High-pressure sintering of highly dense MgB2 and its unique pinning properties

We report on the sintering of highly dense MgB2 at high-pressure condition (p>3 GPa) and its transport and pinning properties. The grains for MgB2 sintered at high pressure were compactly connected without discernible voids and the superconducting transition width was less than 1 K. The magnetization hysteresis M(H) curves at various temperatures were very symmetric with respect to H-axis and nearly overlapped with each other when the field and the magnetization were normalized by the characteristic value H∗ and M∗ at each temperature, respectively. This feature suggests that the pinning mechanism is unique below Tc. Compared to the recent report on the scaling of vortex pinning force (Fp(H)∝BJc∼HJc) for T>0.5×Tc, our analysis gives a simple and direct evidence of the unique pinning in MgB2 over broad temperature region, 0.12×Tc<T<0.9×Tc.