Van der Waals Epitaxy Growth of 2D Single-Element Room-Temperature Ferromagnet.

2D single-element materials, which are pure and intrinsically homogeneous on the nanometer scale, could cut the time-consuming material-optimization process and circumvent the impure phase, bringing about new opportunities to explore new physics and applications. Herein, for the first time, we demonstrated the synthesis of ultrathin cobalt single-crystalline nanosheets with sub-millimeter scale via van der Waals epitaxy (vdWE) using a dihalides reduction strategy. The thickness can be as low as ∼6 nm. Density functional theory calculations reveal their intrinsic ferromagnetic nature and epitaxial mechanism: that is, the synergistic effect between van der Waals interactions and surface energy minimization dominates the growth process for ultrathin cobalt nanosheets. The as-grown cobalt nanosheets exhibit ultrahigh blocking temperature above 710 K and in-plane magnetic anisotropy. Electrical transport measurements further reveals that cobalt nanosheets have significant magnetoresistance (MR) effect, and could realize a unique coexistence of positive MR and negative MR under different magnetic field configurations, which can be attributed to the competition and cooperation effect among ferromagnetic interaction, orbital scattering and electronic correlation. These results provide a valuable case study for synthesizing 2D elementary metal crystals with pure phase and room-temperature ferromagnetism, and pave the way for investigating new physics and related applications in spintronics. This article is protected by copyright. All rights reserved.