced to stabilize the domain wall, and a very high domain wall velocity over 500 m/s is obtained at a moderate current density of $2\times 10^{11} A/m^2$. In principle, this mechanism can be used to drive any types of domain walls. This work thus provides new degrees of freedom in the control of domain wall motion.

Efficient domain wall motion driven by the out-of-plane spin polarization

Effect of Non-uniform Atom Distribution on Ferrimagnetic Domain Wall Motion Based on an Atomistic Model

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