We have studied the spin torque efficiency of Pt1-xBix/Co based heterostructures for spin-orbit torque (SOT) switching devices. While the field-like component of the SOT shows a relatively small change with the Bi concentration (x), the damping-like component (ζDL) abruptly increases with increasing x. The increase in ζDL with x is largely associated with the change in the Pt1-xBix layer resistivity (ρxx). The spin Hall conductivity (σSH) estimated from ζDL and ρxx remains nearly constant at ∼830 (ℏ/e) ω-1 cm-1 for 0 < x ≲ 0.6. Further substitution of Bi results in the formation of PtBi2, which causes smaller σSH than that of alloys with smaller x. The magnetic easy axis of a 0.6 nm thick Co layer points along the film normal when x is smaller than ∼0.7. Exploiting these characteristics, we show current-induced magnetization switching in the heterostructures. The efficiency to switch a perpendicularly magnetized Co layer is the largest when x ∼0.5. These results demonstrate the potential of Pt1-xBix alloys for spin-orbit torque magnetization switching devices.
ASJC Scopus subject areas
- Materials Science(all)