Two-dimensional ferromagnetic superlattices

Journal Article · 15 December 2019 · National Science Review

DOI: https://doi.org/10.1093/nsr/nwz205 · OSTI ID:2470874

Liu, Shanshan ^[1]; Yang, Ke ^[1]; Liu, Wenqing ^[2]; Zhang, Enze ^[1]; Li, Zihan ^[1]; Zhang, Xiaoqian ^[3]; Liao, Zhiming ^[4]; Zhang, Wen ^[5]; Sun, Jiabao ^[6]; Yang, Yunkun ^[1]; Gao, Han ^[4]; Huang, Ce ^[1]; Ai, Linfeng ^[1]; Wong, Ping Kwan Johnny ^[5]; Wee, Andrew Thye Shen ^[5]; N’Diaye, Alpha T. ^[7]; Kou, Xufeng ^[8]; Zou, Jin ^[4]; Xu, Yongbing ^[3]; Wu, Hua ^[1] ; Xiu, Faxian  ^[9]

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1. Fudan University, Shanghai (China)
2. University of London, Egham (United Kingdom)
3. Nanjing University (China)
4. University of Queensland, Brisbane, QLD (Australia)
5. National University of Singapore (Singapore)
6. Royal Holloway University of London, Egham (United Kingdom)
7. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
8. ShanghaiTech University (China)
9. Fudan University, Shanghai (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)

Mechanically exfoliated two-dimensional ferromagnetic materials (2D FMs) possess long-range ferromagnetic order and topologically nontrivial skyrmions in few layers. However, because of the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature (T_C) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their T_C, particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-T_C 2D FM Fe₃GeTe₂ (FGT) via A-type antiferromagnetic material CrSb (CS) which strongly couples to FGT. A superlattice structure of (FGT/CS)_n, where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally discovered that T_C of 4-layer Fe₃GeTe₂ can be significantly enhanced from 140 K to 230 K because of the interfacial ferromagnetic coupling. Meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic CrSb into a ferrimagnetic state as evidenced by double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the T_C enhancement of the Fe₃GeTe₂ films, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in a 4-layer FGT/CS superlattice, T_C can be further enhanced to near room temperature. Our results provide a feasible approach for enhancing the magnetic order of few-layer 2D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 2470874
• Journal Information: National Science Review, Journal Name: National Science Review Journal Issue: 4 Vol. 7; ISSN 2095-5138
• Publisher: China Science PublishingCopyright Statement
• Country of Publication: United States
• Language: English