Two-dimensional itinerant ferromagnetism in atomically thin Fe3GeTe2

Abstract

Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins1,2,3,4. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that Fe3GeTe2 (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (TC) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work introduces an atomically thin ferromagnetic metal that could be useful for the study of controllable 2D itinerant ferromagnetism and for engineering spintronic vdW heterostructures5.

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Fig. 1: Structure and transport characterization of thin FGT flakes.
Fig. 2: RMCD measurements of monolayer FGT.
Fig. 3: Criticality analysis for FGT flakes of different thicknesses.
Fig. 4: Intermediate magnetic states and thickness-dependent phase diagram of FGT.

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Acknowledgements

The authors thank M. den Nijs for the helpful discussion. The work at the University of Washington is mainly supported by NSF MRSEC 1719797. B.H. and D.X. are supported by Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0012509). W.Y. is supported by the Croucher Foundation (Croucher Innovation Award) and the HKU ORA. Synthesis efforts at ORNL (AFM) were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. X.X. and X.Z. acknowledge NSF MRSECs at the University of Washington (DMR-1719797) and the University of Columbia (DMR-1420634) for supporting the exchange visit. X.X. and J.H.C. acknowledge the support from the State of Washington funded Clean Energy Institute and from the Boeing Distinguished Professorship in Physics. Work at Rutgers (W. Wang and W. Wu) was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US Department of Energy under Award number DE-SC0018153.

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X.X., J.H.C. and A.M. conceived the experiment. P.M. and A.M. synthesized and characterized the bulk FGT crystal, assisted by J.S. X.Z. designed the exfoliation on a gold substrate approach. Z.F. and B.H. fabricated the samples, acquired the experimental data, assisted by T.S. and supervised by X.X., J.H.C. and D.C. W.Wang and W.Wu performed and analysed the MFM results. D.X. and W.Y. provided theoretical support. Z.F., B.H., X.X., J.H.C. and D.C. wrote the manuscript with input from all authors. All the authors discussed the results.

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Correspondence to Jiun-Haw Chu or Xiaodong Xu.

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Supplementary Figures 1-6, Supplementary References 1–4

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Fei, Z., Huang, B., Malinowski, P. et al. Two-dimensional itinerant ferromagnetism in atomically thin Fe3GeTe2. Nature Mater 17, 778–782 (2018). https://doi.org/10.1038/s41563-018-0149-7

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