A $\text{}^{55}$Mn NMR Study of La$\text{}_{0.33}$Nd$\text{}_{0.33}$Ca$\text{}_{0.34}$Mn O$\text{}_{3}$ with $\text{}^{16}$O and $\text{}^{18}$O

A $\text{}^{55}$Mn NMR study of $\text{}^{16}$O and $\text{}^{18}$O containing La$\text{}_{0.33}$Nd$\text{}_{0.33}$Ca$\text{}_{0.34}$Mn O$\text{}_{3}$ 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 $\text{}^{18}$O 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$\text{}_{2}$ 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.