Ultrafast spin-dynamics: TDDFT's killer app.

I will talk about all-optical switching of long-range magnetic order. The type of coupling between the constituent atoms of a magnetic solid, usually ferromagnetic (FM) or anti-ferromagnetic (AFM), is a fundamental property of any magnetic material. This coupling is governed by the exchange interaction, for which the time scale of a typical magnetic material is of the order of a few 100s of femtoseconds. In our work, using time-dependent density functional theory (TDDFT), we demonstrate that a rich control over magnetization at
sub-exchange time scales (of the order of few tens of femtoseconds) is possible[1,2,3,4]. This even includes
changing the magnetic order from AFM to FM[5]. By investigating a wide range of multi-sublattice
magnetic materials we are able to formulate three simple rules that predict the qualitative dynamics
of magnetization for ferromagnetic, anti-ferromagnetic, and ferri-magnetic materials on sub-exchange
time scales.
1] Shokeen et al. Phys. Rev. Lett. 119, 107203 (2017)
[2] Elliott et al. Scientific Reports 6, 38911 (2016)
[3] Chen et al. Phys. Rev. Lett. 122, 067202 (2019)
[4] Siegrist et al. Nature 571, 240 (2019)
[5] Dewhurst et al. Nano Lett. 18, 1842, (2018)