  Skyrmions can be stabilized in magnetic systems with broken inversion
symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions
(DMI). Further, compensation of magnetic moments in ferrimagnetic materials can
significantly reduce magnetic dipolar interactions, which tend to favor large
skyrmions. Tuning DMI is essential to control skyrmion properties, with
symmetry breaking at interfaces offering the greatest flexibility. However, in
contrast to the ferromagnet case, few studies have investigated interfacial DMI
in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic
CoGd films by Brillouin light scattering. We demonstrate the ability to control
DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic
layer thickness. The DMI thickness dependence confirms its interfacial nature.
In addition, magnetic force microscopy reveals the ability to tune DMI in a
range that stabilizes sub-100 nm skyrmions at room temperature in zero field.
Our work opens new paths for controlling interfacial DMI in ferrimagnets to
nucleate and manipulate skyrmions.
