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1. Giant Hall Switching by Surface‐State‐Mediated Spin‐Orbit Torque in a Hard Ferromagnetic Topological Insulator

   https://doi.org/10.1002/adma.202406772  

   Tai, Lixuan; He, Haoran; Chong, Su_Kong; Zhang, Huairuo; Huang, Hanshen; Qiu, Gang; Ren, Yuxing; Li, Yaochen; Yang, Hung‐Yu; Yang, Ting‐Hsun; et al (September 2024, Advanced Materials)

   Abstract Topological insulators (TI) and magnetic topological insulators (MTI) can apply highly efficient spin‐orbit torque (SOT) and manipulate the magnetization with their unique topological surface states (TSS) with ultrahigh efficiency. Here, efficient SOT switching of a hard MTI, V‐doped (Bi,Sb)₂Te₃(VBST), with a large coercive field that can prevent the influence of an external magnetic field, is demonstrated. A giant switched anomalous Hall resistance of 9.2 kΩ is realized, among the largest of all SOT systems, which makes the Hall channel a good readout and eliminates the need to fabricate complicated magnetic tunnel junction (MTJ) structures. The SOT switching current density can be reduced to 2.8 × 10⁵ A cm⁻², indicating its high efficiency. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge‐state‐mediated to surface‐state‐mediated transport, thus enhancing the SOT effective field to (1.56 ± 0.12) × 10⁻⁶ T A⁻¹ cm²and the interfacial charge‐to‐spin conversion efficiency to 3.9 ± 0.3 nm⁻¹. The findings establish VBST as an extraordinary candidate for energy‐efficient magnetic memory devices. 

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2. Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au _0.25 Pt _0.75

   https://doi.org/10.1002/aelm.201901131  

   Zhu, Lijun; Zhu, Lujun; Shi, Shengjie; Ralph, Daniel_C; Buhrman, Robert_A (January 2020, Advanced Electronic Materials)

   Abstract Many key electronic technologies (e.g., large‐scale computing, machine learning, and superconducting electronics) require new memories that are at the same time fast, reliable, energy‐efficient, and of low‐impedance, which has remained a challenge. Nonvolatile magnetoresistive random access memories (MRAMs) driven by spin–orbit torques (SOTs) have promise to be faster and more energy‐efficient than conventional semiconductor and spin‐transfer‐torque magnetic memories. It is reported that the spin Hall effect of low‐resistivity Au_0.25Pt_0.75thin films enables ultrafast antidamping‐torque switching of SOT‐MRAM devices for current pulse widths as short as 200 ps. If combined with industrial‐quality lithography and already‐demonstrated interfacial engineering, an optimized MRAM cell based on Au_0.25Pt_0.75can have energy‐efficient, ultrafast, and reliable switching, for example, a write energy of <1 fJ (<50 fJ) for write error rate of 50% (<10⁻⁵) for 1 ns pulses. The antidamping torque switching of the Au_0.25Pt_0.75devices is ten times faster than expected from a rigid macrospin model, most likely because of the fast micromagnetics due to the enhanced nonuniformity within the free layer. The feasibility of Au_0.25Pt_0.75‐based SOT‐MRAMs as a candidate for ultrafast, reliable, energy‐efficient, low‐impedance, and unlimited‐endurance memory is demonstrated. 

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3. Enhanced Voltage‐Controlled Magnetic Anisotropy and Field‐Free Magnetization Switching Achieved with High Work Function and Opposite Spin Hall Angles in W/Pt/W SOT Tri‐Layers

   https://doi.org/10.1002/adfm.202416570  

   Chen, Yu‐Chia; Jia, Qi; Yang, Yifei; Huang, Yu‐Han; Lyu, Deyuan; Peterson, Thomas_J; Wang, Jian‐Ping (November 2024, Advanced Functional Materials)

