ELECTRONIC-STRUCTURE AND MAGNETISM IN RU-BASED PEROVSKITES

The magnetic properties of ruthenates with perovskite-derived structur es, particularly (Ca,Sr)RuO3 and Sr2YRuO6, are studied within the cont est of band-structure-based Stoner theory. First principles calculatio ns are used to demonstrate that in all cases the correct magnetic beha vior and order can be obtained without recourse to strong correlation effects and that the insulating character of Sr2YRuO6 is reproduced. T he different magnetic states of SrRuO3 and CaRuO3 are shown to be due to the different structural distortions in these materials, most signi ficantly the larger rotation of the octahedra in the Ca compound. CaRu O3 is found to be on the Verge of a ferromagnetic instability. leading to the expectation of giant local moments around magnetic impurities and other anomalous effects in analogy with fcc Pd metal. Oxygen 2p-de rived states hybridize strongly with Ru d states in all three compound s, and O, through this hybridization. plays an unusually large role in the magnetic properties. This involvement of O is responsible for the strong magnetostructural coupling that is found in the calculations. Transport properties of CaRuO3 and SrRuO3 are analyzed using the calcu lated Fermiology. Unusually large magnon and paramagnon couplings are found, which are consistent with reported measurements of the low-temp erature specific heat and the resistivity coefficient.