EPR powder pattern analysis for Mn2+ in cubic crystalline fields

Abstract

The EPR powder pattern analysis for a d5 spin system in a cubic crystalline field is discussed. From the study of the EPR absorption curves for the powder, it has been established that if divalent manganese occupies sites of cubic symmetry in single crystal MgO, CaO, and SrO, it also occupies cubic sites in the powder. The EPR spectra of Mn2+ in MgO, CaO, and SrO single crystals were first observed along different magnetic field orientations and compared to the subsequent powder spectra obtained after the same samples were ground to a fine powder. For each host, a one to one correspondence between each allowed EPR transition in the 〈100〉, 〈110〉, 〈111〉 single crystal spectra and the derivative peaks of the powder spectrum was found, leading to the conclusion that the powder spectrum is due solely to the contributions from these principal directions. Spin-Hamiltonian parameters g, a, and A obtained from EPR measurements of the powder spectrum agree with those obtained from the single crystal, and both sets of parameters are in good agreement with those already reported for the single crystal samples. Forbidden hyperfine lines ‖ΔMS‖=1, ΔmI=±1 were also observed in all the powder spectra. Contrary to some previous published works, it was not necessary to use any axial crystal-field term to explain the forbidden lines.