Nontrivial Spin Dimer in the Hexagonal Ruthenate Ba3CaRu2O9 Revealed by Nonmagnetic Ion Substitution

We have prepared a set of polycrystalline samples of Ba3Ca(Ru1−xNbx)2O9 consisting of the face-shared (Ru,Nb)2O9 dimer block from x = 0 to 0.12, and have measured the x-ray diffraction and magnetiz...