Low-temperature physical properties of a new orthorhombic compound Ce$2$Ir$3$Sb$_4$

In order to explore new Ce compounds that show novel physical properties, we focused on the orthorhombic compounds R$_2$Ir$_3$Sb$_4$ (R = La, Ce, Pr, Nd ) (space group $Pnma$, $D_{2h}^{\rm{16}}$, No.62) [1]. From the results of magnetization measurements above 3 K, it has been reported that Ce$_2$Ir$_3$Sb$_4$ does not show any phase transition. In this study, we prepared polycrystalline samples of Ce$_2$Ir$_3$Sb$_4$ and investigated their physical properties by measuring the magnetization, the electrical resistivity, and the specific heat down to 0.4 K. From the measurement of the inverse magnetic susceptibility H/M, the effective magnetic moment per Ce atom was found to be 2.50 ${\mu}_{\rm{B}}$/Ce. Since this value is close to the theoretical value of 2.54 ${\mu}_{\rm{B}}$/Ce for Ce$^{3+}$, it was confirmed that the Ce ions in this compound are in the trivalent state, as reported in the literature [1]. In addition, a paramagnetic Curie temperature ${\theta}_{\rm{P}}$ = -24.4 K was obtained, indicating an antiferromagnetic interaction between the magnetic moments of Ce. Figure 1 shows the temperature dependence of the normalized electrical resistivity $\rho$($T$)/$\rho$(278 K) and the magnetic susceptibility $M$/$H$. The $\rho$ decreases with decreasing temperature, followed by a minimum at 25 K, then shows -ln$T$ dependence between 10.5 K and 5 K and a maximum at 2.1 K. This indicates that Ce$_2$Ir$_3$Sb$_4$ is a Kondo lattice compound. The maximum at 2.1 K does not corresponds to phase transition since $M$/$H$ does not show any anomaly down to 1.8 K. Figure 2 shows the temperature dependence of the specific heat $C$. The specific heat shows a peak at 1.3 K and a steep decrease at lower temperatures. Since the specific heat decreases with decreasing temperature from 10 K to 1.3 K and the electrical resistivity shows no anomaly at 1.3 K, the specific heat peak at 1.3 K is not due to a phase transition but due to the Schottky specific heat caused by the crystal field splitting of the 4f levels of Ce ions.

[1] K. Sch$\rm{\ddot{a}}$fer, W. Hermes, U. Rodewald, R. Hoffmann, and R. P$\rm{\ddot{o}}$ttgen, Z. Naturforsch.B, 66, 777 (2011).

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