Magnetic and electrical properties of the oxide system of La0.8Sr0.2Co1-xCuxO3-delta

This work investigates the electrical resistivity, magnetization and magnet oresistance in polycrystalline La0.8Sr0.2Co1-xCuxO3-delta compounds (0.1 le ss than or equal to x less than or equal to 0.4 and 0.4 less than or equal to delta less than or equal to 0.5) in the temperature range of 5-300 K. In the doping range, all cobaltites are semiconducting state, which displays variable range hopping,and ferromagnetic long-range order behaviors except for T > T-c. Therefore, the magnetic phase transitions are independent of t he electrical resistivity in the system. In addition, a decreasing Cu conte nt causes an increasing of magnetic transition temperature T-c. The large n egative magnetoresistance effect is observed as well. (C) 1999 Elsevier Sci ence B.V. All rights reserved.