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

High-density bulk materials of a recently discovered 40 K intermetallic MgB 2 superconductor were prepared by high-pressure sintering. Superconducting transition with the onset temperature of 39 K was confirmed by both magneti c and resistive measurements. Magnetization versus field (M-H) curve shows the behavior of a typical type-II superconductor and the lower critical fie ld H-c1(0) estimated from the M-H curve is 0.032 T. The bulk sample shows g ood connection between grains and critical current density J(c) estimated f rom the magnetization hysteresis using sample size was 5 x 10(4) Angstrom / cm(2) at 20 K and 1 T. Upper critical field H-c2(0) determined by extrapola ting the onset of resistive transition and assuming a dirty limit is 18 T. (C) 2001 American Institute of Physics.