Interfacial engineering to manipulate the effective spin Hall angle of perpendicularly magnetized systems

Abstract

The spin current can be generated by passing an electric current through a heavy metal. The spin current generation depends on the spin Hall angle (θsh) of the material. To manipulate the effective θsh, a thin layer of Au has been introduced at the bottom Pt/Co and the top Co/Pt interfaces in Ta/Pt/Co/Pt based perpendicularly magnetic anisotropy systems, and current-induced magnetization reversal of Co has been studied to estimate Jc. The introduction of the Au layer at the top Co/Pt interface (Ta/Pt/Co/Au/Pt) did not produce any significant reduction in the Jc. However, a significant reduction of Jc (∼34%) has been observed, while the Au layer has been deposited at the bottom Pt/Co interface (Ta/Pt/Au/Co/Pt), indicating an enhancement in the value of θsh. We also performed a micromagnetic simulation to understand the qualitative change of the θsh. Micromagnetic simulation suggested that the θsh becomes 0.07 in Ta/Pt/Au/Co/Pt multilayer compared to θsh=0.05 of the Ta/Pt/Co/Pt system. Pt/Co/Au/Co/Au exhibits a reduction in Jc up to ∼30% and corresponds to θsh=0.09. A Ta capping layer has been introduced to inject more spin current into the Co layer since Pt and Ta have opposite spin Hall angles. The Jc lowers up to ∼58% in Ta/Pt/Au/Co/Pt/Ta multilayer, corresponding to θsh=0.23. We also achieved field-free switching at Jc=1.55×1011 by depositing an in-plane magnetized layer of Co in Ta/Pt/Au/Co/Pt/Ta/Co/Pt multilayer.