Harmonic alternating-current susceptibilities and alternating-current magnetization of a metallic granular superconductor were measured as a function of temperature, alternating-current field amplitude and additional small direct-current field between 15 and 45K. The temperature- and amplitude-dependent results were similar to those obtained for a typical high-temperature superconductor. In addition, MgB2 had a very narrow transition temperature width and high critical current densities. The experimental results were compared with numerical solutions of a model based upon Bean’s critical state. The odd harmonic susceptibilities (n = 3, 5 and 7) were in good agreement with those obtained numerically using the model. On the other hand, the measured even harmonic susceptibilities exhibited a peak-like behavior below TC; with only small magnitudes of about 10-4 (SI). The results were interpreted in terms of flux penetration into the bulk.

Harmonic Susceptibilities of a Bulk Superconductor MgB2 at Low Magnetic Fields. A.Gencer: Superconductor Science and Technology, 2002, 15, 247-53