Room temperature ferromagnetism in superconducting YBa2Cu3O7−δ/Y2BaCuO5 composites

We report room temperature ferromagnetism in superconducting YBa 2 Cu 3 O 7-δ /Y 2 BaCuO 5 composites prepared by a citric acid complexing-hydrothermal synthesis coupled method. Scanning electron microscopy observation shows the formation of solid and hollow microspheres. These microspheres are composed of many irregular particles with the size of 100–500 nm. A superconducting transition about 93 K is revealed by zero-field-cooling and field-cooling magnetization curves. Electron spin resonance spectra at various temperatures further confirm the superconducting behaviors at low temperatures. X-ray photoelectron spectroscopy and energy dispersive X-ray spectrum indicate the intrinsic nature of the observed ferromagnetism. Post-heating treatment experiments at argon gas and in the air imply that the observed ferromagnetism should be responsible for an interface-induced mechanism.