Abstract
The emergent magnetic two-dimensional (2D) materials provide ideal solid-state platforms for a broad range of applications including miniaturized spintronics, nonreciprocal optics, and magnetoelectric sensors. Owing to the general environmental sensitivity of 2D magnets, the understanding of ambient effects on 2D magnetism is critical. Apparently, the nature of itinerant ferromagnetism potentially makes metallic 2D magnets insensitive to environmental disturbance. Nevertheless, our systematic study showed that the Curie temperature of metallic 2D Fe3GeTe2 decreases dramatically in the air but thick Fe3GeTe2 exhibits self-protection. Remarkably, we found the air exposure effectively promotes the formation of multiple magnetic domains in 2D Fe3GeTe2, but not in bulk Fe3GeTe2. Our first-principles calculations support the scenario that substrate-induced roughness and tellurium vacancies boost the interaction of 2D Fe3GeTe2 with the air. Our elucidation of the thickness-dependent air-catalyzed evolution of Curie temperatures and magnetic domains in 2D magnets provides critical insights for chemically decorating and manipulating 2D magnets.
Highlights
The discovery of magnetic 2D van der Waals materials[1,2,3,4,5] ushered the long-range magnetic order into atomic-thin crystals, presenting unique solid-state platforms where magnetic order and structural order coexist and couple mutually in the ultrathin regime
Thickness characterization of few-layer Fe3GeTe2 In this work, we conducted all experiments based on a prototypical metallic van der Waals (vdW) ferromagnet Fe3GeTe215–20
Layer numbers of 2D Fe3GeTe2 samples were identified by examining the optical contrast and the Curie temperature
Summary
The discovery of magnetic 2D van der Waals (vdW) materials[1,2,3,4,5] ushered the long-range magnetic order into atomic-thin crystals, presenting unique solid-state platforms where magnetic order and structural order coexist and couple mutually in the ultrathin regime. The interaction between 2D materials and the ambient (especially O2 and H2O molecules) represents one possible scenario that explains the instability of many 2D materials such as black phosphorene[8,9] and CrI310 in the air. Elucidating the evolution of 2D magnets in the air would deliver practical guidance on how to protect 2D magnets and how to rationally engineer 2D magnetic properties. An already known phenomenon of stoichiometrydependent Curie temperature of Fe3−xGeTe212–14 suggests the sensitive role of defects in metallic 2D magnets. The large variance in the reported Curie temperatures of 2D Fe3GeTe2 of nominally the same thickness[15,16,17] indicates how sensitively the properties of 2D Fe3GeTe2 depend on the specific sample processing details
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