Using density functional theory, we study the lattice dynamical properties of magnetite (Fe3O4) in the high-temperature cubic and low-temperature monoclinic phases. The calculated phonon dispersion curves and density of states are compared with the available experimental data obtained by inelastic neutron, inelastic x-ray, and nuclear inelastic scattering. We find a very good agreement between the theoretical and experimental results for the monoclinic Cc structure revealing the strong coupling between the charge-orbital (trimeron) order and specific phonon modes. For the cubic phase, clear discrepancies arise due to fluctuation effects, which are not included in the calculation method. Despite this shortcoming, we argue that the main spectral features can be understood assuming that the strong trimeron-phonon coupling is extended above the Verwey transition, with lattice dynamics influenced by the short-range order instead of the average cubic structure. Our results indicate the validity of trimerons (and trimeron-phonon coupling) to explain the physics of magnetite much beyond their original formulation.

Magneto-plasmonic nanoparticles constituted of gold and iron oxide were obtained in an aqueous environment by laser ablation of iron and gold targets in two successive steps. Gold nanoparticles are embedded in a mucilaginous matrix of iron oxide, which was identified as magnetite by both microscopic and spectroscopic analyses. The plasmonic properties of the obtained colloids, as well as their adsorption capability, were tested by surface-enhanced Raman scattering (SERS) spectroscopy using 2,2 '-bipyridine as a probe molecule. DFT calculations allowed for obtaining information on the adsorption of the ligand molecules that strongly interact with positively charged surface active sites of the gold nanoparticles, thus providing efficient SERS enhancement. The presence of iron oxide gives the bimetallic colloid new possibilities of adsorption in addition to those inherent to gold nanoparticles, especially regarding organic pollutants and heavy metals, allowing to remove them from the aqueous environment by applying a magnetic field. Moreover, these nanoparticles, thanks to their low toxicity, are potentially useful not only in the field of sensors, but also for biomedical applications.

Ferromagnetic and ferrimagnetic nanoparticles (NPs) represent one of the most investigated nanomaterial, due to their unique properties and to their wide range of applications like biomedicine, environmental remediation, electromagnetic shielding and other electronic applications (i.e. sensing). Most of the physico-chemical properties of magnetic NPs depends critically on their morphology, therefore in order to design suitable magnetic NPs for a specific application, it is mandatory to achieve a good control not only of their chemical composition, but also of their size and shape. The chapter describes the main wet-chemistry synthesis of magnetic NPs reported in literature. It will focus on the recent development of methods able to control of the size and the shape of the magnetic NPs, highlighting the key parameters able to influence the morphology at the nanoscale. In particular, the chapter will present the methods to control size and shape of magnetic NPs composed of metal, metal alloy and ferrimagnetic iron oxides.

The outstanding relevance of catalysis in stereoselective synthesis is established by the huge number of methodologies developed in order to obtain enantiopure molecules. Supporting enantiopure ligands onto magnetic nanoparticles (MNPs) constitutes a successful strategy in the field of stereoselective synthesis for several reasons. The high surface/mass ratio of the MNPs and the location of the catalytic moieties on the MNP surface does not impede mass transfer. Furthermore, The MNP-supported catalyst can be easily dispersed in and separated from the reaction mixture. Among the many types of MNPs, cubic ferrite MFe2O4 (M = Fe, Mn, Ni, Co, Cu) NPs are particularly suited since they are dispersible but insoluble in all solvents, chemically stable and usually inert. This chapter focuses on stereoselective organic reactions catalysed by MNP-supported chiral nanocatalysts affording enantiopure molecules. Rather than a comprehensive review of the field, the present chapter was shaped as a critical assessment of recent achievements. First, the structural and functional variety of the chiral MNP-supported catalysts are described with brief considerations about the nanocatalyst synthesis. The next section is devoted to the important and complex field of the characterization of MNP-supported chiral nanocatalysts where it is emphasised that the identity, mutual organization, and relative amount of all components of the MNP-supported chiral nanocatalysts need to be known to successfully rationalize the design and performance of catalysts. Thus, their characterization requires a large but rewarding effort. Finally, the stereoselective organic transformations achieved by using MNP-supported chiral nanocatalysts are reviewed according to the reaction type. The use of these nanocatalysts has grown into a successful methodology at the disposal of the organic chemist for the obtainment of small organic molecules in the enantiopure form. Emphasis was given on the comparison with the free or otherwise supported catalyst. The key points behind such success is that (i) all MNP-supported catalysts can be quickly and completely recovered by the application of an external magnet, and (ii) the catalytic performance is often good and sometimes rivals with well-established homogeneous catalysts. A successful asymmetric transformation involving a MNP-supported catalysts is actually the result of the understanding at a multidisciplinary level, involving organic chemistry, physical chemistry and nanoscience. The ongoing interest in this field makes us certain that in the near future an even wider variety of asymmetric organic reactions will be successfully carried out by this methodology.

