•O. Friedt^1,2, M. Braden², G. André¹, P. Adelmann³, S. Nakatsuji⁴ und Y. Maeno^4,5
1Laboratoire Léon Brillouin, CEA/CNRS, F-91191 Gif-sur-Yvette
²II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln
³Forschungszentrum Karlsruhe, IFP, Postfach 3640, D-76021 Karlsruhe
⁴Departement of Physics, Kyoto University, Kyoto 606-8502, Japan
⁵CREST,Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012, Japan

We have studied the phase diagram of Ca_2-xSr_xRuO₄ over the whole region of x by neutron scattering on powder and crystalline samples. The experiments reveal antiferromagnetic order and structural distortions of the K₂NiF₄ structure type characterized by tilts and rotations of the RuO₆ octahedra. Our results strongly suggest that the structural distortions of the isovalent samples tune the magnetic as well as the electronic behaviour. In particular we observe for low Sr concentrations (x < 0.2) characteristic changes of the Ru-O bonds and tilt angles which are associated with a metal-insulator transition and AFM-ordering. Further the suppression of the tilt distortion, observed for x_c @ 0.5, is accompanied by a critical increase of low temperature susceptibility. Additionally we present the phonon dispersion and the magnetic excitations close to x_c.