  Implementation of skyrmion based energy efficient and high-density data
storage devices requires aggressive scaling of skyrmion size. Ferrimagnetic
materials are considered to be a suitable platform for this purpose due to
their low saturation magnetization (i.e. smaller stray field). However, we show
by performing rigorous micromagnetic simulation that such scaling of skyrmion
size by lowering saturation magnetization while applicable in infinite films or
where the skyrmion size is very small compared to the film's lateral dimension,
does not hold in confined geometries. We also found in confined geometries,
where skyrmion occupies the whole volume of a nanodot, high saturation
magnetization helps form stable skyrmions. Specifically, such skyrmions can be
formed in 20 nm lateral dimension nanodots with high saturation magnetization
(1.6-1.71 MA/m) and moderate DMI (3 mJ/m2). This result could stimulate
experiments on implementation of highly dense skyrmion devices. In particular,
we show that Voltage Controlled Magnetic Anisotropy (VCMA) based switching
mediated by an intermediate skyrmion state can be achieved in the soft layer of
a ferromagnetic p-MTJ of lateral dimensions 20 nm with sub 1fJ/bit energy in
the presence of room temperature thermal noise with reasonable DMI ~3 mJ/m2.
