Center for Nonlinear Studies

Wednesday, September 20, 20172:00 PM - 3:00 PMCNLS Conference Room (TA-3, Bldg 1690)
Seminar
Rate theory for magnetic transitions applied to nanoislands, elements of spin ice and skyrmions
Hannes JonssonUniversity of Iceland
The lifetime of magnetic states and the mechanism for thermally activated transitions from one magnetic state to another can be analyzed in terms of the shape of the energy surface, i.e. the energy as a function of the angles defining the orientation of the magnetic moments. Minima on the energy surface correspond to stable or metastable magnetic states and can represent parallel, antiparallel or, more generally, non-collinear arrangements of the magnetic moments. Harmonic transition state theory has been developed and a method for finding minimum energy paths and first order saddle points for magnetic transitions [1,2]. An expression for the pre-exponential factor in the rate expression is obtained from the Landau–Lifshitz–Gilbert equation for spin dynamics. An application of this rate theory to nanoscale Fe islands and full Fe overlayer on W(110) has revealed how the transition mechanism and rate depend on island shape/size and presence of magnetic tip, and led to reinterpretation of experimental observations [3,4]. Calculations for one and two ring elements of kagome spin ice also show close agreement with experimental measurements but give a pre-exponential factor that is three orders of magnitude smaller than has previously been assumed [5]. More recently, this methodology has been used to study ferromagnetic and antiferromagnetic skyrmions which have been proposed as building blocks of future memory devices [6,7]. First steps in the extension of the rate theory to include tunneling of the magnetic moments have been taken [8].

References:

[1] P.F. Bessarab, V.M. Uzdin and H. Jonsson, Phys. Rev. B. 85, 184409 (2012).
[2] P.F. Bessarab, V.M. Uzdin and H. Jonsson, Computer Physics Communications 196, 335 (2015).
[3] P.F. Bessarab, V.M. Uzdin and H. Jonsson, Phys. Rev. Letters 110, 020604 (2013).
[4] A. Ivanov, P.F. Bessarab, V.M. Uzdin and H. Jonsson, Nanoscale 9, 13320 (2017).
[5] S. Liashko, V.M. Uzdin and H. Jonsson, New Journal of Physics (2017, http://iopscience.iop.org/article/10.1088/1367-2630/aa8b96).
[6] I. Lobanov, H. Jonsson and V. M. Uzdin. Phys. Rev. B 94, 174418 (2016).
[7] V. M. Uzdin, M. N. Potkina, I. S. Lobanov, P. F. Bessarab, H. Jonsson, Physica B (in press, https://arxiv.org/abs/1705.02930).
[8] S. Vlasov, P. F. Bessarab, V. M. Uzdin and H. Jonsson, Nanosystems: Physics, Chemistry, Mathematics 8, 454 (2017).

Host: Angel E. Garcia