Seminar über die Physik der kondensierten Materie (SFB/TRR173 Spin+X und SFB/TR288 Kolloquium, TopDyn-Seminar)
June 21, 2012 at 3:30 p.m. in Minkowski-Raum, 05-119, Institut für Physik, Staudingerweg 7, 55128 MainzUniv-Prof. Dr. Jure Demsar
Univ.-Prof. Dr. Hans-Joachim Elmers
Univ.-Prof. Dr. Mathias Kläui
Univ.-Prof. Dr. Thomas Palberg
Understanding the physical limits of magnetization dynamics is of central importance for the development of magnetic data storage and spintronics. Of particular interest is the phenomenon of ultrafast demagnetization on the femtosecond regime [1]. It is expected to give insight into the energy and angular momentum transfer processes between the electronic, spin, and lattice subsystems.
We present results of a novel higher harmonic generation table-top pump-probe approach, by which we investigate the demagnetization behavior in thin film stacks with element selectivity. The resonant reflectivity at the transition metal M-edges in a T-MOKE geometry provides large magnetic signals [2], which enable us to study spin dynamic processes with a time resolution of better than 20 fs, i.e. approaching the time scale of the exchange interaction [3]. In Fe-Ni alloys we find a distinct time delay between the demagnetization of the Fe and Ni constituents which depends on the strength of the exchange coupling [4]. This finding demonstrates that although in the static case Fe and Ni are strongly exchange coupled, this coupling may be overcome by strong optical excitations on very short time scales.
[1] E. Beaurepaire et al., Phys. Rev. Lett. 76 (1996) 4250.
[2] P. Grychtol et al., Phys. Rev. B 82 (2010) 054433.
[3] C. La-O-Vorakiat et al., Phys. Rev. Lett. 103 (2009) 257402.
[4] S. Mathias et al., Proc. Natl. Acad. Sci. USA 109 (2012) 4792.