Coexistence of superconductivity and ferromagnetism in a dilute cobalt-doped La1.89Ce0.11CuO4 +/-delta system

Thin films of the optimally electron-doped T-'-phase superconductor La1.89Ce0.11CuO4 +/-delta are investigated by dilute Co doping, forming La1.89Ce0.11(Cu1-xCox)O-4 +/-delta (LCCCO) with x=0.01-0.05. The following results are obtained: for the whole dilute Co doping range, LCCCO thin films show long-range ferromagnetic ordering in the temperature range from 5 to 300 K, which is likely due to the Ruderman-Kittel-Kasuya-Yosida interaction; for very dilute Co doping, x=0.01 and 0.02, the superconductivity is maintained, and the system shows the coexistence of superconductivity and ferromagnetism in the CuO2 plane. This may be based on the nature of the charge carriers in electron-doped high-T-c cuprate superconductors.