Magnetic ordering and bond geometry in garnets with Fe3+ ions in the tetrahedral sublattice

Neutron diffraction, susceptibility, and other measurements are carried out on the garnets Na3Te2Fe3O12, NaCa2Sb2Fe3O12, Ca3SbSnFe3O12, YCa2Zr2Fesub(2.75)Gasub(0.25)O12, and Ca3ZrSbFe3O12. Different triangle spin configurations are found in all studied garnets, except in the last one, where no long-range order is found. The form factor of Fe3+ exhibits the forward peak associated with covalent spin density. The covalency of Fe3+ in the tetrahedral complex is higher than that in the octahedral one. The bonds of magnetic ions are examined and their geometric parameters are calculated. Appropriate exchange parameters are estimated using stability conditions for the magnetic structures found. The bonds formed by the nonmagnetic octahedral cation and two oxygen ions happen to be considerably more important than those involving only two oxygen ions. (author)