Comparison of flux pinning in Si- and SiCl4- doped MgB2 superconductors: evidence for coexistence of different pinning mechanisms
The transport and magnetic properties of 5 wt% nano-Si- and 10 wt% SiCl4-doped MgB2 have been studied by measuring the resistivity, ρ, critical current density, Jc, irreversibility field, Hirr, and upper critical field, Hc2. Similar scattering mechanisms have been found for both dopants, which are supported by the results for the critical temperature and the upper critical field. The critical current density and the irreversibility field results indicate that there are different pinning mechanisms for nano-Si- and SiCl4-doped MgB2. Pinning mechanisms are studied in terms of the different pinning models. It was found that a variety of pinning mechanisms, e.g. normal point pinning, normal surface pinning, and normal volume pinning mechanisms coexist in both types of doped MgB2. The results show that the contributions of the pinning mechanisms are dependent on the temperature and magnetic field.