EPR study of high-spin ferric ion in a completely rhombic environment. Fe 3+ in CaWO 4

Abstract

X-band EPR studies of Fe 3+-doped synthetic calcium tungstate single crystals carried out at room temperature are reported. The spectra are analyzed in terms of a very general spin Hamiltonian appropriate to the lowest ( 1 = C i ) Laue symmetry. Spin-Hamiltonian parameters, determined by full matrix least-squares refinement showed (i) the site of Fe 3+ is nearly completely rhombic, (ii) there is a small but easily measurable anisotropy in the g -parameter matrix, (iii) the principal directions of the g - and D -parameter matrices are noncoaxial, (iv) coefficients of fourth-degree crystal field terms, though small, indicate a low symmetry site, and (v) coefficients of high-spin Zeeman terms are negligibly small. The principal directions of the D -parameter matrix suggest direct substitution of Fe 3+ for Ca 2+ in the lattice together with an associated charge compensator M + or, alternatively, a cation vacancy, at one of four equivalent adjacent calcium positions.