A Mn-55 NMR study of La0.33Nd0.33Ca0.34MnO3 with O-16 and O-18

A Mn-55 NMR study of O-16 and O-18 containing La0.33Nd0.33Ca0.34MnO3 is reported. The spin-echo spectra measured at 4.2 K and zero field consist of a double exchange line corresponding to the ferromagnetic metallic regions. The line intensity is more than an order of magnitude lower for the O-18 compound, which indicates an order of magnitude lower content of the ferromagnetic metallic phase in this compound. The frequency dependence of the spin-spin relaxation time T-2 shows a pronounced minimum at the center of the double exchange line of both compounds due to the Suhl-Nakamura interaction, which indicates that the ferromagnetic metallic regions are at least 10 nm in size. The results are discussed in terms of the influence of oxygen isotopic substitution on phase segregation.