Magnetic order and superconductivity in single-crystalline

Zero-field μ SR measurements have been performed on CeCu2Si2 single crystals. Antiferromagnetic order shows in an initial rapid damping of the μ + polarization. In a single crystal exhibiting antiferromagnetic order and superconductivity, there exists clear evidence of phase separation of both phenomena with a first order transition from antiferromagnetism at higher temperature to superconductivity at low temperature.