Hybrid three-dimensional solitons for applications

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Chiral magnets (ChMs) comprise a distinct class of magnetic crystals with unique properties, which are significantly distinct from those of other magnetically ordered systems such as common ferro- or antiferromagnets. This class of magnetic crystals includes different Si- and Ge-based alloys, such as MnSi, FeGe and β-Mn-type Co-Zn-Mn alloys. Nanostructured thin films and stripes of such ChMs have properties that are different from those of bulk crystals. The reduced dimensionalities of such systems provide nontrivial mechanisms for the stabilization of particle-like states that are known as magnetic skyrmions and are promising objects for applications in spintronics. Recently, we reported that the presence of natural geometrical confinement and free boundaries in such crystals is responsible for the stabilization of other particle-like objects – chiral bobbers (ChBs). Such hybrid particles have smooth magnetization vector fields and magnetic singularities – Bloch points that are located a certain distance from the surface of the crystal. As a result of the nontrivial spin textures and compact sizes of ChBs, they are interesting objects for fundamental research and practical applications. The aim of the proposed project is a theoretical and experimental study of the static and dynamic properties of such hybrid solitons: their thermal stability, pairwise interaction, spectrum of excitations in an AC magnetic field, mobility under an electric current, behavior in the presence of a thermal gradient and interactions with spin waves. Theoretical descriptions will be based on both commonly used approaches of continuum micromagnetic theory and atomistic spin-lattice models. Direct energy minimization, spin dynamics driven by electric currents and external magnetic fields, Monte Carlo simulations and calculations of energy barriers, as well as other methods implemented in the software developed in our group, will be used to construct magnetic phase diagrams, dispersion curves, energy barriers, velocity dependencies for ChBs, etc.The theoretical work will be supported by high-resolution quantitative measurements of the magnetic fields of skyrmions and ChBs performed using off-axis electron holography (EH) and Lorentz imaging in the transmission electron microscope (TEM), allowing quantitative comparisons of theoretically predicted effects with experimental observations and vice versa. TEM experiments will be performed in the Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C; www.er-c.org), which is a national user centre for electron microscopy and a leading institute in the development and application of advanced electron microscopy methodologies.