Electrical and magnetic properties of a series of ternary barium metal ruthenates: Ba 3 M Ru 2 O 9 „M  Fe, Co, Ni, Cu, and In… J. T. Rijssenbeek Department of Chemistry and Materials Institute, Princeton University, Princeton, New Jersey 08540 P. Matl Department of Physics, Princeton University, Princeton, New Jersey 08544 B. Batlogg Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974 N. P. Ong Department of Physics, Princeton University, Princeton, New Jersey 08544 R. J. Cava Department of Chemistry and Materials Institute, Princeton University, Princeton, New Jersey 08540 Received 13 March 1998 The resistivities and magnetic susceptibilities of the Ba 3 M Ru 2 O 9 series of compounds, with M =Fe, Co, Ni, Cu, and In, are reported. All compounds have regular or distorted versions of the hexagonal barium titanate structure, consisting of chains of face-sharing RuO 6 octahedra interconnected by corner-sharing M O 6 octahe- dra. The compounds are semiconductors with  0.1  cm at ambient temperature. The magnetic suscepti- bilities below 400 K show that the 3 d elements display local moments, and that the variants with M =Co, Ni, and Cu have magnetic transitions near 100 K. S0163-18299802240-1 INTRODUCTION Ruthenium-based oxides have recently attracted consider- able attention due to their wide range of electronic and mag- netic properties. Sr 2 RuO 4 , for example, is believed to be an exotic superconductor with T c =0.93 K. 1,2 SrRuO 3 is a me- tallic ferromagnet ( T c =160 K), CaRuO 3 shows antiferro- magnetic metallic properties, and BaRuO 3 is also metallic. 3–6 The study of these compounds has suggested that ruthenium- based oxides may form the basis of a family of exotic elec- tronic materials, due in part to the proximity of ferromag- netism and superconductivity. The compounds characterized thus far are, from the structural point of view, the simplest possible materials to study. Study of the electronic and magnetic properties of mate- rials as a function of increasing structural complexity is often an important tool for understanding those properties in greater depth. Here we examine the electrical and magnetic properties of some members of a large family of more com- plex ruthenium-based oxides, with both Ru and 3 d transition metals on the electronically active sites. These compounds, with the general formula Ba 3 M Ru 2 O 9 , where M =Fe, Co, Ni, Cu, and In, 7–11 have a hexagonal barium titanate struc- ture type, shown in Fig. 1. The structure consists of units of two face-shared RuO 6 octahedra Ru 2 O 9 dimers, intercon- nected by perovskite-type corner sharing with M O 6 octahe- dra. For the compounds studied here, to our knowledge the one with M =Cu has not previously been synthesized. Mag- netic characterization of only M =Ni and Co has been previously reported, 11,12 and no resistivity data is available. Here we report the results of temperature-dependent mag- netic susceptibility and electrical resistivity measurements between 400 and 2 K for the series of compounds. The elec- tron count varies over a wide range by the chemical varia- tions of the ternary metal. Although barium ruthenate itself is metallic, 3 as are many of the compounds of the simpler 3 d metal oxides, we find, surprisingly, that the compounds of FIG. 1. The crystal structure common to members of the Ba 3 M Ru 2 O 9 family of compounds, with M =Fe, Co, Ni, and In. For M =Cu the same basic structure is found, with some distortion 14. PHYSICAL REVIEW B 15 OCTOBER 1998-II VOLUME 58, NUMBER 16 PRB 58 0163-1829/98/5816/103154/$15.00 10 315 © 1998 The American Physical Society