Spin-to-charge conversion in tantalum with structural phase transition

Tantalum (Ta), which is widely used as a spin sink material, especially for its ss-phase with strong spinorbit coupling (SOC) exhibits a high spin-charge interconversion efficiency. In this work, we investigate the spin-to-charge conversion (SCC) process of Ta/Permalloy (Ta/Py) bilayers with Ta having different crystalline phases. The structural phase transition of Ta film from tetragonal to bodycentered cuboidal (BCC) which corresponds to ss- and alpha-phases was obtained via high-temperature annealing in vacuum atmosphere. By applying ferromagnetic resonance (FMR) and inverse spin Hall effect (ISHE) measurements, the measured spin mixing conductance and SCCDCvoltage show a strong correlation with the crystalline phase of Ta thin films in Ta/Py bilayers. Asignificant enhancement of spin mixing conductance in (ss+ alpha)-Ta/Py has been found and a higher SCCDC voltage was detected for alpha-phase Ta film with a weak SOC than ss-phase Ta film with a strong SOC. These results reveal the significant role of the interfacial constitution in heavy metal/ferromagnet bilayers for spin current transportation, which can promote the development of high-efficiency spinbased devices through interfacial engineering.