Band filling effects on the emergence of magnetic skyrmions: Pd/Fe and Pd/Co bilayers on Ir(111)

Structurally similar transition metal systems can have widely differing magnetic properties. A prime example of this is found for bilayers on Ir(111), where the Pd/Fe/Ir(111) ground state has a well-established noncollinear spin texture, while Pd/Co/Ir(111) presents a ferromagnetic (FM) single domain. To unravel the origins of these different magnetic behaviors, an investigation of Pd/Fe and Pd/Co bilayers on Ir(111) is here performed. Based on the obtained ab initio electronic structure, exchange coupling parameters Ji j,and Dzyaloshinskii-Moriya interactions (DMIs), we demonstrate that, although in Pd/Co/Ir(111) the DMI is significant, two ingredients play a key role in the origin of noncollinearity in Pd/Fe/Ir(111): the presence of magnetic frustrations and a much more in-plane DMI, both with a long-range influence. The Jij and DMI behaviors in both systems can be explained in terms of a simple rigid-band-like model. Also, by performing spin-dynamics simulations with the magnetic parameters tuned from the Pd/Co/Ir(111) to Pd/Fe/Ir(111) ab initio values, we could find conditions for the emergence of skyrmionic phases in the originally FM Pd/Co/Ir(111).