Dresden 2011 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 63: Poster II (Surface Magnetism/ Magnetic Imaging/ Topological Insulators/ Spin Structures and Magnetic Phase Transitions/ Graphene/ Magnetic Thin Films/ Magnetic Semiconductors/ Magnetic Half-metals and Oxides/ Spin-dependent Transport/ Spin Excitations and Spin Torque/ Spin Injection and Spin Currents in Heterostructures/ Spintronics/ Magnetic Storage and Applications)

MA 63.73: Poster

Freitag, 18. März 2011, 11:00–14:00, P2

Anisotropic magneto-resistance as a measure for the phase coexistence in Co₂FeSi layers — •Pawel Bruski, Klaus-Jürgen Friedland, Rouin Farshchi, Jens Herfort, and Manfred Ramsteiner — Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany

The ferromagnetic Heusler alloy Co₂FeSi is closely lattice matched to GaAs but epitaxially grown layers exhibit, in general, the coexistence of the well-ordered L2₁ phase and the Fe-Si disordered B2 phase depending on the substrate temperature T_S. The former one is predicted to be half-metallic, i.e. to be 100 % spin polarized at the Fermi-energy whereas the latter one is not only expected to lack half-metallicity but also to compete with the L2₁ phase by injecting spins of opposite sign. Since the degree of anisotropy is larger in the well-ordered L2₁ phase, the admixture of the disordered B2 phase should reflect itself in anisotropic magnetoresistance (AMR) measurements.

We investigated a series of spin light emitting GaAs/(Al,Ga)As diodes with Co₂FeSi injection layers as well as Co₂FeSi layers on GaAs grown by molecular beam epitaxy at different T_S. The AMR amplitude reveals a monotonic dependence on T_S indicating the coexistence of both phases. The sign reversal of an additional anisotropy constant Δ, which takes into account the deviation from an isotropic structure, gives further evidence for the phase coexistence. Both the AMR amplitude as well as the anisotropy constant Δ can be utilized as a sensitive measure for the phase composition in Co₂FeSi layers.