  The Dzyaloshinskii-Moriya interaction (DMI) that arises in the magnetic
systems with broken inversion symmetry plays an essential role in topological
spintronics. Here, by means of atomistic spin calculations, we study an
intriguing type of DMI (g-DMI) that emerges in the films with composition
gradient. We show that both the strength and chirality of g-DMI can be
controlled by the composition gradient even in the disordered system. The
layer-resolved analysis of g-DMI unveils its additive nature inside the bulk
layers and clarifies the linear thickness dependence of g-DMI observed in
experiments. Furthermore, we demonstrate the g-DMI induced chiral magnetic
structures, such as spin spirals and skyrmions, and the g-DMI driven field-free
spin-orbit torque (SOT) switching, both of which are crucial towards practical
device application. These results elucidate the underlying mechanisms of g-DMI
and open up a new way to engineer the topological magnetic textures.
