Neutron-irradiation effects on critical current densities in single-crystalline YBa2Cu3O7- delta.

Abstract

Neutron-irradiation experiments were made on two high-quality ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ single crystals in the fluence range from 2\ifmmode\times\else\texttimes\fi{}${10}^{21}$ to 2\ifmmode\times\else\texttimes\fi{}${10}^{22}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ (E>0.1 MeV). Critical current densities ${\mathit{J}}_{\mathit{c}}$ and volume-pinning forces ${\mathit{P}}_{\mathit{V}}$ were obtained from magnetization measurements in the temperature range from 5 to 77 K, for magnetic fields up to 8 T, and for field orientations parallel and perpendicular to the crystallographic c direction. All evaluations were made on the basis of an extended anisotropic Bean model. The results show large enhancements of flux pinning, in particular at low neutron fluences, a strong reduction of ${\mathit{J}}_{\mathit{c}}$ anisotropy, and significant changes of the temperature dependence of ${\mathit{J}}_{\mathit{c}}$. The complicated (nonlinear) dependence of critical current densities and pinning forces on neutron fluence is discussed in terms of an interaction between the radiation-induced defects with the preirradiation defect structure, based on electron microscopy of individual defects and the defect distribution measured in one crystal after neutron irradiation to 2\ifmmode\times\else\texttimes\fi{}${10}^{22}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ (E>0.1 MeV).