Manipulating Topological States

Manipulating Topological States by Imprinting Non-Collinear Spin Textures.
Robert Streubel, Luyang Han, Mi-Young Im, Florian Kronast, Ulrich K. Rößler, Florin Radu, Radu Abrudan, Gungun Lin, Oliver G. Schmidt, Peter Fischer, Denys Makarov 

Scientific Reports 5, 8787 (2015)

Imprinting non-collinear magnetic spin textures into out-of-plane magnetised films (Co/Pd multilayers) via interlayer coupling to a vortex state (Permalloy, Py) (a). Calculations are carried out for a Co/Pd anisotropy of K_u = 200 kJ/m³. Depending on the interlayer exchange coupling strength and the magnetic field treatment (remanence or relaxed state), configurations of distinct topology can be imprinted in the out-of-plane magnetised layer as revealed by micromagnetic simulations. Figures (b)–(e) show the magnetic configuration of four different states in Co/Pd films with decreasing strength of interlayer coupling J_i (left to right) after applying an out-of-plane magnetic field. Colours correspond to the normalised out-of-plane magnetisation component: (b) Remanent and relaxed vortex state; (c)–(d) remanent donut state type II and type I (number of domain walls), respectively; and (e) relaxed magnetic spiral. The skyrmion number S of each state is assessed based on the sketched magnetisation configuration in the cross-section. (f) Line profiles through the center of the Co/Pd film for the normalised out-of-plane magnetisation (m_z = M_z/M_s) in remanent state Co/Pd spins illustrate the possibility to tailor the opening angle of the donut state by adjusting J_i. The magnetic spiral also appears after opening the circular domain wall of the donut state by applying a small in-plane magnetic field.