Manipulation of topological spin structures at ultrathin magnetic interfaces by oxygen adsorption and interlayer exchange coupling*

Magnetic skyrmions have been investigated from fundamental physics to applications for next generation high-density information encoding. Such non-collinear magnetic structures at interfaces are usually attributed to the Dzyaloshinskii-Moriya interaction (DMI) when the inversion symmetry is broken.
Here we report two ultrathin ferromagnetic systems, where the first one demonstrates a microscopic insight on how the oxygen adsorption modulates the spin reorientation transition (SRT) of a Fe/Ni bilayer on Cu(100) and consequently impacts on the DMI of the interface. The second case shows that even in a negligible DMI interface, such as Co/Au(111), magnetic skyrmion bubbles can be stabilized at room temperature in the metastable phase of spin canting configuration within the SRT by interlayer exchange coupling across a non-magnetic spacer layer. The magnetic images are measured by X-ray magnetic circular dichroism (XMCD) based photoemission electron microscopy (PEEM), and the experimental results are discussed with the help of micromagnetic simulations.