Investigation of the magnetic ground state of PrRu$_2$Ga$_8$ compound

Abstract

We have investigated the ground state properties of the orthorhombic structure compound PrRu$_2$Ga$_8$ through electronic and magnetic properties studies. The compound crystallizes in the CaCo$_2$Al$_8$-type structure, belonging to space group $Pbam$ (No. 55). The temperature dependence specific heat shows a $\lambda$-type anomaly at $T_N$ = 3.3 K, indicating a bulk phase transition probably of antiferromagnetic origin. At the N\'{e}el temperature $T_N$, the entropy approaches the value of 4.66~J/mol.K which is about 0.8Rln(2), where R is the universal gas constant. The analysis of the low temperature specific heat gives $\gamma$ = 46 mJ/mol.K$^2$. The temperature dependence DC magnetic susceptibility $\chi(T)$ confirms the anomaly at 3.3 K and follows the Curie-Weiss law for temperatures above 50~K, with the calculated effective magnetic moment, $\mu_\mathrm{{eff}}$ = 3.47(2)~$\mu_B$/Pr and Weiss temperature $\theta_p$ = --7.80(1)~K. This effective magnetic moment value is in good agreement with the Hund$^\prime$s rule theoretical free-ion value of 3.58~$\mu_B$ for Pr$^{3+}$. The electrical resistivity data also shows an anomaly at $T_N$ and a broad curvature at intermediate temperatures probably due to crystalline electric field (CEF) effects. The Pr$^{3+}$ in this structure type has a site symmetry of $C_s$ which predicts a CEF splitting of the $J$ = 4 multiplet into 9 singlets and thus rule out in principle the occurrence of spontaneous magnetic order. In this article we discuss the magnetic order in PrRu$_2$Ga$_8$ in line with an induced type of magnetism resulting from the admixture of the lowest CEF level with the first excited state.