Effects of Fe_3O_4 Nano Particles Addition in High Temperature Superconductor YBa_2Cu_3O_(7-δ)

摘要

The effects of nano particles Fe_3O_4 addition on the superconducting and transport properties of YBa_2Cu_3O_(7-δ) (YBCO) were studied. YBa_2Cu_3O_(7-δ) superconductor powders were prepared by using high purity oxide powders via solid state reaction method. Nano Fe_3O_4 with 0.01 - 0.05 wt.% with average size 28 nm was added into YBCO. The transition temperatures (T_c) of the samples were measured by using four point probe method. The critical current (I_c) of the samples has been determined by using the 1 μV/cm criterion from 30 - 77 K. Sample with 0.02 wt.% nano Fe_3O_4 showed the highest T_c at 87 K. It is interesting to note the same sample also exhibited the highest J_c at 77 K up to 1683 mA/cm~2. Nano Fe_3O_4 has acted as effective flux pinning centers in YBCO. A small amount of nano particles Fe_3O_4 addition has successfully improved the superconducting and transport properties of YBCO. The excessive addition of nano Fe_3O_4 (> 0.02 wt.%) suppressed the T_c and J_c. Overall, J_c decreases with increasing temperature (30 - 77 K) as a consequence of thermally activated flux creep. Magnetic impurities normally suppress superconductivity. However, by adding magnetic nano particles, current carrying capacity of superconductors YBCO was enhanced significantly.