  Monosilicides of 3d-metals frequently show a chiral magnetic ordering with
the absolute configuration defined by the chirality of the crystal structure
and the sign of the Dzyaloshinskii-Moriya interaction (DMI). Structural and
magnetic chiralities are probed here for Fe$_{1-x}$Co$_x$Si series and their
mutual relationship is found to be dependent on the chemical composition. The
chirality of crystal structure was previously shown to be governed by crystal
growth, and the value of the DMI is nearly the same for all monosilicides of
Fe, Co and Mn. Our findings indicate that the sign of the DMI in
Fe$_{1-x}$Co$_x$Si is controlled by the Co composition $x$, thus, opening a
route towards controlled design of chiral spintronics devices.
