Hydrogenation inducing antiferromagnetism in the heavy-fermion ternary silicide CeRuSi
Résumé
The hydride CeRuSiH1.0 with space group P4/nmm was synthesized by exposure at 523 K of the heavy-fermion ternary silicide CeRuSi under 4 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, CeRuSiH1.0 presents two antiferromagnetic transitions at TN1=7.5(2) K and TN2=3.1(2) K evidenced by magnetization and specific heat measurements. Hydrogenation changes the moderate heavy-fermion compound CeRuSi, which has a gamma=220 mJ/mol K2, to an antiferromagnet, which has a smaller electronic coefficient gamma=26 mJ/mol K2. In other words, the hydrogen insertion diminishes the influence of the Kondo effect. The transition heavy-fermion behavior-->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 CeCoSiH1.0 or CeCoGeH1.0, where an opposite transition (antiferromagnetic-->spin fluctuation) was evidenced.
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