We calculate the dynamic spin susceptibility in the generalized Kondo model describing the interaction between the band eg electrons and the localized t2g electrons coupled via the antiferromagnetic exchange. We show that the spin-wave spectrum in the ferromagnetic phase has acoustic and optical branches in the mean-field approximation. We evaluate the self-energy corrections to the spectrum and estimate the damping of acoustic magnons.
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Acknowledgments. The authors thank Yu. A. Tserkovnikov and G. V. Jackeli for the useful discussions. This work was supported by INTAS (Grant Nos. 97-0963 and No. 97-11066).