Influence of nano-particle diameter on superconducting properties in BaMO3(MÂ =Â Sn, Hf)/YBa2Cu3Oy quasi-multilayered films

In order to investigate the influence of diameter and spatial distribution of three-dimensional (3D) pinning centers on critical current density Jc, BMO (BaSnO3 (BSO) or BaHfO3 (BHO)) doped YBa2Cu3Oy (YBCO) thin films were fabricated by a quasi-multilayering process using a pulsed laser deposition method. The prepared films are referred as BMO(m,n)Ts, where m and n denotes the number of laser pulse on the BMO target and the total number of BMO/YBCO bilayers, respectively and Ts is the growth temperature. BSO(1,100)750 and BSO(1,100)770 show the improvement of Jc in comparison with the pure YBCO sample in wide range of magnetic field directions at 65 K. However, at 77.3 K, improvement of Jc was seen in only BSO(1,100)770. The BSO nano-particles within BSO(1,100)770 are considered to have larger diameter, so that BSO nano-particles can immobilize the flux lines in the high temperature region. In addition, BSO(1,100)770 shows the high peak of Jc centered at θ = 0° in the angular dependence of Jc. On the other hand, the Jc of BHO(1,100)770 falls below that of pure YBCO samples in all magnetic field orientation. In addition, at 65 K, there is no peak of Jc at any angles except for θ = 90°. These results indicates that the diameter of BHO nano-particles in BHO(1,100)770 might be much smaller than that of BSO nano-particle and BHO nanoparticles cannot work as effective pinning center.