Regensburg 2013 – scientific programme
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MA: Fachverband Magnetismus
MA 16: Poster I
MA 16.52: Poster
Tuesday, March 12, 2013, 10:30–13:30, Poster D
Electronic, structural and magnetic properties of NiFe2O4 ultra thin films — •Michael Voigt1, Christian Caspers1, Bernardus Zijlstra1, Sebastian Flade1, Sven Döring2, Mihaela Gorgoi3, Claus M. Schneider1, and Martina Müller1 — 1Peter-Grünberg-Institut (PGI-6), Forschungszentrum Jülich — 2Experimentalphysik, Universität Duisburg-Essen — 3BESSY II, Helmholtzzentrum Berlin für Materialien und Energie
The spinel NiFe2O4 (NFO) is an insulating oxide that is ferrimagnetic with a Curie-temperature way above room temperature. This rare combination of properties makes this material intriguing for integration into heterostructures for spintronics. The magnetic properties of ultra-thin ferrite films, however, strongly differ from the bulk, i.e. an enhanced magnetization is observed for dNFO ≤ 10 nm, though the reason for this is still unclear.
To gain insights into this phenomenon, we investigated ultra-thin NFO films (d = 2 - 20 nm) deposited on SrTiO3 via pulsed laser deposition, and studied the structural, magnetic and electronic properties via SQUID, XRD, NEXAFS and HAXPES. The latter two methods allow us to probe the oxidation states and the atomic coordination element specifically for the Ni- and Fe-cations. The Ni- & Fe-2p/3p spectra show that the ultra-thin films grow with bulk-like electronic properties. From the spectral shape we conclude, that even for lowest film thickness no cation inversion takes place. Furthermore, we deduce a two-phase growth mode from XRD data, in which NFO grows highly strained for d ≤ 4 nm and starts to relax for larger thicknesses.