Berlin 2012 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Magnetization / Demagnetization Dynamics I

MA 15.2: Talk

Tuesday, March 27, 2012, 10:00–10:15, H 1012

Ultrafast Demagnetization in Ferromagnetic Materials — •Benedikt Y. Mueller, Tobias Roth, Mirko Cinchetti, Martin Aeschlimann, and Bärbel Rethfeld — Department of Physics and Optimas Research Center, University of Kaiserslautern, Germany

Ultrafast demagnetization due to laser irradiation has been studied for more than two decades [1,2,3]. Up to now, no theory explains the large variety of effects on equal footing microscopically. In our model we apply a kinetic approach based on a combination of the Stoner model and the Boltzmann equation [4]. This results in a spin-resolved Boltzmann equation considering three reservoirs: up-electrons, down-electrons and the phononic system. The coupling between these reservoirs is described by electron-electron and electron-phonon collisions whereby spin-flips are realized by Elliott-Yafet type spin-flip scattering. In this spirit, we trace nonequilibrium electrons during and after laser irradiation and additionally this provides a dynamical description for magnetism. We show the solution of the spin-resolved Boltzmann equation for the example of Nickel by implementing the density of states [5] into our model. As a result of our effective two band model, the demagnetization is driven by the equilibration process of the electron temperatures and the chemical potentials of up and down electrons.

[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996)

[2] J. Hohlfeld et al., Phys. Rev. Lett. 78, 25 (1997)

[3] B. Koopmans et al., Nature Materials 9, 3 (2010)

[4] B. Rethfeld et al., Phys. Rev. B 65, 214303 (2002)

[5] Z. Lin et al., Phys. Rev. B 77, 075133 (2008)