Ferrites (spinel structure, MFe2O4) are one of the richest and most studied oxide groups due to their multiple and interesting physical properties and wide applications. Particularly, Zn2+Fe3+2 O4 has been largely studied but its magnetic structure is still unresolved. To contribute to the understanding of its magnetic nature we present here a theoretical study of the role of defects (oxygen vacancies, cationic inversion) on the magnetic interactions in Znferrite. ZnFe2O4 adopts the normal spinel structure where Zn2+ cations are placed at the 8a tetrahedral (A) sites and Fe3+ populates the 16d octahedral (B) sites. Using first-principles calculations based on Density Functional Theory (DFT) and the supercell approach, the energy of multiple magnetic configurations for reduced (ZnFe2O4-b), partially inverted, (Zn1-xFex)[ZnxFe2-x]O4, and partially inverted and reduced, (Zn1-xFex)[ZnxFe2-x]O4-b, Znferrite were calculated and then mapped to a classical Heisenberg spin model to obtain the magnetic exchange couplings Jn up to fifth neighbours. Compared with pristine and normal ZnFe2O4, where the interactions Fe(site B)-Fe(site B) up to fifth neighbours (JBBi) are antiferromagnetic, in the case of ZnFe2O4-b the interaction at second neighbours is ferromagnetic. In the case of (Zn1-xFex)[Fe2-xZnx]O4 and (Zn1-xFex)[ZnxFe2-x]O4-b the interactions Fe(site A)-Fe(site B) resulted to be significantly stronger than iJBB. Moreover, the first-neighbour interaction is predicted to be ferromagnetic, while at second neighbours it is antiferromagnetic and dominant. Our results show that ZnFe2O4 constitutes a delicate magnetic system, where competing magnetic interactions can be easily affected by defects and highlight its crucial role in promoting different magnetic responses, enabling us to explain the ferrimagnetic response observed at room-temperature in ZnFe2O4 nanoparticles and thin films.

MgFe₂O₄ nanoparticles synthesized by a simple autocombustion method were assessed as magnetically recoverable catalysts for the degradation of methylene blue (MB) in water. The NPs exhibit a crystallite size of 9 nm, a band gap of 2.11 eV, and soft ferrimagnetic behavior, enabling efficient photocatalytic and Fenton-like activity. The effects of irradiation, H₂O₂ concentration, agitation mode, catalyst loading, and exposure time were systematically evaluated. Rapid and complete MB discoloration was achieved within minutes in the presence of H₂O₂, even without illumination, indicating that the process is dominated by a surface-mediated heterogeneous Fenton-like mechanism rather than photocatalysis. Kinetic analysis reveals pseudo-first-order behavior, with rate constants governed by the combined effects of catalyst concentration, oxidant dosage, and dye concentration. Structural stability and excellent recyclability confirm the robustness of the catalyst. These findings position MgFe₂O₄ nanoparticles as a low-cost, efficient, and reusable material for sustainable wastewater under operationally simple conditions.

Ab initio total energy calculations were performed to study the adsorption of atomic hydrogen on the polar surface of Zn-ZnO(0001) for different degrees of surface coverage. The most stable configuration was calculated as a function of the distance between H and the surface. The present results show that the manifest ferromagnetism depends on purely surface interactions. It involves charge transfer from the H-1s level to the Zn-4s level, leading to a magnetic moment of 1.0 mu B for full H surface coverage in the supercell. The magnetic interaction between H atoms is ferromagnetic. In addition, for a fully hydrogenated ZnO monolayer with zinc vacancies (VZn) or hydrogen-passivated zinc vacancies (VZn-H), a transition from a nonmagnetic semiconductor to a magnetic half-metal semiconductor has been achieved. Both configurations exhibit a surface magnetic moment of 2.0 mu B, which is twice that obtained for the case without the vacancy. These theoretical calculations agree with our previously published experimental results, where it was observed that hydrogen is incorporated into the ZnO structure and acts as a surface donor.

