Linear and Nonlinear Ac Response of MgB2 Superconductors

We report the experimental study of linear and nonlinear ac properties of two types of samples of MgB2 prepared by different technologies. A commercial sample (Alfa Aesar) demonstrates two stages of a broad phase transition, whereas home-made metallic sample have one sharp transition. The temperature dependence of the rectified signal shows two peaks for the commercial and one peak for the metallic samples. Two types of weak links (intergrain and intragrain) are responsible for the nonlinear response of these samples. The properties of these weak links are discussed.