Charge and magnetic ordering in the electron-doped magnetoresistive materials CaMnO3-δ (δ=0.06,0.11) -: art. no. 064421

The magnetoresistive electron-doped materials CaMnO3-delta (delta =0.06,0.11) have been investigated using powder neutron diffraction. The two materials are n-type semiconductors which exhibit antiferromagnetic ordering at T-N similar to 125 K, but they have different magnetic structures. The CaMnO2.94 sample orders in a simple G-type antiferromagnetic structure, which is also observed in CaMnO3. The CaMnO2.89 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 k = (0,0,1/4) ordering wave vector. A model for the magnetic structure is proposed which involves Mn3+/Mn4+ 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 k = (0,0, 1/4) supercell suggests an oxygen 4 vacancy ordering which may play a role in the charge ordering.