Large exchange bias and low-temperature glassy state in the frustrated triangular-lattice antiferromagnetBa3NiIr2O9

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.