Effect of Nd422 content on the trapped fields of Nd-Ba-Cu-O bulk superconductors

The effect of Nd422 content on the trapped field was studied for Nd-Ba-Cu-O superconductors. In this system, there are two dominant pinning centers of Nd422/Nd123 interfaces and chemical fluctuation in the matrix. In the present experiment, the average diameter of Nd422 was larger than 2 μm and thus excess Nd422 deteriorated both J_c-B properties and crystal growth. However, cracking was introduced in large grain samples with small Nd422 content, which could be prevented by increasing Ag₂O content from 10 to 20 wt.%. The highest trapped field of 1.4 T was achieved in the sample with a molar ratio of Nd123:Nd422 = 10:1.5 with 20 wt.% Ag₂O at 77 K. Furthermore, the secondary peak effect was observed in the field dependence of the trapped field, showing that the field induced pinning is active in large grain samples.