Abstract
Van der Waals magnetic materials are promising candidates for spintronics and testbeds for exotic magnetic phenomena in low dimensions. The two-dimensional (2D) limit in these materials is typically reached by mechanically breaking the van der Waals interactions between layers. Alternative approaches to producing large amounts of flakes rely on wet methods such as liquid-phase exfoliation (LPE). Here, we report an optimized route for obtaining monolayers of magnetic cylindrite by LPE. We show that the selection of exfoliation times is the determining factor in producing a statistically significant amount of monolayers while keeping relatively big flake areas (~1 µm2). We show that the cylindrite lattice is preserved in the flakes after LPE. To study the electron transport properties, we have fabricated field-effect transistors based on LPE cylindrite. Flakes are deterministically positioned between nanoscale electrodes by dielectrophoresis. We show that dielectrophoresis can selectively move the larger flakes into the devices. Cylindrite nanoscale flakes present a p-doped semiconducting behaviour, in agreement with the mechanically exfoliated counterparts. Alternating current (AC) admittance spectroscopy sheds light on the role played by potential barriers between different flakes in terms of electron transport properties. The present large-scale exfoliation and device fabrication strategy can be extrapolated to other families of magnetic materials.
Highlights
Layered magnetic materials [1,2,3] are emerging as the latest acquisition of the van der Waals materials family and their heterostructures [4,5]
The suspension of liquid-phase exfoliation (LPE) cylindrite nanoflakes in iPrOH is obtained via a two-step process: (i) 1 h sonication of 1 mg·mL−1 dispersion of cylindrite powder in iPrOH in an ultrasonic bath kept at 20 ◦C; followed by (ii) 30 min centrifugation of the as-prepared suspension (990 g, 20 ◦C, Beckman Coulter Allegra X-15R, FX6100 rotor, radius 9.8 cm) in order to discard thicker or non-exfoliated flakes
The fine tuning of sonication and centrifugation times can be used to obtain a range of flake areas and thicknesses. We show that this approach provides flakes down to the monolayer limit with average areas of 1 μm2
Summary
Layered magnetic materials [1,2,3] are emerging as the latest acquisition of the van der Waals (vdW) materials family and their heterostructures [4,5]. The most widespread method to obtain thin flakes of vdW materials, from few to a single layer, is the mechanical exfoliation of the bulk compound; that is, the repeated peeling of bulk material with an adhesive tape that breaks the van der Waals forces between layers [13]. This method results in clean flakes, their placement in electrical devices, and the formation of heterostructures by deterministic mechanical stamping [14,15]. AC admittance spectroscopy gives light to the role played by potential barriers between different flakes in electron transport properties
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