Berlin 2015 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 27: Magnetization / Demagnetization Dynamics I
MA 27.10: Vortrag
Mittwoch, 18. März 2015, 12:00–12:15, EB 301
Ultrafast demagnetization of a ferrimagnetic insulator driven by selective phonon excitation — •Sebastian Mährlein1, Ilie Radu2, Pablo Maldonado3, Alexander Paarmann1, Michael Gensch4, Alexandra Kalashnikova5, Roman Pisarev5, Peter Oppeneer3, Martin Wolf1, and Tobias Kampfrath1 — 1FHI der MPG, Berlin — 2HZB, Berlin — 3Uppsala University, Sweden — 4HZDR, Dresden — 5Ioffe Institute, St. Petersburg, Russia
We present a novel pathway for ultrafast demagnetization of spin-ordered solids by resonant excitation of their crystal lattice, while leaving the electronic orbital degrees of freedom in their ground state. More precisely, the oxygen-iron phonon modes (around 19 THz) of the insulating ferrimagnet Y3Fe5O12 (YIG) are excited using intense THz pump pulses (absorbed fluence 4 mJ/cm2) from a femtosecond laser source and, complementarily, a free-electron laser. The resulting spin dynamics are magneto-optically probed over a wide range of time scales from 100 fs to 1 ms. We find a quenching of the magnetization by 3 % with a time constant as short as (1.2±0.2) ps, which recovers very slowly with a time constant on the order of 0.3 ms. The phonon-driven demagnetization observed is surprisingly fast, orders of magnitude faster than spin-lattice relaxation times in YIG. These findings indicate a highly efficient nonequilibrium energy transfer between the optical phonons and spins. Supported by ab initio calculations, we discuss possible microscopic mechanisms of the magnetization dynamics observed.