Spin-dimerization in rare-earth substituted La<Subscript>2</Subscript>RuO<Subscript>5</Subscript>

The Ru-Ru spin-singlet formation in La<Subscript>2 − x </Subscript> L n <Subscript> x </Subscript>RuO<Subscript>5</Subscript> (Ln=Pr, Nd, Sm, Gd, Dy) was investigated by measurements of the specific heat and magnetic susceptibility. After subtraction of the lattice contribution from the specific heat (C <Subscript> p </Subscript>), similar excess entropy values were obtained for all compounds. These entropies can be explained by the formation of antiferromagnetic Ru-spin dimers at low temperatures and provide a lower estimate for the intradimer exchange strength. Pronounced changes in the transition temperatures and a broadening of the corresponding peak in C <Subscript> p </Subscript> were observed. These changes depend on the rare-earth element and are due to local structural changes and heterogeneities caused by the substitution. The magnetic susceptibilities can be described by the sum of a rare-earth paramagnetic moment and the susceptibility of the unsubstituted La<Subscript>2</Subscript>RuO<Subscript>5</Subscript>. Density functional theory (DFT) calculations were performed for various compounds to investigate the origin of the magnetic transition and the relationship between structural changes and the spin-dimerization temperature. The combination of the present results with previous structural investigations supports the model of a spin-pairing of the Ru moments which occurs as a reason of the structural phase transition in La<Subscript>2 − x </Subscript> L n <Subscript> x </Subscript>RuO<Subscript>5</Subscript>. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2012