Critical Current Densities and Irreversibility Fields of High T_c Superconductors, GaSr₂Ca₂Cu₃O₉ and BSr₂Ca_n-1Cu_nO_2n+3 (n= 3, 4)

Abstract

From the hystereses in DC magnetization loops, we measured critical current densities J c and irreversibility fields B irr of high T c superconductors, GaSr 2 Ca 2 Cu 3 O 9 (Ga-1223) and BSr 2 Ca n -1 Cu n O 2 n +3 ( B-12( n -1) n , n =3, 4) prepared at a high pressure of 6 GPa. These three phases with blocking layers consisting of single metal planes were expected to have high J c and high B irr . However, the present experiment revealed that their values for both J c and B irr were much smaller than those of the (Cu, C)-based oxides. This result suggests that the electronic structures of the present three phases are more anisotropic than those in the (Cu, C) phases in spite of their thinner blocking layers and that the thickness of the blocking layer, i.e., the spacing between the CuO 2 multilayers, is not always a key parameter determining J c and B irr .