Molecular diagnostic methods to detect and quantify viral RNA in clinical samples rely on the purification of the genetic material prior to reverse transcription polymerase chain reaction (qRT-PCR). Due to the large number of samples processed in clinical laboratories, automation has become a necessity in order to increase method processivity and maximize throughput per unit of time. An attractive option for isolating viral RNA is based on the magnetic solid phase separation procedure (MSPS) using magnetic microparticles. This method offers the advantage over other alternative methods of making it possible to automate the process. In this study, we report the results of the MSPS method based on magnetic microparticles obtained by a simple synthesis process, to purify RNA from oro- and nasopharyngeal swab samples of patients suspected of COVID-19 provided by three diagnostic laboratories located in the Buenos Aires Province, Argentina. Magnetite nanoparticles of Fe3O4 (MNPs) were synthesized by the coprecipitation method and then coated with silica (SiO2) produced by hydrolysis of tetraethyl orthosilicate (TEOS). After preliminary tests on samples from the A549 human lung cell line and swabs, an extraction protocol was developed. The quantity and purity of the RNA obtained were determined by gel electrophoresis, spectrophotometry, and qRT-PCR. Tests on samples from naso- and oropharyngeal swabs were performed in order to validate the method for RNA purification in high-throughput SARS-CoV-2 diagnosis by qRT-PCR. The method was compared to the spin columns method and the automated method using commercial magnetic particles. The results show that the method developed is efficient for RNA extraction from nasal and oropharyngeal swab samples, and also comparable to other extraction methods in terms of sensitivity for SARS-CoV-2 detection. Of note, this procedure and reagents developed locally were intended to overcome the shortage of imported diagnostic supplies as the sudden spread of COVID-19 required unexpected quantities of nucleic acid isolation and diagnostic kits worldwide.

Maghemite's properties for roles as removable and reusable catalysts or photocatalysts in reactions that promote green chemistry can be enhanced by doping with other metals. We investigated nanostructured aluminum-doped magnetic iron(III) oxides (AlxFe2-xO3, x = 0.33, 0.67, and 1) synthesized via the autocombustion method and characterized using various techniques. These materials were tested as photocatalysts for methylene blue dye degradation without peroxide and as catalysts for the thermal decomposition of ammonium nitrate. The results revealed that the cubic spinel structure predominates in all compositions. Aluminum doping led to decreased cell parameters and grain size and loss of microgranular structure. Saturation magnetization decreased with aluminum doping, reaching a low value (similar to 2 emu/g) for x = 1. The optical band gaps were red-shifted with respect to pure maghemite, with values near 2 eV. Among compositions, x = 0.33 showed the best photocatalytic efficiency, closely matching incident light energy (1.95 eV). The highest degradation efficiency was around 37 % after 80 min. The catalytic effect on ammonium nitrate decomposition was strongly correlated with aluminum concentration, turning the reaction exothermic with energy release of 200 and 400 J/g for x = 0.33 and 0.67, respectively.

In this work we present a combined theoretical and experimental study of the structural, magnetic, and hyperfine properties of Fe doped and (Fe, Sn) co-doped SrTiO3 perovskite (STO). 57Fe-Mössbauer spectroscopy (57Fe-MS) was employed to determine the hyperfine interactions at the Fe sites of doped STO for different Fe and Sn concentrations. The theoretical study was performed in the framework of the Density Functional Theory (DFT) using the full-potential linearized augmented plane wave (FP-LAPW) method. The effect of the oxygen vacancies on the magnetic and hyperfine properties and on the magnetic alignment of Fe and Sn impurities was studied. The combination of the DFT calculations, considering different structural models for doped-STO, and 57Fe-MS enable us to obtain a structural characterization of Fe-doped and (Fe, Sn) co-doped STO and to explain the origin of the observed hyperfine interactions and the magnetic signal.

