  We use co-sputtering to directly synthesize thin films of the A15 phase
intermetallic compound Ta3Sb, which has been predicted to have a giant spin
Hall conductivity. We identify a large window of Ta:Sb flux ratio that
stabilizes single-phase A15 Ta3Sb. Composition analyses of these films show a
Ta:Sb atomic ratio of 4:1, which is consistent with the known Ta-Sb phase
diagram. The spin Hall conductivity of thin film Ta3Sb is -3400+/-400 (hbar/2e)
S/cm and the spin-orbit torque efficiency is -0.6+/-0.1 at 20 K, as determined
from harmonic Hall measurements of Ta3Sb/permalloy bilayer structures. These
giant values make Ta3Sb a promising material for efficient charge-to-spin
conversion in spintronic applications. Large field-like spin-orbit effective
fields that are independent of the ferromagnetic layer thickness have also been
measured in the Ta3Sb/permalloy bilayers. We attribute the field-like
spin-orbit effective field to the Rashba effect at the interface.
