Percolative metal–insulator transition in layered manganites La1.4Sr1.6−yBayMn2O7 (y⩽0.50)

Abstract

We have studied the magnetotransport properties of the La1.4Sr1.6−yBayMn2O7 (y⩽0.50) samples with a bilayered perovskite structure. For lightly doped samples, the metal–insulator transition accompanying a three-dimensional ferromagnetic transition can be understood commonly in terms of the double-exchange interaction. For heavier doped samples, the metal–insulator transition remains without a ferromagnetic transition and shifts to higher temperature with increasing Ba doping level. On account of the coexistence of short-range ferromagnetic ordering and paramagnetic state, the results can be explained by a recent percolation model based on phase separation. The percolative metal–insulator transition is consistent with the relative ferromagnetic metallic fraction change with temperature and doping level.