Robust Formation of Ultrasmall Room-Temperature Neél Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations

Abstract

Neél skyrmions originate from interfacial Dzyaloshinskii Moriya interaction (DMI). Recent studies have explored using thin-film ferromagnets and ferrimagnets to host Neél skyrmions for spintronic applications. However, it is unclear if ultrasmall (10 nm or less) skyrmions can ever be stabilized at room temperature for practical use in high density parallel racetrack memories. While thicker films can improve stability, DMI decays rapidly away from the interface. As such, spins far away from the interface would experience near-zero DMI, raising question on whether or not unrealistically large DMI is needed to stabilize skyrmions, and whether skyrmions will also collapse away from the interface. To address these questions, we have employed atomistic stochastic Landau-Lifshitz-Gilbert simulations to investigate skyrmions in amorphous ferrimagnetic GdCo. It is revealed that a significant reduction in DMI below that of Pt is sufficient to stabilize ultrasmall skyrmions even in films as thick as 15 nm. Moreover, skyrmions are found to retain a uniform columnar shape across the film thickness due to the long ferrimagnetic exchange length despite the decaying DMI. Our results show that increasing thickness and reducing DMI in GdCo can further reduce the size of skyrmions at room temperature, which is crucial to improve the density and energy efficiency in skyrmion based devices.

Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys

“…The diameter of a skyrmion results from the competition between different energies such as the Heisenberg exchange energy, the magnetic anisotropy energy and the DMI strength. Ultrasmall skyrmions can be nucleated at room temperature only in a narrow range of D [32][33][34] . For DMI strength larger than a scale set by the magnetic anisotropy, the formation of stripe domains become energetically favorable 33,34 .…”

“…It was reported that the DMI and the domain wall velocity increased with the difference of roughness and intermixing between the top and bottom interface of a magnetic layer 39,40,44,45 . Finally, as the skyrmion size depends on the magnetic film thickness 22,34 , it is thus important to understand how the interfacial DMI scales with the thickness. evidence of magnetic skyrmions by MfM.…”

Skyrmions in antiferromagnets: Thermal stability and the effect of external field and impurities

“…The DM parameter is then not proportional to the thickness of the film. Nevertheless, recent calculations 45 show that in an amorphous ferrimagnetic GdCo film on Pt, the skyrmion assumes a columnar configuration that extends uniformly across the film thickness of 10 nm despite having near zero DM interaction far away from the interface. Effective DM interaction is still enough to stabilize the skyrmion tube.…”

Interplay between Spin‐Orbit Torques and Dzyaloshinskii‐Moriya Interactions in Ferrimagnetic Amorphous Alloys

“…[ 20 , 21 , 22 ] The skyrmion velocity is predicted to scale linearly with current density and depends on the SOT efficiency and the DMI strength. [ 21 ] In addition, the DMI energy determines the size of the skyrmion [ 13 , 14 ] as well as its overall lifetime.…”