Pietro Gambardella

Heterostructures of 2D materials offer high tunability of magnetic properties, including current-induced magnetization switching by unconventional spin–orbit torques. The microscopic mechanisms governing spin-torque switching in van der Waals systems, however, remain insufficiently understood. Here, we investigate current-induced magnetization reversal in an Fe3GeTe2 (FGT) and WTe2 heterostructure using scanning harmonic magneto-optical Kerr effect microscopy. Spatially resolved magnetization maps show that field-free switching unfolds from asymmetric domain nucleation at the edges of the FGT flake, followed by domain wall propagation. This switching behavior is deterministic and bipolar, consistent with spin–orbit torques arising from the injection of both in-plane and out-of-plane spins from WTe2 into FGT. The critical currents for up-to-down and down-to-up switching differ because of asymmetric domain nucleation and directional domain wall pinning effects. Micromagnetic simulations reproduce the switching behavior observed experimentally, showing how the initial domain nucleation sites are determined by the sample geometry and combined influence of in-plane and out-of-plane spins and Dzyaloshinskii-Moriya interaction. Finally, by systematically varying the field-like and damping-like torque components and sweeping the spin polarization between in-plane and out-of-plane, we identify the torque configurations that yield the most efficient switching in van der Waals magnets with different shapes.

We report direct spectroscopic evidence of antimagnons, i.e., negative-energy spin waves identified by their signature inverted dispersion and left-handed precession with Brillouin light scattering (BLS) spectroscopy. We investigate an ultrathin BiYIG film with a perpendicular magnetic anisotropy that compensates the demagnetizing field. By injecting a spin-orbit torque, the magnetization is driven into auto-oscillation and eventually into a nonequilibrium reversed state above a secondary current threshold ($\ensuremath{\sim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{A}/{\mathrm{cm}}^{2}$). The dispersion is measured by wave-vector-resolved BLS and exhibits a sharp change from an upward dispersion to a downward one, in agreement with theoretical predictions and micromagnetic simulations. Around the threshold current, we observe the coexistence of conventional magnons and antimagnons. Our Letter establishes antimagnons with inverted dispersion and is a first step toward exploring novel phenomena and applications due to magnon-antimagnon coupling, such as magnon amplification and magnon-antimagnon entanglement, which are part of the emerging field of antimagnonics.

Recent advances in spintronics suggest that orbital Hall currents generated by charge injection in light metals can provide nonequilibrium angular momentum without relying on strong spin–orbit coupling (SOC). Here, we examine whether such orbital currents can drive domain wall (DW) motion in an amorphous ferrimagnetic alloy, Gd25(Fe9Co1)75 (GFC), where the rare-earth sublattice offers strong SOC for orbital-to-spin conversion. We compare three representative heterostructures: Pt/GFC as a spin Hall reference, light-metal (Mn or Ti)/GFC for direct orbital-current injection, and light-metal/Pt/GFC incorporating an ultrathin Pt layer for orbital-to-spin conversion. Whereas Pt/GFC exhibits robust and reproducible spin–orbit-torque-driven DW motion, no current-driven DW motion is detected in Mn/GFC or Ti/GFC. Second-harmonic Hall measurements nevertheless reveal finite damping-like torques in both Mn/GFC and Ti/GFC, demonstrating that angular-momentum transfer into GFC does occur but is far weaker than in Pt/GFC. Inserting a 1 nm-thick Pt conversion layer strongly enhances the damping-like torque and restores DW motion. Thickness-dependent analysis further shows that DW mobility and depinning thresholds correlate with the interfacial Dzyaloshinskii–Moriya interaction and domain-wall width, highlighting weak torque conversion and insufficient interfacial stabilization of chiral DWs as key challenges for orbital-driven DW motion in light-metal/ferrimagnet heterostructures.

A key aim in spintronics is to achieve current‐induced magnetization switching via spin‐orbit torques without external magnetic fields. For this, the focus of recent work has been on introducing controlled lateral gradients across ferromagnet/heavy‐metal devices, giving variations in thickness, composition, or interface quality. However, the shallow gradients achievable with growth techniques limit the impact of this approach and understanding of the underlying physical mechanisms. Here, crystalline phase gradients are patterned on a mesoscopic length scale in tungsten thin films using direct‐write laser annealing. Through transmission electron microscopy, resistivity, and second harmonic measurements, the continuous transformation of the phase of tungsten films from the highly spin‐orbit coupled, high‐resistivity phase to the minimally spin‐orbit coupled, low‐resistivity phase with increasing laser fluence is tracked. Gradients with different steepness and arbitrary shapes are patterned in the tungsten phase. When interfaced with CoFeB, current‐induced spin‐orbit torques resulting from tungsten with a sufficiently steep gradient can switch the magnetization without an applied magnetic field. Therefore, exploiting the unique microstructure of mixed‐phase W allows precise control of the local electronic current density and direction, as well as local spin‐orbit torque efficiency, providing a new avenue for the design of efficient spintronic devices.

Orbital angular momentum provides an alternative means of exerting torques on magnetization, thereby extending electrically‐controlled magnetization switching beyond conventional spin torque mechanisms. Although current‐induced orbital torques and orbital switching of magnetization have been demonstrated, their real‐time switching dynamics remain largely unexplored. Here, we demonstrate magnetization switching of Co films driven by orbital currents from CuO _x on a nanosecond timescale, originating from the orbital Rashba‐Edelstein effect and converted into spin currents by an ultrathin Pt spacer. Using time‐resolved Hall effect detection, we separately resolve the incubation and propagation phases of switching, disentangling the roles of torque efficiency and Joule heating. We find that orbital currents can drive magnetization switching at relatively low electric fields compared to Pt devices, while Joule heating strongly assists the switching dynamics by lowering the effective energy barriers. These findings provide direct insight into orbital‐torque‐driven switching dynamics and point to both opportunities and challenges for orbitronics.