An artificial "multigranular" YBCO thin film has been prepared by patterning a network of gridlines, emulating the current-restricting behavior of grain boundaries. This model system allowed us to investigate the magnetic effects of granularity and current percolation problem, having control on the geometry, number of grains, and ratio of inter-to-intragrain critical-current density reduction, JcGB JcG. The dc magnetization cycle at 5 K showed a peak shift to a positive applied magnetic field value, typically ascribed to granularity. ac measurements performed up to very high driving ac magnetic fields show that ac losses are dominated by dissipation over the whole grain boundary network, whereas the contribution of individual grains cannot be resolved. A high-resolution (<5 μm) Hall-probe imaging system has been used to visualize the evolution of the magnetization distribution with a cycled applied magnetic field (at 4.2 and 77 K), and deduce maps of the intragranular and intergranular currents by solving the inverse problem. Quantitative information about the JcGB and JcG magnetic field dependence and the spatial distribution of JcG are presented and discussed. © 2007 The American Physical Society.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 12 Sep 2007|