Magnetization scaling in the ruthenate-cuprate RuSr₂Eu _1.4Ce _0.6Cu₂O_10-δ (Ru-1222)

The magnetic properties of the superconducting ruthenate-cuprate RuSr ₂Eu _1.4Ce_0.6Cu₂O _10-δ (Ru-1222) have been studied by a scaling analysis of the dc magnetization and ac susceptibility measurements. Non-linear M(H) curves reveal the presence of nano-size clusters with a net magnetic moment of 10 ² μ_B at 180 K, near the deviation from a Curie-Weiss behavior. On cooling, no scaling was observed down to 90K, discarding the possibility of magnetic phase separation of collinear ferromagnetic particles. We explain this result in terms of a variable number of contributing particles, with a temperature dependent net magnetic moment. For 70 K ≤ T ≤ 90 K the scaling plots evidence the emergence of a system of non-interacting particles, which couple on further cooling. The observed cluster-glass features are preserved down to the lowest measured temperature (10 K); no signature of long-range order was detected. The frequency shift of the peak in the real part of the ac susceptibility does not follow the Vogel-Fulcher type dependence, as previously reported. The puzzling temperature dependence of the coercive field, H_C(T), is correlated with the changes in the scaling factors.