Dynamics of magnetic flux inhomogeneities in Y-Ba-Cu-O-ceramics

Modified neutron spin echo has been applied to study magnetic inhomogeneiti es in YBa2Cu3O7-delta-ceramics (T-C = 91.5 K) cooled down from 120 to 78 K in the field H = 10-130 Oe. At 78 K and momentum transfer q similar to 0.1 nm(-1) it was observed that the quasielastic magnetic scattering with energ y transfer DeltaE similar to 10-100 mu eV increases near H-C1(ab) similar t o 40 Oe and H-C1(c) similar to 80 Oc when the flux fill up the grains of co rresponding orientation. In the region H-C1(ab) less than or equal to H les s than or equal to H-C1(c) the self-correlations of magnetic inhomogeneitie s have shown pronounced oscillations with amplitudes a similar to 10-15nm a nd the periods tau similar to 90-300ps. (C) 2001 Elsevier Science B.V. All rights reserved.