  We present a self-consistent mean-field model based on a two-component
Pauli-like equation that incorporates quantum and relativistic effects (up to
second-order in 1/c) for both external and internal electromagnetic fields. By
taking the semi-relativistic limit of the Dirac-Maxwell equations in the
presence of an external electromagnetic field we obtain an analytical
expression of a coherent light-induced mean-field Hamiltonian. The latter
exhibits several mechanisms that involve the internal mean fields created by
all the electrons and the external electromagnetic field (laser). The role
played by the light-induced current density and the light-induced second-order
charge density acting as sources in Maxwell's equations are clarified. In
particular, we identify clearly four different mechanisms involving the spins
that may play an important role in coherent ultrafast spin dynamics.
