Improved flux pinning for high-field applications in BaHfO3-Doped SmBa2Cu3 oy-coated conductors with high density of random pinning centers induced by BaHfO3 nanorods

The critical current performance of REBa₂Cu₃O_y-coated conductors must be isotropically improved for use in high-field coil-based applications operated at low temperatures less than 50 K. The high and isotropic critical current densities (J_c) with respect to the directions of the magnetic field under these operating conditions were achieved by a 3.8 vol.% BaHfO₃ (BHO)-doped SmBa₂Cu₃O_y (SmBCO) film on a metallic substrate deposited with low-temperature growth (L-BHO film). In particular, the L-BHO film attained a high flux pinning force density over 1.5 TN/m³ at a temperature of 4.2 K. From the anisotropic scaling approach based on the effective mass model, a high density of random pinning centers in the L-BHO film plays an important role in achieving the high J_c performance at 4.2 K. In order to reveal the reason why the L-BHO film includes high density of random pinning centers, we compared the flux pinning properties and the dominant flux pinning centers between the L-BHO film and the other two samples: A 3.8 vol.% BHO-doped SmBCO film fabricated with relatively high-temperature growth, and a nondoped SmBCO film fabricated with low-temperature growth. From the comparison, it is revealed that the random pinning centers are induced by BHO nanorods.