Rate theory for magnetic transitions with applications to Skyrmion and antivortex annihilation

by Hannes Jonsson (Faculty of Physical Sciences, University of Iceland)

Tuesday 31 Mar 2015, 15:00 → 16:00 Europe/Rome

Aula Touschek (Dip. di Fisica - Edificio G. Marconi)

Methodology for studying temperature assisted transitions between magnetic states has been developed and applied to annihilation/formation of non-collinear localized states such as Skyrmions, antivortices and springs in nanoscale systems. The transition mechanism is determined by finding minimum energy paths using a geodesic formulation of the nudged elastic band method [1], and the transition rate estimated using a harmonic approximation to transition state theory based on Landau-Lifshitz-Gilbert dynamics [2,3]. The variation of the hysteresis loop of a Fe/SmCo spring magnet can be reproduced nicely using the rate theory without introducing temperature dependence of parameters in the Hamiltonian [4]. Previously, such measurements have been interpreted in terms of variations in the anisotropy coefficient with temperature. The annihilation of Skyrmion and antivortex states in nanoisland with a few tens of Fe atoms is shown to have a relatively low energy barrier and involves! a shift followed by concerted rotation of the magnetic momenta [5]. The methodology could, for example, help search for materials and design of high density data recording and other magnetic devices. [1] P.F. Bessarab, V.M. Uzdin, and H. Jónsson, arXiv:1502.05065. [2] P.F. Bessarab, V.M. Uzdin, and H. Jónsson, Phys. Rev. B 85, 184409 (2012). [3] P.F. Bessarab, V.M. Uzdin, and H. Jónsson, Zeitschrift fur Physikalische Chemie 227, 1543 (2013). [4] M. Moskalenko, P.F. Bessarab, V.M. Uzdin, and H. Jónsson, (submitted 2015). [5] P.F. Bessarab, V.M. Uzdin, and H. Jónsson, Phys. Rev. B 89, 214424 (2014).