Dresden 2011 – scientific programme
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MA: Fachverband Magnetismus
MA 38: Magnetization Dynamics IV
MA 38.7: Talk
Wednesday, March 16, 2011, 16:15–16:30, HSZ 403
Distinct Demagnetization Dynamics of Ni and Fe Magnetic Moments in a NiFe Alloy — •Andrea Eschenlohr1, Ilie Radu1,2, Christian Stamm1, Niko Pontius1, Torsten Kachel1, Florin Radu1, Theo Rasing2, and Alexey V. Kimel2 — 1Helmholtz Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Str. 15, 12489 Berlin — 2Radboud University Nijmegen, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
Ultrafast demagnetization has been approached from a variety of experimental and theoretical angles since the first observation of a sub-picosecond quenching of magnetization in Ni [1]. Time constants of demagnetization have been established for elementary transition metals and rare earths. Their compounds and alloys, which are highly relevant for technological applications and for research into the microscopic origins of ultrafast demagnetization, are increasingly investigated with methods like TR-MOKE. Yet experimental methods which combine femtosecond time resolution with an element-sensitive measurement of the magnetization have so far been sparse. We bridge this gap by probing magnetization dynamics in ferromagnetic NiFe alloys in an element-resolved way with 100 fs x-ray pulses generated by the Femtoslicing facility at BESSY II via XMCD. We find different demagnetization time constants for Ni (80 +/- 30 fs) and Fe (240 +/- 30 fs) in Ni50Fe50, evidence of a decoupling of the Ni and Fe dynamics on ultrafast timescales despite the exchange interaction between the two elements. [1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).