Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu₈₀Ir₂₀

Identifying materials with an efficient spin-to-charge conversion is crucial for future spintronic applications. In this respect, the spin Hall effect is a central mechanism as it allows for the interconversion of spin and charge currents. Spintronic material research aims at maximizing its efficiency, quantified by the spin Hall angle θ_SH and the spin-current relaxation length λ_rel . We develop an all-optical contact-free method with large sample throughput that allows us to extract θ_SH and λ_rel. Employing terahertz spectroscopy and an analytical model, magnetic metallic heterostructures involving Pt, W and Cu₈₀Ir₂₀ are characterized in terms of their optical and spintronic properties. The validity of our analytical model is confirmed by the good agreement with literature DC values. For the samples considered here, we find indications that the interface plays a minor role for the spin-current transmission. Our findings establish terahertz emission spectroscopy as a reliable tool complementing the spintronics workbench.