Flux pinning characteristics of Smi+_xBa_2-xCu ₃O_y films with the additional c-axis correlated pinning centers

It is known that columnar defects comprised of self-organized BaZrO ₃ (BZO) nanorods within REBa₂Cu₃O_y (REBCO) films are attractive as c-axis correlated pinning centers. On the other hand, we have fabricated high-J_c Sm_1+xBa _2-aCu₃O_y (SmBCO) films including nanosized low-T_c phases by using the low-temperature growth (LTG) technique. In this study, BZO nanorods were added to the LTG-SmBCO film for a further enhancement of the magnetic flux pinning. Additionally, we also deposited a conventional PLD-SmBCO film including BZO nanorods and discussed differences of the flux pinning properties and microstructures between LTG- and PLD-SmBCO films. In a cross-sectional transmission electron microscopy (TEM) image of the BZO doped PLD-SmBCO film, we could see the self-organized BZO nanorods were about 10 nm in diameter, extending along the c-axis of the film. In contrast, in the BZO doped LTG-SmBCO film, the high density BZO nanorods with smaller diameters tended to be short columns and tilted against the c-axis direction. These facts can be attributed to a suppression of the surface diffusion length of adatoms and/or an increase of nucleation frequency due to the low substrate temperature during the growth of the BZO doped LTG-SmBCO film. Furthermore, we concluded that differences of superconducting properties between the BZO doped PLD- and LTG-SmBCO films might be attributed to the difference in the number density of BZO nanorods which generated lattice strain around them.