  Recent research has indicated that introducing impurities that increase the
resistivity of Pt can enhance the efficiency of the spin Hall torque it
generates. Here we directly demonstrate the usefulness of this strategy by
fabricating prototype 3-terminal in-plane-magnetized magnetic tunnel junctions
that utilize the spin Hall torque from a $\rm{Pt}_{85}\rm{Hf}_{15}$ alloy, and
measuring the critical currents for switching. We find that
$\rm{Pt}_{85}\rm{Hf}_{15}$ reduces the switching current densities compared to
pure Pt by approximately a factor of 2 for both quasi-static ramped current
biases and nanosecond-scale current pulses, thereby proving the feasibility of
this approach to assist in the development of efficient embedded magnetic
memory technologies.
