Deterministic Spin-Orbit Torque Switching by a Light-Metal Insertion.

Spin-orbit torque (SOT) switching of magnetization is a promising emerging technology for nonvolatile spintronic memory and logic applications. However, deterministic switching of perpendicular magnetization with SOTs requires an additional symmetry breaking, which is typically provided by an external magnetic field, making it impractical for applications. In this work, we disclose that by the insertion of a slightly asymmetric light-metal layer at the heavy metal-ferromagnet interface of SOT heterostructures, current-induced out-of-plane effective magnetic fields are introduced that enable deterministic switching without an external magnetic field. We obtain uniform perpendicular magnetic anisotropy and switching current density despite the asymmetry of the light-metal layer, and we show the scalability of our approach by studying device sizes that differ by 2 orders of magnitude. Our work provides a practical route for utilization of SOTs for magnetization switching on the wafer scale and paves the way for the practical application of SOT-based technology.

Roadmap of spin-orbit torques.

Spin-orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin-orbit coupling, conduction electron spins and magnetization. More recently interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this Roadmap paper, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and strain effects. Then, we discuss the materials that enable these effects, including metals, metallic alloys, topological insulators, two-dimensional materials, and complex oxides. We also discuss the important roles in SOT devices of different types of magnetic layers, such as magnetic insulators, antiferromagnets, and ferrimagnets. Afterward, we discuss device applications utilizing SOTs. We discuss and compare three-terminal and two-terminal SOT-magnetoresistive random-access memories (MRAMs); we mention various schemes to eliminate the need for an external field. We provide technological application considerations for SOT-MRAM and give perspectives on SOT-based neuromorphic devices and circuits. In addition to SOT-MRAM, we present SOT-based spintronic terahertz generators, nano-oscillators, and domain wall and skyrmion racetrack memories. This paper aims to achieve a comprehensive review of SOT theory, materials, and applications, guiding future SOT development in both the academic and industrial sectors.

Highly Efficient Spin-Orbit Torque and Switching of Layered Ferromagnet Fe3GeTe2.

Among van der Waals (vdW) layered ferromagnets, Fe3GeTe2 (FGT) is an excellent candidate material to form FGT/heavy metal heterostructures for studying the effect of spin-orbit torques (SOT). Its metallicity, strong perpendicular magnetic anisotropy built in the single atomic layers, relatively high Curie temperature (Tc ∼ 225 K), and electrostatic gate tunability offer a tantalizing possibility of achieving the ultimate high SOT limit in monolayer all-vdW nanodevices. In this study, we fabricate heterostructures of FGT/Pt with 5 nm of Pt sputtered onto the atomically flat surface of ∼15-23 nm exfoliated FGT flakes. The spin current generated in Pt exerts a damping-like SOT on FGT magnetization. At ∼2.5 × 1011 A/m2 current density, SOT causes the FGT magnetization to switch, which is detected by the anomalous Hall effect of FGT. To quantify the SOT effect, we measure the second harmonic Hall responses as the applied magnetic field rotates the FGT magnetization in the plane. Our analysis shows that the SOT efficiency is comparable with that of the best heterostructures containing three-dimensional (3D) ferromagnetic metals and much larger than that of heterostructures containing 3D ferrimagnetic insulators. Such large efficiency is attributed to the atomically flat FGT/Pt interface, which demonstrates the great potential of exploiting vdW heterostructures for highly efficient spintronic nanodevices.

Unidirectional Magneto-Resistance in Modulation-Doped Magnetic Topological Insulators.

Nonlinear unidirectional spin Hall magnetoresistance (USMR) has been reported in heavy metal/ferromagnet bilayers, which could be employed as an effective method in detecting the magnetization orientation in spintronic devices with two-terminal geometry. Recently, another unidirectional magnetoresistance (UMR) was reported in magnetic topological insulator (TI)-based heterostructures at cryogenic temperature, whose amplitude is orders of magnitude larger than the USMR measured in heavy metal-based magnetic heterostructures at room temperature. Here, we report the UMR effect in the modulation-doped magnetic TI structures. This UMR arises due to the interplay between the magnetic dopant's magnetization and the current-induced surface spin polarization, when they are parallel or antiparallel to each other in the TI material. By varying the dopant's position in the structure, we reveal that the UMR is mainly originating from the interaction between the magnetization and the surface spin-polarized carriers (not bulk carriers). Furthermore, from the magnetic field-, the angular rotation-, and the temperature-dependence, we highlight the correlation between the UMR effect and the magnetism in the structures. The large UMR versus current ratio in TI-based magnetic bilayers promises the easy readout in TI-based spintronic devices with two-terminal geometry.

