A study of the Kondo Heisenberg model by means of the
*COM* is reported in
Ref. [106,107]. In particular
the following properties have been computed:

- The electronic single-particle properties (i.e., energy spectra,
density of states) [106]
- The bosonic single-particle properties (i.e., spin-wave dispersion, mode softening) [107]

A paramagnetic solution of the model in the context of cuprate oxide superconductors has been derived in Ref. [106] by considering a two-pole approximation. The effect of spin correlation to the electron energy spectrum has been investigated near the metal-insulator transition.

The ferromagnetic solution has been studied in Ref. [107] in the context of manganites, where both the intersite antiferromagnetic exchange among localized t electron spins and the strong intra-atomic Hund coupling among the t and e electrons is taken into account. The single- and two- particle Green's functions have been calculated in a fully self-consistent formulation by considering fermionic and bosonic basic composite fields. The study suggests that competing ferromagnetic double-exchange and antiferromagnetic super-exchange interaction lead to a rather nontrivial spin-wave spectrum. While spin excitations have a conventional spectrum in the long-wavelength limit, there is a strong deviation from the spin-wave spectrum of the isotropic Heisenberg model close to the zone boundary. The relevance of the results to the experimental data [108,109,110] has been analyzed.