Ulrich Roessler - Leibniz Institute, Dresden
In non-centrosymmetric magnets the chiral Dzyaloshinskii-Moriya (DM) exchange stabilizes tubular baby-Skyrmions as excitations. These string-like objects are topologically stable and smooth and they may condense into extended complex mesophases [1,2,3] similar to textures in chiral liquid crystals. These extended Skyrmionic textures are determined by the stability of the localized `solitonic' Skyrmion cores and their geometrical incompatibility which frustrates an ideal regular space-filling. Two-dimensional models for these inhomogeneous magnetic phases bear strong similarity with Abrikosov-lattices : just as cylindrical vortices arrange into regular arrays in type-II superconductors, Skyrmions form ordered arrays in chiral magnets [1,2]. In magnetic phase diagrams for models of chiral magnets a competition arises between helical and different Skyrmionic phases. Near the ordering temperature defect-ordered half-Skyrmion states may appear which transform into full-Skyrmion states under an applied field . The theoretically predicted Skyrmionic textures may explain recent experimental results on the exotic magnetic phenomena of "partial order", liquid/amorphous-like mesophases above the magnetic order transition temperature, and the field-driven "A-phase" observed in MnSi, and other cubic helimagnets with B20 structure. New theoretical results are presented on the stabilization of Skyrmion lattices in cubic chiral magnets by combined effect of magnetic anisotropy and magnetic field . It is argued that chiral Skyrmionic textures exist in various magnetic systems because, in non-centrosymmetric crystal structures, chiral DM-couplings are a consequence of the leading spin-orbit effects.
 A.N. Bogdanov, D.A. Yablonskii, Sov. Phys. JETP 68 (1989) 101.
 A. Bogdanov, A. Hubert, JMMM 138 (1994) 255.
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