Competitions in layered ruthenates: Ferromagnetism versus antiferromagnetism and triplet versus singlet pairing

Involvement of O in magnetism leads to ferromagnetic fluctuations in Sr2RuO4, while Ca2RuO4 is antiferromagnetic, suggesting a possibility of antiferromagnetic fluctuations in Sr2RuO4 as well. Our calculations show that the ferro- and antiferromagnetic fluctuations coexist, leading to an instability in Ca2RuO4 and to a competition between p- and d-wave superconductivities in Sr2RuO4 The antiferromagnetism is due to the nesting, with Q approximate to(2 pi/3a, 2 pi/3a, O). The p-wave state is more stable than the d-wave one except in close vicinity of the magnetic instability. The d-wave state has a vanishing gap in one out of three bands; in the p channel it is comparable in all three bands. [S0031-9007(99)09181-4].