  Skyrmions are localized solitonic spin textures with protected topology,
which are promising as information carriers in ultra-dense and energy-efficient
logic and memory devices. Recently, magnetic skyrmions have been observed in
magnetic thin films, and are stabilized by the extrinsic interfacial
Dzyaloshinskii-Moriya interaction (DMI) and/or external magnetic fields. The
specific effects in magnetic monolayer materials have not been thoroughly
studied. Here, we investigate the intrinsic magnetic skyrmions in a family of
monolayer Janus van der Waals magnets, MnSTe, MnSeTe, VSeTe, and MnSSe, by the
first-principles calculations combined with the micromagnetic simulations. The
monolayer Janus MnSTe, MnSeTe, and VSeTe with out-of-plane geometric asymmetry
and strong spin-orbit coupling (SOC) have a large intrinsic DMI, which could
stabilize a sub-50 nm intrinsic skyrmions in monolayer MnSTe and MnSeTe at zero
magnetic field. While monolayer VSeTe with in-plane easy axis forms magnetic
domain rather than skyrmions. Moreover, the size and shape of skyrmions can be
tuned by an external magnetic field. Therefore, our work motivates a new vista
for seeking intrinsic skyrmions in atomic-scale magnets.
