Superconducting properties of MgB2 bulk materials prepared by high-pressure sintering

High-density bulk materials of a recently discovered 40 K intermetallic MgB2 superconductor were prepared by high-pressure sintering. Superconducting transition with the onset temperature of 39 K was confirmed by both magnetic and resistive measurements. Magnetization versus field (M–H) curve shows the behavior of a typical type-II superconductor and the lower critical field Hc1(0) estimated from the M–H curve is 0.032 T. The bulk sample shows good connection between grains and critical current density Jc estimated from the magnetization hysteresis using sample size was 5×104 A/cm2 at 20 K and 1 T. Upper critical field Hc2(0) determined by extrapolating the onset of resistive transition and assuming a dirty limit is 18 T.