The investigation of the spin correlations in YBa_2(Cu_(1-x)Fe_x)_3O_y ceramics by the small-angle scattering of polarized neutrons

摘要

A series of samples of the oxygen-rich YBa_2(Cu_(1-x)Fe_x)_3O_(y >= 7) with x = 0.1, 0.13, 0.2 and the oxygen-reduced YBa_2(Cu_(0.9)Fe_(0.1))_3O_(6.36) ceramics were studied by means of the small-angle scattering of polarized neutrons (SAPNS). It was obtained that magnetic phase transition like spin-glass type occurs for all samples at T < 45 K. Moreover, it was found that the magnetic ordering were observed for both the oxygen-reduced and oxygen-rich (x = 0.2) samples in the high-temperature region nearly T approx= 100 and 280 K, respectively. The observed anomalies of the temperature dependencies of the scattering intensity I(T, q), polarization P(T) of transmitted beam and magnetic-nuclear interference term #DELTA#(T, q) (where q is momentum transfer) are uniquely interpreted as scattering of neutrons from the spin density fluctuations. The characteristic scale R_c of the spin correlations is estimated as a few hundred angstrom.