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The crystal site occupancy of different divalent ions and the induction of lattice defects represent an additional tool for modifying the intrinsic magnetic properties of spinel ferrites nanoparticles. Here, the relevance of the lattice defects is demonstrated in the appearance of exchange‐bias and in the improvement of the magnetic properties of doped ferrites of 20 nm, obtained from the mild oxidation of core@shell (wüstite@ferrite) nanoparticles. Three types of nanoparticles (Fe0.95O@Fe3O4, Co0.3Fe0.7O@Co0.8Fe2.2O4 and Ni0.17Co0.21Fe0.62O@Ni0.4Co0.3Fe2.3O4) are oxidized. As a result, the core@shell morphology is removed and transformed in a spinel‐like nanoparticle, through a topotactic transformation. This study shows that most of the induced defects in these nanoparticles and their magnetic properties are driven by the inability of the Co(II) ions at the octahedral sites to migrate to tetrahedral sites, at the chosen mild oxidation temperature. In addition, the appearance of crystal defects and antiphase boundaries improves the magnetic properties of the starting compounds and leads to the appearance of exchange bias at room temperature. These results highlight the validity of the proposed method to impose novel magnetic characteristics in the technologically relevant class of nanomaterials such as spinel ferrites, expanding their potential exploitation in several application fields. [ABSTRACT FROM AUTHOR]

Nowadays, the circular economy is gaining more and more attention in sectors where the raw material supply is critical for both cost and geo-political reasons. Moreover, the environmental impact issue calls for recycling. From this perspective, the recovery of rare earth elements represents a strategic point. On the other hand, the high cost and the dangerous standard recovery methods that apply to NdFeB magnets limits options for traditional recycling. A new mechanical method is proposed, not requiring hydrogen, high temperature, or chemical processes, but instead using an impact mill designed to operate in vacuum. A traditional impact mill operating in a glove box filled with Ar atmosphere has also been used for comparison. The obtained NdFeB powders were analyzed in terms of magnetic properties and chemical composition, particularly in terms of the oxygen content. [ABSTRACT FROM AUTHOR]

The exploitation of the exchange coupling between hard and soft magnetic materials has been proposed for enhancing the magnetic performances of rare-earth free permanent magnets, with the aim of extending their use to all applications where moderate energy product (35–100 kJ m−3) is required. Strontium hexaferrite (SFO)/spinel ferrite composites seem particularly promising to achieve this target, although the conditions to maximize the effect while using techniques easily scalable to industrial production have not yet been identified. Within this framework, the optimization of the structural, chemical, and magnetic properties of the two moieties before the coupling procedure is crucial to enhance the energy product of the final composite. Here we report the syntheses of both nanometric SFO with high coercivity (ca. 525 kA m−1) and quasi-bulk saturation magnetization (68 Am2 kg−1) and a series of nanosized zinc-doped ferrite (ZnxFe3−xO4, 0.0 ⩽ x ⩽ 0.4) through cheap, easily scalable and eco-friendly approaches. The structural and chemical stability of the two magnetic phases as a function of temperature were investigated up to 1100 °C, with the aim of finding the best compromise between preservation of the nanometric scale and magnetic properties. A very high-magnetization (106 Am2 kg−1) ferrite was obtained by annealing Zn0.3Fe2.7O4 nanopowder at the highest investigated temperature. A preliminary attempt at coupling the two phases, starting from a mixture of the nanopowders, was performed through a classic annealing process in the temperature range 500 °C–1100 °C. The adopted procedure allowed for obtaining an exchange coupled composite at 1100 °C where the two phases are intimately and homogeneously mixed, with micrometric (0.3–5 μm) and nanometric (up to 50 nm) spinel ferrite particles. Despite these promising results, no enhancement of the energy product was found, highlighting the need for further experimental efforts to improve the coupling procedure. [ABSTRACT FROM AUTHOR]

Gravity compensation is a key requirement for achieving three-dimensional navigation of magnetic microrobots in fluids. Here we present a brief theoretical introduction to the issue of gravity compensation in the case of magnetic 'pulling' propulsion, explicitly highlighting the constraints it introduces. Therefore, we evaluate the advantages that quasi-neutral buoyancy gives to hydrogel microrobots, demonstrating that despite their relatively weak magnetic properties, for certain size/velocity ranges they could be more easily and efficiently propelled than state-of-the-art metal microrobots. Hence, our analysis endorses the adoption of smart polymers, such as stimuli-responsive hydrogels, for developing truly multifunctional magnetic microrobots. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the efficacy of magnetic fluid hyperthermia (MFH) mediators, we synthesised cobalt ferrite nanoparticles with different sizes (between 5 and 7nm) via successive polyol synthesis. The static and dynamic magnetic properties of the prepared particles, dispersed in a solid matrix, were investigated in order to evaluate the possibility of applying cobalt ferrite as magnetic susceptors in MFH. The effect on magnetic properties coming from the surface anchoring of the model molecule cetyl phosphate, was also investigated. [Copyright &y& Elsevier]