We present a theory of out-of-equilibrium ultrafast spin dynamics in magnetic heterostructures based on the $s\text{−}d$ model of ferromagnetism. Both in the bulk and across interfaces, the exchange processes between the itinerant $s$ and the localized $d$ electrons are described by kinetic rate equations for electron-magnon spin-flop scattering. In our treatment, the magnon distribution function remains nonthermalized on the relevant time scales of the demagnetization process, and the relaxation of the out-of-equilibrium spin accumulation among itinerant electrons provides the principal channel for dissipation of spin angular momentum from the combined electronic system.

• Received 1 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.180412