Head and neck squamous cell carcinomas (HNSCC) are a diverse group of tumors with high morbidity and mortality that have remained mostly unchanged over the past decades. The epidermal growth factor receptor (EGFR) is often overexpressed and activated in these tumors and strongly contributes to their pathogenesis. Still, EGFR-targeted therapies such as monoclonal antibodies and kinase inhibitors have demonstrated only limited improvements in the clinical outcome of this disease. Here, we take advantage of the extraordinary affinity of EGF for its cognate receptor to specifically target magnetite-containing nanoparticles to HNSCC cells and mediate, in vitro, their cellular upload. On the basis of this, we show efficient accumulation, in vivo, of such nanoparticles in subcutaneous xenograft tumor tissues in sufficient amounts to be able to mediate visualization by magnetic resonance imaging. Overall, our EGF-coated nanosystem may warrant, in the near future, novel and very efficient theranostic approaches to HNSCC.

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe3O4) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions.

We present inelastic neutron scattering data across the Verwey transition in magnetite, obtained for a single crystal via a detwinning method. We provide direct evidence of the influence of the charge order on the transverse-acoustic phonons, associated with discontinuous hardening and narrowing at the transition temperature, and energy splitting for different polarizations. This contrasts with the behavior of the transverse-optical X3 mode, which does not present any critical anomaly, contrary to theoretical expectations. Our data indicate that the incommensurate fluctuations occurring above the critical temperature become locked to the lattice at the transition point, through a mechanism similar to the crystallization of a two-dimensional liquid on a solid surface. Our results also contribute to clarify the different dynamics and mutual interactions of the electronic and structural modes in the Verwey transition. © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Recent studies of CO2 sorption on low-cost metal oxides strongly encourage their use as sorbents [Alfè, PROCI, 2015] in CO2 capture and storage (CCS) strategies. Magnetite (Fe3O4, FM) and CO2 interaction proceeds through acid-base interactions involving unsaturated metal and O sites exposed on FM surface. The FM sorption capacity is lowered by the tendency of magnetite particles to agglomerate causing a decrease of the exposed surface area. The dispersion of magnetic particles on carbon-based solid matrices has been proposed to face this limitation. Thanks to their low-cost, high surface area and porosity, carbonized biomasses are good candidates for supporting FM phase. Rice husk (RH) is an agricultural residue abundantly available in rice producing countries, obtained during the milling of paddy (22 wt. % of the weight of unmilled rice is received as husk). It presents a high ash content, which is 92 to 95% silica, highly porosity and a high surface area. RH is a green material that has a great potential for technological applications since it can be converted to different types of fuels and chemical feedstocks through a variety of thermochemical conversion processes. Following the same approach presented in our previous works on the CO2 capture performances of FM supported on a carbon-based reference material (carbon black) [Alfè, PROCI, 2015; Gargiulo, App. Surf. Sci. 2016], the synthesis and characterization of RH/FM composite materials were performed. A set of RH/FM composites were produced by varying the amount of carbonized RH from 20 to 80 wt.% in order to optimize the sorbent properties for CO2 adsorption applications. Preliminary data about the CO2 sorption capacity were also obtained.

Based on the most recent scientific results on intriguing capability of some animals to orient with respect to the hearth magnetic field, two possible candidate material classes have been individuated to be developed. Magnetite nanoparticles composites would be the best candidate materials to be develop in optical sensor.