Effect of sex differences in donor foetal fibroblast on the early development and DNA methylation status of buffalo (Bubalus bubalis) nuclear transfer embryos.

Low efficiency of somatic cell nuclear transfer (SCNT) embryos is largely attributable to imperfect reprogramming of the donor nucleus. The differences in epigenetic reprogramming between female and male buffalo cloned embryos remain unclear. We explored the effects of donor cell sex differences on the development of SCNT embryos. We and then compared the expression of DNA methylation (5-methylcytosine-5mC and 5-hydroxymethylcytosine-5hmC) and the expression level of relevant genes, and histone methylation (H3K9me2 and H3K9me3) level in SCNT-♀ and SCNT-♂ preimplantation embryos with in vitro fertilization (IVF) counterparts. In the study, we showed that developmental potential of SCNT-♀ embryos was greater than that of SCNT-♂ embryos (p < 0.05). 5mC was mainly expressed in SCNT-♀ embryos, whereas 5hmC was majorly expressed in SCNT-♂ embryos (p < 0.05). The levels of DNA methylation (5mC and 5hmC), Dnmt3b, TET1 and TET3 in the SCNT-♂ embryos were higher than those of SCNT-♀ embryos (p < 0.05). In addition, there were no significant differences in the expression of H3K9me2 at eight-stage of the IVF, SCNT-♀ and SCNT-♂embryos (p < 0.05). However, H3K9me3 was upregulated in SCNT-♂ embryos at the eight-cell stage (p < 0.05). Thus, KDM4B ectopic expression decreased the level of H3K9me3 and significantly improved the developmental rate of two-cell, eight-cell and blastocysts of SCNT-♂ embryos (p < 0.05). Overall, the lower levels of DNA methylation (5mC and 5hmC) and H3K9me3 may introduce the greater developmental potential in buffalo SCNT-♀ embryos than that of SCNT-♂ embryos.

Room-Temperature Skyrmions in an Antiferromagnet-Based Heterostructure.

Magnetic skyrmions as swirling spin textures with a nontrivial topology have potential applications as magnetic memory and storage devices. Since the initial discovery of skyrmions in non-centrosymmetric B20 materials, the recent effort has focused on exploring room-temperature skyrmions in heavy metal and ferromagnetic heterostructures, a material platform compatible with existing spintronic manufacturing technology. Here, we report the surprising observation that a room-temperature skyrmion phase can be stabilized in an entirely different class of systems based on antiferromagnetic (AFM) metal and ferromagnetic (FM) metal IrMn/CoFeB heterostructures. There are a number of distinct advantages of exploring skyrmions in such heterostructures including zero-field stabilization, tunable antiferromagnetic order, and sizable spin-orbit torque (SOT) for energy-efficient current manipulation. Through direct spatial imaging of individual skyrmions, quantitative evaluation of the interfacial Dzyaloshinskii-Moriya interaction, and demonstration of current-driven skyrmion motion, our findings firmly establish the AFM/FM heterostructures as a promising material platform for exploring skyrmion physics and device applications.

Tailoring exchange couplings in magnetic topological-insulator/antiferromagnet heterostructures.

Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a platform for the realization of versatile time-reversal symmetry-breaking physics. By constructing heterostructures exhibiting Néel order in an antiferromagnetic CrSb and ferromagnetic order in Cr-doped (Bi,Sb)2Te3, we realize emergent interfacial magnetic phenomena which can be tailored through artificial structural engineering. Through deliberate geometrical design of heterostructures and superlattices, we demonstrate the use of antiferromagnetic exchange coupling in manipulating the magnetic properties of magnetic topological insulators. Proximity effects are shown to induce an interfacial spin texture modulation and establish an effective long-range exchange coupling mediated by antiferromagnetism, which significantly enhances the magnetic ordering temperature in the superlattice. This work provides a new framework on integrating topological insulators with antiferromagnetic materials and unveils new avenues towards dissipationless topological antiferromagnetic spintronics.

Topological Transitions Induced by Antiferromagnetism in a Thin-Film Topological Insulator.