We present an investigation of a nanostructured Fe-Al-O system with x = Al/Al + Fe ratios of 0.17, 0.33 and 0.50, prepared by the autocombustion method. The main phase found in all samples is the cubic spinel phase. The inclusion of Al in the spinel structure resulted in a progressive decrease in both the cell parameter and the grain size, with the former approaching the cell parameter of maghemite rather than magnetite. Although the XRD patterns match those reported for AlFe2O4, Mössbauer spectroscopy and magnetic measurements allows us to determine that the formed spinel phase can be identified as Al-doped maghemite-like Fe2-yAlyO3. The room temperature Mössbauer spectrum of sample x = 0.17 consists of magnetic components belonging to iron at the iron (III) oxide spinel sites, plus a central doublet. For higher Al content, the relative area of the magnetic components decreases, and the spectra mainly consists of a Fe3+ broad doublet corresponding to superparamagnetic iron (III) oxide particles. The 13 K spectrum of x = 0.33 sample (nominally AlFe2O4) is mainly composed of magnetic sites belonging to blocked particle moments of Al-doped maghemite-like particles. The magnetization loops are consistent with a ferro/ferrimagnetic behaviour, whose saturation magnetization decreases with the incorporation of Al.

In this work, the structural, electronic, magnetic, and hyperfine properties of two Fe-Al spinel oxides, namely FeAl2O4 (hercynite) and Fe2AlO4 (Al-ferrite) were studied by means of Density Functional Theory (DFT)-based first principles calculations. To determine the structural and magnetic equilibrium structures of both oxides, different cationic inversion degrees, magnetic configurations and distributions were considered for Fe and Al ions in the octahedral and tetrahedral sites of the spinel structures. Calculations confirmed the preference of the Al ions to occupy the octahedral cationic sites and predicted that both Fe-Al spinel oxides present a semiconductor nature. They also enabled the determination that the lowest energy structure of FeAl2O4 corresponds to an antiferromagnetic normal spinel, in which Fe2+ ions populate the tetrahedral sites and Al+3 ions occupy the octahedral B sites. Partial inversion cases are also discussed for this system. The lowest energy structure of Fe2AlO4 corresponds to a system with a net magnetic moment in which eight Fe+2 ions populate the A sites and eight Fe3+ and eight Al3+ ions populate the B sites. It was also shown that FeAl2O4 presents a lower formation energy than Fe2AlO4. By comparing the predictions for the hyperfine parameters at the Fe sites with the experimental results obtained in the Mössbauer experiments, the validity of the proposed structural and magnetic structure of FeAl2O4 was confirmed. Finally, a discussion is made to compare the results of this study with the Mössbauer results reported in the literature for Fe2AlO4.

Nanostructured aluminium-doped magnetic iron (III) oxide (AlxFe2-xO3 with x= 0.33, 0.67 and 1) have been prepared by autocombustion method. The as-prepared samples were characterized by XRD, thermogravimetric analysis, UV-vis and Mössbauer spectroscopies and magnetometry. The cubic spinel is the main crystalline phase for all compositions. The presence of Al in the spinel phase causes a progressive decrease in both the cell parameter (a) and the grain size (L). The room temperature Mössbauer spectrum of x= 0.33 is mainly composed of a Fe3+ broad sextet while, for higher Al content, the spectra consist of a Fe3+ broad doublet corresponding to superparamagnetic maghemite. The saturation magnetization decreases with the Al doping and reaches a rather low value for the ill-crystalline sample x = 1 (MS ~ 2 emu/g). The optical direct band gap of the samples is red-shifted with respect to pure maghemite, with values close to 2 eV. The photocatalytic performance of AlxFe2-xO3 tested in the decolorization of methylene blue dye showed a good efficiency for the oxide whose band gap energy best matches the energy of the incident light (x= 0.33). The catalytic effect of these samples on the thermal decomposition of ammonium nitrate is more noticeable for those Al concentrations that lead to the reaction being exothermic.

