  We discuss a joint microscopic theory for the laser-induced magnetization
dynamics and spin transport in magnetic heterostructures based on the $s$-$d$
interaction. Angular momentum transfer is mediated by scattering of itinerant
$s$ electrons with the localized ($d$ electron) spins. We use the corresponding
rate equations and focus on a spin one-half $d$ electron system, leading to a
simplified analytical expression for the dynamics of the local magnetization
that is coupled to an equation for the non-equilibrium spin accumulation of the
$s$ electrons. We show that this description converges to the microscopic
three-temperature model in the limit of a strong $s$-$d$ coupling. The equation
for the spin accumulation is used to introduce diffusive spin transport. The
presented numerical solutions show that during the laser-induced
demagnetization in a ferromagnetic metal a short-lived spin accumulation is
created that counteracts the demagnetization process. Moreover, the spin
accumulation leads to the generation of a spin current at the interface of a
ferromagnetic and non-magnetic metal. Depending on the specific magnetic
system, both local spin dissipation and interfacial spin transport are able to
enhance the demagnetization rate by providing relaxation channels for the spin
accumulation that is build up during demagnetization in the ferromagnetic
material.
