  The existence of global weak solutions to a coupled spin drift-diffusion and
Maxwell-Landau-Lifshitz system is proved. The equations are considered in a
two-dimensional magnetic layer structure and are supplemented with
Dirichlet-Neumann boundary conditions. The spin drift-diffusion model for the
charge density and spin density vector is the diffusion limit of a spinorial
Boltzmann equation for a vanishing spin polarization constant. The
Maxwell-Landau-Lifshitz system consists of the time-dependent Maxwell equations
for the electric and magnetic fields and of the Landau-Lifshitz-Gilbert
equation for the local magnetization, involving the interaction between
magnetization and spin density vector. The existence proof is based on a
regularization procedure, $L^2$-type estimates, and Moser-type iterations which
yield the boundedness of the charge and spin densities. Furthermore, the free
energy is shown to be nonincreasing in time if the magnetization-spin
interaction constant in the Landau-Lifshitz equation is sufficiently small.
