Single crystal study of layered UnRhIn3n+2 materials: Case of the novel U2RhIn8 compound

We report on the single crystal properties of the novel U$₂$RhIn$₈$ compound studied in the context of parent URhIn$₅$ and UIn$₃$ systems. The compounds were prepared by In self-flux method. U$₂$RhIn$₈$ adopts the Ho$₂$CoGa$₈$-type structure with lattice parameters a $= 4.6056(6)$ Å and c $= 11.9911(15)$ Å. The behavior of U$₂$RhIn$₈$ strongly resembles that of the related URhIn$₅$ and UIn$₃$ with respect to magnetization, specific heat and resistivity except for magnetocrystalline anisotropy developing with lowering dimensionality in the series UIn$₃$ vs. U$₂$RhIn$₈$ and URhIn$₅$. U$₂$RhIn$₈$ orders antiferromagnetically below T$_{\textrm{N}}$ $= 117$ K and exhibits a slightly enhanced Sommerfeld coefficient $γ= 47$ mJ$\cdot$mol$^-1\cdot$K$^-2$. Magnetic field leaves the value of Néel temperature for both URhIn$₅$ and U$₂$RhIn$₈$ unaffected up to 9 T. On the other hand, T$_{\textrm{N}}$ is increasing with applying hydrostatic pressure up to 3.2 GPa. The weak temperature dependence of $χ(T)$ in all studied compounds might be attributed to the mainly itinerant nature of 5f electrons. The character of uranium 5f electron states of U$₂$RhIn$₈$ was studied by first principles calculations based on the density functional theory. The overall phase diagram of U$₂$RhIn$₈$ is discussed in the context of magnetism in the related URhX$₅$ and UX$₃$ (X = In, Ga) compounds.