OBSERVATION OF HIGH Tc IN THE BILAYERED La2SmxSr1-xMn2O7 PEROVSKITE

Abstract

Bulk layered perovskite samples La 2 Sm x Sr 1-x Mn 2 O 7 (x = 0.4, 0.6 and 0.8) were prepared by the conventional solid-state reaction technique and their temperature dependence of electrical resistance and magnetization measurements were performed. The metal-insulator (M-I) transition, magnetic phase transition and the colossal magnetoresisitance phenomena were observed. The M-I transition peak temperature (T p ) shifts towards lower temperature with increasing x while magnetic field shifts T p to the high temperature regime. Experimental results show that layered manganites La 2 Sm x Sr 1-x Mn 2 O 7 (x = 0.4, 0.6 and 0.8) exhibit ferromagnetic-to-paramagnetic transitions at Curie temperature T c ~ 355, 286 and 277 K for x = 0.4, 0.6 and 0.8, respectively. A large deviation between the metal-insulator transition and the magnetic transition temperature is observed for all the doping concentrations. But in the case of well-known ABO 3 type perovskite manganites like La 0.75 Ca 0.25 MnO 3, the M-I transition was found previously very close to magnetic transition. At 78 K, a sharp increase of magnetoresistance was observed at low magnetic fields.