  Magnetic skyrmions are nanoscale topological spin structures offering great
promise for next-generation information storage technologies. The recent
discovery of sub-100 nm room temperature (RT) skyrmions in several multilayer
films has triggered vigorous efforts to modulate their physical properties for
their use in devices. Here we present a tunable RT skyrmion platform based on
multilayer stacks of Ir/Fe/Co/Pt, which we study using X-ray microscopy,
magnetic force microscopy and Hall transport techniques. By varying the
ferromagnetic layer composition, we can tailor the magnetic interactions
governing skyrmion properties, thereby tuning their thermodynamic stability
parameter by an order of magnitude. The skyrmions exhibit a smooth crossover
between isolated (metastable) and disordered lattice configurations across
samples, while their size and density can be tuned by factors of 2 and 10
respectively. We thus establish a platform for investigating functional sub-50
nm RT skyrmions, pointing towards the development of skyrmion-based memory
devices.
