Fabrication and critical current density analysis of YBa₂Cu₃O₇+(BaSnO₃)′/YBa₂Cu₃O₇+(BaSnO₃)″ multilayer films

Abstract

Multilayers (MLs) comprising of YBa2Cu3O7(YBCO)+BaSnO3(BSO) layers with different BSO content were fabricated, and their critical current density (Jc) was measured to understand influence of ML structure on vortex pinning. Elongated and segmented nanorods were observed in the MLs, and ab-plane aligned nanoparticles appeared depending on BSO content. When BSO formed only elongated and segmented nanorods in MLs, Jc exhibited a linear relationship between Jc in the single layer films. On the other hand, when MLs contained ab-plane aligned nanoparticles in addition to nanorods, Jc decreased with lower-Jc-layer fraction more rapidly. These results suggest that Jc was degraded due to easy vortex flow along the lower-Jc-layers, and that the acceleration of vortex motion depended on the type of lower-Jc-layers. Vortex behavior which is not observed in conventional systems such as single layer films and bulk samples is strongly expected in MLs, since fine tuning of pinning center structure is possible.

Observation of inhomogeneous depinning in YBa2Cu3O7 composite multilayers

“…In a wide range of layer fraction, the BHO (4.7) layers dominate the J c in the CML. Similar J c behavior has been observed in the YBCO+BSO (1.8)/YBCO+BSO (7.2) MLs [20]. Figure 7 shows F p /F p,max -B curves in the (20/10), (10/20), and (30/30) MLs in temperatures of 77 and 65 K, and table 2 shows the F p,max values.…”

“…To discuss the vortex behavior in the present CMLs, it is effective to compare the present CMLs with other types of MLs, YBCO+BaSnO 3 (BSO)/PrBa 2 Cu 3 O 7 MLs [24] and YBCO+BSO (1.8)/YBCO+BSO (3.6 or 5.4) MLs [20,21]. Here, the layer notation (strong-pinning; weak-pinning; non-superconducting) represents layer function.…”

“…Owing to the change in vortex structure, the J c in B//c decreases and the caxis peak in the J c -θ curves disappears in the YBCO + BSO/PrBa 2 Cu 3 O 7 MLs. In the YBCO+BSO (1.8)/ YBCO+BSO (3.6) [20], the average J c values between SLs is obtained. Here, the J c for YBCO+BSO (3.6) is larger than the J c for YBCO+BSO (1.8), suggesting that both YBCO+BSO (3.6) and YBCO+BSO (1.8) are the strongpinning.…”

“…We have fabricated composite multilayer films (CMLs) which consist of the layers with different nanocomposite structure. The characteristic vortex behavior has been observed in the CMLs; J c -B curves have been varied with CML structure [20]; the nanorod edge pinning has been observed in J c -θ characteristics [21]. However, the vortex behavior in the CMLs has not yet been understood since detailed measurement and analysis of J c and irreversibility temperature have not yet been performed.…”