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.
[1] V. Shokeen et al., Phys. Rev. Lett. 119, 107203 (2017)
[2] K. Krieger et al. J. Phys. Condens. Matter 29, 224001 (2017)
[3] P. Elliott et al., Scientific Reports 6, 38911 (2016)
[4] J. K. Dewhurst et al., Computer Phys. Comm. 209, 92 (2016)
[5] K. Krieger et al., J. Chem. Theory Comput. 11, 4870 (2015)