Magnetic Properties of the (1223) Phase of Tl-Sr-Ca-Cu-O Superconductors with Strong Pinning in Liquid Nitrogen

Pinning centers were successfully introduced into the Tl-(1223) phase of the Tl-Sr-Ca-Cu-O system using a partial melt method. The magnetization hysteresis and relaxation were studied between 10-100 K and 0-5.5 T by VSM (Vibrating Sample Magnetometer) and SQUID (Superconducting QUantum Interference Device) magnetometry. The magnetization hysteresis ΔM was 7-25 emu/cm3 at 77 K and 1 T in Tl-(1223) bulk samples. The intragrain Jc at 1 T calculated by Bean's model was 43000 and 230000 A/cm2 at 77 K and 40 K, respectively. From the zero-field-cooled and field-cooled measurements, the irreversible field at 77 K was 6.8 T. The thermal activation energy was estimated to be 250 meV at 77 K and 1 T from the measurement of the magnetization relaxation.