The manipulation of magnetism provides a unique opportunity for the development of data storage and spintronic applications. Until now, electrical control, pressure tuning, stacking structure dependence, and nanoscale engineering have been realized. However, as the dimensions are decreased, the decrease of the ferromagnetism phase transition temperature (T c) is a universal trend in ferromagnets. Here, we make a breakthrough to realize the synthesis of 1 and 2 unit cell (UC) Cr2Te3 and discover a room-temperature ferromagnetism in two-dimensional Cr2Te3. The newly observed T c increases strongly from 160 K in the thick flake (40.3 nm) to 280 K in 6 UC Cr2Te3 (7.1 nm). The magnetization and anomalous Hall effect measurements provided unambiguous evidence for the existence of spontaneous magnetization at room temperature. The theoretical model revealed that the reconstruction of Cr2Te3 could result in anomalous thickness-dependent T c. This dimension tuning method opens up a new avenue for manipulation of ferromagnetism.
generally prepared by molecular beam epitaxy (MBE) or wet-chemical methods, have started attracting attention. [11][12][13][14][15][16] However, due to the limitation of their small lateral size, the electronic properties and applications of 2D copper chalcogenides have rarely been touched despite dimensionality plays a crucial role in determining their properties. For example, the quantum confinement effect in reduced dimensionalities is considered to be effective on enhancing the power factor of thermoelectric materials, thereby improving the thermoelectric performance. [17] Thus, a novel synthetic strategy to prepare 2D copper chalcogenides with nanometer thickness and regular structures is needed to be developed.In addition, the small migration barrier of Cu ions, originated from their relatively loose bonding in copper chalcogenides, would result in a low defect formation energy and ubiquitous Cu vacancies. [4,8,18] Considering that ions/defects motion is the basis for resistive switching (RS) devices and related information storage technologies, it is natural to expect a memristive behavior with small switching thresholds in copper chalcogenides, which is highly desired in memristor research since most of 2D memristors own a switching voltage larger than 1 V. [19][20][21][22][23][24] Memristor-based electronics are a mainstream effort to realize low-power artificial intelligence through their analog multiply-accumulate operations in non von Neumann architecture, [25][26][27] and also they can be a promising platform for mimicking the actual biological synaptic connectivity maps. [26] Recently, memristive switching behavior was observed in relatively thick copper sulfide films, and was attributed to the reversible migration of Cu vacancies, [28] an intrinsic nature of copper chalcogenides. As a contrast, the reported 2D memristors mostly require either active metal (such as Cu and Ag) electrodes [24,[29][30][31] or precise control of oxidation to produce extrinsic mobilizable ions/defects/grain boundaries, [23,[32][33][34] which obviously restricts their further applications in an open architecture such as fabricating 2D heterostructures.van der Waals (vdW) epitaxy, which is based on relatively weak vdW interactions between the epitaxial layers and growth substrates, has been proven to be effective in synthesizing 2D planar structures from both layered and nonlayered materials. [3,35,36] In this work, we demonstrate the controllable preparation of a series of 2D binary copper chalcogenideCopper chalcogenides represent a class of materials with unique crystal structures, high electrical conductivity, and earth abundance, and are recognized as promising candidates for next-generation green electronics. However, their 2D structures and the corresponding electronic properties have rarely been touched. Herein, a series of ultrathin copper chalcogenide nanosheets with thicknesses down to two unit cells are successfully synthesized, including layered Cu 2 Te, as well as nonlayered CuSe and Cu 9 S 5 , via van der Wa...
The discovery of magnetism in ultrathin crystals opens up opportunities to explore new physics and to develop next-generation spintronic devices. Nevertheless, two-dimensional magnetic semiconductors with Curie temperatures higher than room temperature have rarely been reported. Ferrites with strongly correlated d-orbital electrons may be alternative candidates offering two-dimensional high-temperature magnetic ordering. This prospect is, however, hindered by their inherent three-dimensional bonded nature. Here, we develop a confined-van der Waals epitaxial approach to synthesizing air-stable semiconducting cobalt ferrite nanosheets with thickness down to one unit cell using a facile chemical vapor deposition process. The hard magnetic behavior and magnetic domain evolution are demonstrated by means of vibrating sample magnetometry, magnetic force microscopy and magneto-optical Kerr effect measurements, which shows high Curie temperature above 390 K and strong dimensionality effect. The addition of room-temperature magnetic semiconductors to two-dimensional material family provides possibilities for numerous novel applications in computing, sensing and information storage.
Two-dimensional (2D) iron chalcogenides (FeX, X = S, Se, Te) are emerging as an appealing class of materials for a wide range of research topics, including electronics, spintronics, and catalysis. However, the controlled syntheses and intrinsic property explorations of such fascinating materials still remain daunting challenges, especially for 2D nonlayered Fe7S8 with mixed-valence states and high conductivity. Herein, we design a general and temperature-mediated chemical vapor deposition (CVD) approach to synthesize ultrathin and large-domain Fe7S8 nanosheets on mica substrates, with the thickness down to ∼4.4 nm (2 unit-cell). Significantly, we uncover a quadratic-dependent unsaturated magnetoresistance (MR) with out-of-plane anisotropy in 2D Fe7S8, thanks to its ultrahigh crystalline quality and high conductivity (∼2.7 × 105 S m–1 at room temperature and ∼1.7 × 106 S m–1 at 2 K). More interestingly, the CVD-synthesized 2D Fe7S8 nanosheets maintain robust environmental stability for more than 8 months. These results hereby lay solid foundations for synthesizing 2D nonlayered iron chalcogenides with mixed-valence states and exploring fascinating quantum phenomena.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.