Spectrum of dynamic magnetic susceptibility of a randomized f–d magnet with spin–lattice coupling. II. “Opening” of the spin excitation bands.

The transformation of the magnetic absorption spectra of a narrow-band ferromagnetic conductor containing local f and quasilocal d magnetic moments under conditions of weak spin–lattice coupling and spatial randomization of the g factors of the quasilocal and local spin subsystems is investigated. It is shown that randomization of the g factors (e.g., as a result of the introduction of an impurity) leads mainly to the “opening” (i.e., to the appearance in the magnetic absorption spectrum) of acoustic and optical magnon bands formed in the system while not affecting the position and shape of the narrow magnetic resonance lines comprising the spectrum of the impurity-free crystal. The effects of spin–lattice coupling, besides the “opening” of the phonon and magnon bands, lead to a shift and a temperature smearing of the narrow resonance lines. The relative corrections to the effective magnon masses generated by the spin–lattice coupling in a 4f–5d metal amount to ∼2×10-4 for an acoustic mode and to ∼4×10-4 for an optical mode. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]