Microscopic Model of the Coexistence
of Superconductivity and Ferromagnetism
in the Hybrid Ruthenate-Cuprate Oxide RuSr₂GdCu₂O₈

E. V. Kuz’min^1, *, S. G. Ovchinnikov^2, **, I. O. Baklanov², and E. G. Goryachev¹

¹ Krasnoyarsk State University, Krasnoyarsk, 660062 Russia

² Kirenskii Institute of Physics, Siberian Division, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia

*e-mail: evk@iph.krasn.ru

**e-mail: sgo@iph.krasn.ru

Received December 30, 1999

Abstract—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 J I for CuO₂
layers and J I for RuO₂ layers. A superconducting solution of 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)–) orbitals compared with a bulk Sr₂RuO₄ crystal, which leads to stabilization of the fer-
romagnetic state in the RuO₂ layer. © 2000 MAIK “Nauka/Interperiodica”.

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