A study of the mixed state of the YBa2Cu3O6.9 superconducting ceramics by neutron depolarization

The mixed state of the YBaCu₂O_6.9 superconducting ceramics is investigated by neutron depolarization (ND). The magnetic flux penetration into superconductor's granules can be described in terms of Bean's critical state model. The field and temperature dependence of the average angle of the vortex line deflection from the direction of the applied magnetic field are determined. In particular, this angle is zero atT/T _c 0.5 andH/H _c20.015, which is at the sameT/T _c nearH/H _c20.017 for the metalloceramic SnMo₆S₈ superconductor. The latter is also studied in the present work for comparison with the YBa₂Cu₃O_6.9 sample. TheseH/H _c2 are far below the corresponding values ofH/H _c2 for Nb, Nb–Ta. The creep of the flux line misalignments from the applied field direction is examined.