Charge and magnetic ordering in the electron-doped magnetoresistive materials (formula presented) (formula presented)

The magnetoresistive “electron”-doped materials (formula presented) (formula presented) have been investigated using powder neutron diffraction. The two materials are n-type semiconductors which exhibit antiferromagnetic ordering at (formula presented) but they have different magnetic structures. The (formula presented) sample orders in a simple G-type antiferromagnetic structure, which is also observed in (formula presented) The (formula presented) sample, on the other hand, exhibits two magnetic features: the G-type reflections as noted above, and a set of reflections that can be indexed on a (formula presented) ordering wave vector. A model for the magnetic structure is proposed which involves (formula presented) charge ordering concomitant with the magnetic ordering. The presence of a set of weak, temperature independent structural reflections which can also be indexed on a (formula presented) supercell suggests an oxygen vacancy ordering which may play a role in the charge ordering.