  We report the observation of a Pt layer thickness dependence on the induced
interfacial Dzyaloshinskii-Moriya interaction in ultra-thin
Pt($d_{\text{Pt}}$)/CoFeB films. Taking advantage of the large spin-orbit
coupling of the heavy metal, the interfacial Dzyaloshinskii-Moriya interaction
is quantified by Brillouin light scattering measurements of the frequency
non-reciprocity of spin-waves in the ferromagnet. The magnitude of the induced
Dzyaloshinskii-Moriya coupling is found to saturate to a value $0.45$
mJ$/$m${}^2$ for Pt thicknesses larger than $\sim 2$ nm. The experimental
results are explained by analytical calculations based on the 3-site indirect
exchange mechanism that predicts a Dzyaloshinskii-Moriya interaction at the
interface between a ferromagnetic thin layer and a heavy metal. Our findings
open up a way to control and optimize chiral effects in ferromagnetic thin
films through the thickness of the heavy metal layer.
