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. Pr0.7Ca0.15 Sr0.15MnO3 is metallic below T-C and the spectrum consists of a single , motionally narrowed line. In contrast, in Pr0.7Ba0.3MnO3 lines corre sponding to localized Mn3+ and Mn4+ ions were detected at 77 K. In thi s compound the increase of temperature leads to an increased rate of e lectron holes hopping. As a consequence motional narrowing of the NMR spectrum is observed, resulting in a single line for T > 140 K. In bot h compounds the hyperfine fields on Mn-55 nuclei remain finite up to T -C, indicating the first order magnetic transition.