THE PECULIARITIES OF BEHAVIOR OF MAGNETIC-FLUX AND ITS NOISE IN HTSC CERAMICS

The spectral density of magnetic flux noise inside a HTSC ceramics is studied. The time dependence of flux drift velocity is determined for different strengths of frozen magnetic field. The measurements are made on two series of Bi-ceramics samples (Bi2-xPbxSr2Ca2Cu3Oy) prepared by different techniques and on Y-ceramics ones (YBa2Cu3O7-delta). A nonquilibrium component of noise and its dependence on frozen magnetic field are measured. It is shown that the spectral density of white noise independent of magnetic field value is responsible for by HTSC ceramics granularity and defined by grain sizes while the major field-dependent part of white noise is caused by the oscillations of vortices almost at equilibrium. The 1/f noise spectral density is related to thermal excitation of vortices in the HTSC ceramics. Besides, an excess telegraph noise is observed which is caused by the vortex slip into superconducting loops consisting of ceramics granules and Josephson junctions in between. These mechanism can be used to explain qualitatively the experimental data on white noise as well as on equilibrium and nonequilibrium 1/f ones.