Experimental and theoretical reasons for inclusion of fourth-order terms into spin Hamiltonian of glasses doped by d⁵ impurities with ⁶A₁ ground states

Abstract

Isofrequency curves (of magnitude of the magnetic resonance field as a function of its spherical angles θ and Φ were calculated for a number of sets of spin Hamiltonian parameters a, F, D and E. Lowest possible values of the a and D parameters that both fulfil the so-called ‘tetragonal conditions’ and correspond to d⁵ centres with isotropic resonances of g_eff ≊4·3 and g_eff ≊3· 3 were assessed. Model calculations, based on the Boltzmann distribution of energy population, of the temperature dependence of resonance intensities were performed. Their comparison with experiment made it possible to decide which of the two spin Hamiltonians commonly used for the interpretation of the electron paramagnetic resonance (EPR) spectra of d⁵ centres were more plausible in the case of halide glasses doped by Mn²⁺. Objections to the interpretation of the g_eff ≊4· 3 resonance on the basis of the fourth-order spin Hamiltonian were reexamined from the point of view of ligand field theory and reasons for support of this interpretation of the EPR spectra were collected.