Effect of sample size on the magnetic critical current density in nano-SiC doped MgB2 superconductors

The effect of sample size on the critical current density and the flux pinning of pure and SiC doped MgB2 bulk samples has been investigated. At high fields a systematic degradation of magnetic Jc and Hirr was observed as the sample size decreased. However, Jc remarkably increased on decreasing the sample volume at low magnetic fields below 1 T. The SiC doped samples show less sample size effect than the pure samples, indicating a larger n factor and therefore a stronger pinning effect due to SiC doping. Hirr was observed to decrease as a logarithmic function of the sample volume, and the zero field Jc can be fitted as an exponential decay function.