Ac-susceptibility study of critical current density in metal-substituted ErBa2Cu3O7- delta.

Abstract

Studies of the ac susceptibility of the pure ${\mathrm{ErBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (Er-123) and the substituted samples ${\mathrm{ErBa}}_{2}$ (${\mathrm{Cu}}_{0.995}$${\mathit{M}}_{0.005}$${)}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (M=Fe, Ni, Co, Ga) have been made at different ac field amplitudes. Analysis of the temperature dependence of the ac susceptibility at these fields [X-T plots] has been done employing Kim's critical state model. The dopants are found to lower the temperature-dependent intergranular critical current density, ${\mathit{J}}_{\mathit{c}}$(T), of the Er-123 system at different rates. Fe doping decreases the ${\mathit{J}}_{\mathit{c}}$ at the highest rate whereas Ni substitution results in the least rate of ${\mathit{J}}_{\mathit{c}}$ lowering; the depression rates for Ga and Co doped samples are similar and intermediate. These results fully support the findings of our previous study [Phys. Rev. B 52, 1320 (1995)] of the flux creep effects on the same batch of samples wherein it was observed that the concerned substituents had a similar effect on the flux creep activation energy values (${\mathit{E}}_{\mathit{a}}$) of the system. The lower ${\mathit{J}}_{\mathit{c}}$ of the Fe, Ni, Co, and Ga substituted samples is attributed to the reduction in the zero-temperature pinning potential ${\mathit{I}}_{0}$(0) brought about by the dopants. \textcopyright{} 1996 The American Physical Society.