  The field of THz spintronics is a novel direction in the research field of
spintronics that combines magnetism with optical physics and ultrafast
photonics. The experimental scheme of the field involves the use of femtosecond
laser pulses to trigger ultrafast spin and charge dynamics in bilayers composed
of ferromagnetic (FM) and non-magnetic (NM) thin films where the NM layer
features a strong spin-orbit coupling. The key technological and scientific
challenges of THz spintronic emitters is to increase their intensity and
frequency bandwidth. To achieve this the control of the source of the
radiation, namely the transport of the ultrafast spin current is required.
However, the transfer of a spin current from a FM to a NM layer is a highly
interface-sensitive effect. In this work we study the properties of the spin
current transport through the interface measuring the strength of the THz
emission and compare it to the effective spin mixing conductance, one of the
key concepts in the spin current transport through interfaces. The results show
an enhancement of the spin mixing conductance for interfaces with higher degree
of epitaxy similarly to the improvement of the THz emission. The
proportionality between spin mixing conductance and THz emission can define new
directions in engineering the emission of spintronic THz emitters.
