  Itinerant ferromagnetism at room temperature is a key ingredient for spin
transport and manipulation. Here, we report the realization of
nearly-room-temperature itinerant ferromagnetism in Co doped Fe5GeTe2 thin
flakes. The ferromagnetic transition temperature TC (323 K - 337 K) is almost
unchanged when thickness is down to 12 nm and is still about 284 K at 2 nm
(bilayer thickness). Theoretical calculations further indicate that the
ferromagnetism persists in monolayer Fe4CoGeTe2. In addition to the robust
ferromagnetism down to the ultrathin limit, Fe4CoGeTe2 exhibits an unusual
temperature- and thickness-dependent intrinsic anomalous Hall effect. We
propose that it could be ascribed to the dependence of band structure on
thickness that changes the Berry curvature near the Fermi energy level subtly.
The nearly-room-temperature ferromagnetism and tunable anomalous Hall effect in
atomically thin Fe4CoGeTe2 provide opportunities to understand the exotic
transport properties of two-dimensional van der Waals magnetic materials and
explore their potential applications in spintronics.
