Low-field magnetic relaxation effects in high-Tcsuperconductors Sr-La-Cu-O and Ba-La-Cu-O

Abstract

The relaxation of the isothermal dc magnetization $M$ in zero-field-cooled Ba-La-Cu-O and Sr-La-Cu-O has been investigated. After the external magnetic field has been changed or cycled, the resultant magnetization $M$ decays following the law $M\propto \ln \left(\frac{t}{t_0}\right)$ with great accuracy over an observation time period of four decades. At $H=0\mathrm{}$, the logarithmic decay rate $\frac{\partial M}{\partial \ln t}$ is proportional to the temperature $T$ and it is also proportional to ${H_i}^3$. Here $H_i$ is the external field which is reduced to zero before the decay rate of persistent currents is observed.