Peak effect in single crystal MgB(2) superconductor for H axially c-axis.

We have studied the phase diagram of the MgB(2) superconductor using a single crystal for the H parallel c-axis. For the first time we report the existence of peak effect in the screening current in the MgB(2) for the H parallel c-axis. In the magnetic field regime 10<H<13.5 kOe the local fundamental diamagnetic moment displays a very narrow diamagnetic step. For higher fields this step is transformed to a peak (peak effect) and, finally, for H<10 kOe the diamagnetic step is transformed to a gradual transition.