  We report a comprehensive study of the maximization of the spin Hall ratio
({\theta}SH) in Pt thin films by the insertion of sub-monolayer layers of Ti to
decrease carrier lifetime while minimizing the concurrent reduction in the spin
Hall conductivity. We establish that the intrinsic spin Hall conductivity of
Pt, while robust against the strain and the moderate interruption of crystal
order caused by these insertions, begins to decrease rapidly at high
resistivity level because of the shortening carrier lifetime. The unavoidable
trade-off between the intrinsic spin Hall conductivity and carrier lifetime
sets a practical upper bound of {\theta}SH >=0.8 for heterogeneous materials
where the crystalline Pt component is the source of the spin Hall effect and
the resistivity is increased by shortening carrier lifetime. This work also
establishes a very promising spin-Hall metal of [Pt 0.75 nm/Ti 0.2 nm]7/Pt 0.75
nm for energy-efficient, high-endurance spin-orbit torque technologies (e.g.,
memories, oscillators, and logic) due to its combination of a giant {\theta}SH
of 0.8, or equivalently a dampinglike spin torque efficiency per unit current
density of 0.35, with a relatively low resistivity (90 uOhm cm) and high
suitability for practical technology integration.
