Magnetoferritin Nanoparticles Research Articles

Suppression of blocking behavior in a macroscopic fcc crystal of nanoparticles

We have used a protein crystallization technique to fabricate three-dimensional (3D) ordered arrays of magnetoferritin nanoparticles up to a few hundreds of micrometers in size in the form of free standing perfectly faceted crystals. We compare the ac and dc susceptibilities of the nanoparticles in an uncrystallized system (amorphous assembly) and in a macroscopic 3D fcc crystal of nanoparticles. Completely different magnetism is measured due to the different interparticle interactions in the two systems. For example, at temperatures above 50 K the uncrystallized nanoparticle system is superparamagnetic while the 3D crystal displays no superparamagnetism up to 400 K.

The effect of dipolar interactions on the thermal relaxation of magnetoferritin

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