  A new magnetic transition in the ruthenocuprate parent compound
RuSr2EuCeCu2O10 has been observed below 10 K. It shows up only as a kink in the
imaginary part of the ac susceptibility and exhibits a pronounced frequency
dependence. At the same time, the real part of the ac susceptibility and the dc
magnetization study show very little change in the same temperature window
suggesting only a minor fraction of the material to be involved in the
transition. Frequency dependence shows excellent agreement with the predictions
of the Arrhenius law known to describe well the dynamics of the
superparamagnetic particles. The same type of the investigation on the
RuSr2Eu1.1Ce0.9Cu2O10 composition showed no evidence of the similar transition,
which points to a possible intrinsic behavior.
