Etude d'un groupement (Ru3O12)13? en presence de degenerescence orbitale et de couplage spin-orbite

A trinuclear cluster (Ru₃O₁₂)^13? occurs in the Ba₄NbRu₃O₁₂, and Ba₄TaRu₃O₁₂ compounds where the oxydation states of ruthénium are +III and +IV. The exchange interaction between magnetic sites is described by a Hamiltonian, which takes account of the orbital degeneracy of the ${}^2\text{T}{}_{\mathrm{<mtext>2</mtext><mtext>g</mtext>}}\text{(}\text{Ru}{}^{\mathrm{3+}}\text{)}\text{and}{}^3\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>g</mtext>}}\text{(}\text{Ru}{}^{\mathrm{4+}}\text{)}$ terms. For these ions, the spin-orbit coupling is the dominant effect and it appears that the low temperature magnetic susceptibility depends essentially on the orbital reduction factor and the distortion of the coordination octahedra. There is apparently no first order perturbation of the ground state due to the interaction between magnetic ions.