Large exchange bias and low-temperature glassy state in the frustrated triangular-lattice antiferromagnet Ba 3 NiIr 2 O 9

Here, we report both ac and dc magnetization, thermodynamic, and electric properties of hexagonal ${\mathrm{Ba}}_{3}{\mathrm{NiIr}}_{2}{\mathrm{O}}_{9}$. ${\mathrm{Ni}}^{2+}$ (spin 1) forms a layered triangular lattice and interacts antiferromagnetically, while ${\mathrm{Ir}}^{5+}$ is believed to act as a magnetic link between the layers. This complex magnetic interaction results in magnetic frustration, leading to a spin-glass transition at ${T}_{f}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}8.5$ K. The observed magnetic relaxation and aging effect also confirm the nonequilibrium ground state. The system further shows large exchange bias which is tunable with cooling field. Below the Curie-Weiss temperature ${\ensuremath{\theta}}_{CW}$ ($\ensuremath{\sim}\ensuremath{-}29$ K), the magnetic specific heat ${C}_{m}$ displays a broad hump and at low temperature follows ${C}_{m}=\ensuremath{\gamma}{T}^{\ensuremath{\alpha}}$ dependence, where both $\ensuremath{\gamma}$ and $\ensuremath{\alpha}$ show dependence on temperature and magnetic field. A sign change in magnetoresistance is observed which is due to an interplay among the magnetic moment, field, and spin-orbit coupling.