The effect of ferromagnetic buffer layer on the superconducting properties of relatively thick, high temperature superconductors is investigated. Elaborately designed heterostructure films consisting of epitaxial GdBa 2 Cu 3 O 7-x (GdBCO) on top of two types of La 0.7 Sr 0.3 MnO 3 (LSMO) layer and particles, were fabricated by pulsed laser deposition. Unlike a typical superconducting/ferromagnetic system where the superconducting properties are degraded, the superconducting properties of our GdBCO/LSMO system are enhanced depending on the local structural details of the GdBCO and LSMO layers. The strain state of GdBCO characterized from the bond length of the Cu-O and the Mn-O bonds lengths is observed to vary depending on the formation of LSMO. The phase diagram of T c for the GdBCO/LSMO system established by the micro-strain of the Cu-O bond-length shows that T c reaches its maximum at the critical micro-strain. This result suggests the importance of strain state in improving the superconducting properties of thick-GdBCO/LSMO films.

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The effect of magnetic flux pinning is investigated in GdBa2Cu3O7 (GdBCO) thin films with two different types of ferromagnetic La0.7Sr0.3MnO3 (LSMO) buffers (nanoparticles and a layer) deposited on an STO substrate.