The magnetoresistivity and critical current density of well characterized Si-nanoparticle doped and undoped Cu-sheathed MgB2 tapes have been measured at temperatures T≥28 K in magnetic fields B≤0.9 T. The irreversibility line Birr(T) for doped tape shows a stepwise variation with a kink around 0.3 T. Such Birr(T) variation is typical for high-temperature superconductors with columnar defects (a kink occurs near the matching field ) and is very different from a smooth Birr(T) variation in undoped MgB2 samples. The microstructure studies of nanoparticle doped MgB2 samples show uniformly dispersed nanoprecipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped tape supports the above findings.
@article{arxiv.cond-mat/0311425,
title = {Correlated vortex pinning in Si-nanoparticle doped MgB2},
author = {I. Kusevic and E. Babic and O. Husnjak and S. Soltanian and X. L. Wang and S. X. Dou},
journal= {arXiv preprint arXiv:cond-mat/0311425},
year = {2009}
}