Coupled structural and magnetic properties of ferric fluoride nanostructures: part II, a Monte-Carlo Heisenberg study

We present a numerical study of the magnetic structure of nanostructured iron fluoride, using the Monte-Carlo-Metropolis simulated annealing technique and a classical Heisenberg Hamiltonian with a superexchange angle dependence. The parameters are adjusted on experimental results, and the atomic structure and topology taken from a previous atomistic model of grain boundaries in the same system. We find perfect antiferromagnetic crystalline grains and a disordered magnetic configuration (speromagnetic like) at the grain boundary, in agreement with experimental findings. Both the lowest magnetic energy and the rate of magnetic frustration are found to be dependent on the relative disorientation of crystalline grains, i.e. on the cationic topology. By simulating hysteresis loops, we find that the magnetization rotation is not spatially uniform. We conclude on possible extensions of the model.Comment: submitted to JMM

Rheological, Microstructural and Thermal Properties of Magnetic Poly(Ethylene Oxide)/Iron Oxide Nanocomposite Hydrogels Synthesized Using a One-Step Gamma-Irradiation Method

Magnetic polymer gels are a new promising class of nanocomposite gels. In this work, magnetic PEO/iron oxide nanocomposite hydrogels were synthesized using the one-step γ-irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) precursor alkaline aqueous suspensions followed by simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. γ-irradiation dose and concentrations of Fe3+, 2-propanol and PEO in the initial suspensions were varied and optimized. With 2-propanol and at high doses magnetic gels with embedded magnetite nanoparticles were obtained, as confirmed by XRD, SEM and Mössbauer spectrometry. The quantitative determination of γ-irradiation generated Fe2+ was performed using the 1, 10-phenanthroline method. The maximal Fe2+ molar fraction of 0.55 was achieved at 300 kGy, pH = 12 and initial 5% of Fe3+. The DSC and rheological measurements confirmed the formation of a well-structured network. The thermal and rheological properties of gels depended on the dose, PEO concentration and initial Fe3+ content (amount of nanoparticles synthesized inside gels). More amorphous and stronger gels were formed at higher dose and higher nanoparticle content. The properties of synthesized gels were determined by the presence of magnetic iron oxide nanoparticles, which acted as reinforcing agents and additional crosslinkers of PEO chains thus facilitating the one-step gel formation

New iron tetrazolate frameworks : synthesis temperature effect, thermal behaviour, Mössbauer and magnetic studies

The exploration of the FeF3/FeF2-Hamtetraz-HF system in dimethylformamide by solvothermal synthesis evidences two isostructural 3D hybrid fluoroferrates. They are prepared from the same starting mixture at two different synthesis temperatures: 120 °C for [Hdma]·(Fe4IIFeIIIF8(H2O)2(amtetraz)4) (1) and 140 °C for [Hdma]1.5·(Fe4.5IIFe0.5IIIF7(H2O)(HCOO)(amtetraz)4) (2). Both compounds are characterized by single crystal X-ray diffraction, X-ray thermodiffraction, TGA analysis, Mössbauer spectrometry and SQUID magnetometry. They crystallize in the monoclinic system and are built from two distinct chains connected by aminotetrazolate anions. The first chain ∞(FeIIFN4) is common to 1 and 2 and can be found in numerous fluorides. In the second chain ∞(Fe3X12) (X = F, N, O), iron cations adopt both valence states Fe(II)/Fe(III). The hydrolysis of DMF implies the formation of a [Hdma]+ cation and a (HCOO)− anion. The presence of Fe3+ in both phases is evidenced by 57Fe Mössbauer spectrometry. The magnetic properties are studied and two transitions from a paramagnetic regime to a long range ordered state below 30 K and 5 K are identified.PostprintPeer reviewe

Unravelling the corrosion processes at steel/bentonite nterfaces in in situ tests

Microscopic and spectroscopic analyses were conducted on steel/bentonite interface samples removed from four in situ experiments that were carried out in three underground research laboratories at different temperatures and under different hydraulic and geochemical conditions. The results provide valuable information about the corrosion processes occurring in high-level radioactive waste repositories. Systematic patterns can be deduced from the results, irrespective of carbon steel grade, type of bentonite and its degree of compaction, geochemical environment or experimental setup. Thus, a clear dependence of the corrosion rates on temperature and exposure period, as well as on the availability of H2O and O2 provided by the surrounding bentonite buffer, is observed. Furthermore, Fe(II) ions released by corrosion interact with the structural Fe in the clay. Recent developments highlight the usefulness of reactive transport modelling in understanding the coupled corrosion and Fe–clay interaction processes

Unveiling the role of surface, size, shape and defects of iron oxide nanoparticles for theranostic applications

