Strain-induced local structural change and its effect on the superconducting properties of GdBa2Cu3O7-x /La0.7Sr0.3MnO3 heterostructure

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 GdBa2Cu3O7-x (GdBCO) on top of two types of La0.7Sr0.3MnO3 (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 Tc for the GdBCO/LSMO system established by the micro-strain of the Cu-O bond-length shows that Tc 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.