Exchange Coupling-Induced Spin Dynamic Damping Modulation at the Py/FeMn Interface

The spin dynamic damping is crucial for applications in magnetic memory, sensors, and logical systems. Here, focusing on interfacial antiferromagnetic exchange coupling, the magneto-dynamics of Ni₈₀Fe₂₀(Py)/Fe₅₀Mn₅₀(FeMn) bilayers is systematically investigated. When the FeMn thickness exceeds 5 nm, an interfacial exchange bias field appears, significantly increasing the spin dynamic damping of the Py/FeMn bilayer to around 0.015. A Cu spacer is introduced between the Py and FeMn layers, and the interfacial exchange bias effect is eliminated following a dramatic decrease in the spin dynamic damping. However, a slight damping increment is observed in Py/Cu/FeMn trilayers, which is attributed to the spin pumping mechanism. Based on spin pumping theory, the estimated interfacial spin mixing conductance is 3.44 nm^-2 in Py/Cu/FeMn, which is attributed to the weak spin-orbit coupling of the FeMn layer. These findings indicate that the dynamic damping of Py/FeMn bilayers is primarily driven by interfacial exchange coupling rather than the spin pumping effect. Furthermore, by employing FeMn as an insertion at Py/Pt and Py/Cu interfaces, we demonstrate the short spin diffusion length for the FeMn layer, and we confirm the critical role of interfacial exchange coupling in enhancing spin dynamic damping. The exchange coupling at the Py/FeMn interface facilitates spin relaxation, resulting in the damping enhancement and blocking spin transmission from the Py to Pt (Cu) layer. These findings suggest that integrating antiferromagnetic materials with exchange coupling interfaces could significantly boost high-frequency spintronic applications.