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MA: Fachverband Magnetismus

MA 37: Spin Dependent Transport Phenomena

MA 37.17: Vortrag

Donnerstag, 26. März 2009, 19:30–19:45, HSZ 403

Measurement of the spin polarisation of Co₂FeSi with Andreev reflection point-contact spectroscopy — •Samuel Bouvron¹, Michael Marz¹, Gernot Goll¹, and Claudia Felser² — ¹Physikaliches Institut, Universität Karlsruhe (TH), 76128 Karlsruhe, Germany — ²Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität, 55099 Mainz, Germany

With a theoretical spin polarisation P of 100 % at the Fermi level, a Curie temperature of 1100 K and a high magnetic moment of 6 µ_B, the ferromagnetic Heusler alloy Co₂FeSi exhibits advantageous properties for magnetoelectronic or spin-electronic devices. Spin polarisation measurements were performed on polycrystalline and single-crystalline Co₂FeSi and Co₂FeAl_1−xSi_x samples, using Andreev reflection spectroscopy in ferromagnet/superconductor (F/S) point contacts which were realized with the needle-to-anvil method with a mechanical control of a superconductive Pb tip. Analyses of the conductance spectra were carried out by the Cuevas modell, which is based on the Landauer-Büttiker formalism with spin dependent transmission coefficients τ_↑(↓) with P = (τ_↑−τ_↓)/(τ_↑+τ_↓). The extracted polarisation was lower than expected from band-structure calculations, the maximal measured value being 56 %. A decrease of the polarisation both with increasing size of the contact and increasing potential barrier at the F/S interface hints at possible origins of the reduced current spin polarisation among which spin-orbit scattering in the contact region [1] is the most prominent candidate.

[1] M. Stokmaier et al., Phys. Rev. Lett. 101, 147005 (2008)