  We demonstrate that magnetic skyrmions with a mean diameter around 60 nm can
be stabilized at room temperature and zero external magnetic field in an
exchange-biased Pt/Co/NiFe/IrMn multilayer stack. This is achieved through an
advanced optimization of the multilayer stack composition in order to balance
the different magnetic energies controlling the skyrmion size and stability.
Magnetic imaging is performed both with magnetic force microscopy and scanning
Nitrogen-Vacancy magnetometry, the latter providing unambiguous measurements at
zero external magnetic field. In such samples, we show that exchange bias
provides an immunity of the skyrmion spin texture to moderate external magnetic
field, in the tens of mT range, which is an important feature for applications
as memory devices. These results establish exchange-biased multilayer stacks as
a promising platform towards the effective realization of memory and logic
devices based on magnetic skyrmions.
