The comparative study of irreversibility effects in Nb foil and high-temperature superconducting ceramics by μSR

We present the results of investigations of superconducting niobium and high temperature ceramical superconductor La1.9Sr0.1CuO4 by the μSR technique. The experiments with the niobium sample confirm high reliability of the μSR-technique in determining such characteristics of type II superconductors asT c,H c1,H c2, the magnetic field penetration depth λ, and the critical current densityJ c. The analysis of the field dependencies of the distribution width and mean value of the magnetic fields on the muon when the samples are magnetized is carried out. A qualitative difference in the behaviour of the magnetic field distribution width in Nb and LaSrCuO is revealed. Whilst the niobium data are well described in the frame of the critical state model, application of a similar approach to the high-T c superconductor does not give a satisfactory description of our experimental results.