Study of magnetotransport in double-layered La1.4Ca1.6Mn2O7 manganite: Presence of nano-ferromagnetic domains in paramagnetic matrix

Double-layered manganite La1.4Ca1.6Mn2O7 has been synthesized using the solid-state reaction method. It had a metal-to-insulator transition at temperature TM1≈127 K. The temperature dependence of ac susceptibility showed a broad ferromagnetic transition. The two-dimensional (2D)-ferromagnetic ordering temperature (TC2) was observed as ≈245 K. The temperature dependence of its low-field magnetoresistance has been studied. The low-field magnetoresistance of double-layered manganite, in the temperature regions between TM1 and TC2, has been found to follow 1/T5. The observed behaviour of temperature dependence of resistivity and low-field magnetoresistance has been explained in terms of two-phase model where ferromagnetic domains exist in the matrix of paramagnetic regions in which spin-dependent tunneling of charge carriers occurs between the ferromagnetic correlated regions. Based on the two-phase model, the dimension of these ferromagnetic domains inside the paramagnetic matrix has been estimated as ∼12 Å