The effect of oxygen isotope substitution on the phase diagram of nearly half-doped R1-xSrxMnO3 manganites (R = Sm, NdTb, NdEu)

The effect of O16 → O18 isotope substitution on the electrical resistance, magnetic susceptibility and neutron diffraction patterns of nearly half-doped R1-xSrxMnO3 manganites was studied for ceramic samples with R = Sm (x = 0.425-0.525), Nd/Tb (x = 0.45) and Nd/Eu (x = 0.45). In Nd/Tb and Nd/Eu manganites, the composition was chosen to yield the same mean ionic radius as in the Sm compound, but the samples differed in the cation disorder parameter σ. The oxygen isotope substitution leads to fundamental changes in the phase diagram of the manganites studied, favouring enhanced inhomogeneity, stabilizing the insulating antiferromagnetic (AFM) state and even causing a metal-insulator transition (MIT). The MIT induced by the oxygen isotope substitution was found here for the first time in manganites with A-type AFM; earlier this unusual phenomenon was observed only for compounds with the CE-type AFM structure. This suggests that such a MIT is closely related to the ferro-AFM crossover independently on the specific nature of the AFM phase and related orbital order