EPR spectra and linewidths ofMn2+in calcite

Abstract

The constants corresponding to the spin-Hamiltonian terms without cylindrical symmetry for ${\mathrm{Mn}}^{2+}$ in calcite (CaC${\mathrm{O}}_3$) have been measured by EPR techniques; it is shown that the principal axes of the spin Hamiltonian are rotated 15.5° from the crystal axes. This value allows us to obtain information about the charge distribution of the carbonate ligands. Our result is in agreement with the predictions of a simple covalent model for the carbonates. We measured also the angular variation of the linewidth of an EPR transition; our data allow us to explain the source of the inhomogeneous broadening for ${\mathrm{Mn}}^{2+}$ in our sample as random internal stresses. We compare our results with previous data obtained for ${\mathrm{Mn}}^{2+}$ in CaW${\mathrm{O}}_4$ where the source of broadening is a distribution of point defects in the sample. A method for finding the source of inhomogeneous broadening in sites of low symmetry is discussed.