Effect of Ca and Ba doping on the Magnetotransport Properties of NdMnO_3

摘要

Mixed valence manganites of the type Nd_(0.7-x)R_xMnO_3 where, R = divalent cation (Ca and Ba) have been synthesized using citrate pyrolysis process. It is interesting to see that the Ca and Ba doped NdMnO_3 compounds have metal - insulating behavior with different T_(MI) (metal-insulator transition temperature) values at different magnetic fields although the Ca and Ba ions have almost same ionic radii but different density. For Ca-doped NdMnO_3 compound, a magnetoresistance as high as 79 % was observed at the insulator transition temperature T_p =102 K, while for Ba-doped NdMnO_3 compound, lower magnetoresistance ～ 67% was observed at the metal insulator transition temperature T_p = 90 K. For both Ca & Ba doped NdMnO_3 structural characterization shows same orthorhombic phase without impurities in the sample calcined at 900 ℃, with the crystallite sizes in the nanometer scale. Grain size and morphology results show that the compounds have clear grain morphology and also nanoscale grain sizes.