Intrinsic nature of the giant spin Hall conductivity of Pt

More than a decade after the first theoretical and experimental studies of the spin Hall conductivity (SHC) of Pt, both its dominant origin and amplitude remain in dispute. Resolving these questions is of fundamental importance for advancing understanding of very strong spin-orbit effects in conducting systems and for maximizing the spin Hall effect for energy-efficient spintronics applications. Here, we report the experimental determination of the rapid variation of the intrinsic SHC of Pt with the carrier lifetime ({\tau}) in the dirty-metal regime by incorporating finely dispersed MgO inter-site impurities into the Pt while maintaining the essential elements of its band structure (face-centered-cubic order). This findings conclusively validate the theoretical prediction that the SHC in Pt in the dirty-metal regime should be dominated by the intrinsic Berry curvature contribution and should decrease rapidly with shortening {\tau}. This also establishes the limit to which the spin Hall ratio {\theta}SH of pure Pt can be increased by shortening {\tau}. When the spin backflow at the Pt/ferromagnet interface due to the finite interfacial spin-mixing conductance is taken into account, the amplitude of the intrinsic SHC of Pt in the clean limit is found to be at least 1.6x10^6 (h_bar/2e) {\Omega}-1 m-1, more than 3.5 times greater than the available theoretical predictions. Our work also establishes a compelling spin Hall metal Pt0.6(MgO)0.4 that combines a giant {\theta}SH (0.73) with a moderate resistivity (74 {\mu}{\Omega} cm), a strong Dzyaloshinskii-Moriya interaction, easy growth, and good integration compatibility for spintronics technology.