Magnon spectrum at the non-RKKY indirect exchange in conducting ferromagnets

Abstract

The magnon spectrum of conducting ferromagnets is investigated when conditions for the applicability of the Ruderman-Kittel-Kasuya-Yosida (RKKY) theory are not met (double-exchange systems and degenerate magnetic semiconductors). The long-wave magnon frequencies are nonanalytical in the $s\ensuremath{-}f(d)$ exchange integral. The Kohn singularity specific for the RKKY theory is either absent, or the number of the singularities is not less than 2. In the almost-RKKY case there are two different magnon effective masses.