Role of zinc substitution in magnetic hyperthermia properties of magnetite nanoparticles: interplay between intrinsic properties and dipolar interactions

Abstract

Optimizing the intrinsic properties of magnetic nanoparticles for magnetic hyperthermia is of considerable concern. In addition, the heating efficiency of the nanoparticles can be substantially influenced by dipolar interactions. Since adequate control of the intrinsic properties of magnetic nanoparticles is not straightforward, experimentally studying the complex interplay between these properties and dipolar interactions affecting the specific loss power can be challenging. Substituting zinc in magnetite structure is considered as an elegant approach to tune its properties. Here, we present experimental and numerical simulation results of magnetic hyperthermia studies using a series of zinc-substituted magnetite nanoparticles (Zn_xFe_1-xFe₂O₄, x = 0.0, 0.1, 0.2, 0.3 and 0.4). All experiments were conducted in linear regime and the results were inferred based on the numerical simulations conducted in the framework of the linear response theory. The results showed that depending on the nanoparticles intrinsic properties, interparticle interactions can have different effects on the specific loss power. When dipolar interactions were strong enough to affect the heating efficiency, the parameter σ = K_effV/k_BT (K_eff is the effective anisotropy and V the volume of the particles) determined the type of the effect. Finally, the sample x = 0.1 showed a superior performance with a relatively high intrinsic loss power 5.4 nHm²kg^-1.

Figure 1

First quadrant of the magnetization curves of the samples. The inset is the fitted high-field magnetization data with the law of approach, the symbols are experimental data and the lines are the fittings.

Figure 2

The measured SLP values of the samples at H₀ = 7.5 kA/m and different concentrations for (a) 339 kHz, (b) 240 kHz, and (c) 137 kHz. (d) Mean ILP values considering all frequencies.

Figure 3

SLP field dependence (a) for sample x = 0.2, 0.3 and 0.4 and (b) for sample x = 0.0 and 0.1 for c = 1.5 wt.%. (c) SLP field dependence for sample x = 0.1 and c = 3.5, 1.5, and 0.3 wt.%. (d) SLP frequency dependence for all samples at c = 2.5 wt.%.

Figure 4

The dynamic hysteresis loops of the samples considering f = 137 kHz and H₀ = 7.5 kA/m.

Figure 5

(a–e) SLP variation versus σ = K_effV/k_BT considering the volumes obtained from TEM images (the dashed lines represent the experimental values), and (f) the calculated and experimental values of SLP for all samples for f = 339 kHz and at c = 0.3%.

Figure 6

Simulated SLP versus (a) σ and frequency for H₀ = 7.5 kA/m, and (b) field amplitude and frequency for σ = 6.7.

Figure 7

(a) Dipolar coupling constant (λ) and (b) relative strength of the dipolar interaction at different concentrations.

Figure 8

Energy conversion efficiency versus frequency for all samples.