The Ruthenocuprates - Natural Superconductor-Ferromagnet Multilayers

The recently discovered ruthenocuprates have attracted great interest because of the microscopic coexistence of superconducting and ferromagnetic order. Typically, these materials become magnetically ordered at temperatures around 125-145K and superconductivity sets in between 15 and 50K. While superconductivity arises in the CuO2 layers the RuO2 layers in between order magnetically. In this paper we summarize some of the crystallographic, magnetic and superconducting properties of the ruthenocuprates, as obtained from investigations on polycrystalline samples as well as single crystals.