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MA: Fachverband Magnetismus

MA 51: Magnetic Half-metals and Oxides II

MA 51.4: Talk

Thursday, March 17, 2011, 11:45–12:00, HSZ 401

Spectroscopy of the electronic states of the Heusler compounds Co₂FeAl and Co₂Cr_0.6Fe_0.4Al and the influence of oxidation — •Martin Jourdan, Fabian Grosse-Schulte, Michaela Hahn, and Gerd Schönhense — Institut für Physik, Johannes Gutenberg Universität, Staudingerweg 7, 55128 Mainz

Band structure calculations, which predict half metallic properties for several Heusler compounds, initiated great experimental efforts concerning this class of materials. The validation of the calculated electronic properties remains difficult, though. The band structures of the Heusler compounds Co₂Cr_0.6Fe_0.4Al and Co₂FeAl were investigated in-situ by angle resolved ultraviolet photoemission spectroscopy (ARUPS). The samples were prepared by a sputtering process optimized for tunneling junction preparation, the photoemission process in normal direction of the (001)-oriented thin films was excited by a Helium gas discharge lamp (excitation energies 21.2eV and 40.8eV). The spectra of clean samples are compared with calculations of the total and partial bulk density of states and are evaluated within the three-step model of photoemission. Basic agreement with theoretical predictions of the bulk band structure is concluded. At oxygen exposures of only 1 Langmuir a chemisorption phase with significant changes of the valence-band spectrum near the Fermi-energy is observed. At 10L oxygen the spectra are indicative of beginnig oxide formation within the UPS probing depth.