AC susceptibility and harmonic generation in high $T_c$ superconductors

Abstract

High $T_c$ superconductors of $Y_1Ba_2Cu_3O_{7-x} and Bi(Pb)SrCaCuO were prepared by solid state reaction method. These samples are examined for AC susceptibility and Harmonics under several conditions with varying temperatures; AC and DC magnetic intensity, and frequencies. About 0.4-0.8K upshift in $T_c$ for high frequency (1MHz) in case of AC magnetic susceptibility measurement are all observed. Two steps transition is observed for Bi-system, the first transition is sensitive to frequency, but second transition is sensitive to AC and DC magnetic field. From the peak temperatures of x`` of AC susceptibility for AC magnetic intensity are obtained and magnetic response for two samples compared. We observed clearly all odd harmonics in the Harmonics measurement, up to at least n=7 for Y-system and n=31 for Bi-system. The results suggest that high $T_c$ superconductor is composed of grains, and these grains are connected by Josephson junction. The nonlinear properties due to superconducting transition was observed from second harmonics under DC magnetic fields and with temperatures.