SKM 2021 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 17: Skyrmions II (joint session MA/KFM)

MA 17.5: Vortrag

Freitag, 1. Oktober 2021, 11:15–11:30, H5

Skyrmions as quasiparticles: Free energy and entropy — •Daniel Schick, Markus Weißenhofer, Levente Rózsa, and Ulrich Nowak — Fachbereich Physik, Universität Konstanz, DE-78457 Konstanz, Germany

Magnetic skyrmions are quasiparticles primarily investigated due to their exceptional stability enabling data storage [1] and magnetic logic applications[2]. While at low temperatures they are robust against thermal fluctuations, they are rapidly created and annihilated at high temperatures[3]. In our paper[4], we calculated the free energy and entropy of magnetic skyrmions for a (Pt0.95Ir0.05)/Fe bilayer on Pd(111), using atomistic spin simulations at different temperatures. At low temperatures, skyrmions possess a higher entropy than the topologically trivial state, reducing the free-energy difference between skyrmions and collinear states with increasing temperature. At elevated temperatures we find the free energy of skyrmions to be lower than that of topologically trivial states, meaning that they are energetically preferred due to entropic stabilization. While this result is qualitatively in line with linear spin-wave theory, going beyond this approximation reveals deviations and even sign changes in both the energy difference and the entropy difference at increased temperatures.
[1] G. Yu et al., Nano Lett. 17, 1, 261-268, 2017
[2] S. Luo et al., Nano Lett. 18, 2, 1180-1184, 2018
[3] S. von Malottki et al., Phys. Rev. B 99, 060409(R), 2019
[4] D. Schick et al., Phys. Rev. B 103, 214417, 2021