Crystal structure and thermodynamic properties of the non-centrosymmetric PrRu${}_4$Sn${}_6$ caged compound

Abstract

PrRu${}_4$Sn${}_6$ is a tetragonal, non-centrosymmetric structure compound. It is isostructural to the extensively studied Kondo insulator CeRu${}_4$Sn${}_6$ which crystallizes in the YRu${}_4$Sn${}_6$-type structure with space group $I$\={4}2$m$. In this structure, the Pr atom fills the void formed by the octahedral Ru${}_4$Sn${}_6$ units which results in a tetragonal body-centred arrangement. Here we present reports on the physical and magnetic properties of PrRu${}_4$Sn${}_6$. The temperature dependences of specific heat, $C_p(T)$, electrical resistivity, $\rho (T)$, and magnetic susceptibility, $\chi (T)$, reveal the absence of a long-range magnetic ordering down to 2 K. $\chi (T)$ follows a Curie-Weiss behaviour above 100 K with an effective magnetic moment, ${\mu }_{\mathrm{eff}}$ = 3.34 ${\mu }_B$/Pr and paramagnetic Weiss temperature, ${\theta }_p$ = $-$19.47 K indicating a dominant antiferromagnetic interaction. The magnetization at 2 K is quasi-linear in nature and attains a value of 0.86 ${\mu }_B$/Pr at 7 T which is well reduced compared to the calculated value of 3.32 ${\mu }_B$/Pr expected for a free Pr${}^{3+}$ ion. This is attributed to possible magneto-crystalline anisotropy in the system. $C_p(T)$ indicates the presence of a optical-phonon mode which is supported by a glass-like thermal conductivity above $\sim$45 K. This observation is associated with caged structured compounds where the low-frequency optical-phonon mode of the guest atom interacts with the host lattice, resulting in the scattering of heat-carrying quasiparticles.

6 pages, 4 figures, to appear in the Proceedings of SAIP 2018, the 63nd Annual Conference of the South African Institute of Physics