Origin and Shell-Driven Optimization of the Heating Power in Core/Shell Bimagnetic Nanoparticles

Abstract

The magnetic properties of core/shell nanoparticles can be finely tuned through the exchange coupling at the interface, enabling large heating powers under alternating magnetic fields. However, the origin of their heating efficiency is still unclear due to the complex interplay of different heating mechanisms. Here, we show that monodisperse Fe 3 O 4 /Co x Zn 1−x Fe 2 O 4 core/shell nanoparticles can be designed to provide large heating powers for different field amplitudes and dispersion media conditions by modulating their shell composition and thickness. The fine control of the nanoparticles' effective anisotropy provided by the interface coupling between core and shell leads to values up to ∼2400 W g −1 for water colloids and ∼1000 W g −1 for immobilized particles at 80 mT and 309 kHz. A reduction in the shell thickness or Co/Zn ratio results in a transition from a viscous heating regime to a region governed by a collective behavior, characterized by chainlike formation due to interparticle interactions. These results shed light on the origin of the large heating powers of core/shell ferrites and provide an empirical guide to design highly efficient magnetic nanoheaters.

Enhancement of specific absorption rate in CoO.7ZnO.3Fe2O4 and CoO.5ZnO.5Fe2O4 composite nanoparticles

“…6, the SAR is strongly enhanced by the exchange coupling between two magnetic nanoparticles in these composites. This observation is in line with a number of earlier studies [20][21][22][23][24][25][26]. For MFO/CZFO -0.3, the SAR is 2.5 and 2.7 times higher than that of MFO and CZFO -0.3, respectively.…”

“…This is the combination of soft and hard magnetic phases in core-shell structured particles or composite nanoparticles. Lee [26]. This behaviour has also been observed in other works [22][23][24][25].…”

“…An approach to enhancing the heating power in MIH is the improvement of the saturation magnetization by substituting Co by Zn in Co ferrite, as shown by Duong et al who found an increase in the saturation magnetization with increasing Zn concentration [18,19]. Recently, a few studies found that exchange-coupled magnetic nanoparticles are a new means of significant enhancement of SAR/SLP in MIH [20][21][22][23][24][25][26]. This is the combination of soft and hard magnetic phases in core-shell structured particles or composite nanoparticles.…”

Embracing Defects and Disorder in Magnetic Nanoparticles

“…The magnetic anisotropy can be tuned by magnetic coupling in bi‐magnetic hard‐soft and soft‐hard core‐shell magnetic nanoparticles such as CoFe 2 O 4 ‐MnFe 2 O 4 [ 156 ] and Fe 3 O 4 ‐CoFe 2 O 4 . [ 157 ] More in depth insight into these nanosystems can be found in the review by López‐Ortega et al. [ 158 ] The effect of thickness and composition of the shell on the magnetization of bi‐magnetic exchanged bias nanosystems has already been discussed more than a decade ago.…”

Investigation of Magnetic Properties of Magnetic Poly (glycidyl methacrylate) Microspheres: Experimental and Theoretical

“…As we have known, the magnetic properties of the MNPs are strongly affected by intrinsic parameters such as lattice constant, surface energy, and magnetic anisotropy, which depends on particle size and shape [23]. Additionally, for the bioapplications like magnetic hyperthermia (MHT) applications, the magnetic anisotropy constant plays a key role [24][25][26][27][28]. However, the particle size determination methods of the MNPs embedded inside the magnetic PGMA microsphere are, for example, observing with transmission electron microscopy (TEM) or using Scherrer equation from X-ray diffraction (XRD) results, which have not been highly reliable and fully reflect essential information [29].…”