Fe3-?O4/MgO/Co magnetic tunnel junctions (MTJs) are synthesized on top of ~1 inch Si/SiO2 substrates by conducting a full in situ chemical vapour and atomic layer deposition process with no vacuum break. Tunnel magnetoresistance up to 6% is measured at room temperature, increasing to 12.5% at 120 K. Our results demonstrate the possibility of using full-chemical processes to synthesize functional MTJs, and this could provide a path towards the use of cost-effective methods to produce magnetic devices on a large scale.

Metal oxide nanoparticles, hybridized with various polymeric chemicals, represent a novel and breakthrough application in drug delivery, hyperthermia treatment and imaging techniques. Radiolabeling of these nanoformulations can result in new and attractive dual-imaging agents as well as provide accurate in vivo information on their biodistribution profile. In this paper a comparison study has been made between two of the most promising hybrid core-shell nanosystems, bearing either magnetite (Fe3O4) or cobalt ferrite (CoFe2O4) cores, regarding their magnetic, radiolabeling, hyperthermic and biodistribution properties. While hyperthermic properties were found to be affected by the metal-core type, the radiolabeling ability and the in vivo fate of the nanoformulations seem to depend critically on the size and the shell composition.

n this work laser derusting and passivation process of iron objects of conservation interest were investigated. In particular, the effects induced by laser irradiation of three lasers with different temporal emission regimes were studied, exhibiting very different behavior. Nd:YAG(1064 nm) laser systems were employed in the experiments: a Q-Switching laser with pulse duration of 8 ns, a Long Q-Switching laser with pulse duration of 120 ns and a Short Free Running pulse duration in a range of 40-120 ?s. These lasers are commonly used in conservation. Lasers treatments were applied on iron samples subjected to natural weathering in outdoor conditions for about five years. Moreover some experiments were also performed on metallic parts of an original chandelier from the seventies as well as on a deeply corroded Roman sword. Results obtained reveals that longer pulse duration leads to phase changes on the rust layer and a homogeneous black-grayish coating is formed on the surface (identified as magnetite) after treatment. Whereas, QS laser pulses are capable to induce ablation of the corrosion layer exposing the pure metal underneath. Finally, LQS interaction includes deep ablation with localized micro-melting of the metal surface and partial transformation of the residual mineral areas was observed. The irradiation results were characterized through optical and BS- ESEM along with Raman spectroscopy, which allowed a clear phenomenological differentiation among the three operating regimes and provided information on their optimal exploitation in restoration of iron artifacts.

Based on ab initio density functional calculations, we have investigated the validity of the recently proposed "intermediate site/bond-centered charge ordering'' in insulating magnetite, Fe3O4. It is found that, although the FeB2+/FeB3+ bond dimerization along the monoclinic b direction leads to local electric dipole moments, the latter are arranged in an antiferroelectric fashion in the P2/c and Cc crystal structures. Our results, based on the generalized gradient approximation plus Hubbard U (GGA+U) and Berry phase methods, clearly indicate that for the P2/c crystal structure the FeB2+/FeB3+ bond dimerization and the local electric dipole moments are suppressed at large U values. This shows that local electric dipole moments in magnetite with the P2/c symmetry are induced by the "intermediate site/bond-centered charge ordering''.

Optical plastics filled by nano-sized magnetic particles may have relevant applications in magneto-optics. Here, an in-situ method for the preparation of magnetic nanoparticles embedded in polystyrene by thermal decomposition of it-on mercaptide is described. Transparent ferromagnetic and superparamagnetic nanocomposites have been produced using iron (II) and iron (III) mercaptides. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2774-2777, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24733

We report on the growth of magnetite films directly on thin layers of organic semiconductors by means of an electron beam ablation method. The deposition was performed at room temperature in a reactive plasma atmosphere. Thin films show ferromagnetic (FM) hysteresis loops and coercive fields of hundreds of Oersted. Micro Raman analysis indicates no presence of spurious phases. The morphology of the magnetite film is strongly influenced by the morphology of the underlayer of the organic semiconductor. These results open the way for the application of magnetite thin films in the field of organic spintronics. (c) 2007 Elsevier B.V. All rights reserved.