The role of rotational modes in spin-phonon coupling: application to V3+in Al2O3

Abstract
A spin-phonon Hamiltonian for a point charge model is written in a form which displays the symmetry of the interaction including the components due to the cubic T1 rotational modes. The conditions for which the T1 modes could play a significant role are discussed and it is shown that in general they are unimportant for transitions strongly coupled to the lattice but could well be important if the coupling is only moderate or weak. A detailed calculation shows that the T1 coupling could be significant for transitions within the ground state of V3+ in Al2O3.