New electric features in Cu-rich La2CuO4+delta system

A series of light oxygen doped Cu-rich La2CuO4+delta samples. with delta < 0.01 and the nominal composition of cations being La:Cu = 2:1 + x (0 less t han or equal to x less than or equal to 0.18), have been investigated. Char acterization shows that the samples are single phase till x greater than or equal to 0.10. TEM, electron energy loss spectroscopy, magnetization and e lectric transport measurements show that the excess Cu (the substitution of Cu2+ for La3+) can enhance the 3D antiferromagnetic (AF) exchange interact ion and promote electronic phase separation. In the AF background the hole- rich cluster caused by phase separation becomes superconducting below 34 K, and shows ferromagnetism from the superconducting transition temperature T -c to above the Neel temperature T-N. (C) 2001 Elsevier Science B.V. All ri ghts reserved.