Critical-Current densities of Twin-Free Nd(Ba_1-x,Nd_x)_2Cu_3O_7-delta Single Crystals Grown by the Traveling-Solvent Floating-Zone Method

摘要

We have studied the superconducting properties of twin-free Nd(Ba_1-xNd_x)_2Cu_3O_7-delta (Nd123, x approx approx 0.1) single crystals grown by the traveling-solvent floating -zone method. An anomalous peak (fishtail) effect in the magnetization hysteresis (M-B) loop is observed inthe twin-free Nd123 single crystals as well as in twinned Nd123 single crystals. The magnetization peak sifts to the higher magnetic field side with decreasing temperature. it turns out that the peak effect is due to the field-induced pinning centers ascribed to Nd-Ba substitutions in the Nd123 matrix. An anisotropic flux penetration between the a and b-axis directions is observed in the magneto-optical flux observation. This is thought to be caused by the difference of the critical current density between both directions. The ratio Jcb/Jca of 1 approx 1.5 is estimated fro mthe flux penetration depths for the a- and b-axis directions.