Role of Zn²⁺ Substitution on the Magnetic, Hyperthermic, and Relaxometric Properties of Cobalt Ferrite Nanoparticles

Abstract

Zinc substitution is often proposed as an efficient strategy to improve the performances of spinel ferrite nanoparticles, particularly related to their application as theranostic agents. In this work, a series of 8 nm spinel ferrite nanoparticles of formula Co x Zn y Fe 3−(x+y) O 4 is synthesized by thermal decomposition with the purpose of investigating the role of Zn 2+ ions in modifying the structural and magnetic properties. Contrary to most of the literature on this subject, where the sum of Co and Zn is kept constant (x + y = 1), here, the amount of Co is maintained at ca. x = 0.6, corresponding to the maximum of magnetic anisotropy of the Zn-undoped system, whereas the amount of Zn is progressively varied along the series from y = 0.05 to 0.4. This approach allows enlightening the effect of the Zn introduction on the magnetic and crystal structures and, particularly, on magnetic anisotropy, which is deeply investigated by several complementary techniques. A significant increase of the saturation magnetization, M S , upon the Zn content up to y = 0.4 is confirmed only at low temperature, whereas at room temperature, this effect is partially nullified by the weakening of the magnetic exchange coupling constants due to the increasing Zn substitution. Moreover, we demonstrate that the lattice modifications following the Zn introduction are responsible of a strong decrease of the particle magnetic anisotropy. Overall, these effects limit the use of Zn-substituted ferrites in biomedical applications like magnetic resonance imaging and magnetic fluid hyperthermia only to very low amount of Zn, as here confirmed by relaxometric and calorimetric measurements.

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

“…Among different magnetic materials considered to be used in biomedical applications including magnetic hyperthermia, spinel ferrite nanoparticles, in particular magnetite and maghemite, are the most popular materials 24,25 . To date, much effort has been devoted to tune their intrinsic properties using different strategies such as modifying the synthesis procedures 24,26,27 or doping various transition metal cations in their structure 28–30 .…”

Improvements in the Organic-Phase Hydrothermal Synthesis of Monodisperse MxFe3–xO4 (M = Fe, Mg, Zn) Spinel Nanoferrites for Magnetic Fluid Hyperthermia Application

“…Notably, the average size of Zn-doped NPs is higher than that of bare Fe 3 O 4 NPs which could be due to the substitution of larger radius Zn atoms instead of Fe atoms in the iron oxide structure. 28 , 29 …”

Magnetocrystalline and Surface Anisotropy in CoFe2O4 Nanoparticles

“…It provides a tool to tailor their magnetic properties (e.g., magnetic crystalline anisotropy and saturation magnetization) by the variation of the cation distribution between the two sublattices. This can be done by changing the chemical composition, the preparation method, and thermal treatments [8][9][10].…”