  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.
