Spin freezing and ordering in CaV4O9, CaV3O7 and CaV2O5

We have performed muon spin relaxation measurements of CaV4O9, CaV3O7 and CaV2O5. The sublattice magnetization in the antiferromagnetic state of CaV3O7 agrees well with spin wave theory. In CaV4O9 and CaV2O5 we observe spin freezing below 15 and 50 K, respectively, which indicates that a substantial fraction of the vanadium magnetic moment is not in a spin-singlet state at low temperatures in either material.