Transport critical current density of Fe sheath MgB₂ tapes sintered at different temperatures

Fe sheath MgB₂ tapes sintered at 650, 750, 850 and 950 °C, respectively, for 2 h in a high purity argon gas were prepared using the powder-in-tube method. Transport critical current densities of tapes were measured in the fields up to 10 T from 4 to 30 K. Both tapes sintered at 850 and 950 °C completely lost the capacity of carrying superconducting current over the temperature range from 4 to 30 K. Compared to a tape sintered at 650 °C, an improvement in the in-field critical current density J_c and irreversibility field μ₀H^*(T) was observed in a tape sintered at 750 °C. At 20 K, the J_c value was ∼ 1.32 × 10⁵ A/cm² in self-field and the μ₀H^* value 4.2 T for the tape sintered at 750 °C, whereas the J_c in self-field and μ₀H^* values were ∼ 5.9 × 10⁴ A/cm² and 2.8 T for that sintered at 650 °C.