Berlin 2012 – scientific programme
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MA: Fachverband Magnetismus
MA 30: Focus Session "Spin Currents in Magnetic Nanostructures", Organization: Mathias Kläui (Univ. Mainz)
MA 30.4: Talk
Wednesday, March 28, 2012, 16:30–16:50, EB 301
Spin filtering in spinel ferrite CoFe2O4 — •Michael Foerster, Diego F. Gutierrez, and Josep Fontcuberta — Institut de Ciència de Materials de Barcelona ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
Spin filtering promises an effective approach to generate highly spin polarized currents, e.g. for spin injection. Spin filters are realized by tunneling barriers from magnetic insulators, where the exchange split band gap results in spin dependent transmission probabilities. Moodera et al. validated this concept using Europium chalcogenides [1].
However, these compounds have low Curie temperatures and only few magnetic insulators with transitions clearly above room temperature exist. Spinel ferrites, e.g. CoFe2O4 (TC = 790 K), are considered most promising candidates. Using point contact spetroscopy, the spin filtering efficiency of CoFe2O4 thin films on SrRuO3 bottom electrodes has been evaluated [2], but is found to be much below expectations based on calculated band structures. The possible reasons for this low filtering efficiency, which is common for reports on spinel ferrites, are addressed by probing two key properties of ultrathin films: transport, using conducting AFM [3], and magnetic properties when grown on different substrates [4], revealing the points that have to be considered for further optimization.
[1] J.S. Moodera et al., J. Phys.: Condens. Matter 19, 165202 (2007).
[2] F. Rigato et al., Phys. Rev. B 81, 174415 (2010).
[3] M. Foerster et al., Appl. Phys. Lett. 97, 242508 (2010).
[4] M. Foerster et al., Phys Rev. B, published online.