This is a copy of the slides presented at the meeting but not formally written up for the volume.

The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. There has been increasing interest in heterostructures combining oxides with different functionalities and ground states competing at the interface. In structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for modified properties at the interface over nanometer length scales. In this presentation we will focus on cuprate / manganite heterostructures made of YBa2Cu3O7 (YBCO) and La1-xCaxMnO3 (LCMO), where the Ca content is varied over a wide range. The manganite grows epitaxially on the superconductor with different degrees of strain depending on the Ca content. For x=0.3 the manganite is ferromagnetic what causes a strong depression of the superconducting order parameter at the YBCO side. Interestingly, there is also a depression of the ferromagnetic moment at the interface suggesting charge transfer (electrons) from the manganite into the YBCO. This is confirmed growing superlattices combining YBCO with the parent manganite compound with x=0, which is nominally an AF insulator. Actually, for LMO thickness below 6 unit cells (2,4 nm) the layers are non magnetic and insulating as expected. However, above this LMO thickness (6 unit cells) we show that superconductivity is strongly suppressed and ferromagnetism is induced at the interface providing a strong evidence for the charge transfer scenario. The control of layer bulk doping by charge transfer at the interface opens new possibilities of tailoring the electronic states at the interface for the design of novel functionalities and devices. Work supported by CICYT MAT2005 06024 C02-02 and DOE.