Influence of low magnetic fields on ac losses in bulk superconductor Bi_1.84Pb_0.34Sr_1.91Ca_2.03Cu_3.06O₁₀

Abstract

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-Tc 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 Hdc = 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, Hp, 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 Hp, 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.

Influence of magnetic fields on hysteretic ac losses in bulk MgB2superconductor investigated by using Hall probe ac susceptibility method

“…From a comparison of these two figures, it is reasonable to say that the experimental results and the predictions of Bean's model agree well up until H ac = 500 A m −1 . After H ac = 500 A m −1 , the agreement gets worse as the external field is increased, especially at T = 39.55 K [13]. This finding is interesting because Bean's critical state model was found to be valid for a large range of external fields for ceramic high temperature superconductors [14].…”

AC susceptibility analysis on MgB2 bulk and Ti-sheathed wire superconductors

“…According to the literature, a larger ac field suppresses the superconducting properties [20] in the vicinity of T c . Our MgB 2 samples also weakened the superconducting properties slightly but T p values did not shift to the lower temperatures which is easily seen from Fig.…”

Superconducting and mechanical properties of the bulk Bi(pb)SCCO system prepared via solid state and ammonium nitrate precipitation methods

“…The AC magnetic susceptibility as a function of temperature is measured by means of a Lake Shore 7130 AC magnetometer in the temperature range 40-120 K in various magnetic fields, at 125 Hz. The details of the measuring system of the AC susceptibility was described in [11,12]. The electrical resistivity is determined by the four-probe method on a Cryodine CTI-Cryogenics closed cycle cryostat working in the temperature range of 60-140 K. The electrical contacts are realized by application of silver paint on rectangular bars.…”