Spin-polarized image-potential-state electrons as ultrafast magnetic sensors in front of ferromagnetic surfaces

We have gained insight into quasielastic, i.e. resonant intra- and interband scattering processes and their inelastic counterparts. Lifetimes of minority and majority image-potential states differ primarily due to the spin-dependent density of states. In the minority channel of iron thin films quasielastic scattering processes become significant and are interpreted in terms of interband scattering between spin-up and spin-down image-potential-state bands. The latter process involves a spin flip on a sub-hundred femtosecond timescale and hints at quasielastic electron-magnon scattering.