Interfacial Engineering Strategies for Efficient Spin–Orbit Torque Devices with Pt Alloys

To make spin–orbit torque magnetic random-access memories (SOT-MRAMs) become competitive enough to replace the contemporary memory architecture, it is of great importance to utilize conductive SOT materials that possess large damping-like spin–orbit torque (DL-SOT) efficiencies and back-end-of-line (BEOL) compatibility. In this work, we report a BEOL-compatible CoFeB/MgO-based heterostructure with the Pt–Cr alloy as the spin current source (SCS) and inserted a Pt/Co/Pt composite layer to achieve texture decoupling and ferromagnetic coupling. A thermally robust perpendicular magnetic anisotropy (PMA) of the hybrid heterostructure can be retained after annealing at 400 °C for 1 h, while maintaining large DL-SOT efficiencies of the annealed Pt–Cr alloys (ξ DL ∼ 0.34 for Pt 0.70 Cr 0.30 ). Additionally, by optimizing the current distribution with a resistive Pt spacer layer, it is possible to simultaneously enhance the current-to-effective field conversion ratio ( H z eff / I ) and retain the apparent ξ DL (ξ DL ∼ 0.37 for Pt 0.79 Cr 0.21 ). Moreover, the critical switching current density can be reduced from J c Pt ∼ 2.0 × 10 7 A·cm –2 for Pt to J c Pt 0.70 Cr 0.30 ∼ 4.9 × 10 6 A·cm –2 for Pt 0.70 Cr 0.30 without tampering the thermal stability of the annealed heterostructure. These interfacial engineering strategies provide directions to integrate Pt-based SCSs with large ξ DL into a BEOL-compatible platform for future SOT-MRAM devices with PMA.