Danny Thonig – Ultrafast magnetism from ab-initio atomistic magnetisation dynamics

Speaker: Danny Thonig (Örebro Universitet)

Title: Ultrafast magnetism from ab-initio atomistic magnetisation dynamics

Time: Fika 10:30-11:00 , Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
Writing and retrieving information in a magnetic material at high speed and with lower energy consumption has become an intense research field in solid state physics, since there is growing benefits for our society and within technical applications. For instance, by using all-optical control of magnetism, local magnetic moments can achieve remarkably fast switching times. The pioneering work by Beaurepaire et al. [1] demonstrated dynamics on a pico second time-scale. The experiment of Ref. [1] used a high-intensity laser pulse that pumped the sample, and after a time-delay, a second laser pulse was used to probe its magnetic state, via the magneto-optical effect. All hitherto proposed mechanisms of ultrafast magnetism (e.g. Refs. [2] and [3]) have been criticized, for not being consistent with observations and/or for not being physically relevant (reviewed e.g. in Ref.[4]). The most pressing, open questions connected to these experiments concerns the transfer of angular momentum.
To describe ultrafast magnetism from first-principles, we used atomistic magnetisation dynamics combined with density functional theory. The latter serves to calculate fundamental magnetic properties, magnetic interaction, and energy dissipation contributions.
We applied this machinery naturally to a wide range of materials, as recently also to Heusler and inverse Heusler materials. We studied demagnetisation and remagnetisation behaviour for different structural phases of Heusler’s and compared our results to experimental measurements with qualitative good agreement.

[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).
[2] B. Koopmans et al., J. Magn. and Magn. Mater. 286, 271 (2005).
[3] M. Battiato et al., Phys. Rev. Lett. 105, 027203 (2010).
[4] O. Eriksson, A.Bergman, L.Bergqvist and J.Hellsvik, Atomistic Spin-Dynamics, fundamentals and applications (Oxford university press, 2017).