We report on the suitability of core/shell nanoparticles (NPs) for magnetic fluid hyperthermia in a selfregulated and theranostic approach. Aqueous magnetic colloids based on core/shell ZnxMnyFezO4@γ-Fe2O3 and ZnxCoyFe-zO4@γ-Fe2O3 NPs were produced by a three-step chemical synthesis. Systematic deviations from stoichiometry was observed with increasing Zn substitution for both series of samples. We investigated how the chemical composition affects saturation magnetization, magnetic anisotropy and thermomagnetic properties of these core/shell NPs. The heating efficiency through specific power absorption (SPA) was analyzed in the framework of the linear response theory. SPA values obtained for NPs presenting different contrast of anisotropy between the core and shell materials indicate no evidence of enhanced exchange coupling contribution to the heating efficiency.

We investigate here the internal structure of zinc ferrite nanoparticles designed and prepared by a soft chemistry method to elaborate magnetic nanocolloids. The strategy used to avoid acid dissolution modifies the chemical composition of the surface of the nanoparticles, which are described as a core of stoichiometric zinc ferrite surrounded by a maghemite shell. Measurements of X-ray absorption nearedge spectroscopy, extended X-ray absorption fine structure, and X-ray diffraction are undertaken to investigate the local structure of nontreated nanocrystals and of surface-treated ones as a function of their sizes. The qualitative analysis of X-ray absorption results indicates a nonequilibrium cation distribution among the interstitial sites of the zinc ferrite nanocrystals core. Ab-initio calculations of theoretical photoelectron backscattering phases and amplitudes give, by fitting Fourier transformed EXAFS data at both Zn and Fe K-edges, an average inversion degree of 0.34. This value well matches the result of Rietveld refinement of X-ray diffraction data. Magnetization measurements performed on dilute aqueous nanocrystal dispersions, liquid at room temperature and frozen at low temperatures, are carried out in order to test the obtained results.

We investigate the local structure of nanoparticles based on a manganese ferrite core surrounded or not by a maghemite layer obtained after hydrothermal surface treatment. Results of X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) measurements are crossed with those of infield Mossbauer spectroscopy and X-ray absorption spectroscopy (XANES/EXAFS) to study the valence state of Mn ions and the cation distribution at interstitial sites of the core−shell nanoparticle structure. Linear combination fitting of XANES data clearly indicates the existence of mixed valence states of Mn cations in the Mn ferrite phase. As a direct consequence, it induces nonequilibrium cation distributions in the nanoparticle core with the presence of a large amount of Mn cations at octahedral sites. The quantitative results of the inversion degree given by NPD, Mossbauer spectroscopy measurements, and EXAFS are in good accordance. It is also shown that both the proportions of each oxidation degree of Mn ions and their location at tetrahedral or octahedral sites of the spinel nanocrystal core can be modified by increasing the duration of the surface treatment. a χ M is the molar fraction of manganese ions obtained by ICP and AAS techniques, ⟨a⟩ is the average lattice parameter deduced from Bragg's law, ϕ c / ϕ is the volume fraction of the core, and t sh is the thickness of the surface layer. The particle sizes (D XR ) were obtained by Scherrer's equation.

In this work we focus on the surface charging properties of core shell ferrite nanoparticles dispersed in water, namely magnetic nanocolloids. This structural charge results from the Brönsted acid-base behavior of the particles surface sites and is achieved through hydrolysis reactions. It can be modeled by considering identical charged sites behaving as weak diprotic acids. Then, electrochemical techniques could be implemented to study the acid-base equilibrium between the particle surface and the colloid bulk solution. Simultaneous potentio-conductimetric titrations are therefore performed to determine the thermodynamical constants of the p H-dependent reactions and to obtain the p H variations of the surface charge density. The results reveal that the saturation value of the structural charge strongly depends on the nanoparticle mean size. For large particles, the surface tends to be fully ionized whereas for smaller particles the saturated structural charge decreases drastically. This surface charge reduction is attributed to the existence in smaller particles of metallic surface sites, which cannot be accessible to the proton charge. The existence of such dead sites would be related to hydroxo-bonded sites with very low acidity combined with a quantum size effect, which would affect the charging/discharging process at the surface of the semiconductor ferrite quantum dot.

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