  The different pinning strengths of the flux line lattice in the peak effect
(PE) region of a polycrystalline sample of CeRu$_2$ with a superconducting
transition temperature {$T_c = 6.1$ K} have been probed by means of
magnetization measurements with a SQUID magnetometer as the temperature $T$ and
the magnetic field $H$ are varied. Magnetic relaxation measurements were used
to monitor the flux line dynamics in the PE region. For {$T < 4.5$ K} and $H <
H_P$, where $H_P$ is the field where the magnetization reaches a maximum in the
PE region, the relaxation rate was found to be significantly larger in the
descending-field branch of the PE than it is in other sections of the PE
region. For {$T \geq 4.5$ K}, the relaxation rate in the entire PE region is so
large that the magnetization reached a stable (equilibrium) value within
{$10^4$ s}. This experimentally determined stable state appears as an increase
of the magnetization in the PE region and has a dome shape superimposed on a
linear interpolation through the PE region. It was also found that the PE in
CeRu$_2$ can be suppressed by rapid thermal cycling of the sample between {10
K} and {300 K} four times. The reversible magnetization after the PE has been
suppressed coincides with the linear interpolation through the PE region, in
contrast to the behavior of the equilibrium magnetization when the PE is
present.
  PACS number: 74.25.Qt, 74.70.Ad
