  The search for efficient spin conversion in Bi has attracted great attention
in spin-orbitronics. In the present work, we employ spin-torque ferromagnetic
resonance to investigate spin conversion in Bi/Ni80Fe20(Py) bilayer films with
continuously varying Bi thickness. In contrast with previous studies, sizable
spin-transfer torque (i.e., a sizable spin-conversion effect) is observed in
Bi/Py bilayer film. Considering the absence of spin conversion in
Bi/yttrium-iron-garnet bilayers and the enhancement of spin conversion in
Bi-doped Cu, the present results indicate the importance of material
combinations to generate substantial spin-conversion effects in Bi.
