Berlin 2008 – scientific programme

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MA: Fachverband Magnetismus

MA 5: Spindependent Transportphenomena I

MA 5.11: Talk

Monday, February 25, 2008, 12:45–13:00, H 0112

Tunneling junctions with the Heusler electrode Co₂Cr_0.6Fe_0.4Al — •Christian Herbort, Elena Arbelo, and Martin Jourdan — Institute of Physics, Johannes Gutenberg University, 55099 Mainz, Germany

Some ferromagnetic Heusler compounds are theoretically predicted to be half metallic materials, i. e. to be characterized by a huge spin polarization at the Fermi energy. We investigate the correlations between junction preparation conditions, morphology and transport properties of planar MgO−Co₂Cr_0.6Fe_0.4Al−AlO_x−Co/CoO_x−Pt tunnelling junctions. Epitaxial Co₂Cr_0.6Fe_0.4Al (CCFA) thin films were deposited by dc- and rf-sputtering on different buffer layers (Cr, Fe, MgO) on MgO (1,0,0) substrates. By RHEED, LEED and in-situ STM investigations very different surface morphologies were observed for the different preparation processes. With dc-sputtered CCFA films (island morphology) on Fe buffer layers we determined a maximum spin polarization of the Heusler compound of 54% (Jullière model, T=4K). Atomically flat surfaces with CCFA unit cell sized steps (B2 structure) were obtained by rf-sputtering on MgO substrates with e-beam evaporated MgO buffer layers. Considering that the TMR of the CCFA based junctions depends strongly on the interface at the tunneling barrier, the AlO_x layer needs to be optimized separately for the different CCFA morphologies. The barrier optimization process on the new atomically flat CCFA surfaces (rf-sputtered on MgO buffer) is in progress and current results of spectroscopic and TMR measurements will be shown.