Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 74: Focus Session: Ultra-Fast Magnetism under Electronic Nonequilibrium Conditions (organized by MA)

TT 74.2: Hauptvortrag

Mittwoch, 18. März 2015, 15:30–16:00, H 1012

Intra-atomic exchange in ultrafast magnetism — •Martin Weinelt — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany

The exchange interaction is the defining element in the formation of magnetic order in atoms and solids. Therefore the role of intra- and interatomic exchange during ultrafast magnetization dynamics needs to be explored. In the atomic magnetism of lanthanide metals localized 4f and itinerant 5d orbitals contribute to the overall magnetic moment. In general it is assumed that the intra-atomic exchange coupling is fast enough to be treated as an instantaneous process. We studied the magnetization dynamics of the lanthanide metals gadolinium [1] and terbium by time-resolved photoemission employing femtosecond higher-order harmonic vacuum-ultraviolet pulses. Recording in parallel 4f magnetic linear dichroism and 5d exchange splitting we observe distinct spin dynamics in Gd, which show the breakdown of the intra-atomic exchange upon femtosecond laser excitation. An orbital-resolved Heisenberg model [2] explains well the state-dependent two timescales of magnetization dynamics in Gd metal, which differ by one order of magnitude. Due to its much stronger spin-lattice coupling, Tb shows a distinctly different magnetization dynamics.

[1] Robert Carley et al., Phys. Rev. Lett. 109 (2012) 057401.

[2] Soenke Wienholdt et al., Phys. Rev. B 88 (2013) 020406(R).