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Discontinuous magnetic multilayers [CoFe/Al 2 O 3 ] are studied by use of magnetometry, susceptometry and numeric simulations. Soft ferromagnetic Co 80 Fe 20 nanoparticles are embedded in a diamagnetic insulating a-Al 2 O 3 matrix and can be considered as homogeneously magnetized superspins exhibiting randomness of size (viz. moment), position and anisotropy. Lacking intra-particle core-surface ordering, generic freezing processes into collective states rather than individual particle blocking are encountered. With increasing particle density one observes first superspin glass and then superferromagnetic domain state behavior. The phase diagram resembles that of a dilute disordered ferromagnet. Criteria for the identification of the individual phases are given.

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