Correlated Pinning Properties in RE123 Tapes with Nanorods

Abstract

Correlated pinning properties for GdBa₂Cu₃O₇ (Gd123) tapes with BaHfO₃ and BaZrO₃ nanorods are investigated on the basis of the detailed critical current measurements in a wide temperature and magnetic field region. We found that a magnetic field dependency of J_c for the Gd123 tapes with nanorods introduced changes around the matching field B_ while that for the non-doped Gd123 tapes is proportional to B^-0.56 in a wide field region below 20 K. These experimental results suggest that the nanorods are still effective as the c-axis correlated pinning center at low temperatures, although the J_c peaks at B//c in its angular dependency disappear below 20 K at 3 T. The cooperative model of random and correlated pinning centers indicates that the c-axis peaks in angular dependency of J_c disappear when fluctuation of the nanorods' growth direction is large. Therefore, the nanorods are effective as the c-axis correlated pinning centers even at low temperatures around 4.2 K, although their contribution becomes small.