Microstructural defects associated with enhanced magnetic flux pinning in YBCO/DyBCO/YBCO multilayered thin films

In a new paper entitled, “Microstructural defects associated with enhanced magnetic flux pinning in YBCO/DyBCO/YBCO multilayered thin films,” researchers Katherine Develos-Bagarinao and Hirofumi Yamasaki of the National Institute of Advanced Industrial Science and Technology (AIST), based in Tsukuba, Japan, analyzed the unique microstructure of multilayered superconducting thin films.

The films, having an architecture of YBa₂Cu₃O_y(YBCO)/DyBa₂Cu₃O_y(DyBCO)/YBCO, were prepared by pulsed laser deposition and were characterized using a variety of techniques including transmission electron microscopy (TEM). Unlike single layer YBCO films of the same thickness (~400-500 nm), YBCO/DyBCO/YBCO films contained a high density of antiphase boundaries and stacking faults, both of which are crystalline defects that act as magnetic vortex pinning sites in the superconducting film. Due to the increased number of pinning sites, the critical current density (Jc) of multilayers (in zero and applied magnetic field) showed significant enhancement compared to single layers. The stacking faults, assumed to be of the polytypoidal variant YBa₂Cu₄O_y (Y124), were mostly concentrated in the top YBCO layer and the vicinity of the DyBCO layer. In addition, elongated defects were observed to emanate from the DyBCO layer into the top YBCO layer, whereas no similar defects were found in the bottom YBCO layer.

These results strongly suggest that the presence of the DyBCO intermediate layer induced the formation of these elongated defects. The superior performance of the multilayers makes these materials ideal for applications requiring high critical currents in applied magnetic fields. The paper will soon appear in Superconductor Science and Technology, an IOP journal (April 2011).