Eur. Phys. J. B (2012) 85: 413
https://doi.org/10.1140/epjb/e2012-30840-4

Regular Article

Spin-dimerization in rare-earth substituted La₂RuO₅

¹ Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
² Kazan Federal University, 420008 Kazan, Russian Federation
³ Resource Strategy, University of Augsburg, 86159 Augsburg, Germany
⁴ Solid State Chemistry, Martin-Luther University Halle-Wittenberg, 06099 Halle, Germany

^a e-mail: stefan.riegg@physik.uni-augsburg.de

Received: 14 September 2012
Received in final form: 11 October 2012
Published online: 20 December 2012

Abstract

The Ru-Ru spin-singlet formation in La_2 − xLn_xRuO₅ (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_p), 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_p 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 La₂RuO₅. 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_2 − xLn_xRuO₅.