The generation of higher harmonics in the bulk polycrystalline superconductor, when subjected to alternating-current and direct-current magnetic fields, was reported. The sample exhibited the generation of higher odd harmonics when an alternating-current field was applied. The application of a small direct-current field (at a few gauss) in addition to an alternating-current field also led to the generation of second and fourth harmonics, which was an indication of the presence of some weak link grain boundaries in a MgB2 superconductor. The variation of the amplitude of higher harmonics with temperature was studied for various values of the amplitude of the alternating-current field. The observed results were interpreted in terms of weak-link grain boundaries and a critical state model.

Generation of Even Harmonics in a MgB2 Bulk Superconductor - an Indication of the Presence of Weak Link Grain Boundaries. N.Khare, D.P.Singh, A.K.Gupta, D.K.Aswal, S.Sen, S.K.Gupta, L.C.Gupta: Superconductor Science and Technology, 2004, 17, 1372-5