Magnetic ground state of the distorted 6H perovskite Ba3CdIr2O9

Perovskite iridates of $6H$ hexagonal structure present a plethora of possibilities in terms of the variety of ground states resulting from a competition between spin-orbit coupling (SOC), hopping, noncubic crystal field (${\mathrm{\ensuremath{\Delta}}}_{\text{CFE}}^{\text{NC}}$), and superexchange energy scales within the ${\mathrm{Ir}}_{2}{\mathrm{O}}_{9}$ dimers. Here we investigate one such compound, ${\mathrm{Ba}}_{3}{\mathrm{CdIr}}_{2}{\mathrm{O}}_{9}$, by x-ray diffraction, dc magnetic susceptibility ($\ensuremath{\chi}$), heat capacity (${C}_{p}$), and also $^{113}\mathrm{Cd}$ nuclear magnetic resonance (NMR) spectroscopy. We have established that the magnetic ground state has a small but finite magnetic moment on $\mathrm{Ir}^{5+}$ in this system, which likely arises from intradimer Ir-Ir hopping and local crystal distortions. Our heat capacity, NMR, and dc magnetic susceptibility measurements further rule out any kind of magnetic long- or short-range ordering among the Ir moments down to at least 2 K. In addition, the magnetic heat capacity data show linear temperature dependence at low temperatures under applied high fields ($g30$ kOe), suggesting a gapless spin density of states in the compound.