Akademik Veri Yönetim Sistemi
SUPERCONDUCTOR SCIENCE & TECHNOLOGY, cilt.15, sa.4, ss.592-597, 2002 (SCI-Expanded)
The fundamental and third harmonic ac susceptibility measurements as a function of temperature (20-120 K), frequency (5 Hz-1 kHz) and ac magnetic field amplitude (1-1600 A m(-1)) on a bulk Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 high-T-c superconductor prepared by the ammonium nitrate fusion technique are reported. The height and temperature of the peak in the out-of-phase component of the fundamental susceptibility increase with increasing field amplitude and the measuring frequency employed. In the presence of a superimposed H-dc = 1520 A m(-1), an additional small peak appears and the larger peak broadens even at lower ac fields of 20 A m(-1). The third harmonic susceptibility exhibits an interesting temperature dependence with increasing ac field amplitude. Experimental results are qualitatively discussed in the framework of the critical state model. The results are in good agreement with the theory at fields lower than the least field needed for full flux penetration, H-p, below which ac losses are essentially due to the hysteretic intergranular coupling. The critical state model fails to explain the data at high temperatures with ac fields larger than H-p, where the ac losses are interfered by the irreversible flux penetration into the grains. This is presumably due to the weakening of the intergrain coupling with magnetic field penetration.