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Magnetoferritin nanoparticles consist of ferrimagnetic magnetite–maghemite surrounded by a protein shell. Thermal relaxation data for both agglomerated and well-separated magnetoferritin show clear Tln(t/τ0) scaling, thereby permitting a direct evaluation of the influence of magnetostatic interactions on the effective energy barrier distribution for magnetic reversal. For agglomerated magnetoferritin, the effect of the interactions is to broaden the distribution and shift its peak to lower energies, in contrast to the peak in the zero-field-cooled susceptibility, which moves to higher energies. Our result is in good agreement with earlier theoretical predictions (Iglesias and Labarta 2004 Phys. Rev. B 70 144401).

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