Detailed studies of both ${}^{55}\mathrm{Mn}$ NMR spectra and nuclear relaxation, completed by magnetic measurements, have been performed to obtain microscopic information on the magnetic structure of fine scale (∼50 and ∼100–200 nm) particles of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ prepared by the coprecipitation method. Measurements of the resistance and magnetoresistance have also been carried out to assist these data. Our results on nuclear spin dynamics provide direct evidence of previous statements that a grain boundary in magnetoresistive manganites is not a magnetically and electrically sharp interface but should be considered as a transfer region of several monolayers different from the grain’s inner part magnetic and structure orders.

• Received 6 August 2003

DOI:https://doi.org/10.1103/PhysRevB.69.024413