Time: Tuesday, October 23rd, 16:10
Speaker: Sangeeta SHARMA, Berlin
The type of magnetic coupling between the constituent atoms of a solid, i.e. ferromagnetic, anti-ferromagnetic or non-collinear, is one of the most fundamental properties of any magnetic material. This magnetic order is governed by the exchange interaction, which is associated with a characteristic time scale at which spin-flip scattering processes occur and change the intrinsic magnetic structure. These time scales can be determined from the exchange parameters and are of the order of 40-400 fs for transition metal atoms. It is a challenge to manipulate this magnetic order at sub-exchange time scales.
We demonstrate[1,2,3,4,5] that spin transfer driven by inter-site spin-selective charge transfer is one of the key mechanisms that underpins spin manipulation at sub-exchange time scales. This charge flow is induced by optical excitations and represents both the fastest possible response of an electronic system to a laser pulse, as well as a response highly sensitive to pulse intensity and structure. By investigating a wide range of interfaces and multi-sub-lattice magnetic materials we demonstrate a rich phenomena of sub-exchange spin manipulation, including even changing the magnetic order of a material from AFM to FM on femtosecond time scales. We furthermore are able to formulate three simple rules that predict the early time qualitative dynamics of magnetization for ferromagnetic, anti-ferromagnetic and ferri-magnetic materials.
 V. Shokeen et al., Phys. Rev. Lett. 119, 107203 (2017)
 K. Krieger et al. J. Phys. Condens. Matter 29, 224001 (2017)
 P. Elliott et al., Scientific Reports 6, 38911 (2016)
 J. K. Dewhurst et al., Computer Phys. Comm. 209, 92 (2016)
 K. Krieger et al., J. Chem. Theory Comput. 11, 4870 (2015)