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

초록

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 Pt83.4Zr16.6/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/cm2 , a factor of 3 lower than the Pt/Co heterostructure, and operates over a wide temperature range from-55 to 150 degrees C. In addition, we achieve external field-free switching of this heterostructure by placing an underlying ferromagnetic layer.

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