Microscopic model of the coexistence of superconductivity and ferromagnetism in the hybrid ruthenate-cuprate oxide RuSr2GdCu2O8

A microscopic t-J-I model with competing antiferromagnetic (J) and ferromagnetic (I) exchange interactions is proposed for strongly correlated electrons in RuSr2GdCu2O8. It is assumed that Open image in new window for CuO2 layers and Open image in new window for RuO2 layers. A superconducting solution of \(d_{x^2 - y^2 }\) symmetry was obtained for the CuO2 layers while competition between ferromagnetism and p-type triplet superconducting pairing is obtained for RuO2 layers. It is shown that the RuO2 layers have a lower carrier concentration in the Hubbard subband formed by coupled ((d xy -p)-π) orbitals compared with a bulk Sr2RuO4 crystal, which leads to stabilization of the ferromagnetic state in the RuO2 layer.