Effects of C substitution on the pinning mechanism of MgB2

The temperature and magnetic field of the critical current density of four selected pure and C-doped MgB2 samples have been investigated in detail and the flux pinning mechanism has been analyzed. It was found that the sintering temperature and the substitution of carbon can significantly modify the flux pinning mechanism. Below 30 K, the reduced field dependences of the reduced pinning force for all investigated samples were found to closely obey one scaling law, reflecting the presence of only one dominant pinning mechanism. A delta T-c pinning mechanism was found to be mainly responsible in pure MgB2 samples while the delta l pinning mechanism becomes dominant for C-doped samples.