The possibility to finely control nanostructured cubic ferrites (M^IIFe₂O₄) paves the way to design materials with the desired magnetic properties for specific applications. However, the strict and complex interrelation among the chemical composition, size, polydispersity, shape and surface coating renders their correlation with the magnetic properties not trivial to predict. In this context, this work aims to discuss the magnetic properties and the heating abilities of Zn-substituted cobalt ferrite nanoparticles with different zinc contents (Zn_xCo_1−xFe₂O₄ with 0 < x < 0.6), specifically prepared with similar particle sizes (∼7 nm) and size distributions having the crystallite size (∼6 nm) and capping agent amount of 15%. All samples have high saturation magnetisation (M_s) values at 5 K (>100 emu g⁻¹). The increase in the zinc content up to x = 0.46 in the structure has resulted in an increase of the saturation magnetisation (M_s) at 5 K. High M_s values have also been revealed at room temperature (∼90 emu g⁻¹) for both CoFe₂O₄ and Zn_0.30Co_0.70Fe₂O₄ samples and their heating ability has been tested. Despite a similar saturation magnetisation, the specific absorption rate value for the cobalt ferrite is three times higher than the Zn-substituted one. DC magnetometry results were not sufficient to justify these data, the experimental conditions of SAR and static measurements being quite different. The synergic combination of DC with AC magnetometry and ⁵⁷Fe Mössbauer spectroscopy represents a powerful tool to get new insights into the design of suitable heat mediators for magnetic fluid hyperthermia.

The effect of the annealing temperature T_ann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe₂O₄/SiO₂), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing T_ann from 700 to 900 °C. The effective magnetic anisotropy constant (K_eff) increases with decreasing T_ann, due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, K_eff is much larger (1.7 × 10⁶ J/m³) than that of the 15% w/w sample (7.5 × 10⁵ J/m³) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments.

MCM-41 is proposed to build mesostructured γ-Fe₂O₃-based sorbents as an alternative to other silica or alumina supports for mid-temperature H₂S removal.

Bi-magnetic core–shell spinel ferrite-based nanoparticles with different CoFe₂O₄ core size, chemical nature of the shell (MnFe₂O₄ and spinel iron oxide), and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction. The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids.