Particle-in-cell simulation of ultrafast hot-carrier transport in Fe/Au heterostructures

We present a theoretical approach for spin-polarized hot-electron transport, as it occurs after excitation by ultrafast optical pulses in heterostructures formed by ferromagnetic and normal metals. We formulate a spin-dependent particle-in-cell model that solves the Boltzmann equation for excited electrons. It includes lifetimes and transmission coefficients as parameters, which can be taken from ab initio calculations or experiment, and can be easily extended to multilayer systems. This approach is capable of describing electron transport in the ballistic, superdiffusive, and diffusive regime including secondary-carrier generation. We apply the model to optically excited carriers in Fe/Au bilayers and Fe/Au/Fe spin-valve structures and analyze theoretically the hot-electron transport dynamics probed in recent experiments on spin valves. We find contributions to the demagnetization dynamics induced in Fe/Au/Fe trilayers regardless of the parallel or antiparallel magnetic alignment of the Fe layers.