AVS 45th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Tuesday Sessions
       Session MI-TuA

Invited Paper MI-TuA1
Spin Transport Effects in Ferromagnetic/Superconductor Heterostructures Grown using Molecular Beam Epitaxy

Tuesday, November 3, 1998, 2:00 pm, Room 324/325

Session: Emerging Materials and Hybrid Structures
Presenter: A.M. Goldman, University of Minnesota
Authors: A.M. Goldman, University of Minnesota
V.A. Vas'ko, University of Minnesota
K.R. Nikolaev, University of Minnesota
V.A. Larkin, University of Minnesota
P.A. Kraus, University of Minnesota
Correspondent: Click to Email
Heterostructures consisting of half-metallic ferromagnetic oxides in the lanthanum manganite family and high temperature superconductors in the YBCO family have been fabricated using the technique of ozone-assisted molecular beam epitaxy, and characterized using a number of techniques. These compounds have similar perovskite lattices, and therefore can easily be formed as epitaxial heterostructures. The fabrication and characterization of these heterostructures and the physics of the interplay between ferromagnetism and superconductivity at the interface between the ferromagnet and superconductor the will be discussed. High-resolution X-ray diffractometry, Rutherford back scattering and helium ion channeling were used to characterize the composition and crystal quality of samples. Simple patterning techniques were employed to prepare configurations in which the effects of carrier injection on superconductivity and the properties of the interfaces could be investigated. Injection of carriers from the magnetic oxides, which exhibit the phenomenon of "Colossal Magnetoresistance," into high temperature superconductors was shown to lead to the suppression of superconducting properties such as critical current and critical temperature. This suggests that spin-polarized transport can be used to investigate spin-dependent electronic properties of high temperature superconductors, and opens the possibility of a new class of superconducting devices utilizing spin injection. The differential conductances of superconductor-ferromagnet interfaces were also studied. The most striking feature of these investigations was the observation of a differential conductance dip at zero bias which was a decreasing function of temperature and/or magnetic field. This phenomenon has been interpreted using a picture of Andreev reflection as a consequence of the high spin polarization of the carriers in the half-metallic ferromagnet.