Elucidating the role of an Ir insertion layer in mediating interfacial perpendicular anisotropy, Dzyaloshinskii-Moriya interaction, and spin-orbit torque in Pt/Ir/Co

The advancement of spin-orbit torque (SOT)-based spintronic devices hinges on the ability to optimize interfacial spin-orbit coupling phenomena. This work elucidates the modulation of key spintronic parameters by inserting an Ir layer at Pt/Co and PtCr/Pt(0.5)/Co interfaces. A comprehensive investigation into the thickness-dependent perpendicular magnetic anisotropy, Dzyaloshinskii-Moriya interaction, spin-orbit torque efficiency, and switching current density is undertaken. The results reveal that an ultrathin 0.1 nm Ir insertion layer can enhance the dampinglike SOT efficiency by over 26% in Pt/Co and 10% in PtCr/Co systems, attributed to increased interfacial impurity scattering. Strikingly, the magnetic anisotropy and Dzyaloshinskii-Moriya interaction exhibit a nonmonotonic relationship with Ir thickness, minimized at 0.4--0.5 nm, explained by interfacial roughness effects evidenced through first-principles calculations. The critical switching current density becomes widely tunable from 1.6--3.5×10⁷ (A/cm²) in Pt/Ir/Co and 1.0--2.0×10⁷ (A/cm²) in PtCr/Ir/Co, respectively, reduced by nearly 50% with a 0.4 nm Ir insertion. These findings provide significant physical insights into interfacial spin-orbit coupling mechanisms and interface engineering of spintronic devices using insertion layers. The capability to substantially increase SOT efficiency while reducing the switching current highlights the promise of an Ir insertion layer to unlock the full potential of SOT-MRAM technology.