▎ 摘　　要

Flux pinning mechanism of graphene oxide (GO) doped MgB2 has been systematically studied. In the framework of the collective pinning theory, a B-T phase diagram has been constructed. By adjusting the GO doping level, the pinning mechanism in MgB2 transformed from transition temperature fluctuation induced pinning, delta T-c pinning, to mean free path fluctuation induced pinning, delta l pinning, is observed. Furthermore, in terms of the thermally activated flux flow model, the pinning potential in high field (B > 5 T) is enhanced by GO doping. The unique feature of GO is the significant improvement of both low field J(c) and high field J(c). (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4799360]