ELFT HÍRADÓ

[tcsaba <tcsaba AT eik.bme.hu>]

                 M E G H Í V Ó - I N V I T A T I O N

    Seminar Series of the Department of Theoretical Physics at the
           Budapest University of Technology and Economics


                          Levente Rózsa
                     (University of Hamburg)

         Spin waves and damping in noncollinear spin systems


Spin waves or magnons represent elementary excitations of magnetically 
ordered materials. In the field of magnonics, spin waves are expected to 
be used as information carriers, taking advantage of their short 
wavelengths compared to electromagnetic waves possessing similar 
frequencies. The formation of noncollinear spin configurations such as 
domain walls, vortices or magnetic skyrmions is a natural way of 
influencing the properties of magnons in a system. Spin waves are often 
described within the terms of the classical Landau-Lifshitz-Gilbert 
equation. Here we discuss how the noncollinear spin arrangement forces 
the spin waves to be cylindrically instead of circularly polarized, 
leading to an enhancement of the effective damping parameter compared to 
the Gilbert damping [1]. The results are illustrated through the example 
of isolated k\pi skyrmions [2], which represent cylindrically symmetric 
two-dimensional localized spin configurations where the out-of-plane 
component of the magnetization rotates by k\pi between the center of the 
structure and the collinear background. At higher temperatures, 
magnon-magnon interactions lead to a modification of spin wave 
frequencies, which can be taken into account in a micromagnetic model by 
introducing effective temperature-dependent interaction parameters. 
Through the example of a ferromagnetic system, we calculate the 
temperature dependence of the effective Dzyaloshinsky-Moriya interaction 
[3], which also plays a crucial role in the stabilization of 
noncollinear magnetic structures.

[1] L. Rózsa, J. Hagemeister, E. Y. Vedmedenko, and R. Wiesendanger, 
Phys. Rev. B 98, 100404(R) (2018).
[2] L. Rózsa, J. Hagemeister, E. Y. Vedmedenko, and R. Wiesendanger, 
arXiv:1810.06471 (2018).
[3] L. Rózsa, U. Atxitia, and U. Nowak, Phys. Rev. B 96, 094436 (2017).

Időpont: 2018. december 7. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba