  We investigate the THz emission characteristics of ferromagnetic/non-magnetic
metallic heterostructures, focusing on thin Fe/Pt bilayers. In particular, we
report on the impact of optimized crystal growth of the epitaxial Fe layers on
the THz emission amplitude and spectral bandwidth. We demonstrate an
enhancement of the emitted intensity along with an expansion of the emission
bandwidth. Both are related to reduced spin scattering and higher interface
transmission. Our work provides a pathway for devicing optimal spintronic THz
emitters based on epitaxial Fe. It also highlights how THz emission
measurements can be utilized to characterize the changes in out-of-equilibrium
spin current dynamics in metallic heterostructures, driven by subtle structural
refinement.
