Berlin 2015 – scientific programme

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MA: Fachverband Magnetismus

MA 35: Magnetization / Demagnetization Dynamics II

MA 35.9: Talk

Wednesday, March 18, 2015, 17:15–17:30, EB 301

Ultrafast Electron Spin Dynamics at the Fermi Level in Fe3O4 Thin Films — C Cacho¹, M Battiato², J-M Mariot³, •M C Richter⁴, O Heckmann⁴, F Parmigiani⁵, H Ebert⁶, J Minar⁶, and K Hricovini⁴ — ¹Central Laser Facility, STFC, RAL, Harwell, United Kingdom — ²Institute of Solid State Physics, Vienna University of Technology, Austria — ³LCP-MR, Univ. Paris 6/CNRS, France — ⁴LPMS, Univ. de Cergy-Pontoise, France — ⁵Elettra - Sincrotrone Trieste, Italy — ⁶LMU Münich, Germany

Magnetite, Fe3O4 (FO), belongs to the family of half-metals characterized by an insulating gap for one spin state resulting in a fully spin-polarised transport at the Fermi level, which attracts a high interest for spintronic devices. In spite of intensive theoretical and experimental studies, the magnetic and electronic properties of FO remain controversial. We studied the demagnetisation process in FO by spin- and time-resolved pump-probe photoemission experiments using the third harmonic (4.65 eV) of a Ti-Saphire laser with a repetition rate of 250 kHz. For the maximum of the photoexcitation we observe a clear reduction of the spin polarisation in a region of ~200 meV around the Fermi level. At higher binding energy no variation is observed up to a 1000 fs delay indicating that the spin polarisation reduction observed comes from the electron dynamics and not from the demagnetization. The Boltzmann equation for out-of-equilibrium dynamics combined with the calculated spin-resolved electronic density-of-states fully describes the decay of the excited electrons as well as the variation of the spin polarisation.