Stabilization of magnetic bubbles in [Ni/Co]$_{n}$ multilayers on an oxygen-reconstructed Nb(110) surface via an ultra-thin Cu interlayer

Magnetic thin films hosting topological spin textures, such as magnetic skyrmions, hold high potential for breakthroughs in the field of spintronics, due to good scalability and energy efficiency. Novel computational architectures such as memory-in-logic devices rely on material platforms able to host those topological spin textures. Furthermore, recently proposed designs of novel quantum information technologies are based on heterostructures where topological spin textures are in direct proximity to a superconducting layer. Here, we demonstrate the stabilization of out-of-plane magnetic bubbles in highly ordered [Ni/Co]$_{n}$ multilayers on a Nb(110) single crystal. This is achieved without the need for removal of the well-known Nb(110)-oxide surface reconstruction, due to the introduction of a one-atom-thick Cu interlayer in between the Nb substrate and the magnetic multilayer. The Cu interlayer generates a well-ordered hexagonal surface, which is key for the epitaxial growth of the [Ni/Co]$_{n}$ multilayers hosting the desired out-of-plane anisotropy. The magnetic ground state of the prepared material stacks is directly imaged via spin-polarized low energy electron microscopy (SPLEEM), revealing the presence of magnetic bubble domains with lateral sizes as small as 450 nm.