Hall effect and transmission electron microscopy of epitaxial MnSi thin films

We present Hall effect measurements on MnSi/Si(111) epilayers and find an anomalous Hall contribution that is significantly smaller than in bulk crystals, which enables the observation of an additional contribution to the anomalous signal previously overlooked in MnSi. Our measurements indicate the signal is not due to skyrmions in MnSi thin films, which are absent in out-of-plane fields, but rather are the result of scattering from the cone phase. The absence of magnetic contrast in the transmission electron microscopy (TEM) measurements are consistent with this interpretation. We provide a method to model TEM images of skyrmions lattices to determine the conditions necessary for their observation in other B20 epilayers with an anisotropy that is favourable to their formation.T.L.M. and M.N.W. acknowledge support from NSERC and the support of the Canada Foundation for Innovation, the Atlantic Innovation Fund, and other partners which fund the Facilities for Materials Characterization, managed by the Institute for Research in Materials. Work done by J.C.L. was funded by the Royal Society. The work of F.N.R. was supported by RFBR, research project No. 14-02-31012.This is the accepted manuscript of a paper published in Physical Review B (SA Meynell, MN Wilson, JC Loudon, A Spitzig, FN Rybakov, MB Johnson, TL Monchesky, Physical Review B 2014 90, 224419)

KKRnano: Quantum Description of Skyrmions in Chiral B20 Magnets

We present the latest version of the linear-scaling electronic structure code KKRnano, in which an enhanced Korringa-Kohn-Rostoker (KKR) scheme is utilized to perform Density Functional Theory (DFT) calculations. The code allows us to treat system sizes of up to several thousands of atoms per unit cell and to simulate a non-collinear alignment of atomic spins. This capability is used to investigate nanometer-sized magnetic textures in the germanide B20-MnGe, a material that is potentially going to play an important role in future spintronic devices. A performance analysis of KKRnano on Hazel Hen emphasizes the good scaling behaviour with increasing system size and demonstrates the extensive integration of highly optimized libraries

KKRnano: Quantum Description of Skyrmions in Chiral B20 Magnets

We present the latest version of the linear-scaling electronic structure code KKRnano, in which an enhanced Korringa-Kohn-Rostoker (KKR) scheme is utilized to perform Density Functional Theory (DFT) calculations. The code allows us to treat system sizes of up to several thousands of atoms per unit cell and to simulate a non-collinear alignment of atomic spins. This capability is used to investigate nanometer-sized magnetic textures in the germanide B20-MnGe, a material that is potentially going to play an important role in future spintronic devices. A performance analysis of KKRnano on Hazel Hen emphasizes the good scaling behaviour with increasing system size and demonstrates the extensive integration of highly optimized libraries

Topological domain walls in helimagnets

Domain walls naturally arise whenever a symmetry is spontaneously broken. They interconnect regions with different realizations of the broken symmetry, promoting structure formation from cosmological length scales to the atomic level(1,2). In ferroelectric and ferromagnetic materials, domain walls with unique functionalities emerge, holding great promise for nanoelectronics and spintronics applications(3-5). These walls are usually of Ising, Bloch or Neel type and separate homogeneously ordered domains. Here we demonstrate that a wide variety of new domain walls occurs in the presence of spatially modulated domain states. Using magnetic force microscopy and micromagnetic simulations, we show three fundamental classes of domain walls to arise in the near-room-temperature helimagnet iron germanium. In contrast to conventional ferroics, the domain walls exhibit a well-defined inner structure, which-analogous to cholesteric liquid crystals-consists of topological disclination and dislocation defects. Similar to the magnetic skyrmions that form in the same material(6,7), the domain walls can carry a finite topological charge, permitting an efficient coupling to spin currents and contributions to a topological Hall effect. Our study establishes a new family of magnetic nano-objects with non-trivial topology, opening the door to innovative device concepts based on helimagnetic domain walls