Dresden 2020 – scientific programme

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MA: Fachverband Magnetismus

MA 30: Ultrafast Magnetization III

MA 30.10: Talk

Wednesday, March 18, 2020, 12:00–12:15, HSZ 101

Macroscopic effects due to atomistic colored noise in magnetization dynamics — •Unai Atxitia¹ and Oksana Chubykalo-Fesenko² — ¹Fachbereich Physik, Freie Universitaet Berlin, 14195 Berlin, Germany — ²Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain

The atomistic spin dynamics has recommended itself as a tool for modeling magnetization dynamics in the ultrafast timescale. This approach is based on the Langevin dynamics within the white noise approximation [1]. Here we investigate the macroscopic effects arising from the assumption that at the atomic level the noise is colored [2]. We derive analytically an equation of motion for the macrospin dynamics. We show that the colored noise assumption (i) introduces a red shift in the precession frequency which is temperature and correlation time dependent and (ii) slows down both transverse and longitudinal relaxation times. The increase of the transverse relaxation time effectively means the decrease of the so-called Gilbert damping. We compare the results with direct atomistic Langevin dynamics simulations using the colored noise approach [1]. For the transverse dynamics the effect of the colored noise becomes significant for the correlation times larger than 1 ps while for the longitudinal relaxation the effects are already visible for correlation times of the order of several femtoseconds (timescale of the precession in the exchange field). References: [1] R.F.L. Evans et al. J.Phys.:Cond.Matt 26, 103202 (2014) [2] U.Atxitia et al. Phys Rev.Lett. 102 057203 (2009).