The investigation of the spin correlations in YBa2(Cul(1-x)Fe(x))(3)O-y ceramics by the small-angle scattering of polarized neutrons

A series of samples of the oxygen-rich YBa2(Cu1-xFex)(3)O-y greater than or equal to 7 with x = 0.1, 0.13, 0.2 and the oxygen-reduced YBa2(Cu0.9Fe0.1) (3)O-6.36 ceramics were studied by means of the small-angle scattering of p olarized neutrons (SAPNS). It was obtained that magnetic phase transition l ike spin-glass type occurs for all samples at T < 45 K. Moreover, it was fo und that the magnetic ordering were observed for both the oxygen-reduced an d oxygen-rich (x = 0.2) samples in the high-temperature region nearly T app roximate to 100 and 280 K, respectively. The observed anomalies of the temp erature dependencies of the scattering intensity I(T, ri), polarization P(T ) of transmitted beam and magnetic-nuclear interference term Delta(T, q) (w here q is momentum transfer) are uniquely interpreted as scattering of neut rons from the spin density fluctuations. The characteristic scale R-c of th e spin correlations is estimated as a few hundred angstrom. (C) 2000 Elsevi er Science B.V. All rights reserved.