Cluster spin glass and superparamagnetism in RuSr2Eu1.5Ce0.5Cu2O10- (delta)

We investigate in detail the dc magnetization and nonlinear ac susceptibility behavior of the superconducting ferromagnet RuSr2Eu1.5Ce0.5Cu2O10- δ (Ru1222) to develop a comprehensive understanding of the spin glass and superparamagnetism in this material. The structural properties of the system result in the formation of magnetic (ferromagnetic) clusters of different sizes, shapes and properties. The magnetic clustering of the system leads to observation of various features in dc magnetization and ac susceptibility consistent with superparamagnetism and cluster spin glass states, which can coexist or stand alone, depending on the temperature range considered. Experimental results of magnetic measurements in combination with their analysis have enabled us to explain and distinguish these phenomena, as well as to propose a temperature dependent scenario of the system behavior.