Magnetically measured irreversibility temperatures in superconducting oxides and alloys

Abstract

Irreversibility temperatures T_r(H) were magnetically measured for the aligned powders of superconducting oxides, La_1.85Sr_0.15CuO₄, YBa₂Cu₃O₇, Bi₂Sr₂CaCu₂O₈, and Bi₂Sr₂Ca₂Cu₃O₁₀ and for the metallic superconductors Nb, Nb-Ti, Nb₃Sn and PbMo₆S₈. The results are briefly discussed in terms of the thermally activated flux creep and the lattice or the glass melting models for the irreversibility temperatures. Also, the measurement procedures for T_r(H) using a SQUID magnetometer are described in detail, since the measuring methods and the criteria which are used for T_r(H) are important in the determination and interpretation of the temperatures.