Ferromagnet / superconductor oxide superlattices

The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) and La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Pe\~{n}a$^{1}$, Z. Sefrioui$^{1}$, J. Garcia-Barriocanal$^{1}$, C. Visani$^{1}$, D. Arias$^{1}$, C. Leon$^{1}$ , N. Nemes$^{2}$, M. Garcia Hernandez$^{2}$, S. G. E. te Velthuis$^{3}$, A. Hoffmann$^{3}$, M. Varela$^{4}$, S. J. Pennycook$^{4}$. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic Energy Sciences, contract No.W-31-109-ENG-38. \newline \newline $^{1}$\textit{GFMC, Departamento de F\'{\i}sica Aplicada III, Universidad Complutense de Madrid, 28040 Madrid, Spain} \newline $^{2}$\textit{Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). 28049 Cantoblanco. Madrid}. \newline $^{3}$\textit{Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA} \newline $^{4}$\textit{Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6031, USA}