  To achieve a large terahertz (THz) amplitude from a spintronic THz emitter
(STE), materials with 100\% spin polarisation such as Co-based Heusler
compounds as the ferromagnetic layer are required. However, these compounds are
known to loose their half-metallicity in the ultrathin film regime, as it is
difficult to achieve L2$_1$ ordering, which has become a bottleneck for the
film growth. Here, the successful deposition using room temperature DC
sputtering of the L2$_1$ and B2 ordered phases of the Co$_2$FeAl full Heusler
compound is reported. Co$_2$FeAl is used as ferromagnetic layer together with
highly orientated Pt as non-ferromagnetic layer in the Co$_2$FeAl/Pt STE, where
an MgO(10 nm) seed layer plays an important role to achieve the L2$_1$ and B2
ordering of Co$_2$FeAl. The generation of THz radiation in the CFA/Pt STE is
presented, which has a bandwidth in the range of 0.1-4 THz. The THz electric
field amplitude is optimized with respect to thickness, orientation, and growth
parameters using a thickness dependent model considering the optically induced
spin current, superdiffusive spin current, inverse spin Hall effect and the
attenuation of THz radiation in the layers. This study, based on the full
Heusler Co$_2$FeAl compound opens up a plethora possibilities in STE research
involving full Heusler compounds.