In this work, we report direct evidence of ferromagnetism in hydrogenated ZnO sub-micrometric powders. Hydrogen (H-2) was incorporated under a high-pressure heat treatment in a sealed reactor. Ferromagnetism at room temperature can be activated and deactivated by annealing in H-2 and air atmospheres, respectively. Hydrogen incorporation in ZnO structure was observed from X-ray absorption near-edge structure spectra where hydrogen acts as a shallow donor transferring electrons to the conduction band (Zn 4s). The Raman measurements evidence clear distortions in chemical environments of Zn atoms associated with defect formation. Our results suggest that magnetism is a superficial phenomenon probably related to the surface bonding of hydrogen to Zn (or O) on polar ZnO surfaces.

Ammonium nitrate (NH4NO3) represents a cheap, chlorine-free alternative to ammonium perchlorate for use as an oxidant for solid propellants. But its poor ignitability and low burning rate are all disadvantages to achieve such purposes. For this reason, it is necessary to carry out studies to improve its combustion characteristics, seeking to combine it with catalysts or fuels. The present work explores the possibility of improving its combustion characteristics by adding ferrites as catalysts. Nanostructured ferrites MFe2O4 (M = Mg, Co, Cu, and Zn) synthesized by autocombustion method were tested as catalysts for the thermal decomposition reaction of ammonium nitrate under open, partially open or sealed conditions. The ferrites were characterized by XRD, SEM, UV-vis spectrophotometry and Mossbauer spectroscopy. All the MFe2O4 samples are single phased with a cubic spinel structure and average sizes, L , ranging from about 9 (CoFe2O4) to 25 nm (CuFe2O4). The catalytic effect of MFe2O4 on the thermal decomposition of NH4NO3 was investigated by thermogravimetric analysis and differential scanning calorimetry techniques. The process was also followed in a volumetric Sieverts type apparatus. The results indicate that only under sealed conditions the addition of these ferrites has influence in the decomposition process of AN. The incorporation of any of these ferrites decreases the onset temperature of the process manifested itself through an exothermic reaction, and also increases the amount of heat released in the reaction. The Co-ferrite showed the best efficiency causing the onset temperature to drop around 60 & DEG;C. The catalytic performance is correlated with the electronegativity of M 2 + cations, which act as Lewis acid sites that interact with the gas molecules.

In this work we present an experimental and theoretical study of the magnetic and hyperfine properties of (Fe, Co) co-doped rutile SnO2 (FexCoySn1-x-yO2). Ab initio calculations were performed in the framework of the Density Functional Theory (DFT) using the full-potential linearized augmented plane wave (FP-LAPW) method. The effect of the oxygen vacancies on the magnetic and hyperfine properties and on the magnetic alignment of Fe and Co impurities was studied considering different vacancy concentrations and distributions in the host. Our calculations predicted that the Fe and Co impurities tend to be located as close as possible and favors the generation of oxygen vacancies, forming a pair of magnetic impurities sharing oxygen vacancies with an antiparallel spin alignment, giving rise to a ferrimagnetic entity. Ab initio predictions were compared with experimental results: magnetization curves obtained by vibrating sample magnetometry (VSM) at room temperature and Mössbauer spectroscopy (MS) studies obtained for SnO2 samples doped with 1.0% of Fe and co-doped with Co concentrations ranging from 0.0 to 0.5%, grown by sol-gel and thermal decomposition method. The comparison enabled us to identify the observed hyperfine interactions in MS experiments and characterize the local structure around the Fe atoms unambiguously. Finally, based on our theoretical results for the lowest energy Fe–Fe, Fe–Co and Co–Co magnetic configurations we can understand and reproduce the experimental behavior obtained by VSM measurements of the saturation magnetization (MS) (similar to the magnetic moment per magnetic atom) as a function of the Co concentration.

