Berlin 2012 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 13: Magnetic Materials

MA 13.15: Vortrag

Montag, 26. März 2012, 18:45–19:00, H 0112

An effective quantum parameter for strongly correlated metallic ferromagnets — •Bhaskar Kamble¹ and Avinash Singh² — ¹Institut fuer Theoretische Physik III, Ruhr Universitaet Bochum, 44801 Bochum, Germany — ²Department of Physics, Indian Institute of Technology Kanpur, 208016, India

The correlated motion of electrons in multi-orbital metallic ferromagnets is investigated in terms of a realistic Hubbard model with N-fold orbital degeneracy and arbitrary intra- and inter-orbital Coulomb interactions U and J using a Goldstone-mode-preserving non-perturbative scheme. An effective quantum parameter ′ℏ′=U²+(N−1)J²/(U+(N−1)J)² is obtained which determines, in analogy with 1/S for quantum spin systems and 1/N for the N-orbital generalized Hubbard model, the strength of correlation-induced quantum corrections to magnetic excitations. The rapid suppression of this quantum parameter with Hund’s coupling J, especially for large N, provides fundamental insight into the phenomenon of strong stabilization of metallic ferromagnetism by orbital degeneracy and Hund’s coupling. This approach is illustrated for the case of ferromagnetic iron and the half-metallic Heusler alloy Co₂ MnSi. For realistic values of iron, the calculated spin stiffness and Curie temperature values obtained are in quantitative agreement with measurements. Significantly, the contribution of long wavelength modes is shown to yield a nearly ∼ 25% reduction in the calculated Curie temperature.