Spin–orbit coupling driven novel magnetism in d⁵ 6H-perovskite iridates Ba₃IrTi₂O₉ and Ba₃TiIr₂O₉

In the present paper, we have carried out a comparative first principles as well as model Hamiltonian study to understand the novel magnetism in 6H perovskite iridates Ba₃IrTi₂O₉ and Ba₃TiIr₂O₉ resulting from an unusual combination of geometrical as well as exchange frustration owing to their unique crystal geometry. Our model calculations corroborated with multipolar analysis provides a comprehensive understanding of the spin–orbit entangled pseudo-spin states in both materials. While, the character is quite robust in the former compound, it is found to be directly related to the nature of magnetism in the latter iridate. The identification of the relevant spin model for the ideal structure of Ba₃IrTi₂O₉ suggests that the Heisenberg exchange interaction dominates the Kitaev term favoring long range magnetic order in the system in line with the ab initio study while the other iridate Ba₃TiIr₂O₉ has the posibility to host novel spin–orbital singlet state with no resultant moment. (paper)