Competition between the double exchange and charge ordering interactions in the bandwidth controlled (La,Nd) 0.8Na 0.2MnO 3 manganites

Abstract

Structural, magnetic, and transport properties of ( La 1−x Nd x) 0.8 Na 0.2 MnO 3 (0⩽x⩽1) are studied. The system exhibits a rhombohedrally distorted perovskite structure for x⩽0.2 and it converts to an orthorhombic structure for x⩾0.4. Re-entrant ferromagnetic-type charge ordering transitions are observed in the narrow bandwidth samples ( x⩾0.8). For T>77 K , the compounds show metal to insulator transitions except Nd 0.8Na 0.2MnO 3. The transition temperatures are equal to the corresponding Curie temperatures. Combining our results with the published data on manganites doped with divalent alkali earth cations, we propose that the double exchange interaction in (La 1− x Nd x ) 0.8Na 0.2MnO 3 is stronger than that of the divalent cations doped manganites with the same average A-site radius and hole concentrations. The resistivity data above the metal to insulator transition temperature for the charge ordered sample are discussed in the frame work of the variable-range hopping model.