The structure of domain walls determines to a large extent the properties of magnetic materials, in particular their hardness and switching behavior, it represents an essential ingredient of spintronics. Common domain walls are of Bloch and Neel types in which the magnetization rotates around a fixed axis, giving rise to a one-dimensional magnetization profile. Domain walls in helical magnets, most relevant in multiferroics, were never studied systematically. Here we show that domain walls in helical magnets are fundamentally different from Bloch and Neel walls. They are generically characterized by a two-dimensional pattern formed by a regular lattice of vortex singularities. In conical phases vortices carry Berry phase flux giving rise to the anomalous Hall effect. In multiferroics vortices are charged, allowing to manipulate magnetic domain walls by electric fields. Our theory allows the interpretation of magnetic textures observed in helical magnetic structures.
Electronic structure of single-wall silicon nanotubes and silicon nanorribons: Helical symmetry treatment and effect of dimensionality
Helical method of tube formation for band structure calculations and Hartree-Fock self-consistent field method (HF-SCF) modified for periodic solids have been applied in study of electronic properties of single-wall silicon nanotubes (SWSiNT), graphene-like parent 2D-hP silicone sheet and nanoribbons (SiNR). The results obtained for nanotubes of the length of ${\approx}$ 358 Åin diameter range ${\approx}$ 3.7 Å-- 116 Åof different helicity-types have shown that only small-diameter SWSiNTs up to} $φ$ {6.3 Å~ are metallic due to the effect of curvature which induces coupling of}{ $σ$ }{and}{ $π$…
