Thermal Evolution of Skyrmions in Synthetic Ferrimagnets of Co/Gd Heterostructure for Topological Spintronic Applications

TL;DR

This work investigates how skyrmions can be stabilized and controlled in synthetic ferrimagnets formed by Pt/Co/Gd multilayers. By combining structural and magnetic characterization with a minimal two-layer spin model, the authors capture how temperature and external fields drive the evolution from labyrinthine domains to nanoscale skyrmions and how Co and Gd sublattices differentially respond with temperature. The key findings include room-temperature formation of ~70 nm skyrmions and a temperature-dependent net magnetization governed by interlayer antiferromagnetic exchange and proximity effects, reproduced by simulations. The study provides design principles for SFiM heterostructures aimed at room-temperature topological spintronic devices, highlighting a route to engineer robust, detectable skyrmions through sublattice tuning and interlayer coupling.

Abstract

Synthetic ferrimagnetic (SFiM) multilayers offer a versatile platform for hosting skyrmions with tunable magnetic properties, combining the advantages of ferromagnets and antiferromagnets. Unlike synthetic antiferromagnets, SFiMs retain a finite magnetization that allows direct observation of magnetic textures while still benefiting from reduced dipolar fields and a suppressed skyrmion Hall effect. However, a systematic investigation of their temperature and field dependent magnetization evolution, including the labyrinthine-to-skyrmion transition in Co/Gd-based SFiMs, remains less explored. Here, we demonstrate the stabilization of 70 nm-radius skyrmions at room temperature and reveal how the Co and Gd sublattices influence the temperature-dependent net magnetization. Further, we develop a microscopic spin model for SFiM incorporating the relevant magnetic interactions, which reproduces the experimental observations and captures the temperature-dependent magnetic phase evolution. This framework highlights the interplay of fundamental interactions controlling skyrmion stability in SFiM and provides a pathway for engineering heterostructures for topological spintronic applications.

Figures (9)

• Figure 1: (a) Structural representation of sample FS, where N denotes one stacking unit of Pt/Co/Gd, repeated five times, (b) schematic illustration of spin alignment of Co and Gd in a SFiM, (c) simulated magnetization of the individual Co and Gd layers, highlighting their temperature dependence of magnetization (in units of the hopping amplitude), (d) simulated layer-resolved magnetization profiles of Co and Gd, after stacking as Co/Gd.
• Figure 2: (a) Room temperature hysteresis loops for both OOP and IP magnetic fields for sample FS, (b) zoomed in image of OOP loop shown in (a) and, (c) hysteresis loop obtained from the simulation at effective temperature $T = 0.21$ approximating the room temperature.
• Figure 3: (a) Magnetic hysteresis loops recorded at 25 K, 100 K, 200 K, and 300 K, showing the temperature dependent evolution of magnetization for sample FS, (b) extracted saturation magnetization ($M_s$) plotted as a function of temperature, illustrating the thermal variation of the magnetic moment.
• Figure 4: Experimental hysteresis loops of sample FS measured at (a) 200 K, and (b) 25 K, simulated hysteresis loop at effective temperature, (c) $T=0.09$ approximating to 200 K, (d) $T=0.01$ approximating to 25 K.
• Figure 5: (a) Shows the experimental MFM image of sample FS in the demagnetized state at RT, while (b) presents the corresponding simulated demagnetized-state domain configuration at effective temperature $T=0.21$ , (c) and (d) represent simulated layer resolved domain structure in Co and Gd sublayers, respectively.