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 ferromag netic (I) exchange interactions is proposed for strongly correlated electro ns in RuSr2GdCu2O8 . It is assumed that J much greater than I for CuO2 laye rs and J much less than I for RuO2 layers. A superconducting solution of d( x2-y2) symmetry was obtained for the CuO2 layers while competition between ferromagnetism and p-type triplet superconducting pairing is obtained for R uO2 layers. It is shown that the RuO2 layers have a lower carrier concentra tion in the Hubbard subband formed by coupled ((d(xy)-p)-pi) orbitals compa red with a bulk Sr2RuO4 crystal, which leads to stabilization of the ferrom agnetic state in the RuO2 layer. (C) 2000 MAIK "Nauka/Interperiodica".