ANTIFERROMAGNETIC ORDER WITH SPATIALLY INHOMOGENEOUS ORDERED MOMENT SIZE OF ZN-DOPED AND SI-DOPED CUGEO3

We report muon spin relaxation measurements of the doped spin-Peierls system (Cu1-xZnx)- (Ge1-ySiy)O-3. Spontaneous muon spin precession in zero applied field was observed, confirming the presence of antiferrom agnetic order in this series of compounds. In contrast to usual antife rromagnets, muon spin precession is accompanied by a relaxation signal indicating a large spatial inhomogeneity of the ordered moment size. Assuming an exponential decay of the moment size away from the doping centers, we estimated a decay length of xi similar to 10 lattice units along the chain. We suggest that both Zn and Si doping induces the sa me maximum moment size around the doping center.