  We have investigated the dilute magnetic impurity effect on the magnetic
properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped
compound Ba3CaRu2O9. The magnetic ground state of each compound stands against
2% substitution of magnetic impurities for Zn or Ca. We have found that the
magnetic response of these impurities, which behave as paramagnetic spins,
depends on the host materials and the difference of the two manifests itself in
the Weiss temperature, which can hardly be explained by the dilute magnetic
impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the
Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a
possible physical meaning of the observed Weiss temperature.
