Mechanism of a high irreversibility field for (Nd, Eu, Gd)Ba/sub 2/Cu/sub 3/O/sub 7/ bulk

In order to study the mechanism of the high irreversibility field, we measured the high field transport properties for bulk NEG123 samples with high irreversibility field. It was found that the Bose glass behavior is observed for both NEG123 bulk samples with 3% and 40% NEG211 additions. However, the 40%NEG211 sample with a low irreversibility field showed a higher effective matching field of the c-axis correlated disorder than the 3%NEG211 sample with a high irreversibility field. It is suggested that the c-axis correlation varies among samples and the strong correlation along the c-axis, which may arise from the alignment of the RE-rich NEG211 clusters, is important for the realization of the high irreversibility field.