Electron-transport and magnetic properties of the layered perovskite La2−2xSr1+2xMn2O7

Polycrystals of double-layered perovskite La2−2xSr1+2xMn2O7 ( x = 0.3 ,0.33,0.4) were prepared by solid-state reactions at the same temperature. We have performed resistance and magnetization measurements on these samples. They exhibit both colossal magnetoresistance (CMR) (MR>64% for H = 5 T ) near magnetic transition Tc, and 2D short-range magnetic order. Additionally, these compounds showed two distinct resistance peaks. The resistance peak near Tc was sharp, whereas the second peak below Tc was a broad one. Especially, it is notice that there are wide plateaus of CMR form Tc to 20 K for two samples.