Enhancement of writing efficiency for multilevel memory in perpendicularly magnetized Pt/Co/Pt/IrMn multilayers

Abstract

Spin orbit torques (SOTs) induced partial ferromagnetic/antiferromagnetic domains reversal in perpendicularly magnetized heavy metal/ferromagnet/antiferromagnet trilayers have attracted lots of attention due to the potential application in the polymorphic memory using the remanence as recording bits. In this work, an ultra-thin Pt layer was used to engineer the interface between the ferromagnetic Co and the antiferromagnetic IrMn in Pt/Co/Pt/IrMn multilayers. Although both the exchange bias field and the effective SOT efficiency decrease with the increase in the thickness of Pt interfacial layer, the SOT induced polymorphic remanent Hall resistance still can be observed either by changing the current density while fixing the assistant in-plane field, or vice versa. Moreover, the decrease in the critical switching current density or in-plane assistant field was observed with the thickness of interfacial Pt layer increasing from 0.2 to 0.8 nm. The results suggest that the interfacial layer caused smaller decrease rate of the damping-like SOT efficiency than that of the exchange bias field is responsible for the decreased writing current density to achieve polymorphic states. Our work provides an effective method to enhance the writing efficiency for polymorphic memory by SOT.