Crystal structure and antiferromagnetic spin ordering of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) perovskites

• Stoichiometric polycrystalline samples of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) have been prepared by solid-state reaction and studied by means of x-ray and neutron powder diffraction as well as Mossbauer spectroscopy and magnetic measurements. All samples were found to be of single phase and to have Pnma symmetry with valence state +3 of Fe and Mo. It is demonstrated that the B-site cations of LnFe(2/3)Mo(1/3)O(3) in accord with LnFeO(3) order in a G-type antiferromagnetic structure with the magnetic moments aligned along the b axis. However, with significantly lower Neel temperatures than their LnFeO(3) parent compounds. The Fe-O-Fe bond lengths and bond angles and thus themagnitude of the antiferromagnetic superexchange interaction are found to systematically change with the ionic radius of Ln such that T-N increases with increasing radius. Only the CeFe2/3Mo1/3O3 compound experiences a low temperature spin reorientation from alignment along the b axis to the a axis.

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