High Frequency Hysteresis Losses on γ-Fe2O3 and Fe3O4: Susceptibility as a Magnetic Stamp for Chain Formation

Abstract

In order to understand the properties involved in the heating performance of magnetic nanoparticles during hyperthermia treatments, a systematic study of different γ-Fe2O3 and Fe3O4 nanoparticles has been done. High-frequency hysteresis loops at 50 kHz carried out on particles with sizes ranging from 6 to 350 nm show susceptibility χ increases from 9 to 40 for large particles and it is almost field independent for the smaller ones. This suggests that the applied field induces chain ordering in large particles but not in the smaller ones due to the competition between thermal and dipolar energy. The specific absorption rate (SAR) calculated from hysteresis losses at 60 mT and 50 kHz ranges from 30 to 360 W/gFe, depending on particle size, and the highest values correspond to particles ordered in chains. This enhanced heating efficiency is not a consequence of the intrinsic properties like saturation magnetization or anisotropy field but to the spatial arrangement of the particles.

In Vitro Intracellular Hyperthermia of Iron Oxide Magnetic Nanoparticles, Synthesized at High Temperature by a Polyol Process

“…Both the dispersion of MNPs in an environment like water (where they keep their mobility) and the increase of their concentration favor the chain formation under the effect of the AMF. This behavior is typically observed for highly coercive ferromagnetic IOMNPs, as shown in the case of nanorods [57] or 35 nm magnetite nanoparticles suspended in water, as suggested by AC hysteresis, susceptibility, and SAR data [58]. Other reports have also shown that the changes in magnetic susceptibility data (Ms, Mr, χ) are related to the length of the chains formed by the MNPs [59].…”

Exploring the potential of the dynamic hysteresis loops via high field, high frequency and temperature adjustable AC magnetometer for magnetic hyperthermia characterization

“…Indeed, AC magnetometry provides additional and very valuable magnetic information that is not directly accessible by calorimetry alone. For instance, collective phenomena of MNPs, related to the type of assembling, disordered or forming well-defined structures, are easily detected from the AC hysteresis loop [25][26][27][28][29]. AC magnetometry has also allowed to correlate the shape of the MNPs and their hyperthermia performance [30], or to clarify why the heating power of MNPs tends to fall in cellular enviroments [31].…”

Colossal heating efficiency via eddy currents in amorphous microwires with nearly zero magnetostriction

“…Let's assume that a MW30 with L = 5 mm has a perfectly square hysteresis loop with the M s and H c values measured at f = 50 Hz, and these values are still valid at f = 625 kHz, this would be then the maximum possible area under the hysteresis cycle. In the case of nanoparticles, remanence and coercivity can be much smaller at high frequencies than at low frequencies 45 , and, additionally, depending on relation between magnetic and thermal energy, the susceptibility can vary with the frequency. Unlike nanoparticles, the coercivity in MWs can increase at high frequencies because the induced current creates a field that opposes to the applied field, giving place to an effective coercive field higher than at low frequencies.…”

“…As it is well known, the dipolar interactions can improve or decrease the SLP depending on the magnetic properties of the materials and the applied field 44,45 . In the case of MWs, the dipolar interactions are often significant and can even give rise to hysteresis loops splitting in MWs with positive magnetostriction 46,47 .…”