Magnetic transitions and ferromagnetic clusters in RuSr 2 „ Eu , Ce

The macroscopic magnetizations of a RuSr2(Eu0.7Ce0.3)2Cu2O101d sample were investigated. A ferromagnetlike transition occurs around TM in the low-field magnetization. Highly nonlinear M (H), non-Curie-Weiss susceptibility, and slow spin dynamics, however, were observed up to T1'(2 –3)TM . In addition, an antiferromagnetlike differential-susceptibility maximum of Ru appears around a separate temperature TAM between T1 and TM . The data are therefore consistent with a phase-separation model: superparamagnetic clusters ~or short-range spin orders! are first precipitated from the paramagnetic matrix below T1, followed by an antiferromagnetic transition of the matrix at TAM and an apparent ferromagnetic ~FM! transition around TM , where the long-range spin order is established in the FM species embedded in the matrix.