EPR study of tetragonal and monoclinic Fe3+ centres in Rb2ZnF4 crystals

Abstract

EPR measurements have been made on tetragonal and monoclinic Fe3+ centres in Rb2ZnF4 at room temperatures. The fine-structure terms for the monoclinic centre are separated into uniaxial and cubic terms for comparison with the Fe3+-VK centre in KZnF3 and for the uncompensated tetragonal centre. The monoclinic centre is ascribed to a Fe3+ ion associated with the nearest Rb+ vacancy and the principal z-axis is found to be 7 degrees from the (001)-axis in the opposite direction to that of the Rb+ vacancy. Rudowicz's NCC parameters for the monoclinic Fe3+ and Cr3+ centres are examined in relation to the separation of the spin-Hamiltonians. The calculated metal-ligand distances and deviation angles for the front and back fluorines by Newman's superposition model are in good agreement with, respectively, the distances for the uncompensated centre and angles for the Fe3+-VK centre in KZnF3 determined from 19F-ENDOR measurements. The relationships between the bnm and the axial and cubic parameters obtained by the superposition model are similar to those obtained from the spin-Hamiltonian separation.