Defect induced, layer-modulated magnetism in ultrathin metallic PtSe2

• Published in: Nature nanotechnology Vol. 14; no. 7; pp. 674 - 678
• Main Authors: Avsar, Ahmet, Ciarrocchi, Alberto, Pizzochero, Michele, Unuchek, Dmitrii, Yazyev, Oleg V., Kis, Andras
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2019; Nature Publishing Group
• Subjects: 639/766/1130/2798; 639/925/357/997; Antiferromagnetism; Chemistry and Materials Science; Couplings; Crystal defects; Crystals; Electric fields; Electrical measurement; Ferromagnetism; First principles; Letter; Magnetic fields; Magnetic properties; Magnetism; Magnetoresistance; Magnetoresistivity; Materials Science; Nanotechnology; Nanotechnology and Microengineering; Thin films; Transport properties; Two dimensional materials; Vacancies
• ISSN: 1748-3387; 1748-3395; 1748-3395
• DOI: 10.1038/s41565-019-0467-1

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 ordering 1 , a long-time subject of theoretical investigations 1 – 3 . Intrinsic, two-dimensional (2D) magnetic materials 4 – 7 are attracting increasing attention for their unique properties, which include layer-dependent magnetism 4 and electric field modulation 6 . Yet, to induce magnetism into otherwise non-magnetic 2D materials remains a challenge. Here we investigate magneto-transport properties of ultrathin PtSe 2 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 PtSe 2 are responsible for the observed layer-dependent magnetism. Given the existence of such unavoidable growth-related vacancies in 2D materials 8 , 9 , these findings can expand the range of 2D ferromagnets into materials that would otherwise be overlooked. Magneto-transport measurements on thin metallic crystals of the transition metal dichalcogenide PtSe 2 show signatures of ferro- and antiferromagnetic order depending on the number of layers and first-principles calculations suggest Pt vacancies at the surface as a plausible cause.