Abstract2D magnetic materials have aroused widespread research interest owing to their promising application in spintronic devices. However, exploring new kinds of 2D magnetic materials with better stability and realizing their batch synthesis remain challenging. Herein, the synthesis of air‐stable 2D Cr5Te8 ultrathin crystals with tunable thickness via tube‐in‐tube chemical vapor deposition (CVD) growth technology is reported. The importance of tube‐in‐tube CVD growth, which can significantly suppress the equilibrium shift to the decomposition direction and facilitate that to the synthesis reaction direction, for the synthesis of high‐quality Cr5Te8 with accurate composition, is highlighted. By precisely adjusting the growth temperature, the thickness of Cr5Te8 nanosheets is tuned from ≈1.2 nm to tens of nanometers, with the morphology changing from triangles to hexagons. Furthermore, magneto‐optical Kerr effect measurements reveal that the Cr5Te8 nanosheet is ferromagnetic with strong out‐of‐plane spin polarization. The Curie temperature exhibits a monotonic increase from 100 to 160 K as the Cr5Te8 thickness increases from 10 to 30 nm and no apparent variation in surface roughness or magnetic properties after months of exposure to air. This study provides a robust method for the controllable synthesis of high‐quality 2D ferromagnetic materials, which will facilitate research progress in spintronics.

Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches our understanding of two-dimensional (2D) magnetic orders and presents several advantages over ferromagnetism in spintronic applications. However, studies of 2D intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. Here, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular-beam epitaxy. We observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is ferromagnetic, and correlate its imaged zigzag spin texture with the atomic lattice structure. The AFM order exhibits an intriguing noncollinear spin reorientation under magnetic fields, consistent with its calculated moderate magnetic anisotropy. The findings of this study demonstrate the intricacy of 2D vdW magnetic materials and pave the way for their in-depth analysis.

Fe3GeTe2/MnPS3 and Fe3GeTe2/MnPSe3 van der Waals heterostructures were fabricated by mechanical exfoliation. Via the magneto-optical Kerr effect and reflected magnetic circular dichroism measurements, we have observed nearly three times enhancement of the coercive field, improvement of Curie temperature, and exchange bias effect in both heterostructures. These observations may provide new insights into the emergent heterostructure devices between itinerant ferromagnets and metal thio- and selenophosphates for both applied and fundamental research studies in magnetic correlations.

Lifting the valley degeneracy in two-dimensional transition metal dichalcogenides could promote their applications in information processing. Various external regulations, including magnetic substrate, magnetic doping, electric field, and carrier doping, have been implemented to enhance the valley splitting under the magnetic field. Here, a phase engineering strategy, through modifying the intrinsic lattice structure, is proposed to enhance the valley splitting in monolayer WSe 2 . The valley splitting in hybrid H and T phase WSe 2 is tunable by the concentration of the T phase. An obvious valley splitting of ∼4.1 meV is obtained with the T phase concentration of 31% under ±5 T magnetic fields, which corresponds to an effective Landeǵ eff factor of −14, about 3.5-fold of that in pure H-WSe 2 . Comparing the temperature and magnetic field dependent polarized photoluminescence and also combining the theoretical simulations reveal the enhanced valley splitting is dominantly attributed to exchange interaction of H phase WSe 2 with the local magnetic moments induced by the T phase. This finding provides a convenient solution for lifting the valley degeneracy of two-dimensional materials.

The discovery of 2D intrinsic magnetic materials with ultrathin structures and smooth surfaces has enabled the investigation of fundamental magnetism physics and creation of spintronic devices. By vertically stacking 2D magnetic materials with other magnetic or nonmagnetic materials, various magnetic heterostructures and spintronic devices can be developed. Recent progress in emergent 2D magnetic heterostructures and spintronic devices is reviewed. First, various typical 2D magnetic materials and methods for constructing and characterizing magnetic heterostructures are briefly introduced. Then, magnetic heterostructures composed of magnetic/nonmagnetic and magnetic/magnetic materials are summarized, and recent advances in spintronic devices fabricated using magnetic heterostructures and the device performance are presented. Finally, an outlook for the future development of 2D magnetic heterostructures and spintronic devices is presented.

The third-order optical nonlinearities and the hot electron relaxation time (τ) of random-distributed gold nanorods arrays on glass (R-GNRA) have been investigated by using Z-scan and optical Kerr effect (OKE) techniques. Large third-order optical susceptibility (χ(3)) with the value of 2.5 × 10–6 esu has been obtained around the plamsonic resonance peak under the excitation power intensity of 0.1 GW/cm2. Further decrease of the excitation power intensity down to 0.3 MW/cm2 will lead to the significant increase of χ(3) up to 6.4 × 10–4 esu. The OKE results show that the relaxation time of R-GNRA around the plasmonic peak is 13.9 ± 0.4 ps, which is more than 4 times longer than those of the individual gold nanostructures distributed in water solutions. The Finite-difference time domain simulations demonstrate that this large enhancement of χ(3) and slow down of τ are caused by the gap-induced large local field enhancement of GNRs dimers in R-GNRA. These significant results offer great opportunities for plasmonic nanostructures in applications of photonic and photocatalytic devices.

Two-dimensional (2D) magnets are crucial in the construction of 2D magnetic and spintronic devices. Many devices, including spin valves and multiple tunneling junctions, have been developed by vertically stacking 2D magnets with other functional blocks. However, owing to limited local interactions at the interfaces, the device structures are typically extremely complex. To solve this problem, the nonlocal manipulation of magnetism may be a good solution. In this study, we use the magneto–optical Kerr effect technique to demonstrate the nonlocal manipulation of magnetism in an itinerant 2D ferromagnet, Fe3GeTe2 (FGT), whose magnetism can be manipulated via an antiferromagnet/ferromagnet interface or a current-induced spin–orbital torque placed distant from the local site. It is discovered that the coupling of a small piece of MnPS3 (∼40 μm2) with FGT can significantly enhance the coercive field and emergence of exchange bias in the entire FGT flake (∼2000 μm2). Moreover, FGT flakes with different thicknesses have the same coercive field at low temperatures if they are coupled together. Our study provides an understanding of the basic magnetism of 2D itinerant ferromagnets as well as opportunities for engineering magnetism with an additional degree of freedom.

Femtosecond transient reflection spectroscopy was employed to study the carrier dynamics in few-layered MoS2 crystals prepared by either a chemical vapor deposition (CVD) technique or a mechanical exfoliation method. Three decay processes were observed in samples prepared by both methods. The faster processes were approximately 300–500 fs and could be attributed to defect-assisted scattering. The slower processes varied from 1 to 250 ps and were related to carrier–carrier and carrier–phonon scattering. Comparative studies between the CVD and exfoliated samples with different thicknesses demonstrated that faster decay processes occurred in thinner samples, in which the interface and defects had stronger effects. Wavelength-dependent transient reflection spectra demonstrated that a change in the sign of the signal occurred around the exciton absorption peaks, which could be attributed to competition of the stimulated emission and excited-state absorption processes around the exciton absorption peaks. Our results are useful for understanding the dynamic behaviors of two-dimensional materials, which are of particular importance for their applications in ultrafast optical devices and photonic devices.