New electric features in Cu-rich La2CuO4+δ system

Abstract A series of light oxygen doped Cu-rich La 2 CuO 4+ δ samples, with δ = 2:1+ x (0⩽ x ⩽0.18), have been investigated. Characterization shows that the samples are single phase till x ⩾0.10. TEM, electron energy loss spectroscopy, magnetization and electric transport measurements show that the excess Cu (the substitution of Cu 2+ for La 3+ ) can enhance the 3D antiferromagnetic (AF) exchange interaction 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 .