Voltage relaxation and Abrikosov–Josephson vortices in Bi-2223 superconductors doped with α-Al2O3 nanoparticles

Abstract

We have observed a change in the behaviour of voltage-relaxation curves with remnant magnetic flux, when the maximum magnetic field applied before starting the relaxation process, $$H_{am}$$ , reaches 80 Oe in two samples of $$\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_{2}\hbox {Ca}_{2}\hbox {Cu}_{3}\hbox {O}_{10+\delta }$$ (Bi-2223) doped with $$\alpha $$ - $$\hbox {Al}_{2}\hbox {O}_{3}$$ nanoparticles. This modification consists in the emergence of a maximum in the temporal dependence of the voltage, V(t), which appears in the vicinity of the first 5 s after applying to the sample an excitation current lightly higher than the superconducting critical current of the material. In addition to that, the voltage drop rate increases appreciably with increasing applied magnetic fields. As complementary studies, X-ray diffraction patterns, scanning electron microscopy, measurements of magnetization as a function of applied magnetic field and critical current density are also included. The experimental results corroborate the occurrence of intragranular Abrikosov–Josephson vortices in Bi-2223 ceramic superconductors. Furthermore, the analysis provides a new procedure for detecting penetration of the magnetic flux into intragranular planar defects and clean regions of the grains (crystallites), with increasing applied maximum magnetic field, $$H_{am}$$ .