Low-field magnetic-relaxation effects in CeCu2Si2

We have found time effects in the magnetization $M$ of the heavy-fermion Ce${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$ at $H<\mathrm{}400\mathrm{}$ Oe similar to the effects we recently reported for the high-$T_c$ superconductors Sr-La-Cu-O and Ba-La-Cu-O. If a small field $H_i$ is applied to a virgin bulk polycrystalline specimen, the magnetization $M$ relaxes with time accurately following the law $M\left(t\right)-M\left(t_0\right)\propto \ln \left(\frac{t}{t_0}\right)$ over observation times of ${10}^5$ sec. The same law is followed at $H=0\mathrm{}$ when the field $H_i$ is removed. For $H<\mathrm{}{H}_{c1\mathrm{}}$ the logarithmic rate $\frac{\partial M}{\partial \ln t}$ is directly proportional to $H_i^4$ and becomes almost independent of $H_i$ when flux penetrates into the sample.