Abstract
Layered and pseudocubic Ru-based perovskites have been the subject of considerable recent attention, due to their unusual magnetic properties and the discovery of superconductivity in one member of the family, Sr 2RuO 4. From a magnetic point of view, interest derives from the stable ferromagnetism in SrRuO 3, gradually disappearing to a non-magnetic phase upon substituting Sr with isovalent Ca, a very unusual kind of behavior for three-dimensional perovskites. On the superconducting side, interest was stimulated by theoretical conjectures and experimental indications that Sr 2RuO 4 might be a p-wave superconductor. We report first-principles LSDA calculations for ferromagnetic SrRuO 3, antiferromagnetic Sr 2YRuO 6, non-magnetic CaRuO 3, and superconducting Sr 2RuO 4. In all cases, magnetic properties are well reproduced by the calculations. Anomalous properties are explained in terms of simple TB models and Stoner theory. An important result is that O bears sizable magnetic moments and plays an important role in the formation of the magnetic states. Based on these calculations, we have built a model for the q-dependent Stoner interaction, which we consequently applied to Sr 2RuO 4 to estimate superconducting and mass-renormalization electron–paramagnon coupling constants. We found that spin-fluctuation induced p-wave superconductivity is possible in Sr 2RuO 4. The estimated critical temperature, specific heat and susceptibility renormalizations are all in good agreement with the experiment.
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