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Register a new userNeel-type skyrmion in WTe2/Fe3GeTe2 van der Waals heterostructure
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The promise of high-density and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. At the same time, layered structures provide a new platform for the discovery of new physics and effects. Recently discovered long-range intrinsic magnetic orders in the two-dimensional van der Waals materials offer new opportunities. Here we demonstrate the Dzyaloshinskii-Moriya interaction and Neel-type skyrmions are induced at the WTe2/Fe3GeTe2 interface. Fe3GeTe2 is a ferromagnetic material with strong perpendicular magnetic anisotropy. We demonstrate that the strong spin orbit interaction in 1T-WTe2 does induce a large interfacial Dzyaloshinskii-Moriya interaction at the interface with Fe3GeTe2 due to the inversion symmetry breaking to stabilize skyrmions. Transport measurements show the topological Hall effect in this heterostructure for temperatures below 100 K. Furthermore, Lorentz transmission electron microscopy is used to directly image Neel-type skyrmions along with aligned and stripe-like domain structure. This interfacial coupling induced Dzyaloshinskii-Moriya interaction is estimated to have a large energy of 1.0 mJ/m^2, which can stabilize the Neel-type skyrmions in this heterostructure. This work paves a path towards the skyrmionic devices based on van der Waals heterostructures.
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The advent of ferromagnetism in two-dimensional (2D) van der Waals (vdW) magnets has stimulated high interest in exploring topological magnetic textures, such as skyrmions for use in future skyrmion-based spintronic devices. To engineer skyrmions in vdW magnets by transforming Bloch-type magnetic bubbles into Neel-type skyrmions, the heterostructure of heavy metal/vdW magnetic thin film has been made to induce interfacial Dzyaloshinskii-Moriya interaction (DMI). However, the unambiguous identification of the magnetic textures inherent to vdW magnets, e.g., whether the magnetic twists (skyrmions/domain walls) are Neel- or Bloch-type, is unclear. Here we demonstrate that the Neel- or Bloch-type magnetic twists can be tuned in the vdW magnet Fe3GeTe2 (FGT) with/without interfacial DMI. We use an in-plane magnetic field to align the modulation wavevector q of the magnetizations in order to distinguish the Neel- or Bloch-type magnetic twists. We observe that q is perpendicular to the in-plane field in the heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated angle with respect to the field direction in the thin plate by thinning bulk FGT. We find that the aligned domain wall twists hold fan-like modulations, coinciding qualitatively with our computational results.
Two-dimensional (2D) van der Waals (vdW) magnetic materials have recently been introduced as a new horizon in materials science and enable the potential applications for next-generation spintronic devices. Here, in this communication, the observations of stable Bloch-type magnetic skyrmions in single crystals of 2D vdW Fe3GeTe2 (FGT) are reported by using in-situ Lorentz transmission electron microscopy (TEM). We find the ground-state magnetic stripe domains in FGT transform into skyrmion bubbles when an external magnetic field is applied perpendicularly to the (001) thin plate with temperatures below the Curie-temperature TC. Most interestingly, a hexagonal lattice of skyrmion bubbles is obtained via field cooling manipulation with magnetic field applied along the [001] direction. Owing to their topological stability, the skyrmion bubble lattices are stable to large field-cooling tilted angles and further reproduced by utilizing the micromagnetic simulations. These observations directly demonstrate that the 2D vdW FGT possesses a rich variety of topological spin textures, being of a great promise candidate for future applications in the field of spintronics.
We demonstrate a new method of designing 2D functional magnetic topological heterostructure (HS) by exploiting the vdw heterostructure (vdw-HS) through combining 2D magnet CrI$_3$ and 2D materials (Ge/Sb) to realize new 2D topological system with nonzero Chern number (C=1) and chiral edge state. The nontrivial topology originates primarily from the CrI$_3$ layer while the non-magnetic element induces the charge transfer process and proximity enhanced spin-orbit coupling. Due to these unique properties, our topological magnetic vdw-HS overcomes the weak magnetization via proximity effect in previous designs since the magnetization and topology coexist in the same magnetic layer. Specifically, our systems of bilayer CrI$_3$/Sb and trilayer CrI$_3$/Sb/CrI$_3$ exhibit different topological ground state ranging from antiferromagnetic topological crystalline insulator (C$_M$= 2) to a QAHE. These nontrivial topological transition is shown to be switchable in a trilayer configuration due to the magnetic switching from antiferromagnetism to ferromangetism in the presence an external perpendicular electric field with value as small as 0.05 eV/A. Thus our study proposes a realistic system to design switchable magnetic topological device with electric field.
The exfoliation of two naturally occurring van der Waals minerals, graphite and molybdenite, arouse an unprecedented level of interest by the scientific community and shaped a whole new field of research: 2D materials research. Several years later, the family of van der Waals materials that can be exfoliated to isolate 2D materials keeps growing, but most of them are synthetic. Interestingly, in nature plenty of naturally occurring van der Waals minerals can be found with a wide range of chemical compositions and crystal structures whose properties are mostly unexplored so far. This Perspective aims to provide an overview of different families of van der Waals minerals to stimulate their exploration in the 2D limit.
Controlling magnetic states by a small current is essential for the next-generation of energy-efficient spintronic devices. However, it invariably requires considerable energy to change a magnetic ground state of intrinsically quantum nature governed by fundamental Hamiltonian, once stabilized below a phase transition temperature. We report that surprisingly an in-plane current can tune the magnetic state of nm-thin van der Waals ferromagnet Fe3GeTe2 from a hard magnetic state to a soft magnetic state. It is the direct demonstration of the current-induced substantial reduction of the coercive field. This surprising finding is possible because the in-plane current produces a highly unusual type of gigantic spin-orbit torque for Fe3GeTe2. And we further demonstrate a working model of a new nonvolatile magnetic memory based on the principle of our discovery in Fe3GeTe2, controlled by a tiny current. Our findings open up a new window of exciting opportunities for magnetic van der Waals materials with potentially huge impacts on the future development of spintronic and magnetic memory.
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