Ultrafast spin-to-charge conversions of antiferromagnetic (111)-oriented $\mathrm{L}{1}_2$-$\mathrm{M}{\mathrm{n}}_3\mathrm{I}\mathrm{r}$

Antiferromagnetic $\mathrm{L}{1}_2$-$\mathrm{M}{\mathrm{n}}_3\mathrm{I}\mathrm{r}$ 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 $\mathrm{L}{1}_2$-$\mathrm{M}{\mathrm{n}}_3\mathrm{I}\mathrm{r}$ 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 $\mathrm{L}{1}_2$-$\mathrm{M}{\mathrm{n}}_3\mathrm{I}\mathrm{r}$ as a spintronic THz emitter but also provide insights into the THz spin transport properties of $\mathrm{L}{1}_2$-$\mathrm{M}{\mathrm{n}}_3\mathrm{I}\mathrm{r}$.