Magnetization Reversal and Domain Nucleation in Ultra-Thin Co/Re(0001) Capped by Graphitic C

By using X-ray magnetic circular dichroism-photoemission electron microscopy, we study the magnetic behavior of ultra-thin Co on Re(0001) covered by a single layer of graphitic carbon. The carbon overlayer is lithographically fabricated via electron-stimulated dissociative adsorption of CO and subsequent annealing to 650 K. Graphitization is found to induce perpendicular magnetic anisotropy in cobalt at a thickness in the range 4-5 atomic layers, where out-of-plane domains separated by chiral Neél type walls are observed. The graphitic overlayer efficiently protects Co from oxidation upon exposure to ambient conditions, leaving its magnetic structure completely unaffected. The magnetic response of the Co film to an external field is imaged in situ across the hysteresis loop, allowing a quantitative analysis of the field-dependent domain area and structure. Our observations pinpoint the influence of the step morphology on the local magnetic behavior. Moreover, below the saturation field, the domains with chiral walls evolve into nanometric-sized magnetic structures resembling skyrmionic bubbles for applied fields <;20 G.