High-J_c Gd-Ba-Cu-O epitaxial films prepared by pulsed laser deposition

For applications of high-temperature cuprate superconductors in magnetic fields at 77 K, a RBa₂Cu₃O_x (R123; R = Nd, Sm, Gd, etc.) film is one of the promising materials due to its high critical temperature T_c and high irreversibility field B_irr. Especially, a substitution between R and Ba sites that results in a T _c degradation is not likely to occur in GdBa₂Cu ₃O_x (Gd123) films, compared to the cases of Nd and Sm ions. This is an advantage for an application of Gd123 film. We studied the c-axis oriented Gd123 film for obtaining a high critical current density J _c in a magnetic field at 77 K. The substrate temperature to deposit the epitaxial films on MgO(100) was varied between 700-800°C under an oxygen partial pressure of 200 mTorr. T_c values of the films were within 89.8-92.7 K. Interestingly, the J_c at 77 K for 5 T (B//c) reached 0.2 MA/cm². The values are three times higher than those of Y123 films, which indicate that Gd123 films have the superior potentiality in magnetic fields at 77 K.