Effect of X-ray irradiation on the magnetic properties of REBa2Cu3Oy (RE = Y, Nd, or Gd)

We examined the effect of X-ray irradiation on the magnetic properties of REBa₂Cu₃O_y (REBCO; RE = Y, Nd, or Gd). In all the samples, T_c0, which is defined as the temperature below which the magnetic susceptibility is lower than zero, did not change significantly after irradiation within the measurement accuracy. On the other hand, the magnetic susceptibilities after irradiation were lower than those before irradiation in all the samples. These results, which are consistent with those observed under light irradiation, indicate that X-ray irradiation enhances the superconductive properties of these materials. This enhancement results from hole doping in the CuO₂ plane via the generation of electron–hole pairs by X-ray irradiation and subsequent trapping of the electrons at oxygen vacancies. Relaxation of the irradiation effect and the electron behavior after irradiation were studied by analyzing the magnetic properties and Raman spectra.