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MA: Fachverband Magnetismus
MA 40: Skyrmions III (joint session MA/TT)
MA 40.6: Vortrag
Mittwoch, 18. März 2020, 16:15–16:30, POT 6
The effects of disorder on hysteresis loops in chiral magnets — David Cortes1, Marijan Beg1, Hans Fangohr1,2, Tom Lancaster3, Peter Hatton3, Thorsten Hesjedal4, and •Ondrej Hovorka1 — 1University of Southampton, UK — 2European XFEL GmbH, Schenefeld, Germany — 3Durham University, UK — 4Oxford University, UK
In this talk we investigate the effect of random pinning sites on magnetization behaviour in systems with Dzyaloshinskii-Moriya interaction (DMI). We consider a standard classical spin Hamiltonian with Heisenberg exchange and DMI energy terms, and model the disorder through statistical Gaussian distribution of anisotropy. We first develop a mean-field model which allows to compute systematically and efficiently the magnetisation versus field hysteresis loops for variable temperature, and can be used for computing qualitative thermodynamic phase diagrams to guide computationally costly Monte-Carlo simulations. We show that as the standard deviation of the anisotropy distribution increases, relative to the strength of exchange interaction and DMI, the nature of the reversal modes observed along a typical hysteresis loop changes in a certain temperature window. Namely, in 'clean' systems with narrow anisotropy distribution, the reversal proceeds through the appearance of skyrmion lattices at low external fields, while in 'dirty' systems with broad anisotropy distribution, the reversal is through the nucleation of individual or small groups of skyrmions. We systematically quantify this effect and discuss its broader implications for applications.