Complete flux jump in bulk MgB2 sintered under high pressure

Sintered MgB2 system was prepared under 3.5 GPa in the WC cubic anvil cell above 1100 °C for 1 h from the commercial MgB2. In this system, a few large flux jumps (FJ) were observed in the magnetization curve at 5 K on the field increasing process. Especially, the complete FJ occurred near 0 field. The number of large FJ decreased at higher temperature of 20 K. We estimated the flux density difference between the center and surface of the sample from the extended critical state model and magnetization data. The generation condition of FJ was discussed using Schwartz-Bean's theory and Wipf's theory. The FJ was suppressed at 20 K by the MgCu2 doping. We assumed that the present large FJ's were induced by the enlarged sample thickness by high pressure sintering. A few mol% of MgCu2 impurities reduced the thickness of MgB2 phase or enhanced the thermal conductivity of HP sample.