Dresden 2009 – wissenschaftliches Programm
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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 µB, 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 Co2FeAl1−xSix 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)