Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping

Abstract

The effects of correlation-induced coupling between spin and charge fluctuations on spin-wave excitations in a band ferromagnet are investigated by including self-energy and vertex corrections within a systematic inverse-degeneracy expansion scheme which explicitly preserves the Goldstone mode. Arising from the scattering of a magnon into intermediate spin-excitation states (including both magnon and Stoner excitations) accompanied with charge fluctuations in the majority spin band, this spin-charge coupling results not only in a substantial reduction of magnon energies but also in anomalous softening and significant magnon damping for zone-boundary modes lying within the Stoner gap. Our results are in good qualitative agreement with recent spin-wave excitation measurements in colossal magneto-resistive manganites and ferromagnetic ultrathin films of transition metals.

8 pages, 7 figures

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• Orbital fluctuations, spin-orbital coupling, and anomalous magnon softening in an orbitally degenerate ferromagnet
• Orbital degeneracy, Hund's coupling, and band ferromagnetism: effective quantum parameter, suppression of quantum corrections, and enhanced stability
• Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites
• Magnon self energy in the correlated ferromagnetic Kondo lattice model: spin-charge coupling effects on magnon excitations in manganites
• Effect of strain-induced orbital splitting on the magnetic excitations in undoped cuprates