Internal structure of hexagonal skyrmion lattices in cubic helimagnets

McGrouther, D. , Lamb, R.J., Krajnak, M., McFadzean, S., McVitie, S. , Stamps, R.L. , Leonov, A.O., Bogdanov, A.N. and Togawa, Y. (2016) Internal structure of hexagonal skyrmion lattices in cubic helimagnets. New Journal of Physics, 18, 095004. (doi:10.1088/1367-2630/18/9/095004)

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Abstract

We report the most precise observations to date concerning the spin structure of magnetic skyrmions in a nanowedge specimen of cubic B20 structured FeGe. Enabled by our development of advanced differential phase contrast (DPC) imaging (in a scanning transmission electron microscope (STEM)) we have obtained high spatial resolution quantitative measurements of skyrmion internal spin profile. For hexagonal skyrmion lattice cells, stabilised by an out-plane applied magnetic field, mapping of the in-plane component of magnetic induction has revealed precise spin profiles and that the internal structure possesses intrinsic six-fold symmetry. With increasing field strength, the diameter of skyrmion cores was measured to decrease and accompanied by a nonlinear variation of the lattice periodicity. Variations in structure for individual skyrmions across an area of the lattice were also studied utilising a new increased sensitivity DPC detection scheme and a variety of symmetry lowering distortions were observed. To provide insight into fundamental energetics we have constructed a phenomenological model, with which our experimental observations of spin profiles and field induced core diameter variation are in good agreement with predicted structure in the middle of the nanowedge crystal. In the vicinity of the crystal surfaces, our model predicts the existence of in-plane twisting distortions which our current experimental observations were not sensitive to. As an alternative to the requirement for as yet unidentified sources of magnetic anisotropy, we demonstrate that surface states could provide the energetic stabilisation needed for predomination over the conical magnetic phase.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:McGrouther, Dr Damien and Togawa, Dr Yoshihiko and McVitie, Professor Stephen and LAMB, Raymond and Stamps, Professor Robert and Krajnak, Mr Matus and McFadzean, Dr Sam
Authors: McGrouther, D., Lamb, R.J., Krajnak, M., McFadzean, S., McVitie, S., Stamps, R.L., Leonov, A.O., Bogdanov, A.N., and Togawa, Y.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:New Journal of Physics
Publisher:Institute of Physics Publishing Ltd.
ISSN:1367-2630
ISSN (Online):1367-2630
Copyright Holders:Copyright © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
First Published:First published in New Journal of Physics 18: 095004
Publisher Policy:Reproduced under a Creative Commons License
Data DOI:/10.5525/gla.researchdata.353

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
683531Consortium for advanced materials based on spin chiralityRobert StampsEngineering & Physical Sciences Research Council (EPSRC)EP/M024423/1S&E P&A - PHYSICS & ASTRONOMY