Studies of oxygen superconductors REBa2Cu3O7-δ (where RE rare earth) using an EPR method

The samples of well-oxidized REBa2Cu3O7-delta with different trivalent RE (rare earth) ions, were studied with use of EPR method at the temperature above of liquid nitrogen (77 K). The measured samples were obtained by the solid phase synthesis method. The aim of these measurements was to find and describe the relation between critical temperature, critical magnetic field, and the shape of the resonance signal. It was expected that samples possess the HTSC transition at about 90 K. For most samples, both a nonresonant absorption and emerging of HTSC state were visible in the EPR experiment. The evolution of these signals allowed determining the critical temperature, as well as the evolution of the critical magnetic fields as a function of temperature. Additionally, EPR signal of Cu (II) ions was detected and explained by insufficiently oxidized samples or the existence of contaminated phases.