Flux-pinning mechanism in silicone-oil-doped MgB2: Evidence for charge-carrier mean free path fluctuation pinning

Abstract

Flux-pinning mechanism of MgB2 doped with 10 wt% silicone-oil sintered at low and high temperatures has been investigated by magnetic measurements. The field dependence of the critical current density, jc (B), was analyzed within the collective pinning model. A crossover field, Bsb, from the single vortex to the small vortex bundle-pinning regime was observed. For both types of sintered samples, the temperature dependence of Bsb (T) at low temperature is in good agreement with the δl pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation. At temperatures close to the critical temperature, however, there is evidence for δ Tc pinning, which is associated with spatial fluctuations of the transition temperature. These results provide strong evidence that the liquid precursor, silicone oil, produces very small pinning centers and enhances the jc (B). © 2008 The American Physical Society.