Berlin 2015 – scientific programme

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MA: Fachverband Magnetismus

MA 35: Magnetization / Demagnetization Dynamics II

MA 35.4: Talk

Wednesday, March 18, 2015, 15:45–16:00, EB 301

Transfer of angular momentum from the electrons to the lattice during ultrafast demagnetization — •Thodoris Tsatsoulis, Michael Haag, Christian Illg, and Manfred Faehnle — Max-Planck-Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany

After irradiation of a magnetic film with a femtosecond (fs) optical laser pulse there is an ultrafast demagnetization of the film on a time-scale of few 100 fs. For a theoretical explanation it is often assumed (see [1] and references therein) that the electrons excited by the beam are scattered at phonons and that thereby in systems with spin-orbit coupling the spin- and orbital-angular momentum of these electrons, which are related to magnetic moments, change. In all these theories only the change of the electronic magnetic moment is calculated explicitly, whereas it is implicitly assumed that the lattice acts as a perfect sink for the angular momentum. The reason is that for the construction of the electron-phonon scattering operator the lattice dynamics is represented in terms of linearly polarized phonons, which do not have a well-defined angular momentum. Therefore the change of the angular momentum of the lattice cannot be calculated from the change of the phononic occupation numbers. We calculate the modification of the angular momentum of the lattice explicitly by representing the lattice dynamics in terms of the magnetoelastic eigenmodes of a ferromagnetic system which carry a well-defined angular momentum [2], respectively.

[1] C.Illg, M. Haag and M. Faehnle, Phys. Rev. B 88, 214404 (2013).

[2] L. Zhang and Q. Niu, Phys. Rev. Letters 112, 085503 (2014).