Mössbauer, electron spin resonance, optical, and magnetic studies of iron(III) in oxide host lattices

Abstract

Spectroscopic and magnetic studies have been made on Fe³⁺ ions in a variety of oxide host lattices, namely NaSc_1–xFe_xTiO₄, NaFeSnO₄, CaSc_2–xFe_xO₄, Sc_2–xFe_xTiO₅, NaFeTi₃O₈, α-NaSc_1–xFe_xO₂, Cs_xSc_x–yFe_yTi_2–xO₄, β-NaAl_1–xFe_xO₂, Cs_xSc_x–yFe_yTi_4–xO₈, LiFeTiO₄, and CsFeSi₂O₆. The ¹¹⁹Sn Mössbauer spectra of NaFeSnO₄ and NaScSnO₄ were also recorded. In most of these lattices the crystal fields at the iron sites depart significantly from cubic symmetry and we have found that isolated Fe³⁺ ions give rise to a strong e.s.r. signal at g′= 4·3 and a magnetic Mössbauer spectrum. These spectra are strongly concentration and temperature dependent. We conclude that the magnetic Mössbauer spectra are the result of a pure spin-alignment effect, while the g′= 4·3 e.s.r. signal is the result of ground-state splitting which occurs even when the spins are not strictly aligned. The electronic spectra of these compounds have been analysed and the bands corresponding to a particular transition are found to be remarkably constant. Only those transitions which correspond to the two lowest levels, and whose energies are crystal-field dependent, show significant changes in band position.