Magnetism in topological insulators (TIs) opens a topologically nontrivial exchange band gap, providing an exciting platform for manipulating the topological order through an external magnetic field. Here, we show that the surface of an antiferromagnetic thin film can magnetize the top and the bottom TI surface states through interfacial couplings. During the magnetization reversal, intermediate spin configurations are ascribed from unsynchronized magnetic switchings. This unsynchronized switching develops antisymmetric magnetoresistance spikes during magnetization reversals, which might originate from a series of topological transitions. With the high Néel ordering temperature provided by the antiferromagnetic layers, the signature of the induced topological transition persists up to ∼90 K.

Room-Temperature Skyrmion Shift Device for Memory Application.

Magnetic skyrmions are intensively explored for potential applications in ultralow-energy data storage and computing. To create practical skyrmionic memory devices, it is necessary to electrically create and manipulate these topologically protected information carriers in thin films, thus realizing both writing and addressing functions. Although room-temperature skyrmions have been previously observed, fully electrically controllable skyrmionic memory devices, integrating both of these functions, have not been developed to date. Here, we demonstrate a room-temperature skyrmion shift memory device, where individual skyrmions are controllably generated and shifted using current-induced spin-orbit torques. Particularly, it is shown that one can select the device operation mode in between (i) writing new single skyrmions or (ii) shifting existing skyrmions by controlling the magnitude and duration of current pulses. Thus, we electrically realize both writing and addressing of a stream of skyrmions in the device. This prototype demonstration brings skyrmions closer to real-world computing applications.

Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition Metal Dichalcogenide/Ferromagnet Bilayers.

The electronic and optoelectronic properties of two-dimensional materials have been extensively explored in graphene and layered transition metal dichalcogenides (TMDs). Spintronics in these two-dimensional materials could provide novel opportunities for future electronics, for example, efficient generation of spin current, which should enable the efficient manipulation of magnetic elements. So far, the quantitative determination of charge current-induced spin current and spin-orbit torques (SOTs) on the magnetic layer adjacent to two-dimensional materials is still lacking. Here, we report a large SOT generated by current-induced spin accumulation through the Rashba-Edelstein effect in the composites of monolayer TMD (MoS2 or WSe2)/CoFeB bilayer. The effective spin conductivity corresponding to the SOT turns out to be almost temperature-independent. Our results suggest that the charge-spin conversion in the chemical vapor deposition-grown large-scale monolayer TMDs could potentially lead to high energy efficiency for magnetization reversal and convenient device integration for future spintronics based on two-dimensional materials.

Scale-invariant quantum anomalous Hall effect in magnetic topological insulators beyond the two-dimensional limit.

We investigate the quantum anomalous Hall effect (QAHE) and related chiral transport in the millimeter-size (Cr(0.12)Bi(0.26)Sb(0.62))2Te3 films. With high sample quality and robust magnetism at low temperatures, the quantized Hall conductance of e²/h is found to persist even when the film thickness is beyond the two-dimensional (2D) hybridization limit. Meanwhile, the Chern insulator-featured chiral edge conduction is manifested by the nonlocal transport measurements. In contrast to the 2D hybridized thin film, an additional weakly field-dependent longitudinal resistance is observed in the ten-quintuple-layer film, suggesting the influence of the film thickness on the dissipative edge channel in the QAHE regime. The extension of the QAHE into the three-dimensional thickness region addresses the universality of this quantum transport phenomenon and motivates the exploration of new QAHE phases with tunable Chern numbers. In addition, the observation of scale-invariant dissipationless chiral propagation on a macroscopic scale makes a major stride towards ideal low-power interconnect applications.

A non-canonical visual cortical-entorhinal pathway contributes to spatial navigation.

Visual information is important for accurate spatial coding and memory-guided navigation. As a crucial area for spatial cognition, the medial entorhinal cortex (MEC) harbors diverse spatially tuned cells and functions as the major gateway relaying sensory inputs to the hippocampus containing place cells. However, how visual information enters the MEC has not been fully understood. Here, we identify a pathway originating in the secondary visual cortex (V2) and directly targeting MEC layer 5a (L5a). L5a neurons served as a network hub for visual processing in the MEC by routing visual inputs from multiple V2 areas to other local neurons and hippocampal CA1. Interrupting this pathway severely impaired visual stimulus-evoked neural activity in the MEC and performance of mice in navigation tasks. These observations reveal a visual cortical-entorhinal pathway highlighting the role of MEC L5a in sensory information transmission, a function typically attributed to MEC superficial layers before.

Long-term efficacy of transanal local excision versus total mesorectal excision after neoadjuvant treatment for rectal cancer: A meta-analysis.

