Microstructural evolution and enhanced spin-orbit torque in Pt-Zr alloyed magnetic heterostructures

• The Pt-Zr alloy layers exhibited a face-centered cubic (1 1 1) preferred orientation in the out-of-plane direction within the solid solution range. • The Pt 83.4 Zr 16.6 /Co heterostructure demonstrated a spin–orbit torque efficiency of 0.175, attributed to the intrinsic spin Hall effect in the dirty metal regime. • The heterostructure with 16.6 atomic percent of Zr enabled reduced magnetization switching current, thermal robustness, and feasibility of field-free switching operation. Platinum (Pt) holds great promise for generating spin–orbit torque (SOT) due to its large spin Hall conductivity and low resistivity. Like Pt/Co, Pt-based magnetic heterostructures exhibit perpendicular magnetic anisotropy (PMA). However, despite these advantages, the Pt/Co heterostructures have small SOT efficiency, which limits their practical applications. One promising strategy is alloy engineering, particularly using a solid solution of Pt-based alloys. This study demonstrates that zirconium (Zr) alloying into the Pt layer can induce microstructural changes, showing that the crystallinity of the Pt-Zr alloy layer depends on the Zr composition, maintaining face-centered cubic ( fcc ) (111) structure within the solid-solution region. Also, the magnetic and electrical properties of the Pt-Zr/Co heterostructure change due to the microstructural effect and intrinsic properties of Zr, amplifying the SOT efficiency within the solid solution region. The Pt 83.4 Zr 16.6 /Co heterostructure exhibited an enhanced SOT efficiency of 0.175, compared to 0.081 for the Pt/Co heterostructure. This heterostructure exhibits an SOT switching current density of 12.14 MA/cm 2 , a factor of 3 lower than the Pt/Co heterostructures, and operates over a wide temperature range from −55 to 150 ℃. In addition, we achieve external field-free switching of this heterostructure by placing an underlying ferromagnetic layer.