High-density bulk materials of a newly discovered 40K intermetallic MgB2superconductor were prepared by high pressure sintering. Superconductingtransition with the onset temperature of 39K was confirmed by both magnetic andresistive measurements. Magnetization versus field (M-H) curve shows thebehavior of a typical Type II superconductor and the lower critical fieldHc1(0) estimated from M-H curve is 0.032T. The bulk sample shows goodconnection between grains and critical current density Jc estimated from themagnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Uppercritical field Hc2(0) determined by extrapolating the onset of resistivetransition and assuming a dirty limit is 18T.
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