Absorption and generation of femtosecond laser-pulse excited spin currents in noncollinear magnetic bilayers

It it has been found in recent years that a spin current can be generated when a ferromagnetic (FM) thin film is excited with a femtosecond laser pulse. Here, the authors use a noncollinear magnetic bilayer to investigate both the absorption and generation of these optical spin currents. It is demonstrated that the very local absorption of the spin current near the injection interface of a FM layer allows for terahertz spin wave excitation in such noncollinear magnetic bilayers, and advance of much relevance for the upcoming field of ultrafast magnonics.