The hydride $\mathrm{Ce}\mathrm{Ru}\mathrm{Si}{\mathrm{H}}_{1.0}$ with space group $P4∕nmm$ was synthesized by exposure at $523\mathrm{K}$ of the heavy-fermion ternary silicide CeRuSi under $4\mathrm{MPa}$ of hydrogen gas. The investigation of the hydride by x-ray powder diffraction reveals that the hydrogenation induces a pronounced anisotropic expansion of the unit cell. Moreover, $\mathrm{Ce}\mathrm{Ru}\mathrm{Si}{\mathrm{H}}_{1.0}$ presents two antiferromagnetic transitions at $T_{N1}=7.5\left(2\right)\mathrm{K}$ and $T_{N2}=3.1\left(2\right)\mathrm{K}$ evidenced by magnetization and specific heat measurements. Hydrogenation changes the moderate heavy-fermion compound CeRuSi, which has a $\gamma =220\mathrm{mJ}∕\mathrm{mol}{\mathrm{K}}^2$, to an antiferromagnet, which has a smaller electronic coefficient $\gamma =26\mathrm{mJ}∕\mathrm{mol}{\mathrm{K}}^2$. In other words, the hydrogen insertion diminishes the influence of the Kondo effect. The transition heavy-fermion $\text{behavior}\to \text{antiferromagnet}$ can be well understood in terms of the classical Doniach diagram where the hydrogenation plays a role opposite to the pressure. The expansion of the lattice induced by hydrogen insertion is here much more important than the role of Ce-H bonding observed in other hydrogenated compounds $\mathrm{Ce}\mathrm{Co}\mathrm{Si}{\mathrm{H}}_{1.0}$ or $\mathrm{Ce}\mathrm{Co}\mathrm{Ge}{\mathrm{H}}_{1.0}$, where an opposite transition ($\text{antiferromagnetic}\to \text{spin}$ fluctuation) was evidenced.

• Received 3 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.014414