#
APS March Meeting 2022

## Volume 67, Number 3

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Monday–Friday, March 14–18, 2022;
Chicago

### Session T00: Poster Session III (1pm- 4pm CST)

1:00 PM,
Thursday, March 17, 2022

Room: McCormick Place Exhibit Hall F1

### Abstract: T00.00257 : Calculations of the lifetime of magnetic skyrmions and antiskyrmions in discrete systems with large number of spins

Abstract

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Presenter:

Hannes Jonsson

(Univ of Iceland)

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Author:

Hannes Jonsson

(Univ of Iceland)

Topological stabilization of magnetic skyrmions is investigated for discrete 2D systems with ferromagnetic ground state. While a skyrmion is topologically protected in a continuous system, this is not so for discrete systems and the question is what limit is reached for a discrete system as the lattice constant becomes infinitesimal. Calculations of the skyrmion lifetime within harmonic transition state theory [1] are performed as a function of lattice constant [2]. The parameters of the Hamiltonian, i.e exchange (J) and anisotropy (K) and Dzyaloshinsky-Moriya (D) parameters, are chosen to keep the size of the skyrmion and its energy unchanged for sufficiently small lattice constants, in all cases consistent with a skyrmion in a given continuous micromagnetic model. The number of magnetic moments is over a million for the finest lattice. The energy barrier for skyrmion collapse in the limit of infinitesimal lattice constant approaches the value corresponding to the minimum energy of the Belavin-Polyakov topological soliton. The entropy contribution to the pre-exponential factor in the Arrhenius expression for the skyrmion lifetime also approaches a constant. The lifetime, therefore, reaches a finite value in the limit of infinitesimal lattice constant [2]. Secondly, calculations are presented for large antiskyrmions in Mn-Pt-Sn tetragonal Heusler material [3]. The calculations involve nearly a million spins and the parameter values in the extended Heisenberg Hamiltonian are chosen to reproduce experimental observations, in particular the 150-nm diameter. The calculated lifetime is consistent with the reported laboratory observations and this exceptional stability at room temperature is found to result from large activation energy for collapse due to strong exchange coupling while the pre-exponential factor in the Arrhenius expression has a typical value. The long lifetime is, therefore, found to result in this case from energetic rather than entropic effects.