Current persistence and magnetic shielding properties of ${\mathrm{Y}}_1{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$ tubes

We have studied the time and temperature dependence of trapped magnetic fields in ceramic tubes of the high-$T_c$ superconductor ${\mathrm{Y}}_1{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$. The maximum field in a particular tube is largely a function of temperature, although decays of the form $t^{-\alpha }$ occur for fields at the maximum values. For fields away from the critical values, limits on the decay rates give $\rho \le {10}^{-16\mathrm{}}$ Ω cm. These results are consistent with the superconductor being in a spin-glass-like state.