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

Abstract

Abstract Electron spin resonance spectra of Fe3+ in hydrothermally grown single crystals of AlPO4 , GaPO4, AlASO4 and GaAsO4 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 AlPO4 to GaAsO4. 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 c0/a0 . The variation of D indicates a site distortion for GaPO4 about twice as large as in AlPO4 . 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 31P and 75As, and estimates of 0.5 and 1% spin density resp. at these nuclei are obtained, again showing increased covalency for the arsenate compounds.