Epitaxial stabilization of ε-Fe2O3 (00l) thin films on SrTiO3 (111)

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Thin films of the metastable and elusive ε-Fe2O3 have been epitaxially stabilized on SrTiO3 (111) substrates. The ε-Fe2O3 films present a (001) orientation perpendicular to the substrate and three in-plane domains measuring a few nanometers and showing atomically sharp interfaces. We argue that this domain structure, rather than the epitaxial-strain, plays an essential role in stabilizing the ε-Fe2O3 by minimizing the energy of (100) surfaces. The ε-Fe2O3 films show a large in-plane coercivity ∼ 8 kOe which combined with the magnetoelectric character claimed for this oxide may lead to novel applications in spintronics

Unveiling a New High-Temperature Ordered Magnetic Phase in ϵ-Fe2O3

Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-FeO is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-FeO nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2' magnetic symmetry, but only involving two of the four Fe sublattices which are ordered below T ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-FeO with a critical temperature of T ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-FeO may open the door to further expand the working range of this multifunctional iron oxide

Magnetic Mesoporous Silica Nanorods Loaded with Ceria and Functionalized with Fluorophores for Multimodal Imaging

Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol-gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-FeO) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assesse

Prevalence and seasonality of viral respiratory infections in a temperate climate region : A 24-year study (1997-2020)

Background: Few long-term reports have been published on the epidemiology of respiratory viruses despite their frequent involvement in extremely common infections. The aim here was to determine the frequency and distribution of respiratory viruses in a temperate climate area (Barcelona, Spain) throughout a 24-year period. Methods: We collected data on all respiratory viruses detected from 1997 to 2020 in our institution. Clinical specimens were analyzed mainly by conventional techniques, and molecular techniques were also used. Results: Of the 59,579 specimens analyzed, 21,382 (35.9%) were positive for at least one virus. The number of positive samples during cold months was significantly higher than in warm months. Respiratory virus infections were detected in patients of all ages, above all in children under 3 years of age, who were most frequently infected with the respiratory syncytial virus, whereas Influenza A virus predominated in the other groups, especially in adults. A clear demographic and seasonal pattern was established for some viruses. Circulation of other respiratory viruses during the FLUAV H1N1pdm09 and SARS-CoV-2 pandemics was observed. Conclusions: This long-term study provides new knowledge about the prevalence of respiratory viruses in a Mediterranean region. Throughout the study period, the frequency of some viruses remained constant, whereas others varied with the year. A clear demographic and seasonal pattern was established for some viruses. Patients suffering from severe respiratory infections should be examined for a range of respiratory viruses regardless of gender, age, or season

High-temperature magnetic properties of epsilon-Fe2O3

Resumen del póster presentado a la 61st Annual Conference on Magnetism and Magnetic Materials, celebrada en New Orleans, Louisiana (US) del 31 de octubre al 4 de noviembre de 2016.The epsilon-Fe2O3 phase is attracting great interest after the discovery of a huge coercivity (20kOe), magnetoelectric response and multiferroicity. These appealing physical properties stem from a complex structure, with four Fe3+ sublattices, and are also related to the existence of a substantial spin-orbit coupling. So, its complex structure favours magnetic frustration and successive magnetic and structural transitions. The collinear ferrimagnetic phase (Tc=500K) is substituted by two different incommensurate magnetic orderings on cooling below 150K and 110K respectively. In this work we have investigated the magnetic and structural properties of epsilon-Fe2O3 between room temperature and 925 K by means of magnetic, synchrotron and neutron diffraction measurements. The diffraction experiments were performed using high-resolution powder diffractometers at ALBA synchrotron and ILL neutron reactor. Upon heating, the saturation magnetization undergoes a monotonical decrease but the coercivity and remanence sharply drop between 480 and 500 K, as the net ordered ferromagnetic component. Above Tc=500K the compound is not paramagnetic but exhibit partial magnetic ordering with Pna'21' magnetic symmetry up to temperatures as high as 870 K. In contrast to its superhard behavior below 500 K, epsilon-Fe2O3 was found to exhibit soft magnetic properties in the high-temperature magnetic phase. Concurrent with this transition from superhard to soft ferrimagnetism, lattice anomalies indicating magnetostriction effects have been observed and described.We thank financial support from MINECO under projects MAT2012-38213-C02-02 and MAT2015-68760-C2-2-P, cofunded by ERDF from EU.Peer Reviewe

Unveiling a New High-Temperature Ordered Magnetic Phase in ϵ-Fe2O3

Iron oxides are among the most abundant materials on Earth, and yet there are some of their basic properties which are still not well-established. Here, we present temperature-dependent magnetic, X-ray, and neutron diffraction measurements refuting the current belief that the magnetic ordering temperature of ϵ-FeO is ∼500 K, i.e., well below that of other iron oxides such as hematite, magnetite, or maghemite. Upon heating from room temperature, the ϵ-FeO nanoparticles' saturation magnetization undergoes a monotonic decrease while the coercivity and remanence sharply drop, virtually vanishing around ∼500 K. However, above that temperature the hysteresis loops present a nonlinear response with finite coercivity, making evident signs of ferrimagnetic order up to temperatures as high as 850 K (T). The neutron diffraction study confirms the presence of ferrimagnetic order well above 500 K with Pna'2' magnetic symmetry, but only involving two of the four Fe sublattices which are ordered below T ≈ 480 K, and with a reduced net ferromagnetic component, that vanishes at above 850 K. The results unambiguously show the presence of a high-temperature magnetic phase in ϵ-FeO with a critical temperature of T ∼ 850 K. Importantly, this temperature is similar to the Curie point in other iron oxides, indicating comparable magnetic coupling strengths. The presence of diverse magnetic phases is further supported by the nonmonotonic evolution of the thermal expansion. The existence of a high-temperature ferrimagnetic phase in ϵ-FeO may open the door to further expand the working range of this multifunctional iron oxide

Magnetic properties of Cr-substituted ε-(Fe1-xCrx)2O3 nanoparticles with epsilon structure

ε-Fe2O3 has gained considerable interest due to its intriguing properties and great application potentials. In this work ε-(Fe1−xCrx)2O3 (x = 0, 0.03, 0.075) nanoparticles encapsulated in silica have been successfully prepared by sol–gel chemistry. Synchrotron diffraction confirms that the polar Pna21 structure of ε-Fe2O3 is robust against the substitution of Fe by Cr. The incorporation of chromium is accompanied by a softer magnetic behaviour, and also a gradual decrease in the ferromagnetic signal associated to the super-hard FM2 ferrimagnetic phase. While the Cr substitution has little impact on the low temperature incommensurate transition, it is found that Cr substitution shifts the super-hard and soft ferrimagnetic transitions (respectively, TN2 and TN1) to notably lower temperatures.This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. [819623]). We also acknowledge financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MINCIU), through Project No. RTI2018-098537-B-C21, cofunded by ERDF from EU, and “Severo Ochoa” Programme for Centres of Excellence in R&D (Grant No. SEV-2015-0496) and from Generalitat de Catalunya through the projects 2017SGR00765 and 2017SGR1632. Z.M. was financially supported by China Scholarship Council (CSC) with No. 201606070094. Z.M’s work was done as a part of the Ph.D program in Materials Science at Universitat Autònoma de Barcelona. We also acknowledge ALBA synchrotron (exp. No. 2018093113) for provision of beam time.Peer reviewe