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 74.1: Hauptvortrag

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

Ultrafast optical tuning of ferromagnetism in EuO via the carrier density — •Manfred Fiebig — ETH Zürich, Department of Materials, Vladimir-Prelog-Weg 4, 8093 Zurich, Switzerland

The interest in manipulating magnetic order by ultrashort laser pulses has thrived since it was observed that such pulses can be used to alter magnetization on a sub-picosecond timescale. In many cases demagnetization by laser heating dominates the dynamics; this is well described by the classic three-temperature model — assuming energy exchange between thermalized reservoirs of electrons, spins, and the lattice. Here we demonstrate a mechanism that allows the magnetic order of a material to be enhanced or attenuated at will. This is possible in systems simultaneously possessing a low, tunable density of conduction band carriers and a high density of magnetic moments. In such systems the thermalization time can be set such that adiabatic processes dominate the photoinduced change of the magnetic order — the three-temperature model is bypassed. In ferromagnetic Eu_1−xGd_xO we thereby demonstrate strengthening as well as weakening of the magnetic order by ∼10% and within ≤3 ps by optically controlling the magnetic exchange interaction. A theory backing up and expanding our experimental results will be presented.