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

The electronic and magnetic properties of the ABO₃ type manganites (A=rare earth, B=Mn) depend sensitively on the ratio of divalent and trivalent 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 turn may affect the structure and magnetic ordering temperature. If these compounds 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 may be formed, (b) two phase materials with stoichiometric manganites and Mn₃O₄ 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 Sr_0.3-xMnO₃ with nominal x=0.0, 0.1 and 0.2, at 300 K and 10 K. The ND data clearly show the presence of Mn₃ O₄ 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, reveal that vacancies can be induced on the A site. In the x=0.2 sample, about 5.5% of the A sites are found to be vacant. The refined Mn moments in the z=0.0 and 0.1 samples at 10 K are found to be nearly equal (3.4 μ_B). The Pr moments are parallel to the Mn moments With magnitude of 0.27 μ_B and 0.33 μ_B, respectively, in these two samples. The magnetic structure of x=0.2 sample is more complex due to the presence of an antiferromagnetic component