Document Type
Dissertation
Date of Award
8-31-2024
Degree Name
Doctor of Philosophy in Mathematical Sciences - (Ph.D.)
Department
Mathematical Sciences
First Advisor
Cyrill B. Muratov
Second Advisor
Michael Siegel
Third Advisor
Anand Uttam Oza
Fourth Advisor
David Shirokoff
Fifth Advisor
Anne Bernand-Mantel
Sixth Advisor
Valeriy Slastikov
Abstract
Magnetic skyrmions are topologically protected, localized, nanoscale spin textures in non-centrosymmetric thin ferromagnetic materials and heterostructures. At present they are of great interest to physicists for potential applications in information technology due to their particle-like properties and stability. In a system of multiple thin ferromagnetic layers, the stray field interaction was typically treated with various simplifications and approximations. It is shown that extensive analysis of the micromagnetic equations leads to an exact representation of the stray field interaction energy in the form of layer interaction kernels, a so-called 'finite thickness' representation. This formulation reveals the competition between perpendicular magnetic anisotropy (PMA) and stray field in the stabilization of skyrmions, and gives new existence and collapse criteria. This is demonstrated in detail in the case of a monolayer of finite thickness and compared to past results which cannot reveal the collapse criteria. The layer interaction kernels are then treated asymptotically for thin films to obtain the nonlocal stray field interaction energies of multilayers. It is thereby shown that a system of PMA multilayers interacting with each other only through the stray field can support bound columns of concentric skyrmions in each layer, enabled by the stray field interaction alone. The multilayer skyrmions are shown to be larger than those of a monolayer, and exhibit a full range of Bloch-Neel hybrid combinations depending on certain constraints given by the interlayer volume charge energy. Further solutions are given for Dzyaloshinskii-Moriya interaction enabled skyrmions in a system of multilayers interacting with each other through both ferromagnetic and antiferromagnetic exchange.
Recommended Citation
Dubicki, Nicholas J., "A micromagnetic study of skyrmions in thin-film multilayered ferromagnetic materials" (2024). Dissertations. 1771.
https://digitalcommons.njit.edu/dissertations/1771
