High critical current density in high field in Sm1+xBa2-xCu3O6+y thin films

Critical current density (J_c), irreversibility field (B_irr) and microstructure in epitaxial SmBa₂Cu₃O_7-x (SmBCO) films are reported. We have developed a novel approach to deposit high performance Sm_1+xBa_2-xCu₃O_6+y (Sm-123) at relatively low substrate temperature on MgO. The use of thin SmBCO seed layer grown at a high substrate temperature enabled us to obtain fully c-axis oriented SmBCO films with high critical current density (J_c) of 2.8×10⁵ A/cm² under 5 T for B//c at 77 K. This value is as high as in the optimized NbTi superconducting wires achieved for 5 T at 4.2 K. Compared with YBa₂Cu₃O_7-y films, Sm-123 films showed higher J_c in high fields at 77 K. Transmission electron microscopy TEM analyses clarified the Sm/Ba composition ratio fluctuations in the Sm-123 matrix composition in the range of x=0∼0.14 with a wavelength of 50∼100 nm.