Mössbauer Study of the Electronic and Magnetic Properties of Fe2+ Ions in Some Spinel-Type Compounds

We discuss here the results and interpretation of some Mössbauer experiments on ${\mathrm{FeCr}}_2{\mathrm{O}}_4$ , ${\mathrm{FeV}}_2{\mathrm{O}}_4$ , and ${\mathrm{GeFe}}_2{\mathrm{O}}_4$ . A detailed study of the thermal variation of the spectra leads to a determination of both quadrupolar coupling and hyperfine field at the ⁵⁷Fe nucleus as a function of temperature. Knowing the local symmetry around the Fe²⁺ ion, which is tetragonal in the first two cases, and trigonal in the last one, it is possible to deduce from the quadrupolar coupling the form of the lowest orbital wavefunction of the Fe²⁺ ion. In ${\mathrm{FeCr}}_2{\mathrm{O}}_4$ and ${\mathrm{FeV}}_2{\mathrm{O}}_4$ , this may be combined with the optical data obtained by Slack on the very similar compound ${\mathrm{FeAl}}_2{\mathrm{O}}_4$ , to predict the form and magnitude of the spin Hamiltonian and magnetic anisotropy, as well as that of the hyperfine field tensor (using a reasonable estimate for the core hyperfine field). In ${\mathrm{GeFe}}_2{\mathrm{O}}_4$ similar predictions can be made after deducing the distance to the first excited orbital level from the thermal variation of $e^2\mathrm{qQ}$ . The interest of such calculations in connection with the determination of the magnetic structures and properties of these types of compounds is examined.