Effect of Co doping on the transport critical current density of rapidly heat-treated filamentary (Nd,Sm,Gd)-Ba-Cu-O superconductors

We investigated the effect of Co doping on the superconducting properties and microstructure of ternary (Nd0.33Sm0.33Gd0.33)1.18Ba2.12Cu3.09O7−δ (NSG123) filaments. Filamentary NSG123 superconductors chemically doped with a nominal Co concentration between 0 and 0.5 at% were prepared by a solution spinning method. Filamentary samples were partially melted at 1050 °C for 30 min and rapidly cooled to 910 °C at a rate of 60 °C h−1 under an atmosphere of flowing 0.1% O2 + Ar gas. The filamentary NSG123 superconductor with 0.05 at% Co exhibited a high critical current density ( Jc) of 2.0 × 104 A cm−2, whereas the pure NSG123 sample exhibited a maximum transport Jc value of 3.0 × 103 A cm−2. Furthermore, the sample doped with 0.05 at% Co maintained a high transport Jc value of 4.5 × 103 A cm−2 under an applied magnetic field up to 17 T at 77 K, whereas the superconductivity of the pure sample disappeared at approximately 11 T. The Co-doped samples also exhibited low electrical resistivity at normal state compared to that of the pure sample. These results confirm that Co doping effectively enhances the Jc and connectivity in the microstructure of filamentary NSG123 samples subjected to a heat treatment with rapid cooling.