NMR Probe of Phase Segregation in Electron Doped Mixed Valence Manganites

A ${}^{55}\mathrm{Mn}$ and ${}^{139}\mathrm{La}$ NMR study of ${\mathrm{La}}_{0.35}{\mathrm{Ca}}_{0.65}{\mathrm{MnO}}_3$ is reported. The zero field ${}^{55}\mathrm{Mn}$ spectra consist of two lines centered at 290 and 375 MHz. Their behavior under an applied magnetic field makes it possible to attribute them to regions of antiferromagnetically and ferromagnetically coupled Mn spins, respectively. This gives evidence for the existence of electronic phase segregation of microscopic ferromagnetic regions of double exchange coupled Mn spins over a charge ordered antiferromagnetic background. The behavior of these ferromagnetic regions in the applied magnetic field is related to the magnetoresistive properties of the manganites.