Dresden 2014 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 29: Magnetization Dynamics II

MA 29.4: Vortrag

Mittwoch, 2. April 2014, 15:45–16:00, HSZ 401

Ultrafast demagnetization in transition metals - comparing ab-initio electron-phonon and electron-magnon rates — •Michael Haag, Christian Illg, and Manfred Fähnle — Max Planck Institute for Intelligent Systems, D-70569 Stuttgart, Heisenbergstr. 3, Germany

In 1996 Beaurepaire [1] found that a thin ferromagnetic Ni film, which is excited by a fs laser pulse, exhibits an ultrafast demagnetization on 100fs timescale. Despite years of fruitful research the underlying mechanisms remain unclear. Many mechanisms have been suggested including electron-phonon, and electron-magnon spin flips. Carpene [2] suggested that electron-magnon scattering can describe the demagnetization, because in presence of spin-orbit coupling, where spin- is transferred to orbital-angular momentum, which is rapidly quenched by the crystal field. Since the angular momentum is conserved [3] it has to be transferred to the lattice to allow the demagnetization. However Illg [4] could prove that rates and available phase space of electron-phonon coupling alone are too small to explain the demagnetization. We calculate the electron-magnon rates to check whether a combined process of electron-magnon and electron-phonon scatterings explains ultrafast demagnetization. In addition Carpene's assumption is checked by calculating the transferred orbital angular momentum rate.

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

[2] E. Carpene, et al., Phys. Rev. B 78, 174422 (2008)

[3] M. Fähnle, et al., J. Magn. Magn. Mater. 347, 45 (2013)

[4] C. Illg, M. Haag, M. Fähnle, Phys. Rev. B. accepted