Enhancement of perpendicular magnetic anisotropy and anomalous hall effect in Co/Ni multilayers

• The perpendicular magnetic anisotropy and anomalous Hall effect of Co/Ni multilayer films were studied.
• The PMA thermal stability of the Co/Ni ML can be enhanced by HfO2 capping layer and Pt insertion.
• The anomalous Hall resistivity of Co/Ni ML covered by HfO2 was enhanced by post-annealing treatment.

The perpendicular magnetic anisotropy (PMA) and the anomalous Hall effect (AHE) in Co/Ni multilayer were optimized by manipulating its interface structure (inducing HfO2 capping layer and Pt insertion) and post-annealing treatment. A strong PMA can be obtained in Co/Ni multilayers with HfO2 capping layer even after annealing at 400 °C. The heavy metal Hf may improve the interfacial spin-orbit coupling, which responsible for the enhanced PMA and high annealing stability. Moreover, the multilayer containing HfO2 capping layer also exhibited high saturation anomalous Hall resistivity through post-annealing, which is 0.85 μΩ cm after annealing at 375 °C, 211% larger than in the sample at deposited state which is only 0.27 μΩ cm. The enhancement of AHE is mainly attributed to the interface scattering through post-annealing treatment.