Nanostructured MgFe2O4 ferrites of crystallite sizes 7 -16 nm synthesized by either autocombustion or polymerization methods were employed as catalysts in the degradation of methylene blue (MB) dye under dark and light irradiation conditions. The Mg-ferrites were characterized by XRD, atomic absorption, SEM, BET surface, thermograyimetric analysis, Mossbauer spectroscopy and magnetometry. All the catalysts can be described as hybrid composites of Mg-ferrites (with a 1:2 Mg:Fe ratio) and residual organic compounds coming from the precursors, whose band gap energy is in the visible region (E-g similar to 2.3 eV). The magnetic responses at ambient temperature correspond to a soft material composed by the combination of superparamagnetic and blocked particle moments. The degradation of MB occurs under both dark and light conditions only when the catalyst is incorporated to the aqueous solution. The largest degradation efficiency percentages (PDE%) achieved after an interval of 35 min are around 60 and 75 % under dark and light conditions, respectively. In the presence of visible light, the efficiency of the catalysts is enhanced in a percentage that depends on the surface area of the ferrite particles. The role of organic residues as well as the exposed surface area in the catalytic process are analysed.

Magnetic nanoparticles have been synthesized on mesoporous silica by a simple method without the need for either an alkali or an organic solvent, nor for rigorous pH control, making it a safe procedure for the nanomedicine field. The systems have been exhaustively characterized through different instrumental techniques, including the analysis of physicochemical properties by N2 adsorption, TEM, HAADF/STEM, SAED, EDS, XRD, XPS, and UV/Vis DRS. Magnetic properties have been tested by means of magnetization curves at room temperature and 5 K, ZFC-FC curves, and Mössbauer spectroscopy. The nanocomposite obtained by heating in N2 atmosphere showed good specific surface area and structural order, as well as high magnetization and negligible magnetic hysteresis and remanence, arising from the presence of finely dispersed magnetite nanospecies. These features are very relevant for future application as carriers for drug delivery systems, among other uses.

We present a Density Functional Theory (DFT) based study of the structural and magnetic properties of the (001) surface of the semiconducting oxide ZnFe2O4 (spinel structure). The calculations were performed using the DFT based ab initio plane wave and pseudopotential method as implemented in the Quantum Espresso code. The all electron Full-potential linearized-augmented-plane-wave method (FP-LAPW) was also employed to check the reproducibility of the plane wave method. In both calculations the DFT + U methodology was employed and different (001) surface terminations of ZnFe2O4 were studied. We find that the surface terminated in Zn is the stable one. For all the (001) surface terminations our calculations predict that the Zn-Fe cationic inversion (antisites), which are defects in bulk ZnFe2O4, becomes stable and an integral part of the surface. Also, a ferri-magnetic behavior is predicted for the case of anti-sites in the superficial layer. Our results for different properties of the surface of ZnFe2O4 are compared with those obtained in bulk samples and those reported in the literature.

Background: Mandibular condyle fractures account for 9–45% of all mandibular fractures. The treatment for these fractures is diverse, 2 methods are mainly used: open or surgical reduction with internal fixation and closed or functional reduction with maxillomandibular fixation and mandibular dynamic exercises. Within open reduction for mandibular condylar fracture treatment, there are different surgical techniques, one of them is endoscopic assisted open reduction and internal fixation (EAORIF), this surgical technique is a minimally invasive technique, provides excellent visibility about structures involved, facilitating correct reduction, segments alignment and reducing surgical procedure morbidity.

Durante las ultimas dos decadas varios trabajos han reportado la aparicion de ordenamiento magnetico a temperatura ambiente en oxidos semiconductores dopados con iones magneticos. Sin embargo, ahora se acepta que el origen del estado magneticamente ordenado en oxidos semiconductores diluidos esta relacionado con la formacion de defectos estructurales y/o agregados ionicos, que no son necesariamente magneticos, fenomeno llamado magnetismo inducido por defectos (DIM). Se ha demostrado teoricamente que es posible el orden magnetico en solidos intrinsecamente no magneticos debido a la influencia del hidrogeno, y se ha observado experimentalmente en grafito asi como en muestras de ZnO no dopado y dopado. Trabajos publicados recientemente demostraron que el tratamiento con plasma de hidrogeno a bajas energias de implantacion (300 eV) y temperaturas relativamente bajas (T 700 K) puede desencadenar el orden magnetico a temperatura ambiente en monocristales de ZnO despues de la implantacion de H atomico a bajas concentraciones. En este trabajo presentamos el desarrollo de una camara de implantacion de iones de Ar+H2 producidos en un plasma remoto de corriente directa (DC). Fueron implantadas capas delgadas de ZnO obtenidas por RF-Magnetron Sputtering. Analizamos la relacion existente entre la formacion de defectos estructurales, condiciones de deposito de las peliculas delgadas y propiedades magneticas.

