Generation of even harmonics in a MgB₂bulk superconductor: an indication of the presence of weak link grain boundaries

Abstract

In this paper we report the generation of higher harmonics in a bulk polycrystalline MgB2 superconductor when it is subjected to ac and dc magnetic field. The MgB2 sample shows the generation of higher odd harmonics when an ac field is applied. The application of a small dc field ( gauss) in addition to an ac field also leads to the generation of second and fourth harmonics, which is an indication of the presence of some weak link grain boundaries in a MgB2 superconductor. We have studied the variation of the amplitude of higher harmonics with temperature for different values of amplitude of ac field. The observed results are interpreted in terms of weak link grain boundaries and a critical state model.

Temperature dependence of conduction noise of MgB2 superconductor

“…The studied aspects include critical current density [2,3], nature of grain boundaries [4][5][6], energy gaps [7] and vortex dynamics [8][9][10][11][12][13][14]. The relatively high upper critical field ($18T) [8] of polycrystalline MgB 2 superconductor is a very interesting feature of this superconducting material.…”