Exchange bias and spin–orbit torque in the Fe3GeTe2-based heterostructures prepared by vacuum exfoliation approach

Abstract

Magnetic two-dimensional (2D) van der Waals (vdWs) materials are receiving increased attention due to their exceptional properties and potential applications in spintronic devices. Because exchange bias and spin–orbit torque (SOT)-driven magnetization switching are basic ingredients for spintronic devices, it is of pivotal importance to demonstrate these effects in the 2D vdWs material-based magnetic heterostructures. In this work, we employ a vacuum exfoliation approach to fabricate Fe3GeTe2 (FGT)/Ir22Mn78 (IrMn) and FGT/Pt bilayers, which have high-quality interfaces. An out-of-plane exchange bias of up to 895 Oe is obtained in the former bilayer, which is larger than that of the previously studied bilayers. In the latter bilayer, the SOT switching of the perpendicularly magnetized FGT is realized, which exhibits higher SOT-driven switching performance compared to the previously studied FGT/Pt bilayer devices with interfacial oxidation. The minimum of SOT efficiency is further determined to be 0.18 ± 0.04, comparable to the previously reported values for the Pt/Co and Pt/CoFeB bilayers. This work highlights the importance of the high-quality interface for the exchange bias and SOT effect and may pave the way for implementing 2D vdWs in spintronic devices.

Two-Dimensional Van Der Waals Materials for Spin-Orbit Torque Applications

“…SOTs in FGT/Pt heterostructures have been studied by Wang et al (2019) and Alghamdi et al (2019). Similar results show that the lower-bound damping-like torque in FGT/Pt bilayer is about 0.1, and the critical current density for magnetization switching is in the order of 10 7 A/cm 2 , as shown in Figure 3A-C Most recently, by further improving the quality of the interface, the minimum of SOT efficiency in FGT/Pt is determined to be 0.18 (Zhang et al, 2021), which is higher than that in previous studies, and comparable to the values for the Pt/Co and Pt/CoFeB bilayers (Pai et al, 2015;Nguyen et al, 2016), indicating the importance of the high-quality interface for SOT devices.…”

“…On the other hand, by mechanical exfoliation, multiple combinations of van der Waals heterostructures can be stacked, which is beneficial to develop novel SOT devices. However, potential problems such as organic residues, hydrolysis, and oxidation at the interface during exfoliation may become key factors restricting the performance of SOT devices (Zhang et al, 2021).…”

“…At present, there are still difficulties in preparing large-area 2D vdW materials with high quality and controllable thickness, thus interfacial engineering remains a challenge for most of the 2D SOT devices. Innovative exfoliation techniques such as the vacuum exfoliation approach (Zhang et al, 2021) need to be developed. CVD methods could be further optimized, especially in the synthesis of large-scaled complex alloys.…”

Hidden interplay of current-induced spin and orbital torques in bulk Fe$_3$GeTe$_2$

“…Since then, FGT has been researched extensively and it shows exciting characteristics such as being a nodal line semimetal [8] and exhibiting skyrmionic spin textures [9,10]. In particular, recent experiments demonstrated magnetization switching in Pt/FGT heterostructures via current-induced spin-orbit torque [11,12].…”

“…We note that the magnetization switching demonstrated in Refs. [11,12] utilized the spin-Hall effect in Pt, where the physical principle is analogous to conventional SOT devices with transition-metal bilayers. A unique role played by the low crystal symmetry of FGT was pointed out by Johansen et al [13], which allows for the generation of a current-induced torque without the need of an interface.…”