Binary information represented by chiral spin textures

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Conventional racetracks where the information is encoded by the presence or absence of a skyrmion require engineered pinning structures between which a chain of skyrmions is moved. This increases the current density to transport the information and leads to an unacceptably high bit error rate. The approach followed here, represents the binary states with different topologically protected spin textures and does not require pinning sites for stable bit information allowing to overcome the reported bit error rate issues. In this joint research project, we rely on (i) tubular and incomplete skyrmions (artificial bobbers), where we will use ferro-/ferrimagnetic multilayer systems and on (ii) recently discovered Gd/Fe/Ir multilayers that permits the coexistence of skyrmions and antiskyrmions stabilized solely by dipolar interactions to represent the two states. For the controlled local generation of these distinct spin structures, the systems magnetic properties will be altered either by a variation of the multilayer composition or by local ion irradiation. Using Lorentz transmission electron and high resolution magnetic force microscopy the distinct spin structures can be characterized and their motion under current pulses inducing either spin orbit or spin transfer torque can be investigated. The existence and stability of distinct topologically protected magnetic spin textures in the magnetic multilayer structures fabricated here will be analyzed by advanced micromagnetic simulations that allow for a fully self-consistent solution of the micromagnetic equations and spin drift diffusion equation. The stability of the structures will be derived from the energy barriers and attempt frequencies calculated from atomistic models based on the string method. A feedback loop between experiments and simulations will be used to calibrate the simulations and, in turn, use the simulation for the prediction of spintronic properties of various functional multilayer structures.