Ba${}_3$M${}_x$Ti${}_{3-x}$O${}_9$(M = Ir, Rh): A family of 5\textit{\textcolor{black}{d}}/4\textit{\textcolor{black}{d}}-based, diluted quantum spin liquids

Abstract

We report the structural and magnetic properties of the 4}\textit{\textcolor{black}{d }}\textcolor{black}{(M = Rh) based and 5}\textit{\textcolor{black}{d }}\textcolor{black}{(M = Ir) based systems Ba${}_3$M${}_x$Ti${}_{3-x}$O${}_9$ (nominally $x$ = 0.5, 1). The studied compositions were found to crystallize in a hexagonal structure with the centrosymmetric space group }$P{6}_3/mmc$.\textcolor{black}{{} The structures comprise of A${}_2$O${}_9$ polyhedra (with the A site (possibly) statistically occupied by M and Ti) in which pairs of transition metal ions are stacked along the crystallographic }\textit{\textcolor{black}{c}}\textcolor{black}{-axis. These pairs form triangular bilayers in the $ab$-plane. The magnetic Rh and Ir ions occupy these bilayers, diluted by Ti ions even for $x$ = 1. These bilayers are separated by a triangular layer which is dominantly occupied by Ti ions. From magnetization measurements we infer strong antiferromagnetic couplings for all of the materials but the absence of any spin-freezing or spin-ordering down to 2~K. Further, specific heat measurements down to 0.35~K show no sign of a phase transition for any of the compounds. Based on these thermodynamic measurements we propose the emergence of a quantum spin liquid ground state for Ba${}_3$Rh${}_{0.5}$Ti${}_{2.5}$O${}_9$, and Ba${}_3$Ir${}_{0.5}$Ti${}_{2.5}$O${}_9$, in addition to the already reported Ba${}_3$IrTi${}_2$O${}_9$. }

12 pages, 11 figures, accepted in Phys. Rev. B (regular article)