Oxygen-isotope effect on crystal and magnetic structures of (La 1-y Pr y ) 0.7 Ca 0.3 MnO 3

The oxygen 16O/18O isotope effect on the crystalline and magnetic structures of (La1-yPry)0.7Ca0.3MnO3 has been studied by neutron powder diffraction in the temperature range from 10 to 293 K. The isotope-enriched samples with 16O and 18O have been found to be identical in crystalline and antiferromagnetic (AFM) structures down to the metallic ferromagnetic (FM) phase transition temperature (TFM) of the 16O sample. At low temperatures, both the crystalline and magnetic structures of the samples are different. The study of the samples with partial isotope substitution shows that both the FM-phase fraction and TFM strongly depend on 18O oxygen content, disappearing at about a 60% concentration of 18O. In comparison, the temperature of the AFM transition does not depend on isotope content.