Magnetic hysteresis anomalies in ferritin

Abstract

Ferritin, an antiferromagnetic nanoparticle with a net magnetic moment, exhibits some unusual magnetic behavior. Above its blocking temperature, T B Ϸ12 K, the magnetization can be fit with the Langevin function only by including an additional linear term. The saturation moment decreases linearly with increasing temperature, and suggests an ordering temperature of about 460 K. Below T B , both zero-field-cooled and fieldcooled hysteresis loops exhibit large coercivity (ϳ1800 Oe͒ and irreversibility in the loops is found up to Hϭ35 kOe. An exchange field H e of few hundred Oe is observed at low temperatures. The dependencies of H e and H c on temperature were also studied. ͓S0163-1829͑97͒52022-4͔

Thermoinduced Magnetization in Nanoparticles of Antiferromagnetic Materials

“…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.…”

“…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].…”

“…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.'' Makhlouf et al [11] found that the magnetic moment of ferritin particles at finite temperatures was considerably larger than expected from the low-temperature value. Vollath et al [12] observed a substantial increase with increasing temperature of the magnetic moment of Cr 2 O 3 particles with diameters below 4 nm.…”

Shifted loops and coercivity from field-imprinted high-energy barriers in ferritin and ferrihydrite nanoparticles

“…4,5 Many of these studies were performed to enlighten the possible existence of quantum tunneling in ferritin in the Kelvin range. Less attention has been paid to the magnetic hysteresis, although it was termed "anomalous" in an early report due to the large coercivity (∼1800 Oe at 5 K), irreversibility up to relatively high fields (∼35 kOe), and loop displacement found after field cooling.…”

“…Less attention has been paid to the magnetic hysteresis, although it was termed "anomalous" in an early report due to the large coercivity (∼1800 Oe at 5 K), irreversibility up to relatively high fields (∼35 kOe), and loop displacement found after field cooling. 4 Ferritin consists of a hollow spherical shell composed of 24 protein subunits surrounding a ferrihydritelike core. The diameter of the cavity is of the order of 7-8 nm and the average size of the core of horse spleen ferritin is 5 nm.…”