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Materials research has driven the development of modern nanoelectronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gatetunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.
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Atomically thin, layered van der Waals crystals represent ideal two-dimensional (2D) material systems with exceptional electronic structures. Vast opportunities in 2D material research arise from (1) emerging physical properties as a result of reduced dimensionality, and (2) new gating capabilities to modulate the material properties now that the entire crystal is a surface. The former underpins the rapid permeation of 2D materials in areas ranging from semiconductors to highly correlated materials and superconductors. The trend continues with the recent addition of magnetic crystals in the 2D material family5,6. In particular, ferromagnetic order has been observed in monolayer CrI3 in the form of a 2D Ising ferromagnet6. The intrinsic ferromagnetism in these 2D materials is unlike the ferromagnetism in conventional, molecular-beam-epitaxy-grown ultrathin metals12,13, which is determined by the interface with the substrate. This suggests device concepts based on magnetic van der Waals heterostructures14-16.
Here we report the discovery of 2D itinerant ferromagnetism in atomically thin Fe3GeTe2 (FGT). As in the case of CrI3, intrinsic magnetocrystalline anisotropy in FGT monolayers counteracts thermal fluctuations and preserves the 2D long-range ferromagnetic order, which is otherwise precluded in an isotropic...