The ferrimagnetic structure of Fe2Mo3O12: dependence of Fe-O-O-Fe supersuperexchange couplings on geometry

The magnetic structure of Fe2Mo3O12 was determined by neutron powder diffraction and magnetization studies. The magnetic unit cell is identical with the monoclinic chemical one (Z=8), and the magnetic space group is P21/a. The magnetic moments are ferromagnetically aligned along the b-axis for each sublattice corresponding to each Fe-site. There are four different Fe-sites, and the magnetic moments are parallel within two of them, but antiparallel to those of the other two sublattices, so that a ferrimagnetic structure results. The dominant antiferromagnetic supersuperexchange couplings are those along Fe-O-O-Fe paths with the two bridging oxygens belonging to one [MoO4]-tetrahedron and forming large Fe-O-O and O-O-Fe angles