The interconversion between spin and charge currents is vital for developing spintronics technologies, which require materials with high spin-to-charge-current conversion efficiency (SCC). The alloy IrAl was shown to exhibit a large spin Hall angle at gigahertz frequencies. Here, we use spintronic terahertz emission spectroscopy to investigate terahertz SCC in IrxAl1-x|FM heterostructures with a ferromagnetic layer FM of CoFeB and Ni as a function of the composition ratio x. We observe a strongly x-dependent terahertz-signal amplitude, whereas no change in the dynamics of the ultrafast in-plane charge current is seen. For x=0.48, we find that the SCC efficiency in IrxAl1-x reaches up to 65% of that of Pt. Signals from IrxAl1-x|Ni suggest that orbital contributions to the signal are minor. This study highlights the potential of IrAl alloys for SCC in ultrafast spintronic applications.
