Oxygen content dependence of the EPR line shape in GdBa2Cu3O7−y single crystal

X-band electron paramagnetic resonance (EPR) spectra of a GdBa2Cu3O7−y single crystal were obtained at room temperature before and after reducing its oxygen content by, annealing. Before annealing, the sample exhibited superconductivity atTc≊90 K; the EPR line was asymmetrical and was described with a Dysonian shape because of the skin effect. After annealing, superconductivity was not observed; the EPR line, less affected by the skin effect, was symmetrical and more intense, approximately described with a Lorentzian shape.