   Abstract Voltage‐Gated Spin‐Orbit‐Torque (VGSOT) Magnetic Random‐Access Memory (MRAM) is a promising candidate for reducing writing energy and improving writing speed in emerging memory and in‐memory computing applications. However, conventional Voltage Controlled Magnetic Anisotropy (VCMA) approaches are often inefficient due to the low VCMA coefficient at the CoFeB/MgO interface. Additionally, traditional heavy metal/perpendicular magnetic anisotropy (PMA) ferromagnet bilayers require an external magnetic field to overcome symmetry constraints and achieve deterministic SOT switching. Here, a novel and industry‐compatible SOT underlayer for next‐generation VGSOT MRAM by employing a composite heavy metal tri‐layer with a high work function is presented. This approach achieves a VCMA coefficient exceeding 100 fJ V⁻¹m⁻¹through electron depletion effects, which is ten times larger than that observed with a pure W underlayer. Furthermore, it is demonstrated that this composite heavy metal SOT underlayer facilitates the integration of VCMA with opposite spin Hall angles, enabling field‐free SOT switching in industry‐compatible PMA CoFeB/MgO systems. 

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4. FP-SMR: A Fully Digital Floating-Point Processing-in-SAS-MRAM for Session-based Recommender System

   https://doi.org/10.1145/3716368.3735206  

   Ali, Asmer Hamid; Sridharan, Amitesh; Guo, Cheng; Hwang, William; Tsai, Wilman; Zhang, Jeff; Chen, Yiran; X_Wang, Shan; Fan, Deliang (June 2025, ACM)

   With the rapid advancement of DNNs, numerous Process-in-Memory (PIM) architectures based on various memory technologies (Non-Volatile (NVM)/Volatile Memory) have been developed to accelerate AI workloads. Magnetic Random Access Memory (MRAM) is highly promising among NVMs due to its zero standby leakage, fast write/read speeds, CMOS compatibility, and high memory density. However, existing MRAM technologies such as spin-transfer torque MRAM (STT-MRAM) and spin-orbit torque MRAM (SOT-MRAM), have inherent limitations. STT-MRAM faces high write current requirements, while SOT-MRAM introduces significant area overhead due to additional access transistors. The new STT-assisted-SOT (SAS) MRAM provides an area-efficient alternative by sharing one write access transistor for multiple magnetic tunnel junctions (MTJs). This work presents the first fully digital processing-in-SAS-MRAM system to enable 8-bit floating-point (FP8) neural network inference with an application in on-device session-based recommender system. A SAS-MRAM device prototype is fabricated with 4 MTJs sharing the same SOT metal line. The proposed SAS-MRAM-based PIM macro is designed in TSMC 28nm technology. It achieves 15.31 TOPS/W energy efficiency and 269 GOPS performance for FP8 operations at 700 MHz. Compared to state-of-the-art recommender systems for the same popular YooChoose dataset, it demonstrates a 86 ×, 1.8 ×, and 1.12 × higher energy efficiency than that of GPU, SRAM-PIM, and ReRAM-PIM, respectively. 

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5. Monolayer WSe2 induced giant enhancement in the spin Hall efficiency of Tantalum

   https://doi.org/10.1038/s41699-020-0153-z  

   Debashis, Punyashloka; Hung, Terry Y. T.; Chen, Zhihong (June 2020, npj 2D Materials and Applications)

   Abstract Spin Orbit Torque Magnetic RAM (SOT-MRAM) is emerging as a promising memory technology owing to its high endurance, reliability and speed. A critical factor for its success is the development of materials that exhibit efficient conversion of charge current to spin current, characterized by their spin Hall efficiency. In this work, it is experimentally demonstrated that the spin Hall efficiency of the industrially relevant ultra-thin Ta can be enhanced by more than 25× when a monolayer (ML) WSe₂is inserted as an underlayer. The enhancement is attributed to spin absorption at the Ta/WSe₂interface, suggested by harmonic Hall measurements. The presented hybrid spin Hall stack with a 2D WSe₂underlayer has a total body thickness of less than 2 nm and exhibits greatly enhanced spin Hall efficiency, which makes this hybrid a promising candidate for energy efficient SOT-MRAM. 

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