Interfacial modification to enhance the effective spin hall angle of perpendicularly magnetized systems

Maximizing the spin-orbit torque (SOT) strength to reduce the current density of magnetization switching (J_c) in heavy metal (HM)/ferromagnet (FM)/HM based perpendicularly magnetized systems have played a key role in constructing SOT-driven memory devices. The SOT strength is proportional to the material's spin Hall angle (θ_sh). We introduced an Au layer at the HM/FM interface to manipulate θ_sh. We deposited Ta/Pt/Co/Pt, Ta/Pt/Co/Au/Pt and Ta/Pt/Au/Co/Pt systems. We observed no significant difference in J_c between Ta/Pt/Co/Pt and Ta/Pt/Co/Au/Pt systems. In contrast, J_c reduces ∽34% in the Ta/Pt/Au/Co/Pt system compared to the Ta/Pt/Co/Pt system. We also prepared Ta/Pt/Co/Au and Ta/Pt/Au/Co/Au systems. We observed a reduction of J_c upto ∽30% in the Ta/Pt/Au/Co/Au multilayer compared to the Ta/Pt/Co/Pt system. To reduce J_c further, another set of samples was prepared with Ta as a capping layer. This set consists of Ta/Pt/Co/Pt/Ta, Ta/Pt/Au/Co/Pt/Ta and Ta/Pt/Au/Co/Pt/Ta/Co/Pt samples. The J_c of the Ta/Pt/Au/Co/Pt/Ta sample was reduced upto ∽58% compared to the Ta/Pt/Co/Pt sample. Experiments show that by introducing an Au layer at the bottom Pt/Co interface, J_c can be reduced. Micromagnetic simulation suggests an increase of θ_sh for these samples. Field-free magnetization switching was realized by depositing an in-plane magnetized layer Co layer in Ta/Pt/Au/Co/Pt/Ta/Co/Pt system. Hence, our findings represent a noteworthy advancement in fabricating magnetic memory devices with reduced J_c.