The macroscopic magnetizations of Ru_1-xCu_xSr_2EuCu_2O_8+d with x between 0 and 0.15 were investigated. A ferromagnet-like transition as well as an antiferromagnet-like transition appear around T_M in the low-field magnetization and around T_AM in the high-field differential susceptibility, respectively. The separation between them, which is accompanied by a flat plateau in the magnetic C_p, increases with x. Superparamagnetic M(H) and slow spin dynamics, i.e. characteristics of nanomagnetic clusters, were observed far above T_M. A comparison with RuSr_2(Eu_1-yCe_y)Cu_2O_10+d and some manganites further suggests that a phase separation occurs, which can describe well the conflicting magnetic-superconductivity data previously reported.
@article{arxiv.cond-mat/0304163,
title = {Separation Between Antiferromagnetic and Ferromagnetic Transitions in Ru_1-xCu_xSr_2EuCu_2O_8+d},
author = {Y. Y. Xue and F. Chen and J. Cmaidalka and R. L. Meng and C. W. Chu},
journal= {arXiv preprint arXiv:cond-mat/0304163},
year = {2009}
}