Magnetic interaction and anisotropy axes arrangement in nanoparticle aggregates can enhance or reduce the effective magnetic anisotropy

Abstract

The magnetic response of nanostructures plays an important role on biomedical applications being strongly influenced by the magnetic anisotropy. In this work we investigate the role of temperature, particle concentration and nanoparticle arrangement forming aggregates in the effective magnetic anisotropy of Mn-Zn ferrite-based nanoparticles. Electron magnetic resonance and coercivity temperature dependence analyses, were critically compared for the estimation of the anisotropy. We found that the temperature dependence of the anisotropy follows the Callen-Callen model, while the symmetry depends on the particle concentration. At low concentration one observes only an uniaxial term, while increasing a cubic contribution has to be added. The effective anisotropy was found to increase the higher the particle concentration on magnetic colloids, as long as the easy axis was at the same direction of the nanoparticle chain. Increasing even further the concentration up to a highly packed condition (powder sample) one observes a decrease of the anisotropy, that was attributed to the random anisotropy axes configuration.

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

“…It should be noted that, such form of thermal dependence (as M 2 ) cannot be extrapolated to lower temperatures in our case, due to the presence of the Verwey phase transition at around 100 K. A detailed analysis of this issue requires the collection of additional data as a function of temperature and a more complex modeling to take account for the thermal dependence of the magnetocrystalline contribution to the anisotropy that is out of the scope of this work. This type of study have been already done in the literature, either with magnetosome [64], whose thermal behavior is expected to be similar to the samples presented in this work, or very recently with Mn-Zn ferrites [65]. The overall agreement between experiments and simulations in both SAR evolution ( Figure 10) as well as in AC hysteresis loops (see Supporting Information Figure S13) is quite surprising since simplifications made in the modeling are really strong: size distribution has been not taken into account and, most importantly, magnetic dipolar interactions have not been explicitly considered.…”

How size, shape and assembly of magnetic nanoparticles give rise to different hyperthermia scenarios

“…Finally, we observe a striking 14-fold increase in the case of the disks. Such variety of behaviours reflects the delicate interplay between easy axes arrangement and interparticle interactions, which has been experimentally shown it can enhance or reduce the effective anisotropy 58 responsible for the local energy barrier, and consequently the achievable heat release. 59 In all cases, the rotation of magnetization orientation is against the anisotropy forces.…”

In vivo magnetic nanoparticle hyperthermia: a review on preclinical studies, low-field nano-heaters, noninvasive thermometry and computer simulations for treatment planning

“…According to this criteria it is clear from Figure 1 that no preclinical study from the literature is satisfactory (as far as we know) which means, in principle, that the experimental conditions that have been studied would not be applicable for human use, since they are predicted to generate a lot of non-localized heat by eddy currents. This is very disappointing, and suggests that several studies had not focused enough on the priority for clinical translation, which is related to improving the heating efficiency of magnetic nanoparticles at low-field condition [147,148]. On the other hand, Dutz and Hergt suggest that this limit can increase by a factor of 10 [25,26]; even so, note that only a few investigations are within the expected safety range of the second clinical limit.…”

“…The Brownian relaxation is influenced through temperature dependence of the viscosity, while for N eel relaxation temperature appears in the exponential term, not forgetting that even the anisotropy of the material is temperature dependent. This might be described by the Zener-Callen model, which relates the magnetic anisotropy temperature dependence with the magnetization and the symmetry of anisotropy [147]. Indeed, the MNT technique was suggested some time ago, and relies on taking advantage of the temperature dependence of the harmonic signals, commonly obtained using MPI technology [189].…”