Prominent bulk pinning effect in the MgB_2 superconductor

Abstract

We report the magnetic-field dependence of the irreversible magnetization of the recently discovered binary superconductor MgB${}_2$. For the temperature region of $T<0.9T_c$, the contribution of the bulk 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 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 $H^{\ast }(T)$ and $M^{\ast }(T)$, respectively. This feature suggests that the pinning mechanism determining the hysteresis in $M(H)$ is unique below $T=T_c$.

4pages and 4 figures. Phys. Rev. B (accepted)