  Antiferromagnetic $\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ combines outstanding
spin-transport properties with magnons in the terahertz (THz) frequency range.
However, the THz radiation emitted by ultrafast spin-to-charge conversion via
the inverse spin Hall effect remains unexplored. In this study, we measured the
THz emission and transmission of a permalloy/(111)-oriented
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ multilayer by THz time-domain spectroscopy.
The spin Hall angle was determined to be approximately constant at 0.035 within
a frequency range of 0.3-2.2 THz, in comparison with the THz spectroscopy of a
permalloy/Pt multilayer. Our results not only demonstrate the potential of
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ as a spintronic THz emitter but also provide
insights into the THz spin transport properties of
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$.
