Electron-nuclear quadrupole interaction in exchange clusters III. Mössbauer spectra in hybrid states of tetrameric clusters

The Mössbauer spectra of tetrameric antiferromagnetic clusters possessing spin-coupled orbitally degenerate ground states are considered. The orbital degeneracy of the electronic exchange sub-system leads to the origin of hybrid electron-nuclear states. Transitions between the ground state and the excited hybrid states allow us to observe the absorption of gamma radiation even in those cases, when the local crystal fields possess cubic symmetry and individual ions exist in orbitally non-degenerate states. An essentially new type of Mossbauer spectra for those systems is predicted. The peculiarities of spectra of mono- and polycrystalline samples are investigated. The Mossbauer spectrum, taking into account the static distortions of the cluster is considered.