Excess spin and the dynamics of antiferromagnetic ferritin

Abstract

Temperature-dependent magnetization measurements on a series of synthetic ferritin proteins containing from 100 to 3000 Fe(III) ions are used to determine the uncompensated moment of these antiferromagnetic particles. The results are compared with recent theories of macroscopic quantum coherence which explicitly include the effect of this excess moment. The scaling of the excess moment with protein size is consistent with a simple model of finite size effects and sublattice noncompensation.

Thermoinduced Magnetization in Nanoparticles of Antiferromagnetic Materials

“…Although other explanations for the anomalous behavior of antiferromagnetic nanoparticles have been suggested [9,12,14,15], the experimental data and the fit, shown in Fig. 1, together with a number of similar experimental observations, give experimental evidence for a temperature dependent magnetic moment that is in accordance with the model for thermoinduced magnetization.…”

“…Still, the dependence of the magnetization on particle size and temperature has shown features that are not fully understood. Several studies have revealed that the temperature dependence is not in accordance with the Langevin behavior, i.e., the magnetization does not decrease with increasing temperature in the expected way [8][9][10][11][12][13][14][15]. These results have been observed in several synthetic samples, in the iron storage protein ferritin, and in ferrihydrite, which can be found in sediments in nature.…”

“…(4). The increase in magnetic moment with temperature in ferritin particles with nominally 1000, 2000, and 3000 iron atoms, found by Harris et al [9], also shows a linear temperature dependence with a slope corresponding to ! 0 0:4 10 12 s ÿ1 .…”

“…1, together with a number of similar experimental observations, give experimental evidence for a temperature dependent magnetic moment that is in accordance with the model for thermoinduced magnetization. Thus the thermoinduced magnetization can explain anomalous magnetic properties of nanoparticles of antiferromagnetic materials, which have been discussed in the literature [4,[8][9][10][11][12][13][14][15].…”

“…1. Harris et al [9] found in a study of ferritin samples with different particle sizes that the magnetic moment of the particles increases with temperature, and the authors remarked that ''the reason for this temperature dependence is not clear.'' In another study of ferritin particles with about 4000 iron atoms, Kilcoyne and Cywinski [10] noted that ''above 120 K, is surprisingly found to increase slowly with increasing temperature.''…”