Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 35: Spin-Dynamics / Spin-Torque IV

MA 35.3: Vortrag

Donnerstag, 26. März 2009, 15:45–16:00, HSZ 04

Demagnetization processes on ultrashort timescales revisited — •Jakob Walowski¹, Andreas Mann¹, Henning Ulrichs¹, Benjamin Lenk¹, Markus Münzenberg¹, Unai Atxitia², and Oksana Fesenko² — ¹I. Physikalisches Institut, Universität Göttingen, Germany — ²Instituto de Ciencia de Materiales de Madrid (CSIC), Spain

All-optical pump-probe experiments give an insight into magnetization dynamics on ultrashort timescales. Femtosecond pulses generated by a Ti:Sa laser are used to trigger magnetization dynamics. Having an optical penetration depth of up to 15 nm the deposited energy is highest for of the topmost layers. A two-temperature type model including the electron heating after excitation and the equilibration with the phonon system, describes the dynamics. Within this process two timescales are of interest, first the demagnetization within the first 150−200 fs and second the magnetization recovery which takes place on the timescale of 1−20 ps after excitation. On the first timescale the characteristic slowing down of the demagnetization was revisited, since it is a fingerprint of the correlation effect from incoherent spin-waves occuring at high pump fluencies. The connection between the electron temperatures in the magnetic system is established by a Langevin field term in the modeling of this process. For the modeling an atomistic level description using Landau-Lifshitz-Bloch equations is applied. We find a scaling behavior of the total demagnetization as a function of the pump fluency (10−50 mJ/cm²) and the thickness of the magnetic layer (d_Ni=10−40 nm). Support by the DFG within the priority program SPP 1133 is gratefully acknowledged.