Li Xi

Topological insulators (TIs) with spin-momentum-locked surface states exhibit high charge-to-spin (C2S) conversion efficiency. However, binary and ternary TIs are constrained by a narrow tunable composition window for their insulating bulk states, which limits spintronic performance due to interference from bulk conduction. This work reports the development of a high-quality quaternary TI, [Sb2Te3(5−t)/Bi2Se3(t)]4, fabricated via scalable magnetron sputtering. By tuning the Bi2Se3 layer thickness, the quaternary TI exhibits high resistivity and low carrier concentration, effectively suppressing bulk conduction across a broad tunable window. Over a wide Bi2Se3 thickness range (t = 0.2–1.5 nm, corresponding to 3%–23% Bi2Se3 content), a high spin Hall angle (θSH) of 0.4–0.99 is maintained. Furthermore, in heterostructures based on this quaternary TI, the critical magnetization switching current density drops to as low as 3.3 × 105 A/cm2, which is two orders of magnitude lower than that of heavy metal Pt. Owing to the large spin Hall angle, the quaternary TI also exhibits power consumption approximately 20 times lower than ternary TIs for t = 0.2–1.5 nm. These results confirm that scalable quaternary TIs enable low-power spintronic devices with enhanced efficiency and processing flexibility, paving the way for advanced spintronic applications.

Efficient charge-to-spin conversion requires strong spin–orbit coupling and tunable electronic transport. Here we use chalcogen chemistry to regulate spin–orbit-torque generation in c-axis-oriented PtX2 (X = Te, Se) thin films. PtTe2/Py and PtSe2/Py heterostructures were fabricated using the same sputtering–chemical vapor deposition and lithographic framework for direct spin-transport comparison. Harmonic Hall measurements, current-partition correction, and thickness-dependent drift-diffusion analysis yield an effective spin Hall angle of θSH ≈ 0.23 for PtSe2/Py, more than twice that of PtTe2/Py (θSH ≈ 0.10). X-ray photoelectron spectroscopy, transport measurements, and bulk electronic-structure calculations link Te-to-Se substitution to changes in Pt–X bonding, near-Fermi-level states, and metallicity. Over the investigated thickness range, PtTe2/Py shows a predominantly bulk-SHE-like response, whereas the larger damping-like torque in PtSe2/Py is consistent with a proximity-modified interfacial contribution. Chalcogen chemistry controls the balance between bulk and interfacial charge-to-spin conversion in Pt-based dichalcogenide heterostructures.

With the rapid expansion of terahertz (THz) applications in next-generation communication systems, imaging technologies, and quantum manipulation, the realization of efficient and highly integrated THz sources that do not rely on complex auxiliary components has emerged as a key challenge. Although spintronic THz emitters have advanced considerably in recent years, most existing schemes still depend on external magnetic fields to stabilize the magnetization orientation, which constitutes a major structural constraint for practical device integration. In this work, we introduce exchange bias into spintronic THz emission by employing a ferromagnetic/antiferromagnetic FeNi/IrMn3 heterostructure, thereby enabling field-free operation of the emitter. Through interfacial exchange coupling, the magnetization of the FM layer is pinned in a well-defined direction, which ensures reliable spin-current injection and spin-to-charge conversion in the absence of an external magnetic field. As a result, robust THz emission can be achieved under zero-field conditions. Beyond eliminating the magnetic field requirement inherent to conventional spintronic THz sources, the incorporation of a stripe-patterned metasurface further allows efficient generation and controllable manipulation of broadband chiral THz waves. A field-free spintronic THz source with controllable polarization state and high efficiency has been achieved.

Surface acoustic waves (SAWs) have emerged as an efficient approach for the acoustic manipulation of magnetization and the generation of spin currents, attracting significant attention in spintronics. In this work, we systematically investigate the magnetotransport properties of a lithium niobate/nickel (LiNbO ₃ /Ni) device under nonresonant SAW excitation using time‐resolved electrical measurements. The time‐resolved SAW‐induced voltage is measured as a function of delay time, external magnetic field magnitude, and magnetic field orientation. The SAW‐induced voltage exhibits pronounced magnetization‐dependent modulation, characterized by a double‐valley structure with two valleys appearing near zero magnetic field and the magnetization switching field during magnetic field sweeps and a fourfold angular dependence. These features differ markedly from the single switching‐related feature and twofold angular dependence expected for the conventional anisotropic magnetoresistance effect (AMR). We attribute the SAW‐induced response to dynamic strain‐mediated magnetoelastic coupling, which modulates the magnetization configuration and spin‐dependent scattering in the Ni film. Our results demonstrate a feasible route for using SAWs to probe and control strain‐mediated spin–lattice interactions in magnetic thin‐film devices.

Owing to magnetostrictive effects, nonlocal magnon transport in yttrium iron garnet (YIG) is often accompanied by phonon excitation. However, the influence of these phonons on magnon spin transport remains unclear. In our experiment, an external microwave field is applied to excite ferromagnetic resonance (FMR) in the YIG during nonlocal magnon transport measurements. We observe that an additional signal emerges in the thermal magnon transport. Angular-dependent measurements under varying magnetic fields further reveal that this additional signal is well described by our Landau–Lifshitz–Gilbert (LLG) simulation when enhanced magnetoelastic coupling is considered. This result indicates that the signal originates from the rotational lattice motion driven by magnetization precession, which generates phonons that subsequently couple to propagating magnons. This behavior contrasts with previously reported magnon–magnon scattering and parametric pumping, which occur strictly under resonant FMR conditions and require nonlinear excitation. Our results provide evidence that phonons actively participate in magnon spin transport and suggest viable opportunities for developing high-speed, phonon-assisted magnonic devices.