CERU2 - A MAGNETIC SUPERCONDUCTOR WITH EXTREMELY SMALL MAGNETIC-MOMENTS

Muon-spin-relaxation experiments and ac low-held magnetization measure ments have been carried out on the superconductor CeRu2. The relaxatio n rate of the muon-spin polarization in zero field exhibits a small bu t significant increase below T-M similar or equal to 40 K, which is su ppressed by applying a longitudinal held. This result taken together w ith magnetization measurements provides definite evidence for the occu rrence of static electronic magnetism involving extremely small magnet ic moments. Our work shows that CeRu2 is a member of a restricted fami ly of superconducting compounds that order magnetically with extremely small magnetic moments at a temperature much higher than that at whic h they become superconducting.