Deposition-Temperature Dependence of Vortex Pinning Property in YBa₂Cu₃O₇+BaHfO₃ Films

Abstract

Improvement of critical current density (J c) in magnetic fields is required in YBa 2 Cu 3 O 7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa 2 Cu 3 O 7 +BaHfO 3 films to control the nanorod structure, and its influence on J c was analyzed. The YBa 2 Cu 3 O 7 +BaHfO 3 film deposited at 850°C exhibited pinning force maximum (F p,max) as high as 413 GN/m 3 at 40 K, while the F p,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa 2 Cu 3 O 7 +BaHfO 3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the F p,max in high temperatures, since the critical temperature and matching field dependences of J c value dominate the F p,max. On the other hand, low deposition temperature improves the F p,max in low temperatures since the F p shift in accordance with matching field is dominant to the F p,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa 2 Cu 3 O 7 films containing nanorods considering the J c variation with critical temperature and matching field.

Simultaneous achievement of high J c and suppressed J c anisotropy by hybrid pinning in YBa2Cu3O7 three-phase-nanocomposite film

“…This demonstrates that the F p at 4.2 K for the present TP is as high as the record levels of F p,max reported in (Gd,Y)BCO + BaZrO 3 (1.7 TN m −3 ) [15] and SmBCO + BHO (1.6 TN m −3 ) [16]. Figure 4(b) compares a temperature dependence of F p,max for the TP with the high F p,max values in literatures [12,15,16,25,27,28]. Thus, the J c of the TP is high in low temperature, while the J c of the TP is not so high in high temperature.…”

“…The pinning situations of NR1 and NR2 are almost the same due to the same deposition conditions, which is confirmed by the F p,max and T c values in table 1. The J c and T irr data for NR3 was taken from our previous report [25].…”

“…Our previous discussion on the microstructures of NRs (YBCO + BaSnO 3 ) and TPs (YBCO + BaSnO 3 + Y 2 O 3 ) has clarified that the Y 2 O 3 introduction forms nanoparticles [19]. Our previous TEM observations for the conventional NRs have demonstrated that the nanoparticles are not formed whereas the well-defined nanorods are observed in the YBCO + BHO (NR system) [25]. Y-rich regions where the Ba concentration decreased were locally detected, suggesting the formation of Y-O nanoparticles with a diameter of 5-10 nm.…”

“…The NR3 showed the highest matching field among the present NRs due to lower deposition temperature. The matching field increases with lowering the deposition temperature [25], leading to the difference in J c between the NR1 and the NR3. GN m −3 at (77 K, 6 T) in the TP.…”

“…The difference in the effective matching field cannot explain the dip 5. T irr -B curves for the TP, NR2, and NR3 [25] in magnetic field parallel to the c-axis. Inset shows the T irr /Tc-B curves.…”