Crystal and magnetic structure of Pr0.7Sr0.3-xMnO3 (0 <= x <= 0.2) compounds

The electronic and magnetic properties of the ABO(3) type manganites (A = r are earth, B = Mn) depend sensitively on the ratio of divalent and trivalen t atoms on the A sublattice. The substitution of rare-earth by Ca or Sr not only affects the total valence, but also the lattice spacing, which, in tu rn may affect, the structure and magnetic ordering temperature. If these co mpounds are synthesized with less than stoichiometric amounts of the A site constituents, (relative to the Mn content), three possible outcomes may be considered: a) single phase materials with vacancies on the A sublattice m ay be formed, b) two phase materials with stoichiometric manganites and Mn3 O4 may result, or c) some combination of A and B may occur. We have carried out neutron diffraction (ND) studies on samples of Pr(0.7)rSr(0.3-x)MnO(3) with nominal x = 0.0, 0.1 and 0.2, at 300 K and 10 K. The ND data clearly show the presence Of Mn3O4 as a second phase in samples with x = 0.1 and 0. 2. Refinements of the manganite structure, based on the assumption that the ratio of Pr to Sr on the A site is equal to the nominal concentration, rev eal that vacancies can be induced on the A site. In the x = 0.2 sample, abo ut 5.5% of the A sites are found to be vacant. The refined Mn moments in th e x = 0.0 and 0.1 samples at 10 K are found to be nearly equal (3.4 mu (B)) . The Pr moments are parallel to the Mn moments with magnitude of 0.27 mu ( B) and 0.33 mu (B), respectively, in these two samples. The magnetic struct ure of x = 0.2 sample is more complex due to the presence of an antiferroma gnetic component.