Electric-Field Control of Spin–Orbit Torques in WS₂/Permalloy Bilayers

Transition metal dichalcogenides (TMDs) have drawn great attention owing to their potential for electronic, optoelectronic, and spintronic applications. In TMDs/ferromagnetic bilayers, an efficient spin current can be generated by the TMDs to manipulate the magnetic moments in the ferromagnetic layer. In this work, we report on the electric-field modulation of spin–orbit torques (SOTs) in WS₂/NiFe bilayers by the spin-torque ferromagnetic resonance technique. It is found that the radio frequency current can induce a spin accumulation at the WS₂/NiFe interface because of the interfacial Rashba–Edelstein effect. As a consequence, the SOT ratio between the field-like and antidamping-like torques can be effectively controlled by applying the back-gate voltage in WS₂/NiFe bilayers. These results provide a strategy for controlling the SOT by using semiconducting TMDs

Sulfur-Doped Black Phosphorus Field-Effect Transistors with Enhanced Stability

Black phosphorus (BP) has drawn great attention owing to its tunable band gap depending on thickness, high mobility, and large <i>I</i>_on/<i>I</i>_off ratio, which makes BP attractive for using in future two-dimensional electronic and optoelectronic devices. However, its instability under ambient conditions poses challenge to the research and limits its practical applications. In this work, we present a feasible approach to suppress the degradation of BP by sulfur (S) doping. The fabricated S-doped BP few-layer field-effect transistors (FETs) show more stable transistor performance under ambient conditions. After exposing to air for 21 days, the charge-carrier mobility of a representative S-doped BP FETs device decreases from 607 to 470 cm² V^–1 s^–1 (remained as high as 77.4%) under ambient conditions and a large <i>I</i>_on/<i>I</i>_off ratio of ∼10³ is still retained. The atomic force microscopy analysis, including surface morphology, thickness, and roughness, also indicates the lower degradation rate of S-doped BP compared to BP. First-principles calculations show that the dopant S atom energetically prefers to chemisorb on the BP surface in a dangling form and the enhanced stability of S-doped BP can be ascribed to the downshift of the conduction band minimum of BP below the redox potential of O₂/O₂^–. Our work suggests that S doping is an effective way to enhance the stability of black phosphorus

High-Power Coherent Microwave Emission from Magnetic Tunnel Junction Nano-oscillators with Perpendicular Anisotropy

The excitation of the steady-state precessions of magnetization opens a new way for nanoscale microwave oscillators by exploiting the transfer of spin angular momentum from a spin-polarized current to a ferromagnet, referred to as spin-transfer nano-oscillators (STNOs). For STNOs to be practical, however, their relatively low output power and their relatively large line width must be improved. Here we demonstrate that microwave signals with maximum measured power of 0.28 μW and simultaneously narrow line width of 25 MHz can be generated from CoFeB–MgO–based magnetic tunnel junctions having an in-plane magnetized reference layer and a free layer with strong perpendicular anisotropy. Moreover, the generation efficiency is substantially higher than previously reported STNOs. The results will be of importance for the design of nanoscale alternatives to traditional silicon oscillators used in radio frequency integrated circuits