Letter | Published:

Defect induced, layer-modulated magnetism in ultrathin metallic PtSe2

Abstract

Defects are ubiquitous in solids and often introduce new properties that are absent in pristine materials. One of the opportunities offered by these crystal imperfections is an extrinsically induced long-range magnetic ordering1, a long-time subject of theoretical investigations1,2,3. Intrinsic, two-dimensional (2D) magnetic materials4,5,6,7 are attracting increasing attention for their unique properties, which include layer-dependent magnetism4 and electric field modulation6. Yet, to induce magnetism into otherwise non-magnetic 2D materials remains a challenge. Here we investigate magneto-transport properties of ultrathin PtSe2 crystals and demonstrate an unexpected magnetism. Our electrical measurements show the existence of either ferromagnetic or antiferromagnetic ground-state orderings that depends on the number of layers in this ultrathin material. The change in the device resistance on the application of a ~25 mT magnetic field is as high as 400 Ω with a magnetoresistance value of 5%. Our first-principles calculations suggest that surface magnetism induced by the presence of Pt vacancies and the Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange couplings across ultrathin films of PtSe2 are responsible for the observed layer-dependent magnetism. Given the existence of such unavoidable growth-related vacancies in 2D materials8,9, these findings can expand the range of 2D ferromagnets into materials that would otherwise be overlooked.

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Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

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Acknowledgements

We acknowledge A. H. C. Neto for fruitful insights and discussions. We acknowledge the help of Z. Benes (CMI) with electron-beam lithography and K. Marinov for training on the measurement set-up. A.A., A.C., D.U. and A.K. acknowledge support by the European Research Council (ERC, grant 682332), Swiss National Science Foundation (grant 153298) and Marie Curie-Sklodowska COFUND (grant 665667). A.K. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no 785219 (Graphene Flagship). M.P. and O.V.Y. acknowledge support by the Swiss National Science Foundation (grants 162612 and 172543). First-principles simulations were carried out at the Swiss National Supercomputing Centre (CSCS) under project s832.

Author information

A.A. and A.K. designed the experiments. A.A. and A.C. fabricated the samples. A.A. performed the transport measurements. A.C. and D.U. performed the Raman spectroscopy measurements. M.P. and O.V.Y. devised the theoretical models and performed the first-principles calculations. A.A., M.P. and A.K. wrote the manuscript with input from A.C.

Correspondence to Ahmet Avsar or Andras Kis.

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Fig. 1: Device structure and basic characterization.
Fig. 2: Bias and temperature-dependent magnetoresistance measurements in device A.
Fig. 3: Bias and temperature-dependent magnetoresistance measurements in device B (~9 nm thick).
Fig. 4: Layer-dependent magnetoresistance measurements.
Fig. 5: Theoretical investigations of PtSe2.