Synthesis atmosphere (i.e., air and nitrogen) effects on the physical properties and formation mechanism of spinel iron oxide nanoparticles prepared via the co-precipitation method have been investigated using a multi-technique approach. The obtained magnetic nanoparticles (MNPs) were characterized using the X-ray diffraction, transmission electron microscopy (TEM), SQUID magnetometry, Mössbauer spectroscopy and X-ray absorption near-edge Structure spectroscopy techniques. The synthesis procedure leads to the formation of a spinel structure with an average crystallite size of 9.0(9) nm. The morphology of the particles synthetized under an inert atmosphere was quasi-spherical, while the nanoparticles prepared in air present a faceted shape. The small differences observed in morphological properties are explained by the influence of the reaction atmosphere on the formation mechanism of the MNPs. The magnetic characterization indicates that both samples exhibit superparamagnetic behavior at 300 K. The investigation by means of the Langevin approach at 300 K also leads to equal values for the mean size of the magnetic cores (D_m). Additionally, the analysis of the Mössbauer spectra revealed the lack of spin disorder for both samples, resulting in a high saturation magnetization. The fit of XANES spectrum suggests that about 2/3 of the iron ions reside in a local environment close to that of γ-Fe₂O₃ and about 1/3 close to that of Fe₃O₄ for the sample synthetized in inert atmosphere.

Cobalt ferrite nanoparticles of different stoichiometries synthesized by a sol–gel autocombustion method were used as a starting material to obtain high-moment Fe₅₀Co₅₀ and Fe₆₆Co₃₄ metal nanoparticles by topochemical hydrogen reduction. Structural and magnetic investigations confirmed the formation of FeCo nanoparticles with crystallite sizes of about 30 nm and magnetization at 0.5 T of ~265 Am²/kg (0 K), which was larger than the expected bulk value, likely because of the incorporation in the body-centered cubic (bcc) FeCo structure of the residual C atoms present on the surface of the oxide particles. Temperature-dependent magnetization measurements in the H₂ atmosphere were also performed to investigate in detail the reduction mechanism and the effect of an external magnetic field on the process efficiency.

Hybrid materials that integrate photonic and magnetic functionalities are a major focus of next-generation nanotechnology, but their scalable production remains a significant challenge. Here, we present a facile strategy to produce hybrid photonic microparticles by coassembling poly-(styrene)-b-poly-(2-vinylpyridine) (PS-P2VP) block copolymers with 10 nm cobalt ferrite nanoparticles within emulsion droplets. This method allows the formation of highly ordered, hierarchical, onion-like structures with alternating concentric layers. Selective localization of the nanoparticles within P2VP domains preserves the periodicity essential for structural coloration while introducing tunable magnetic properties. Optical characterization confirms that the microparticles exhibit a vivid blue structural color and maintain a well-defined photonic bandgap up to a critical nanoparticle concentration, after which the structural order is disrupted. Remarkably, the nanostructure order of the polymer matrix induces a partial alignment of the magnetic easy axis of the nanoparticles, increasing the thermal stability of the magnetization (i.e., increase in the reduced remanent magnetization). This distinctive synergy between photonic and magnetic properties establishes a platform for multifunctional materials with potential applications in magnetically tunable photonic devices, advanced sensors, and responsive materials. The results demonstrate a scalable and versatile approach to fusing photonic architectures with functional nanomaterials, providing design opportunities for next-generation hybrid materials.

The sun bathes our planet with far more energy than humankind will possibly ever need (> 8,000 times the current demand). Yet, sustainable energy provision is among the most pressing challenges faced today. In order to unlock the vast potential of clean solar energy, we need disruptive technologies capable of efficiently harvesting sunlight, while being deployable at unprecedented scales. Available commercial photovoltaics (PV) can hardly cope sustainably with the sheer scale of this challenge. Silicon solar panels are the major commercial PV, they are based on a very Earth-abundant element, but their fabrication is extremely energy intensive. Conversely, thin film solar panels based on CdTe and Cu(In,Ga)Se2 (CIGS) require far less energy to produce, but some of their constituent elements are quite rare on the Earth’s crust. Hence, in both cases, the short term economic and ecologic sustainabilities are dubious. Recently, an advanced PV concept, called microconcentrator PV [1], has been conceived, which is free from raw materials availability constraints and is based on sunlight absorbers requiring low energy to grow. Additionally, semi-transparent panels could be created, consisting of stripes having width on the order of 100 micrometers [2]. To demonstrate such advanced PV concepts at laboratory scale, research groups have been using optical projection lithography (OPL), generating arrays of Cu(In,Ga)Se2 circles with tens of micrometer diameter. However, OPL cannot be scaled credibly to terawatt deployment. Industrial uptake of microconcentrator PV is only possible with a technique that ensures both high semiconductor quality, and high throughput at capital expenditure comparable to or lower than currently available PVs. Inspired by the research of Gary Friedman on ferrofluid lithography [3], a disrupting microfabrication technique is being pursued within REMAP [5], and e-APP projects [6]. Our intent is to pioneer a method that could be scaled economically to deploy terawatts of microconcentrator or semi-transparent PV [4]. Herein, we outline the progress made on the formulation of magnetorheological electrolytes: bifunctional fluids intended for effective reusable masking, from synthesis to application. Acknowledgements The Authors acknowledge funding from the European Commission PathFinder Open programme under grant agreement No. 101046909 (REMAP, reusable mask patterning). This work was also supported by the European Union and by the Italian Ministry of University and Research through the Clean Energy Transition Partnership scheme under grant agreement No. 2022-00327 (TRANSMIT, semi-transparent micro-striped thin-film photovoltaics for energy-harvesting windows). This work was supported in part by the Italian Ministry of Foreign Affairs and International Cooperation under grant agreement No. PGR11541 (e-APP, empowering advanced photovoltaic pioneers). Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Innovation Council and SME Executive Agency (EISMEA). Neither the European Union nor the granting authority can be held responsible for them. References [1] M. Alves, A. Pérez-Rodríguez, P. J. Dale, C. Domínguez, and S. Sadewasser, ‘Thin-film micro-concentrator solar cells’, J. Phys. Energy, vol. 2, 012001, 2019, doi: 10.1088/2515-7655/ab4289. [2] TRANSMIT. Semi-transparent micro-stripped thin-film photovoltaics for energy-harvesting windows. https://transmit.squarespace.com/about [3] B. B. Yellen, G. Fridman, and G. Friedman, ‘Ferrofluid lithography’, Nanotechnology, vol. 15, S562–S565, 2004, doi: 10.1088/0957-4484/15/10/011. [4] D . Colombara, ‘Method for patterning a surface of a substrate’ 2019. Available: https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2020136057 [5] REMAP. Reusable mask patterning. https://re-map.eu/ [6] e-APP. Empowering advanced photovoltaic pioneers. https://project-maeci.netlify.app/