Tunable Dzyaloshinskii-Moriya Interaction in Ferrimagnetic GdCo alloy through Interface Engineering*

Magnetic skyrmions are quasiparticles with potential applications in memory and logic devices. Controlling the interfacial Dzyaloshinskii-Moriya Interaction (DMI) plays a crucial role in manipulating skyrmion properties. We present a systematic analysis of the DMI variation in ferrimagnetic Pt/GdCo/Pt_1-xW_x multilayer as a function of Tungsten (W) composition (x) using Density Functional Theory (DFT). We find that ~10% W in the capping layer produces a non-zero DMI, and the DMI increases as the W composition increases but saturates at higher W composition in agreement with the experiment. We show that the vanishing of spin-orbit coupling (SOC) energy to the adjacent metal layers of the top interface and the simultaneous constancy of the bottom interface is responsible for such a saturating behavior of the DMI. Furthermore, we investigate Pt/GdCo/X (X = Ta, W, Ir) to demonstrate the impact of capping layer heavy metals on the DMI. We predict that W in the capping layer favors a higher DMI than Ta and Ir that shows a matching trend with the experimentally measured Spin Hall angle. Our results open up exciting combinatorial possibilities for controlling the DMI in ferrimagnets to nucleate and manipulate ultrasmall high-speed skyrmions.