Isotope effect in nearly half-doped R1−xSrxMnO3 manganites (R=Sm, NdTb, NdEu)

The effect of 16O→18O isotope substitution on the electrical resistance and magnetic susceptibility of nearly half-doped R1−xSrxMnO3 manganites was studied for ceramic samples with R=Sm (x=0.425-0.525), NdTb and NdEu (x=0.45). In these compounds, x=0.5 is a critical doping level for the crossover between ferromagnetic (FM) metal and A-type antiferromagnetic (AFM) insulator. It was demonstrated that the oxygen isotope substitution drastically affects the phase diagram of the studied manganites favoring their enhanced inhomogeneity, stabilizing the insulating AFM state, and even causing the metal-insulator transition (MIT). This suggests that such a MIT is closely related to the FM-AFM crossover independent of the specific nature of magnetic state in manganites.