X-ray photoemission spectra and the electro-transport properties studies on the layered manganites Sm2−2xSr1+2xMn2O7

Layered perovskite manganite ceramics with a nominal chemistry Sm2−2xSr1+2xMn2O7 (x = 0.2, 0.4, 0.5) were prepared using sol–gel method. X-ray photoemission spectroscopy (XPS) was used to investigate their electronic structures. The manganese ions are highly mixed states of Mn3+ and Mn4+. It is found that the Mn3+/Mn4+ ratio decreases with the Sr doping content increasing. The O 1s photoemission spectra show that there are lattice oxygen and chemical absorbed oxygen in all the samples. Meanwhile, the conductivity and magnetoresistance (MR) of Sm2−2xSr1+2xMn2O7 (x = 0.2, 0.4, 0.5) were studied. The sample of x = 0.2 shows metal insulator transition (MIT) at 115 K. The MIT peak temperature (Tp) shifts towards higher temperature with increasing applied magnetic field. All the samples can be well fitted to the variable-range hopping (VRH) model. The maximum value of MR (%) [ρ(0) − ρ(H)]/ρ(0) × 100 for x = 0.2 is 79.05% (105 K, 3 T).