Effects of doping Na on the structure and physical properties of La2/3Ca1/3MnO3

Effects of doping Na on the structure, electrical and magnetic properties of La2/3Ca1/3MnO3 are investigated. A structural phase transition from orthorhombic to rhombohedral structure takes place at y = 0.375 . All samples show metal–insulator (M–I) transition at the transition temperature T MI and undergo the transition from paramagnetism to ferromagnetism at the Curie temperature T C . T MI and T C increase monotonically with increasing Na content. However the Na-doped samples have a shoulder in their electrical transport curves found below T MI and shows a widened magnetic transition process. On the other hand, intrinsic colossal magnetoresistance (CMR) peaks are observed in all the samples, but samples with y around 0.25 show two MR peaks which can be attributed to magnetic inhomogeneity induced by the doped Na+ ions. Here we propose a method to broaden the CMR peak of perovskite manganite, which is beneficial for practical applications.