Macroscopic phase separation in layered manganite induced by a surface effect

We report on the origin of the perovskite phase intergrown in the layered manganite, Sr1.6La1.4Mn2O7. X-ray powder diffraction, magnetization, and transport measurements on the Sr1.6La1.4Mn2O7 materials prepared under various conditions show that the perovskite phase is grown predominantly on the surface region in contact with either air or the substrate. With intermediate grinding and sintering the perovskite impurity increases rather than transforms to Sr1.6La1.4Mn2O7. The results provide important information for the understanding of the layered manganite system in which the compositional fluctuation occurs naturally due to the intergrown perovskite phase.