AIM: The purpose of this meta-analysis is to compare the long-term efficacy of transanal local excision (TLE) versus total mesorectal excision (TME) following neoadjuvant therapy for rectal cancer. METHOD: The Web of Science, Pubmed, Medline, Embase, and the Cochrane Library were systematically searched for correlational research. The Newcastle-Ottawa Scale and the Cochrane risk of bias tool were used to assess the quality of cohort studies (CSs) and randomized controlled trials (RCTs), respectively. Statistically analyzed using RevMan5.4. RESULT: A total of 13 studies, including 3 randomized controlled trials (RCTs) and 10 cohort studies (CSs), involving 1402 patients, were included in the analysis. Of these, 570 patients (40.66%) underwent TLE, while 832 patients (59.34%) underwent TME. In the meta-analysis of CSs, no significant difference was observed between the TLE group and TME group regarding 5-year overall survival (OS) and 5-year disease-free survival (DFS) (P > 0.05). However, the TLE group had a higher rates of local recurrence (LR) [risk ratio (RR) = 1.93, 95%CI (1.18, 3.14), P = 0.008] and a lower rates of 5-years local recurrence-free survival (LRFS) [hazard ratio (HR) = 2.79, 95%CI (1.04, 7.50), P = 0.04] compared to the TME group. In the meta-analysis of RCTs, there was no significant difference observed between the TLE group and TME group in terms of LR, 5-year OS, 5-year DFS, and 5-year disease-specific survival (P > 0.05). CONCLUSION: After undergoing neoadjuvant therapy, TLE may provide comparable 5-year OS and DFS to TME for rectal cancer. However, neoadjuvant therapy followed by TLE may has a higher LR and lower 5-year LRFS compared to neoadjuvant therapy followed by TME, so patients should be carefully selected. Neoadjuvant therapy followed by TLE may be a suitable option for patients who prioritize postoperative quality of life. However, the effectiveness of this approach requires further research to draw a definitive conclusion.

Laminar and dorsoventral organization of layer 1 interneuronal microcircuitry in superficial layers of the medial entorhinal cortex.

Layer 1 (L1) interneurons (INs) participate in various brain functions by gating information flow in the neocortex, but their role in the medial entorhinal cortex (MEC) is still unknown, largely due to scant knowledge of MEC L1 microcircuitry. Using simultaneous triple-octuple whole-cell recordings and morphological reconstructions, we comprehensively depict L1IN networks in the MEC. We identify three morphologically distinct types of L1INs with characteristic electrophysiological properties. We dissect intra- and inter-laminar cell-type-specific microcircuits of L1INs, showing connectivity patterns different from those in the neocortex. Remarkably, motif analysis reveals transitive and clustered features of L1 networks, as well as over-represented trans-laminar motifs. Finally, we demonstrate the dorsoventral gradient of L1IN microcircuits, with dorsal L1 neurogliaform cells receiving fewer intra-laminar inputs but exerting more inhibition on L2 principal neurons. These results thus present a more comprehensive picture of L1IN microcircuitry, which is indispensable for deciphering the function of L1INs in the MEC.

Acute inflammatory reaction during anti-angiogenesis therapy combined with immunotherapy as a possible indicator of the therapeutic effect: Three case reports and literature review.

The posterior line treatment of unresectable advanced or metastatic gastrointestinal (GI) tumors has always been a challenging point. In particular, for patients with microsatellite stable (MSS)/mismatch repair proficient (pMMR) 0GI tumors, the difficulty of treatment is exacerbated due to their insensitivity to immune drugs. Accordingly, finding a new comprehensive therapy to improve the treatment effect is urgent. In this study, we report the treatment histories of three patients with MSS/pMMR GI tumors who achieved satisfactory effects by using a comprehensive treatment regimen of apatinib combined with camrelizumab and TAS-102 after the failure of first- or second-line regimens. The specific contents of the treatment plan were as follows: apatinib (500 mg/d) was administered orally for 10 days, followed by camrelizumab (200 mg, ivgtt, day 1, 14 days/cycle) and TAS-102 (20 mg, oral, days 1-21, 28 days/cycle). Apatinib (500 mg/d) was maintained during treatment. Subsequently, we discuss the possible mechanism of this combination and review the relevant literature, and introduce clinical trials on anti-angiogenesis therapy combined with immunotherapy.

Room temperature field-free switching of perpendicular magnetization through spin-orbit torque originating from low-symmetry type II Weyl semimetal.

