AC and DC magnetic measurements have been performed on polycrystalline RuSr2GdCu2O8 and RuSr2Gd1. 6Ce0. 4Cu2O10 samples with the aim to study the complex magnetic structure of these compounds. Our results indicate that RuSr2GdCu2O8, in addition to the well-known antiferromagnetic ordering, exhibits another magnetic feature at temperature slightly higher than the antiferromagnetic ordering temperature, that we attribute to the presence of ferromagnetic nanoclusters that exhibit superparamagnetic …