Vortex pinning at low temperature under high magnetic field in SmBa₂Cu₃O_y superconducting films with high number density and small size of BaHfO₃ nano-rods

We have fabricated 5.6 vol.% BaHfO₃ (BHO)-doped SmBa₂Cu₃O_y (SmBCO) films at a low substrate temperature of 750�C by using the low temperature growth (LTG) technique with a seed layer. Using the LTG technique, we can obtain a purely c-axis oriented SmBCO film even at low growth temperatures. The LTG technique also greatly increases the number density of BHO nanorods. The size and matching field of the BHO nanorods in the films were 5.4 nm and 9.9 T. Transport measurements were carried out, and a high irreversibility field (B _irr) and strong flux pinning force density (F _p) were obtained. The B _irr was 15.1 T at 77 K for B//c. The maximum F _p of 407 GN m^-3 in 10 T at 40 K and 770 GN m^-3 from 9 to 17 T at 20 K have been measured. We believe that the LTG technique can be considered as important for improving of flux pinning performance in BaMO₃ (BMO: M= Zr, Sn and Hf)-doped SmBCO coated conductors.