Effects of Pb-ion irradiation on the vortex pinning in melt-textured YBa2Cu3Ox

Melt-textured YBa₂Cu₃O_x quasicrystalline samples were studied for the effects of Pb-ion irradiation on the vortex pinning. The strength of the pinning was monitored by measurements of the saturation remanent magnetization (M_R) as a detailed function of temperature from 4.2 K up to T_c (≈92 K). Our results show that M_R is greatly enhanced by the Pb-ion irradiation at all temperatures below T_c. Specifically, when compared to a similar but nonirradiated sample, the M_R of an optimally irradiated sample is raised by a factor of 3.4 at 4.2 K and, more strikingly, by 12.7 at 77 K. Contrastingly, in an earlier study of a γ-ray irradiated Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀ sample, the vortex pinning was seen to be enhanced but mainly near 4.2 K, suggesting that the γ-ray irradiation produces highly localized pinning sites. Hence, our present results imply conversely that the Pb-ion irradiation creates extended structural defects that are effective as vortex pinning sites up to relatively high temperatures, including that of liquid nitrogen.