Prominent bulk pinning effect in the MgB2 superconductor -: art. no. 012511

We report the magnetic-field dependence of the irreversible magnetization of the recently discovered binary superconductor MgB2. For the temperature region of T<0.9T(c), the contribution of the bull; pinning to the magnetization overwhelms that of the surface pinning. This: was evident from the fact that the magnetization curves M(H) were well described by the critical-state model without considering the reversible magnetization and the surface-pinning effect. It was also found that the M(H) curves at various temperatures scaled when the field and the magnetization were normalized by the characteristic scaling factors H*(T) and M*(T), respectively. This feature suggests that the pinning mechanism determining the hysteresis in M(H) is unique below T-c.