Above-room-temperature chiral skyrmion lattice and Dzyaloshinskii-Moriya interaction in a van der Waals ferromagnet Fe3-xGaTe2.

Skyrmions in existing 2D van der Waals (vdW) materials have primarily been limited to cryogenic temperatures, and the underlying physical mechanism of the Dzyaloshinskii-Moriya interaction (DMI), a crucial ingredient for stabilizing chiral skyrmions, remains inadequately explored. Here, we report the observation of Néel-type skyrmions in a vdW ferromagnet Fe3-xGaTe2 above room temperature. Contrary to previous assumptions of centrosymmetry in Fe3-xGaTe2, the atomic-resolution scanning transmission electron microscopy reveals that the off-centered FeΙΙ atoms break the spatial inversion symmetry, rendering it a polar metal. First-principles calculations further elucidate that the DMI primarily stems from the Te sublayers through the Fert-Lévy mechanism. Remarkably, the chiral skyrmion lattice in Fe3-xGaTe2 can persist up to 330 K at zero magnetic field, demonstrating superior thermal stability compared to other known skyrmion vdW magnets. This work provides valuable insights into skyrmionics and presents promising prospects for 2D material-based skyrmion devices operating beyond room temperature.

Strain-Induced Reversible Motion of Skyrmions at Room Temperature.

Magnetic skyrmions are topologically protected swirling spin textures with great potential for future spintronic applications. The ability to induce skyrmion motion using mechanical strain not only stimulates the exploration of exotic physics but also affords the opportunity to develop energy-efficient spintronic devices. However, the experimental realization of strain-driven skyrmion motion remains a formidable challenge. Herein, we demonstrate that the inhomogeneous uniaxial compressive strain can induce the movement of isolated skyrmions from regions of high strain to regions of low strain at room temperature, which was directly observed using an in situ Lorentz transmission electron microscope with a specially designed nanoindentation holder. We discover that the uniaxial compressive strain can transform skyrmions into a single domain with in-plane magnetization, resulting in the coexistence of skyrmions with a single domain along the direction of the strain gradient. Through comprehensive micromagnetic simulations, we reveal that the repulsive interactions between skyrmions and the single domain serve as the driving force behind the skyrmion motion. The precise control of skyrmion motion through strain provides exciting opportunities for designing advanced spintronic devices that leverage the intricate interplay between strain and magnetism.

Large-scale fabrication and Mo vacancy-induced robust room-temperature ferromagnetism of MoSe2 thin films.

Molybdenum selenide (MoSe2) has recently attracted particular attention due to its room-temperature ferromagnetism (RTFM) and related spintronic applications. However, not only does the FM mechanism of MoSe2 remain controversial, but also the synthesis of MoSe2 thin films with robust RTFM is still an unmet challenge. Here it is shown that using polymer-assisted deposition under appropriate growth conditions, large-scale (4 cm × 4 cm) synthesis of MoSe2 thin films with robust RTFM and a smooth surface (roughness average ∼0.22 nm) is possible. A new record-high saturation magnetization (6.69 emu g-1) is achieved in the prepared MoSe2 thin films, about 5 times the previously reported record (1.39 emu g-1) obtained in 2H-MoSe2 nanoflakes. Meanwhile, the coercivity of the MoSe2 films can be tuned down to a new record-low value (5.0 Oe), one-tenth of the previously reported record. Notably, detailed analysis combining the experimental findings and calculation results shows that the robust RTFM mainly comes from the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction between the magnetic moments induced by abundant Mo vacancies (VMos) in the MoSe2 films. Our results give insights into the large-scale production and robust RTFM of MoSe2 thin films and may provide a platform for designing and fabricating spintronic materials and devices based on transition-metal dichalcogenides.

Synthesis and high-temperature ferromagnetism of Fe-doped SiGe diluted magnetic semiconductor thin films.

Fe-doped SiGe (Si0.25Ge0.75:Fex, x = 0.01, 0.025, and 0.05) thin films were prepared by radio frequency magnetron sputtering and subsequent rapid thermal annealing on a Ge (100) substrate and their structural, magnetic and magneto-transport properties were investigated. Structural characterization using AFM, SEM, XRD, and HRTEM shows that the obtained samples are polycrystalline and their lattice constants increase with the Fe concentration. Analysis of their electronic and spintronic states using XPS and XMCD reveals that Fe dopants mainly exist as substitutional Fe2+ ions in the SiGe lattice, providing both local magnetic moments and hole carriers. Furthermore, magnetization measurements indicate that all the samples exhibit ferromagnetism, and their Curie temperature increases with the Fe concentration up to 294 K; meanwhile, magneto-transport measurements reveal a giant magnetoresistance (GMR) effect of over 800% and an anomalous Hall effect (AHE), as well as semiconducting behaviors, in the samples. Further analysis suggests that the ferromagnetism comes from a hole-mediated process originating from substitutional Fe dopants in the SiGe matrix and this is enhanced by the tensile strain in the films. The synthesis and high-temperature ferromagnetism of Fe-doped SiGe thin films may play a key role in group IV-based spintronic applications.