Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 5: Spin Structures and Magnetic Phase Transitions

MA 5.5: Vortrag

Montag, 26. März 2012, 10:30–10:45, H 0112

Modulated states in chiral helimagnets with easy-plane anisotropy — •Anna B. Butenko¹, Alexei N. Bogdanov¹, Ulrich K. Rößler¹, Eric A. Karhu², Michael D. Robertson³, and Theodore L. Monchesky² — ¹IFW Dresden, Germany — ²Dalhousie University, Halifax NS, Canada — ³Acadia University, Wolfville NS, Canada

A surface-induced uniaxial anisotropy of easy-axis type can stabilize hexagonal Skyrmion lattices in nanostructures of isotropic or cubic chiral magnets. In these modulated states with field applied along the anisotropy axis, the Skyrmions run along the axis. This effect explains experimental observations of Skyrmion lattices in thin layers of cubic helimagnets (Fe,Co)Si and FeGe. We find that another type of Skyrmion lattice can be stabilized in uniaxial magnets of easy-plane type, when the field is applied perpendicularly to the axis. Detailed results from calculations of the magnetic phase diagram for the model of an isotropic chiral helimagnet with induced easy-plane uniaxial anisotropy are presented. Depending on the strength of the anisotropy, different sequences of magnetization processes can occur with phase transitions between helicoidal transverse modulations, elliptically distorted conical helices and Skyrmion lattices. The theoretical results are shown to be relevant for epitaxial MnSi (111) thin films with strain-induced easy-plane anisotropy. Ab initio calculations confirm the easy-plane character of the induced magnetic anisotropy in rhombohedrally distorted MnSi (111) with isotropic and tensile strains in the basal plane.