Dresden 2009 – scientific programme

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MA: Fachverband Magnetismus

MA 27: Spin Electronics / Spininjection in Heterostructures

MA 27.1: Talk

Wednesday, March 25, 2009, 16:45–17:00, HSZ 103

The interface of tunnelling junctions with the Heusler electrode Co₂Cr_0.6Fe_0.4Al — •Martin Jourdan, Christian Herbort, Elena Arbelo Jorge, Michael Kallmayer, and Hans Joachim Elmers — Institut für Physik, Johannes Gutenberg Universität, Staudingerweg 7, 55128 Mainz, Germany

The compound Co₂Cr_0.6Fe_0.4Al was the first Heusler material for which half metallic properties and a magnetic ordering temperature well above room temperature were predicted. However, no Jullière spin polarisation larger than ≃ 60 % could be observed up to now. The affinity of Cr for oxidation is considered to be the origin for this reduced value. We improved the vacuum condition of our preparation system to below 10⁻⁹mbar. This resulted in a pronounced change of the morphology of the rf sputter deposited Al layer which is deposited on top of the Heusler electrode in order to become the tunnelling barrier after oxidation. In situ STM investigation show the growth of Al islands on the Co₂Cr_0.6Fe_0.4Al surface. This growth mode results in an increased roughness of the barrier, which limits the achievable tunnelling magnetoresistance (TMR). Alternative methods of barrier deposition are employed and investigated by in situ STM and RHEED. Additionally, the effect of the Al deposition method and oxidation process on the surface magnetisation of the Heusler electrode is investigated by XMCD-TEY experiments.