CRITICAL CURRENT-DENSITY IN IRON-DOPED Y-BA-CU-O SINGLE-CRYSTALS

Critical current densities calculated from magnetization measurements are investigated in YBa2Cu(3-x)Fe(x)O7 single crystals with x = 0 to 0.24. The measurements are done over a wide temperature range, 5 K to T(c), and in magnetic fields up to 5.5 T. The results indicate that the critical current density in low-iron-composition samples has a small field dependence but a strong temperature dependence. The critical cuff ent density decreases as the Fe content increases. The model of twin boundaries acting as effective pinning centers in YBa2Cu(3-x)Fe(x)O7 systems is not supported by these results, at least for T > 10 K.