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The magnon excitation spectrum of ferromagnetic quasicubic manganites is studied by using the linearized spin-wave approximation for the double-exchange and the superexchange interactions. Two situations are distinguished: 1) a rigid coupling of the t2g and eg spins via a large Hund's rule coupling and 2) a softened coupling between these spins (e.g., due to coupling of the eg electrons to Jahn-Teller modes). Case 2) leads to a softening of the magnon dispersion (compared to the Heisenberg model) close to the zone boundary.
Date of Publication: June 2010