Multistate Magnetization Switching Driven by Spin Current From a Ferromagnetic Layer

Spin-charge interconversion in ferromagnets has recently drawn great attention due to its ability to generate spin current via the anomalous Hall, planar Hall, or intrinsic spin Hall effect. In this work, we demonstrate the magnetization switching of perpendicular anisotropy ferromagnets by the transversely polarized spin current generated from an easy-plane ferromagnet such as (Fe, Mn)Pt and (Co, Fe)B. The spin-torque efficiency is characterized to be about 21% of that of the same structure with the easy-plane ferromagnet replaced by Ta. In addition, we find that the magnetization switching consists of multiple intermediate states, which can be robustly set by the applied current pulse amplitude and repetition number. This behavior can be used to mimic synaptic devices that is potentially useful for neuromorphic computing.