  We investigated photon-helicity-induced magnetization precession in
Co$_{1-x}$Pt$_{x}$ alloy thin films. In addition to field-like torque,
attributable to magnetic field generation owing to {\it the inverse Faraday
effect}, we observed non-trivial and large damping-like torque which has never
been discussed for single ferromagnetic layer. The composition dependence of
those two torques is effectively elucidated by a model that considers mutual
coupling via spin-orbit interaction between magnetization and the electronic
orbital angular momentum generated by photon-helicity. This work significantly
enhances our understanding of the physics relevant to the interplay of
photon-helicity and magnetization in magnetic metals.
