Atomic-scale interface mixing controls all-optical switching in Gd/Fe multilayers

The control of interfacial mixing at the atomic scale presents a powerful yet underexplored pathway to tailor thermally induced magnetization switching (TIMS) in Gd/Fe-based spintronic devices. By integrating atomistic spin dynamics with thermal modeling, we demonstrate that the parametrized interfacial mixing degree critically governs the TIMS activation conditions. Specifically, an elevated mixing degree raises the magnetization reversal energy threshold and shifts the operational energy density window to higher values across all laser pulse durations. We attribute this effect to the reduction of the effective Gd–Fe exchange coupling as the interface becomes more diffuse, which impedes efficient angular momentum transfer between sublattices. Consequently, the switching time of Gd 4f spins is significantly prolonged, while the Fe sublattice remains largely unaffected. This work establishes a correlation between interfacial architecture and ultrafast spin dynamics, providing a design guideline for low-energy magnetic memories through interface engineering.