Real-space imaging reveals rich microscopic details of the quantum spin Hall edge conduction in monolayer WTe2.

The magnetic properties in two-dimensional van der Waals materials depend sensitively on structure. CrI3, as an example, has been recently demonstrated to exhibit distinct magnetic properties depending on the layer thickness and stacking order. Bulk CrI3 is ferromagnetic (FM) with a Curie temperature of 61 K and a rhombohedral layer stacking, while few-layer CrI3 has a layered antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a monoclinic stacking. In this work, we use cryogenic magnetic force microscopy to investigate CrI3 flakes in the intermediate thickness range (25 -200 nm) and find that the two types of magnetic orders hence the stacking orders can coexist in the same flake, with a layer of ~13 nm at each surface being in the layered AFM phase similar to few-layer CrI3 and the rest in the bulk FM phase. The switching of the bulk moment proceeds through a remnant state with nearly compensated magnetic moment along the c-axis, indicating formation of c-axis domains allowed by a weak interlayer coupling strength in the rhombohedral phase. Our results provide a comprehensive picture on the magnetism in CrI3 and point to the possibility of engineering magnetic heterostructures within the same material.

opportunities for exploring magnetism, and toward spintronic applications in the 2D limit. [7][8][9] Among all the interface engineered heterostructures based on vdW layered systems, magnetic proximity effect is integral to manipulating spintronic, [10][11][12] superconducting, [13][14][15] and topological phenomena. [16][17][18] Magnetic skyrmions have been well studied due to their nontrivial topology, which leads to many interesting fundamental and dynamical properties. [19][20][21] These have been reported mostly for noncentrosymmteric single crystals, [22][23][24] ultrathin epitaxial system, [25,26] and magnetic multilayers. [27][28][29][30][31] Recently Néel-type skyrmions were observed in a vdW ferromagnet interfaced with an oxidized layer [32] or a transition metal dichalcogenide [33] with a control of the skyrmion phase through tuning of the ferromagnet thickness. Furthermore, with a variety of vdW magnets, skrymions phase could be created in their new interfaces with unique properties.Materials hosting multiple skyrmion phases add richness to the field, with an additional degree of freedom in designing Multiple magnetic skyrmion phases add an additional degree of freedom for skyrmion-based ultrahigh-density spin memory devices. Extending the field to 2D van der Waals magnets is a rewarding challenge, where the realizable degree of freedoms (e.g., thickness, twist angle, and electrical gating) and high skyrmion density result in intriguing new properties and enhanced functionality. In this work, a van der Waals interface, formed by two 2D ferromagnets Cr 2 Ge 2 Te 6 and Fe 3 GeTe 2 with a Curie temperature of ≈65 and ≈205 K, respectively, hosting two groups of magnetic skyrmions, is reported. Two sets of topological Hall effect signals are observed below 6s0 K when Cr 2 Ge 2 Te 6 is magnetically ordered. These two groups of skyrmions are directly imaged using magnetic force microscopy, and supported by micromagnetic simulations. Interestingly, the magnetic skyrmions persist in the heterostructure with zero applied magnetic field. The results are promising for the realization of skyrmionic devices based on van der Waals heterostructures hosting multiple skyrmion phases.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202110583.