Theoretical seminar | 22 June 2022

Reduction of the size of magnetic bits for data storage, transfer and processing of information down to the nanoscale would lay the foundation for large advances in information technology, both in terms of processing speed and energy efficiency. Such a development requires analysis of the stability of localized magnetic states with respect to thermal fluctuations and random external influences. These issues are investigated in the framework of harmonic transition state theory.
The lifetime of skyrmions and antiskyrmions, two examples of chiral magnetic structures, is calculated using various values of materials parameters, such as the ratio of the lattice constant
to the skyrmion size. As a result, the skyrmion lifetime can, for large enough number of spins, correspond to thermal stability at room temperature even without magnetic dipole–dipole interaction. Properties of skyrmions in antiferromagnets (AFM) are compared with skyrmions in ferromagnets (FM). The rates of skyrmion collapse and escape through the boundary of a track, as well as the binding to and collapse at a non-magnetic impurity, are calculated as a function of an applied magnetic field in both FM and AFM. The lifetime of antiskyrmions in an Mn–Pt–Sn tetragonal Heusler material has been calculated using an atomic scale representation including nearly a million spins. The long lifetime observed experimentally at room temperature is found to result from energetic effects rather than entropic effects in this system. The dynamics as well as thermal stability of skyrmions and antiskyrmions in FM and AFM was compared using energy conserving transformations of spin configuration and vectors in the extended Heisenberg Hamiltonian.

References:
1. M. N. Potkina, I. S. Lobanov, H. Jónsson, V. M. Uzdin, Lifetime of skyrmions in discrete systems with infinitesimal lattice constant, Journal of Magnetism and Magnetic Materials 549, 168974 (2022).
2. M. N. Potkina, I. S. Lobanov,  H. Jónsson, V. M. Uzdin, Skyrmions in antiferromagnets: Thermal stability and the effect of external field and impurities, Journal of Applied Physics 127, 213906 (2020).
2. M. N. Potkina, I. S. Lobanov, O. A. Tretiakov, H. Jónsson, and V. M. Uzdin, Stability of long-lived antiskyrmions in the Mn-Pt-Sn tetragonal Heusler material, Physical Review B 102, 134430 (2020).
4. A. S. Varentcova,  S. von Malottki,  M. N. Potkina, G. Kwiatkowski, S. Heinze, P. F. Bessarab, Toward room-temperature nanoscale skyrmions in ultrathin films, npj Computational Materials 6, 193 (2020).
5. V. M. Uzdin, M. N. Potkina, I. S. Lobanov, P. F. Bessarab, H. Jónsson, The effect of confinement and defects on the thermal stability of skyrmions, Physica B: Condensed Matter 549, 6-9 (2018).