The models proposed to account for the variation of the blocking temperature of a magnetic particle in an assembly of interacting particles are re-discussed. Experimental results on the thermal variation of the relaxation time are reported in support of the discussion. Except few cases related to a collective state, all data are well explained by the Dormann-Bessais-Fiorani model accounting for the interparticle interactions, in the framework of the superparamagnetic Neel-Brown model. The energy barrier unambiguously increases with increasing interactions, even when they are very weak, in disagreement with the Morup-Tronc model.
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