EPR of Fe³⁺ in Low Quartz Isomorphs A(III)B(V)O₄

Abstract

Abstract Electron spin resonance spectra of Fe 3+ in hydrothermally grown single crystals of AlPO 4 , GaPO 4 , AlASO 4 and GaAsO 4 were measured at X-band and analyzed using a Spin-Hamiltonian for rhombic symmetry. The zero field splitting was found to be between about one and two times the microwave frequency, increasing regularly from AlPO 4 to GaAsO 4 . This increase is largely due to an increase in the axial parameter D whereas the second order rhombic parameter E is practically constant. The fourth order parameter a increases exponentially with the lattice parameter ratio c 0 /a 0 . The variation of D indicates a site distortion for GaPO 4 about twice as large as in AlPO 4 . For the arsenates, influences of increased covalency are apparent in addition to site distortions of comparable size. Halfwidths in the range of 18 Gauss for the phosphates and 38 Gauss for the arsenates indicate hyperfine interactions with 31 P and 75 As, and estimates of 0.5 and 1% spin density resp. at these nuclei are obtained, again showing increased covalency for the arsenate compounds.