Magnetic inhomogeneity and variable-range hopping transport at temperatures above the ferromagnetic transition inLa1.4Sr1.6

The magnetic and transport properties of the layered manganites ${\mathrm{La}}_{1.4}{\mathrm{Sr}}_{1.6}{\mathrm{Mn}}_{2\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{7}$ $(y<~0.10)$ are investigated. For the undoped and doped samples, magnetization and electron-spin-resonance experiments exhibit coexistence of the short-range ferromagnetic ordering and paramagnetic states at temperatures above the ferromagnetic transition. Meanwhile, the random potential in the systems increases with increasing Ti substitution. The magnetic inhomogeneities and random potential result in the Anderson localization. So the variable-range hopping processes dominate the transport behaviors at temperatures above the ferromagnetic transition in the ${\mathrm{La}}_{1.4}{\mathrm{Sr}}_{1.6}{\mathrm{Mn}}_{2\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{7}$ $(y<~0.10)$ systems.