Project leader: PD Dr. M. Jourdan, firstname.lastname@example.org
Supported by the DFG via project Jo404/9-1
The magnitude of the room temperature spin polarization of ferromagnetic materials is a key property for their application in spin transport-based electronics. Values close to 100 % were observed for the metastable CrO2 and for Fe3O4, but these materials did not allow for large spin transport effects and are not compatible with applications. Thus intermetallic Heusler compounds with their predicted half-metallic properties, i. e. 100 % spin polarization at the Fermi energy, moved into the focus of interest. In addition to being interesting for applications, intermetallic Heusler materials are a test for modern band structure calculations for materials with electronic correlations of moderate strength.
A powerful direct spectroscopic method for the investigation of electronic band structures and spin polarizations is photoemission spectroscopy, where a photon excites an electron which is emitted and energy analysed. The electron is excited from an initial bulk or surface state into a final state which is a free electron outside the sample and a Bloch or damped surface state inside the sample.
Investigating optimized thin films of the compound Co2MnSi by in-situ spin resolved UPS, we were able to demonstrate for the first time half-metallicity in combination with directly measured (93+7−11) % spin polarization at room temperature in the surface region of a Heusler thin film. Novel band structure and photoemission calculations including all surface related effects show that the observation of a high spin polarization in a wide energy range below the Fermi energy is related to a stable surface resonance in the majority band of Co2MnSi extending deep into the bulk of the material.
For more details please see