Interplay between superparamagnetic and blocked behavior in an ensemble of lanthanum–strontium manganite nanoparticles

Abstract

Magnetic nanoparticles constitute promising tools for addressing medical and health-related issues based on the possibility to obtain various kinds of responses triggered by safe remote stimuli. However, such richness can be detrimental if different performances are not adequately differentiated and controlled. The aim of this work is to understand and systemize different kinds of magnetic-field-induced response for an ensemble of lanthanum-strontium manganite nanoparticles, which are considered as promising materials for self-controlled magnetic hyperthermia. A complex set of static and dynamic magnetic measurements accompanied by a numerical simulation of DC and AC magnetic behavior has been carried out. It is shown that to achieve adequate results, the dispersion of particle sizes and/or magnetic parameters should necessarily be taken into account. A quantitative description of the magnetic behavior of the ensemble should comprise two groups of nanoparticles differentiated according to the regime of their magnetization reversal: one group, which demonstrates non-hysteretic behavior similar to a superparamagnet and another one, which shows magnetic hysteresis characteristic of blocked particles. The fraction of nanoparticles in each group depends not only on the nanoparticles' parameters (in particular, their size), but also on the parameters of the external AC magnetic field (amplitude and frequency) used for remagnetization. The main outcome of this work is the development of a procedure which allows one to separately analyze contributions from different groups of nanoparticles and find the regularities of the redistribution of nanoparticles between these groups on changing the parameters of the external AC magnetic field. The results show the directions to enhance the heating efficiency of ensembles of magnetic nanoparticles and pave the way for further optimization of their characteristics and the parameters of the external field.

Role of the Fraction of Blocked Nanoparticles on the Hyperthermia Efficiency of Mn-Based Ferrites at Clinically Relevant Conditions

“…An interesting special case is the two-level approximation (TLA), which takes into account the field direction energy barriers on a simple two-level system. The TLA model shows frequency-dependent hysteresis and has been reported by Kalita et al to play a role in the ac magnetic response of nanoparticle ensembles. Because the TLA model shows hysteresis, some authors named these particles blocked.…”

Tunable Control of the Structural Features and Related Physical Properties of MnxFe3–xO4 Nanoparticles: Implication on Their Heating Performance by Magnetic Hyperthermia

“…Under both regimens, the NPs are not efficient for heat generation because of their negligible dynamic hysteresis. On the contrary, when the condition τ m ≈ τ R is fulfilled, the nanoparticles are in the transitional region between the SPM and the FM regimes; in this case, the dynamic hysteresis is maximized and thus the maximum heating efficiency is achieved …”

“…On the contrary, when the condition τ m ≈ τ R is fulfilled, the nanoparticles are in the transitional region between the SPM and the FM regimes; in this case, the dynamic hysteresis is maximized and thus the maximum heating efficiency is achieved. 110 Based on these ideas, we analyzed the obtained results. Figure 7B shows the frequency variation of the SAR at a constant field amplitude of 16 kA/m, while Figure 7C shows the field variation of the SAR at a constant frequency of 200 kHz.…”

Magnetic Properties of Fe3O4/CoFe2O4 Composite Nanoparticles with Core/Shell Architecture

“…Namely, an increase of the CoFe 2 O 4 content led to a saturation magnetization reduction and a coercive force growth, but the magnitudes of the s and c changes in Mix1 and Mix2 specimens were less pronounced. The distorted shape of the hysteresis loops for those specimens may arise because the particles could rotate in the course of the remagnetization process [21].…”