Synthesis and colossal magnetoresistance effect of layered perovskites Sm2−2xSr1+2xMn2O7 (x = 0.2, 0.4, 0.5)

Polycrystalline layered perovskite manganites Sm2−2xSr1+2xMn2O7 (x = 0.2, 0.4, 0.5) were synthesized by the citrate-gel method. Their magnetic and electric properties were investigated. The samples with x = 0.4 and 0.5 show insulating behavior. However, a metal–insulator (M–I) transition is observed for x = 0.2. The maximum value of MR [ρ(0) − ρ(H)]/ρ(0) × 100%] for x = 0.2 is 89.88% (105 K, 5 T) and 66.36% (105 K, 2 T). The MR is efficiently decreased from 57.62% (105 K, 5 T) for x = 0.4 to 33.44% (105 K, 5 T) for x = 0.5. Moreover, the Curie temperature (Tc) decreases with increasing x.