Manipulating exchange bias in 2D magnetic heterojunction for high-performance robust memory applications

Article https://doi.org/10.1038/s41467-023-37918-7 Manipulating exchange bias in 2D magnetic heterojunction for high-performance robust memory applications Received: 29 August 2022 3 , Check for updates 1234567890():,; 1234567890():,; Accepted: 5 April 2023 Xinyu Huang1,2,7, Luman Zhang3,7, Lei Tong1,7, Zheng Li1, Zhuiri Peng1, Runfeng Lin1, Wenhao Shi1, Kan-Hao Xue 1, Hongwei Dai3, Hui Cheng Danilo de Camargo Branco 4, Jianbin Xu 5, Junbo Han 3 , Gary J. Cheng 4 , Xiangshui Miao 1,2 & Lei Ye 1,2,6 The exchange bias (EB) effect plays an undisputed role in the development of highly sensitive, robust, and high-density spintronic devices in magnetic data storage. However, the weak EB field, low blocking temperature, as well as the lack of modulation methods, seriously limit the application of EB in van der Waals (vdW) spintronic devices. Here, we utilized pressure engineering to tune the vdW spacing of the two-dimensional (2D) FePSe3/Fe3GeTe2 heterostructures. The EB field (HEB, from 29.2 mT to 111.2 mT) and blocking temperature (Tb, from 20 K to 110 K) are significantly enhanced, and a highly sensitive and robust spin valve is demonstrated. Interestingly, this enhancement of the EB effect was extended to exposed Fe3GeTe2, due to the single-domain nature of Fe3GeTe2. Our findings provide opportunities for the producing, exploring, and tuning of magnetic vdW heterostructures with strong interlayer coupling, thereby enabling customized 2D spintronic devices in the future. Natural two-dimensional (2D) magnetic crystals and related van der Waals (vdW) heterostructures are premium candidates for studying novel magnetic phenomena and realizing innovative device structures1–8. In particular, ferromagnets-based vdW heterostructures constructed from various 2D materials have exhibited interesting properties and functionalities9–13, which offer great potential in nanoscale spintronics applications14–17. A central research goal in 2D spintronics lies in developing effective methods for generating, transmitting, and detecting spin information based on 2D vdW materials. The exchange bias (EB) effect, for which the spins of a ferromagnet (FM) are pinned by those of an antiferromagnet (AFM)18–20, has become an integral part of modern magnetism and is essential to this goal, as it provides a well-defined principal direction of spin polarization for spintronic devices. Especially, fundamental research interests and numerous device applications have widely embedded 2D spin valves and 2D MTJs for in-memory technologies such as storage media, readout sensors, and magnetic random-access memory (MRAM)7,21,22. Recently, the EB effect of magnetic 2D vdW heterostructures has been studied in CrCl3/Fe3GeTe223, MnPS3/Fe3GeTe224, MPSe3/ Fe3GeTe225, FePS3/Fe5GeTe226, and Fe3GeTe227systems. However, EB effect of 2D vdW heterostructures faces challenges such as weak EB field HEB and low blocking temperature Tb, because the existence of vdW interface gap and interfacial contamination in the 2D heterostructure tend to yield weak interlayer coupling, which cannot provide a sufficient EB field28–30. Consequently, it is crucial to effectively 1 School of Integrated Circuits, Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China. Hubei Yangtze Memory Laboratories, Wuhan 430205, China. 3Wuhan National High Magnetic Field Center and Department of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. 4School of Industrial Engineering and Birck Nanotechnology Centre, Purdue University, West Lafayette, IN 47907, USA. 5Department of Electronic Engineering, Materials Science and Technology Research Center, The Chinese University of Hong Kong, Hong Kong, China. 6State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics Chinese Academy of Sciences, Shanghai e-mail: ; ; 200083, China. 7These authors contributed equally: Xinyu Huang, Luman Zhang, Lei Tong. ; 2 Nature Communications | (2023)14:2190 1 Article enhance interlayer coupling for the purpose of a stronger EB effect in 2D heterostructure-based spintronic devices. Specifically, the sensitivity to interlayer coupling enables effective tuning of material properties through external modulation of the vdW interface distance31–33. Thus, manipulating the interlayer vdW spacing in magnetic 2D vdW heterostructures has been considered an effective way towards exchange coupling enhancement16,34,35, but was paid with less attention thus far. To obtain strong magnetic coupling rapidly without damage by manipulating the vdW interface spacing of magnetic vdW heterostructures over large areas remains a challenge, which is a key to the observation and application of the EB effect in many new spintronic devices. In this work, we demonstrated a proximity-induced EB effect in vdW magnetic heterostructures formed by Fe3GeTe2 (FGT) and FePSe3 (FPSe), which can be effectively modulated via vdW interface spacing turning with the aid of laser shocking engineering (LS). After controllably applying high-pressure shocking in an ultra-short time (few picoseconds), the vdW spacing can be permanently tuned to enhance its interlayer coupling. The enhanced interlayer coupling of the FPSe/ FGT heterostructure led to an impressive improvement of the EB field (HEB, from 29.2 to 111.2 mT) and the blocking temperature (Tb, 110 K near the Néel temperature of FPSe (113 K)). In addition, a high-quality tunneling spin valve (FPSe/FGT/h-BN/FGT) was fabricated and investigated. After LS, the enhanced magnitude of the tunneling magnetoresistance (TMR) of 154% and the field window of 320 mT at 5 K was observed, respectively. The field window is around 15 times larger than the vertical FGT/h-BN/FGT spin valves before LS in our work. Interestingly, the exposed region of FGT connected to the heterostructure (connected FGT covered by FPSe) showed a similar improvement of HEB and Tb, completely contrary to the results measured from bare FGT that was isolated from the heterostructure. This phenomenon is attributed to the single-domain nature of ferromagnetic FGT. Our findings offer new insights for regulating the AFM/FM interlayer coupling through pressure engineering and show the possibility of developing novel and extensive vdW heterostructures with adjustable interlayer coupling. Furthermore, the robust and sizable EB effect for vdW magnets persisting up to relatively high temperatures presents a significant advance for realizing practical next-generation 2D spintronics devices. Results VdW heterostructure interlayer spacing regulation via laser shocking A typical MRAM based on the EB effect is composed of a matrix of spin valves of vdW heterostructures. To obtain higher performance requirements such as high tunneling magnetoresistance and high read fault tolerance5,7, the modulation of the EB effect can enhance the interlayer coupling to optimize performance. As shown in Fig. 1a, according to the (...truncated)