Potential ability of 3 T-class trapped field on MgB2 bulk surface synthesized by the infiltration-capsule method

We successfully synthesized a dense (similar to 90%-filled) MgB2 bulk with no residual Mg via an infiltration process by overcoming the problems in this process such as the expansion of a B precursor disk under a liquid Mg infiltration and the residuals of unreacted Mg in the bulk using a specially designed capsule. As a result, we have achieved a record-high trapped field to date, B-T, of 2.4 T at the center of the bulk surface at the lowest temperature of 15.9 K among the infiltration-processed MgB2 bulks. The trapped-fields simulated for a model with the experimental J(c)(mu H-0) characteristics well reproduced the experimental B-T's and gave a reliable estimated B-T below 15.9 K. The extrapolation of the experimental and simulated B-T curve reached 3 T at 4.2 K. The critical current densities, J(c)(mu H-0)'s, at 20 K were 1.8 x 10(5) A cm(-2) under the self-field and 4.5. x 10(3) A cm(-2) under the magnetic-field of mu H-0 = 3 T. The connectivity, K, of 16% of the present bulk was comparable with that of the similar to 50%-filled MgB2 bulk. The high B-T with low K and the microstructure of the present bulk suggested that the high- and low-J(c) regions coexisted because of the wide variation of the MgB2 grain-size.