Heat generation in agglomerated ferrite nanoparticles in an alternating magnetic field

Abstract

The role of agglomeration and magnetic interparticle interactions in heat generation of magnetic ferrofluids in an ac magnetic field is still unclear, with apparent discrepancy between the results presented in the literature. In this work, we measured the heat generating capability of agglomerated ferrite nanoparticles in a non-invasive ac magnetic field with f = 100 kHz and H 0 = 13 kA m −1 . The nanoparticles were morphologically and magnetically characterized, and the specific absorption rate (SAR) for our ac magnetic field presents a clear dependence on the diameter of the nanoparticles, with a maximum SAR = 48 W g −1 for 15 nm. Our agglomerated nanoparticles have large hydrodynamic diameters, thus the mechanical relaxation can be neglected as a heat generation mechanism. Therefore, we present a model that simulates the SAR dependence of the agglomerated samples on the diameter of the nanoparticles based on the hysteresis losses that is valid for the non-linear region (with H 0 comparable to the anisotropy field). Our model takes into account the magnetic interactions among the nanoparticles in the agglomerate. For comparison, we also measured the SAR of non-agglomerated nanoparticles in a similar diameter range, in which Néel and Brown relaxations dominate the heat generation.

Energy dissipation in single-domain ferromagnetic nanoparticles: Dynamical approach

“…While the heating of nanoparticles is undesirable for most applications, this property is of crucial importance for magnetic hyperthermia applications [14,16,17] (see also Refs. [18][19][20] and references therein). In a ferrofluid subjected to an external periodic magnetic field two heating mechanisms are usually considered [21,22], one of which is related to Brownian rotation of nanoparticles and the other to their Néel relaxation.…”

Influence of size distribution and field amplitude on specific loss power

“…(1)) has severe consequences, as it excludes large share of particles, depending on the applied field, and their significant contribution to heating is then unaccounted for ( Figure 7). The omission of linearity condition in the calculation of SLP is a common practice, 21,22 and the agreement of calculated data with measurements can be taken as a main justification for such action. Instead we used the weaker condition, s R ðHÞ À1 > 2pf -only the particles relaxing faster than the rate of change of the external field are included in the calculations (see Figure 7).…”

Quantitative study of FORC diagrams in thermally corrected Stoner– Wohlfarth nanoparticles systems

“…The dash line in figure 6 (b) corresponds to the curve descript by equation (16). It is noticeable that the asymptotic approximation is outstanding.…”

“…The nanoparticles "universe" does not escape to this reality, and the difficulty increases due to the fact that the experimental results usually strongly depend on temperature [14]. The need to know the magnetic properties of nanostructured systems is becoming important because these parameters determine the behavior and magnetic relaxation of the magnetization, essential in applications, e.g., the use of nanoparticles in hyperthermia [15,16]. In this case, the magnetic relaxation channels are strongly determined by the distribution of anisotropy energies as well as interactions between particles.…”