Spin-orbit torque (SOT) is a promising strategy to deterministically switch the perpendicular magnetization, but usually requires an in-plane magnetic field for breaking the mirror symmetry, which is not suitable for most advanced industrial applications. Van der Waals (vdW) materials with low crystalline symmetry and topological band structures, e.g., Weyl semimetals (WSMs), potentially serve as an outstanding system that may simultaneously realize field-free switching and high energy efficiency. Yet, the demonstration of these superiorities at room temperature has not been realized. Here, we achieve a field-free switching of perpendicular magnetization by using a layered type II WSM, TaIrTe4, in a TaIrTe4/Ti/CoFeB system at room temperature with the critical switching current density ~2.4 × 106 A cm-2. The field-free switching is ascribed to the out-of-plane SOT allowed by the low crystal symmetry. Our work suggests that using low-symmetry materials to generate SOT is a promising route for the manipulation of perpendicular magnetization at room temperature.

Electrical detection of spin pumping in van der Waals ferromagnetic Cr2Ge2Te6 with low magnetic damping.

The discovery of magnetic order in atomically-thin van der Waals materials has strengthened the alliance between spintronics and two-dimensional materials. An important use of magnetic two-dimensional materials in spintronic devices, which has not yet been demonstrated, would be for coherent spin injection via the spin-pumping effect. Here, we report spin pumping from Cr2Ge2Te6 into Pt or W and detection of the spin current by inverse spin Hall effect. The magnetization dynamics of the hybrid Cr2Ge2Te6/Pt system are measured, and a magnetic damping constant of ~ 4-10 × 10-4 is obtained for thick Cr2Ge2Te6 flakes, a record low for ferromagnetic van der Waals materials. Moreover, a high interface spin transmission efficiency (a spin mixing conductance of 2.4 × 1019/m2) is directly extracted, which is instrumental in delivering spin-related quantities such as spin angular momentum and spin-orbit torque across an interface of the van der Waals system. The low magnetic damping that promotes efficient spin current generation together with high interfacial spin transmission efficiency suggests promising applications for integrating Cr2Ge2Te6 into low-temperature two-dimensional spintronic devices as the source of coherent spin or magnon current.

Transferred metal gate to 2D semiconductors for sub-1 V operation and near ideal subthreshold slope.

Ultrathin two-dimensional (2D) semiconductors are regarded as a potential channel material for low-power transistors with small subthreshold swing and low leakage current. However, their dangling bond­free surface makes it extremely difficult to deposit gate dielectrics with high-quality interface in metal-oxide-semiconductor (MOS) field-effect transistors (FETs). Here, we demonstrate a low-temperature process to transfer metal gate to 2D MoS2 for high-quality interface. By excluding extrinsic doping to MoS2 and increasing contact distance, the high­barrier height Pt-MoS2 Schottky junction replaces the commonly used MOS capacitor and eliminates the use of gate dielectrics. The MoS2 transferred metal gate (TMG) FETs exhibit sub-1 V operation voltage and a subthreshold slope close to thermal limit (60 mV/dec), owing to intrinsically high junction capacitance and the high-quality interface. The TMG and back gate enable logic functions in a single transistor with small footprint.

Two-Dimensional Materials for Energy-Efficient Spin-Orbit Torque Devices.

Spin-orbit torques (SOTs), which rely on spin current generation from charge current in a nonmagnetic material, promise an energy-efficient scheme for manipulating magnetization in magnetic devices. A critical topic for spintronic devices using SOTs is to enhance the charge to spin conversion efficiency. Besides, the current-induced spin polarization is usually limited to in-plane, whereas out-of-plane spin polarization could be favored for efficient perpendicular magnetization switching. Recent advances in utilizing two important classes of two-dimensional materials-topological insulators and transition-metal dichalcogenides-as spin sources to generate SOT shed light on addressing these challenges. Topological insulators such as bismuth selenide have shown a giant SOT efficiency, which is larger than those from three-dimensional heavy metals by at least 1 order of magnitude. Transition-metal dichalcogenides such as tungsten telluride have shown a current-induced out-of-plane spin polarization, which is allowed by the reduced symmetry. In this review, we use symmetry arguments to predict and analyze SOTs in two-dimensional material-based heterostructures. We summarize the recent progress of SOT studies based on topological insulators and transition-metal dichalcogenides and show how these results are in line with the symmetry arguments. At last, we identify unsolved issues in the current studies and suggest three potential research directions in this field.