Iron oxide nanoparticles (IONPs) are well-known contrast agents for MRI for a wide range of sizes and shapes. Their use as theranostic agents requires a better understanding of their magnetic hyperthermia properties and also the design of a biocompatible coating ensuring their stealth and a good biodistribution to allow targeting of specific diseases. Here, biocompatible IONPs of two different shapes (spherical and octopod) were designed and tested in vitro and in vivo to evaluate their abilities as high-end theranostic agents. IONPs featured a dendron coating that was shown to provide anti-fouling properties and a small hydrodynamic size favoring an in vivo circulation of the dendronized IONPs. While dendronized nanospheres of about 22 nm size revealed good combined theranostic properties (r2 = 303 mM s−1, SAR = 395 W gFe−1), octopods with a mean size of 18 nm displayed unprecedented characteristics to simultaneously act as MRI contrast agents and magnetic hyperthermia agents (r2 = 405 mM s−1, SAR = 950 W gFe−1). The extensive structural and magnetic characterization of the two dendronized IONPs reveals clear shape, surface and defect effects explaining their high performance. The octopods seem to induce unusual surface effects evidenced by different characterization techniques while the nanospheres show high internal defects favoring Néel relaxation for magnetic hyperthermia. The study of octopods with different sizes showed that Néel relaxation dominates at sizes below 20 nm while the Brownian one occurs at higher sizes. In vitro experiments demonstrated that the magnetic heating capability of octopods occurs especially at low frequencies. The coupling of a small amount of glucose on dendronized octopods succeeded in internalizing them and showing an effect of MH on tumor growth. All measurements evidenced a particular signature of octopods, which is attributed to higher anisotropy, surface effects and/or magnetic field inhomogeneity induced by tips. This approach aiming at an analysis of the structure–property relationships is important to design efficient theranostic nanoparticles.The Region Alsace, France, and the Labex Chimie des Systemes Complexes, University of Strasbourg, France are gratefully acknowledged for the doctoral fellowship to Geoffrey Cotin. This research project was also co-funded by Labex CSC, Alsace contre le cancer, INCA (project PRTK14, THERAMAG 2014-225) and the INTERREG project NANOTRANSMED. The “NANOTRANSMED” project is co-funded by the European Regional Development Fund (ERDF) and by the Swiss Confederation and the Swiss cantons of Aargau, Basel-Landschaft and Basel-Stadt, in the framework of the INTERREG V Upper Rhine program (“Transcending borders with every project”). The authors thank Morgane Rabineau for epifluorescence imaging and Nadia Messaddeq for TEM imaging of cells. The authors thank the Center for Microscopy and Molecular Imaging (CMMI, supported by the European Regional Development Fund and the Walloon Region). This work was supported by the Fond National de la Recherche Scientifique (FNRS), UIAP VII, ARC Programs of the French Community of Belgium and the Walloon region (Gadolymph and Holocancer programs). All the authors acknowledge the COST action TD1402 “RADIOMAG”. D. Ortega and F. J. Teran acknowledge support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686), the Spanish Ministry of Economy and Competitiveness for the NANOLICO project (MAT2017-85617-R), the Spanish Ministry of Science through the NaNoCAR grant PID2020-117544RB-I00, the Ramón y Cajal grant RYC2018-025253-I and Research Networks grant RED2018-102626-T, the HEATOOLS project (BIO2017-84246-C2-1-R), the Comunidad de Madrid for grant NANOMAGCOST (P2018/NMT-4321), DGA for public funding from Fondo Social (grupos DGA), and the European Commission for the funding received through the H2020 “NoCanTher” project (GA No. 685795).Peer reviewe

Co genetic Cr-bearing tourmaline and emerald in the Novo Cruzeiro pegmatite field (Minas Gerais, Brazil)

The Novo Cruzeiro pegmatite field in Minas Gerais (Brazil), located between Téofilo Otoni and the Jequitinhonha River, belongs to the areas of the EBPP with tourmaline and emerald occurrences. The pegmatites show beside of coloured tourmalines, Cr-rich black tourmaline cogenetic with Cr-bearing emerald. General crystallization conditions of pegmatites show, based on the obtained data, important changes during the final phase of tourmaline crystallisation which caused variations in tourmaline chemistry and reflects differences in the chemistry of the participating fluids. The crystallization of tourmaline ceased and after a period of co-crystallization, emerald was the only formed mineral. The obtained information suggests a crystallization sequence from tourmaline over tourmaline+emerald to emerald. A part of B and Fe may come from the host rock, Be and B from the intrusive granites and Cr from regional mafic to ultramafic rocks like amphibolite or Bt-Qz-schist