Point contact spectroscopy on ferromagnetic/superconducting hetero structures

The interplay between superconductivity and ferromagnetism is an interesting subject of experimental and theoretical research. The observation of this effect became possible only recently due to the great progress in the preparation of high-quality hybrid ferromagnet/superconductor (F/S) systems. In this paper we present conductance characteristics of point contact junctions realized between a normal Pt-Ir tip and YBa2Cu3O7-x/La0.7Ca0.3MnO3 (YBCO/LCMO) bilayers. The point contact characteristics show a zero bias conductance peak, as a consequence of the formation of Andreev bound states at the YBCO Fermi level. The temperature evolution of the spectra reveals a depressed zero bias peak and a reduced superconducting energy gap. We had already observed similar effects in the conductance spectra on polycrystalline RuSr2GdCu2O8 pellets. By comparing spectra on both materials, we can thus conclude that these features are explainable in terms of spin polarization effects due to the ferromagnetic layer. (c) 2007 Elsevier B.V. All rights reserved.