  Magnetic skyrmions are chiral spin structures that have recently been
observed at room temperature (RT) in multilayer thin films. Their topological
stability should enable high scalability in confined geometries - a
sought-after attribute for device applications. While umpteen theoretical
predictions have been made regarding the phenomenology of sub-100 nm skyrmions
confined in dots, in practice their formation in the absence of an external
magnetic field and evolution with confinement remain to be established. Here we
demonstrate the confinement-induced stabilization of sub-100 nm RT skyrmions at
zero field (ZF) in Ir/Fe(x)/Co(y)/Pt nanodots over a wide range of magnetic and
geometric parameters. The ZF skyrmion size can be as small as ~50 nm, and
varies by a factor of 4 with dot size and magnetic parameters. Crucially,
skyrmions with varying thermodynamic stability exhibit markedly different
confinement phenomenologies. These results establish a comprehensive foundation
for skyrmion phenomenology in nanostructures, and provide immediate directions
for exploiting their properties in nanoscale devices.