We present a numerical study of the magnetic properties of ZnFe2O4 using Monte-Carlo simulations performed considering a Heisenberg model with antiferromagnetic couplings determined by Density Functional Theory. Our calculations predict that the magnetic susceptibility has a cusp-like peak centered at 13 K, and follows a Curie-Weiss behavior above this temperature with a high and negative Curie-Weiss temperature ( Θ C W = - 170 K). These results agree with the experimental data once extrinsic contributions that give rise to the deviation from a Curie-Weiss law are discounted. Additionally, we discuss the spin configuration of ZnFe2O4 below its ordering temperature, where the system presents a high degeneracy.

We present here an experimental and theoretical study of the Ti-ferrite (TiFe2O4, ulvospinel). The theoretical study was performed in the framework of density functional theory using the full-potential linearized augmented plane waves method and employing different approximations for the exchange and correlation potential. In order to discuss the magnetic ordering and the electronic structure of the system, we considered different distributions of the Fe/Ti atoms in the two cationic sites of the structure and, for each distribution, different spin arrangements (ferromagnetic, ferrimagnetic and antiferromagnetic cases). We found that the equilibrium structure corresponds to an inverted spinel structure with an antiferromagnetic spin configuration in which the magnetic moments of the Fe ions in both A and B sublattices are ferromagnetically ordered, while the magnetizations of these two sublattices are antiparallel with respect to each other. Our calculations predict that TiFe2O4 is a wide-band gap semiconductor (band gap in the order of 2.3 eV) and successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field, and quadrupole splitting) at the Fe sites that are seen by Mossbauer spectroscopy (MS) experiments at 4.2 K reported in the literature and MS performed at 300 K in the present study. We also measured and simulated the X-ray absorption near-edge spectroscopy (XANES) spectra of TiFe2O4 at both Ti and Fe K-edges. Our calculations correctly reproduce the XANES spectra and enable us to separate the contribution of each site to the experimental spectra. All these studies enable us to obtain a complete structural, electronic, magnetic, and hyperfine characterization of TiFe2O4.

In this work the effects of defects (oxygen vacancies, cationic inversion) on the structural, electronic and the magnetic response of the spinel ZnFe2O4(ZFO) are studied by using a density functional theory (DFT) based ab initio method (the Full-Potential Linearized Augmented Plane Waves plus Local Orbitals, LAPW+lo) on the framework of the Generalized Gradient Approximation plus U (GGA+U) level. The changes induced by the defects in the hyperfine interactions at the Fe sites of the structure are also presented. In order to discuss the magnetic ordering and the electronic structure of the system we considered different spin arrangements. We found that, similar to the normal and pristine case, reduced and partially inverted ZFO presents an energy landscape characterized by a large number of metastable states. Our calculations successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field and quadrupole splitting) at the Fe sites that are seen by Mossbauer Spectrocopy (MS) at 4 and 300 K, enabling us to characterize the local structure around Fe atoms. Our LAPW+lo predictions also demonstrate the relevance of both oxygen vacancies and antisites (cationic inversion) in the formation of local ferromagnetic coupling between Fe ions, giving rise to a ferrimagnetic ordering in an otherwise antiferromagnetic compound. This results support conclusions based in experimental results obtained in x-ray magnetic circular dichroism and magnetization measurements performed on zinc ferrites with different cation distributions and oxygen vacancy concentrations reported in the literature. (C) 2018 Elsevier B.V. All rights reserved.