The influence of the 16O–18O isotope substitution on spin dynamics of (La0.25Pr0.75)0.7Ca0.3MnO3: 139La NMR data

The 139La NMR spectra and spin–spin relaxation times have been measured for the 16O and 18O isotope-substituted manganite (La0.25Pr0.75)0.7Ca0.3MnO3 in the external magnetic field of 5 T. The NMR signal wipe-out has been observed in the 18O-enriched sample in the charge-ordered state. This phenomenon is connected with a sharp increase in the spin–spin relaxation rate. The great isotope-effect observed provides a clear evidence of an essential role of oxygen motion in controlling the long-range magnetic order in manganites.