Interface Engineering to Control the Dzyaloshinskii-Moriya Interaction in Ferrimagnetic GdCo: ab initio Calculations

Abstract

The interfacial Dzyaloshinskii-Moriya Interaction (DMI), an anti-symmetric exchange originating from strong spin-orbit coupling (SOC) in systems with broken inversion symmetry, plays a critical role in stabilizing chiral spin textures such as magnetic skyrmions. Magnetic skyrmions with their non-trivial properties have recently emerged as a potential candidate for next-generation spintronics applications such as race-track memory and logic devices [1, 2]. Recently, ferrimagnetic materials have been found to be more attractive for hosting stable ultra-small skyrmions at room temperature than conventional ferromagnets, due to their low saturation magnetization, low stray field, and fast spin dynamics [3, 4]. However, to manipulate skyrmions properties, controlling the DMI is essential. Herein, we present a systematic analysis of the DMI variation in compensated ferrimagnetic Pt/GdCo/Pt1-xWx multilayer as a function of Tungsten (W) composition (x) using Density Functional Theory (DFT). We find that a small amount of W (~10%) is sufficient to give rise to a non-zero DMI by breaking the inversion symmetry of Pt/GdCo/Pt. We also find that our calculated DMI increases as the W composition increases, but saturates at higher W composition, in agreement with experiment [5]. 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 are responsible for such a saturating behavior of the DMI. Additionally, we investigate Pt/GdCo/X, where X=Ta, W, Ir to demonstrate the effect of capping layer heavy metals on the DMI. Our results predict that W in the capping layer favors a higher value of the DMI than Ta and Ir. Our results open up exciting combinatorial possibilities for controlling the DMI in ferrimagnets to nucleate and manipulate ultrasmall high-speed skyrmions.