We report muon spin relaxation measurements of the doped spin-Peierls system $\left({\mathrm{Cu}}_{1-x}{\mathrm{Zn}}_x\right)-\left({\mathrm{Ge}}_{1-y}{\mathrm{Si}}_y\right){\mathrm{O}}_3$. Spontaneous muon spin precession in zero applied field was observed, confirming the presence of antiferromagnetic order in this series of compounds. In contrast to usual antiferromagnets, 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 $\xi \sim 10$ lattice units along the chain. We suggest that both Zn and Si doping induces the same maximum moment size around the doping center.

• Received 10 January 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.503