Temperature dependence of Mn-55 NMR in Pr0.7Ca0.15Sr0.15MnO3 and Pr0.7Ba0.3MnO3 ferromagnetic manganites

The NMR on Mn-55 nuclei was measured in two manganites, which have the same formal valency of Mn and similar Curie temperatures. Pr0.7Ca0.15Sr0.15MnO3 is metallic below T-C and the spectrum consists of a single, motionally narrowed line. In contrast, in Pr0.7Ba0.3MnO3 lines corresponding to localized Mn3+ and Mn4+ ions were detected at 77 K. In this compound the increase of temperature leads to an increased rate of electron holes hopping. As a consequence motional narrowing of the NMR spectrum is observed, resulting in a single line for T > 140 K. In both compounds the hyperfine fields on Mn-55 nuclei remain finite up to T-C, indicating the first order magnetic transition.