  Strong evidences of a spin glass phase on polycrystalline
RuSr2Ln1.5Ce0.5Cu2O10-x (LnRu-1222, Ln = Y, Ho and Dy) is provided by ac
susceptibility and dc magnetization measurements. The fingerprint of a spin
glass transition, the frequency-dependent cusp in ac susceptibility vs. T
measurements at low magnetic field, is observed for all LnRu-1222 samples. The
strong supression of the cusp in the ac susceptibility measurement in the
presence of magnetic fields as low as 500 Oe, and the results of thermoremanent
magnetization (TRM) and isothermal remanent magnetization (IRM) measurements
are also evidences of a spin glass behavior. By comparing these results with
measurements on a YRu-1212 sample we conclude that the glassy behavior is
characteristic of the Ru-1222 phase, not being observed for the studied
YRu-1212 sample. We suggest that the spin glass transition occur only in the
Ru-1222 phase possibly due to the larger number of oxygen vacancies present in
these compounds.
