The influence of the geometric characteristics of nanorods on the flux pinning in high-performance BaMO₃-doped SmBa₂Cu₃O_y films (M = Hf, Sn)

Recently, the BaHfO₃ (BHO) nanorod has attracted attention as a new c-axis-correlated pinning center in REBa₂Cu₃O_y films. We fabricated SmBa₂Cu₃O_y (SmBCO) films with BHO nanorods using an alternating-targets technique with pulsed laser deposition on single-crystal LaAlO₃(100) substrates, and then compared the microstructure and flux pinning properties with those of BaSnO₃ (BSO)-doped SmBCO films. Transmission electron microscopy observations indicated that the BHO and BSO nanorods both grew straight, but the inclination of the BHO nanorods from the c-axis of the SmBCO was less than that of the BSO nanorods. The inclination had a strong influence on the flux pinning property. The flux pinning force of the BHO-doped SmBCO film (F_p^MAX=28.0 GN m⁻³ with J_c = 2.0 MA cm⁻² at 77 K under 1.4 T) became stronger than that of the BSO-doped SmBCO film (F_p^MAX=24.5 GN m⁻³ with J_c = 1.4 MA cm⁻² at 77 K under 1.8 T) due to the shape of the BHO nanorods without inclining. (paper)