Competition between Magnetic Order and Superconductivity in CeCu2.2Si2

We describe muon spin relaxation measurements of the magnetic heavy fermion compound CeCu2.2Si2. Static magnetic order appears below about 1 K, most likely of spin glass nature. We find that the superconducting transition onsetting at 0.6 K partially destroys the magnetic state and that the magnetic volume fraction decreases within the superconducting state. This observation supports the idea that in CeCu2.2Si2, magnetic order and superconductivity compete with each other rather than coexist.