Skyrmions in twisted van der Waals magnets

Magnetic skyrmions in two-dimensional (2D) chiral magnets are often stabilized by a combination of a Dzyaloshinskii-Moriya interaction and an external magnetic field. Here, we show that skyrmions can also be stabilized in twisted moir\'e superlattices with a Dzyaloshinskii-Moriya interaction in the absence of an external magnetic field. Our setup consists of a 2D ferromagnetic layer twisted on top of an antiferromagnetic substrate. The coupling between the ferromagnetic layer and the substrate generates an effective alternating exchange field. We find a large region of the skyrmion crystal phase when the length scales of the moir\'e periodicity and skyrmions are compatible. Unlike chiral magnets under a magnetic field, skyrmions in moir\'e superlattices show an enhanced stability for the easy-axis (Ising) anisotropy which can be essential to realize skyrmions since most van der Waals magnets possess easy-axis anisotropy.