Giant Magnetoresistance Effect Of The Nanoscale Layered-Perovskite La2.5-Xk0.5+Xmn2o7 (0 < X < 0.5)

Nanoscale layered-perovskite La2.5-xK0.5+xMn2O7 (0 < x < 0.5) have been prepared by the modified sol-gel method, and their structural, magnetic and electric properties have been studied. The experimental results show that these materials exhibit paramagnetic-to-ferromagnetic phase transitions at 183, 216, 230, 238 and 249K for x = 0.05, 0.15, 0.25, 0.35 and 0.45, respectively. For all compositions of La2.5-xK0.5+xMn2O7 investigated here, we have observed no metal-nonmetal transition phenomena for the whole temperature region (80 - 300 K). The nanoscale samples exhibit highly enhanced magnetoresistance (MR) effects especially at low temperatures (< T-C). The MR behaviour can be explained by taking into account the two-dimensionality with anisotropy of the Mn-O networks and nanoscale grain size effect in the layered manganese perovskites.