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 (1610.04527v1)

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 }$P6_{3}/mmc$.\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$_{9}$. }