Stabilizing spin spirals and isolated skyrmions at low magnetic field exploiting vanishing magnetic anisotropy

The stabilization of non-collinear chiral magnetic structure is usually attributed to a large Dzyaloshinskii-Moriya interaction (DMI). DMI is enhanced at surfaces and interfaces via the hybridization of the magnetic atoms with 5d elements. Here, we show that a strong DMI is not a necessary condition to obtain a chiral magnetic order in ultra-thin films. Our spin-polarized scanning tunneling microscopy study show that Co/Ru(0001) possesses a spin spiral ground state, although the DMI is weak. Under moderated magnetic field (≈150 mT) isolated skyrmion can be stabilized. We attribute the stability of this spin texture to the vanishing of the magnetic anisotropy energy.