Large exchange bias and low temperature glassy state in frustrated triangular-lattice antiferromagnet Ba$_3$NiIr$_2$O$_9$

Abstract

Here, we report both ac and dc magnetization, thermodynamic and electric properties of hexagonal Ba$_3$NiIr$_2$O$_9$. The Ni$^{2+}$ (spin-1) forms layered triangular-lattice and interacts antiferromagnetically while Ir$^{5+}$ is believed to act as magnetic link between the layers. This complex magnetic interaction results in magnetic frustration leading to a spin-glass transition at $T_f$ $\sim$ 8.5 K. The observed magnetic relaxation and aging effect also confirms the nonequilibrium ground state. The system further shows large exchange bias which is tunable with cooling field. Below the Curie-Weiss temperature $\theta_{CW}$ ($\sim$ -29 K), the magnetic specific heat $C_m$ displays a broad hump and at low temperature follows $C_m = \gamma T^\alpha$ dependence where both $\gamma$ and $\alpha$ show dependence on temperature and magnetic field. A sign change in magnetoresistace is observed which is due to an interplay among magnetic moment, field and spin-orbit coupling.