Easy-plane magnetocrystalline anisotropy in the multi-step metamagnet CeIr3Si2

Highly anisotropic properties of CeIr$_3$Si$_2$ have been observed by the magnetization $M$($B$), electrical resistivity $\rho$, and specific heat measurements on a single-crystalline sample. This compound with an orthorhombic structure having zigzag chains of Ce ions along the a-axis undergos magnetic transitions at 3.9 K and 3.1 K. At 0.3 K, metamagnetic transitions occur at 0.68 T and 1.3 T for $B$$//$$b$ and 0.75 T for $B$$//$$c$. Easy-plane magnetocrystalline anisotropy is manifested as $M$($B//b$) $\cong$ $M$($B//c$) $\cong$ 11$M$($B//a$) at $B$ = 5 T. Electrical resistivity is also anisotropic; $\rho_{b}$ $\cong$ $\rho_{c}$ $\ge$ 2$\rho_{a}$. The magnetic part of $\rho$ exhibits a double-peak structure with maxima at 15 K and 250 K. The magnetic entropy at $T$$\rm_{N1}$ = 3.9 K is a half of $R$ln2. These observations are ascribable to the combination of the Kondo effect with $T$$\rm_{K}$ $\sim$ 20 K and a strong crystal field effect. The analysis of $M$($B$) and paramagnetic susceptibility revealed unusually large energy splitting of 500 K and 1600 K for the two excited doublets, respectively.