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A co-precipitation synthesis method was used to obtain iron oxide nanoparticles coated with Yerba Mate (Ilex paraguariensis) extract. These particles have a core–shell structure with the iron oxide phase surrounded by an organic shell provided by an organic component which come from the Yerba Mate extract. Obtained nanoparticles were exhaustively characterized as powders and in aqueous colloidal suspensions using several techniques such as TEM, XRD, SAXS, TGA, ATR-FTIR, Raman and XPS spectroscopy, magnetic moment measurement and specimen ac susceptibility. All results together show that the obtained particles are single-crystal iron oxide particles with magnetite as the most probable phase. Yerba Mate extract shell mass to iron oxide core mass, mS/mc, could be increased up to 6.2 × 10−2, depending on the synthesis conditions. As a function of mS/mc the crystallite size of the nanoparticles decreased from about 15 nm to 11 nm, while saturation magnetization Ms and coercive field Hc of powders decreased. Ms. diminution was associated to increasing modification of core surface electronic states due to chemical bond of iron in iron oxide to Yerba Mate extract components; on the other hand, coercivity reduction was modelled on the basis of the increasing interparticle separation and dipolar interaction weakening, which occurs as shell thickness grows. Differences between the particle core mean size obtained with TEM, SAXS, XRD and magnetic measurements are observed. The fact that magnetic size was smaller than particle and crystallite sizes was attributed to the existence of intense dipolar interactions. It was found that low field susceptibility in a colloid sample was about 2.5 times that of the powder specimen, a result that shows that demagnetizing effects prevail in the powder specimen, while they may be absent in the colloid due to the larger interparticle mean separation expected in the latter. Analysis of powder and colloid susceptibility was done based on a recently developed model was in agreement with the one performed for the coercive field behaviour. Fil: Mercado Castro, Donaldo Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Cipollone, Mariano Enrique. YPF - Tecnología; Argentina Fil: González, Mónica C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Sánchez, Francisco Homero. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina

Scientific and technological researches are devoted to obtain materials capable of retaining different kinds of pollutants, contributing to contamination solutions. In this context, hydrogels have emerged as great candidates because of their excellent absorption properties as well as good mechanical, thermal and chemical properties. More specifically, ferrogels (magnetic gels) present the extra advantage of being easily manipulated by a permanent magnet. Here, we present the results derived from the application of ferrogels as efficient tools to extract heavy metal pollutants from wastewater samples. The gels were prepared following the method of freezing and thawing of a polyvinyl alcohol aqueous solution with magnetic nanoparticles coated with polyacrylic acid. Ferrogels were fully characterized and their ability to retain Cu2+ and Cd2+, as model heavy metals, was studied. Thus kinetics and mechanisms of adsorption were evaluated and modeled. The concentration of MNPs on the PVA matrix was key to improve the adsorption capability (approximately the double of retention is improved by the MNPs addition). The adsorption kinetics was determined as pseudo-second order model, whereas the Langmuir model was the most appropriate to explain the behavior of the gels. Finally reuse ability was evaluated to determine the real potential of these materials, the ferrogels demonstrated high efficiency up to about five cycles, retaining about 80–90% of their initial adsorption capability. All the results indicated that the materials are promising candidates able to compete with the commercial technology regarding to water remediation. Fil: Areal, Maria Pia. Universidad Nacional de Mar del Plata; Argentina Fil: Arciniegas Vaca, Magda Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Horst, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Lassalle, Verónica Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Sánchez, Francisco Homero. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina Fil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Gonzalez, Jimena Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

Magnetic hyperthermia, a modality that uses radio frequency heating assisted with single-domain magnetic nanoparticles, is becoming established as a powerful oncological therapy. Much improvement in nanomaterials development, to enhance their heating efficiency by tuning the magnetic colloidal properties, has been achieved. However, methodological standardization to accurately and univocally determine the colloidal properties required to numerically reproduce a specific heating efficiency using analytical expressions still holds. Thus, anticipating the hyperthermic performances of magnetic colloids entails high complexity due to polydispersity, aggregation and dipolar interactions always present in real materials to a greater or lesser degree. Here, by numerically simulating the experimental results and using real biomedical aqueous colloids, we analyse and compare several approaches to reproduce experimental specific absorption rate values. Then, we show that the relaxation time, determined using a representative mean activation energy consistently derived from four independent experiments accurately reproduces experimental heating efficiencies. Moreover, the so-derived relaxation time can be used to extrapolate the heating performance of the magnetic nanoparticles to the other field conditions within the framework of the linear response theory. We thus present a practical tool that may truly aid the design of medical decisions., Facultad de Ciencias Exactas, Instituto de Física La Plata

We present a simple, scalable, and low-cost route for producing aqueous colloids of nanometer size Fe cores coated with iron oxide and stabilized with sodium citrate. The Fe cores were obtained by mechanosynthesis by means of a highly exothermic solid-state reaction between FeCl3 and Mg, in a dispersive inert NaCl medium. The optimal experimental conditions for achieving a full reaction were determined with a Retsch 2000 oscillatory mill. Then the production yield was successfully 16-fold scaled using a rotatory Fritsch Pulverissete 7 mill. To provide biocompatibility and facilitate colloid stabilization, the Fe cores were coated with a Fe-oxide shell produced by chemical coprecipitation, and finally, the system Fe/FeOx was functionalized with sodium citrate in water. The so-obtained Fe/FeOx@Cit (4/3

A comprehensive study of relevant aspects of the physics behind in vitro magnetic assisted transfection, or magnetofection is presented. Magnetofection experiments were performed as a function of culture-magnet distance for a fixed time of 30 min, as a function of time for a fixed separation of about 1 mm, and under special geometries chosen to elucidate the relative effects of gravitational and magnetic forces. It is shown that under appropriate conditions, in vitro magnetofection can be performed with almost equal easiness in any desired space direction, even against gravity. Redistribution of magnetic nanoparticles in a colloid, with an initial uniform distribution, was studied with the same experimental setup used in magnetofection experiments, as a function of time, and as a function of culture-magnet relative position. It was found that magnetic nanoparticles tend to arrange into concentrated regions with ring or circle shapes, and that final distribution depends strongly on relative position. Cellular uptake of magnetic nanoparticles was estimated for standard magnetofection and for no applied magnetic field experiments. A consistent description of results is given by comparing magnetofection efficiency, nanoparticles uptake and redistribution experiments. The results presented here constitute novel information that will contribute to gaining deeper understanding of how magnetofection proceeds and how can be improved. They impact directly on in vivo procedures, providing conceptual tools to optimize setup geometry and magnetic field application time.

A model describing the effect of magnetic dipolar interactions on the susceptibility of magnetic nanopillars is presented. It is an extension of a recently reported model for three-dimensional randomlike dispersions of nearly spherical nanoparticles in equilibrium [Sánchez et al., Phys. Rev. B 95, 134421 (2017)2469-995010.1103/PhysRevB.95.134421], to well-ordered arrays of nanoparticles out of equilibrium. To test it, a high-quality benchmark consisting of a two-dimensional hexagonal arrangement of quasi-identical parallel nickel nanopillars embedded in a porous alumina template was fabricated. This model is based on an effective demagnetizing tensor, which only depends on a few morphological parameters of the sample, as the nearest-neighbor distance between pillars and the volume fraction of pillars in the specimen. It allows us to obtain the nanopillar intrinsic susceptibility tensor from the magnetic response of the nanopillar ensemble. The values of the in-plane and normal-to-plane susceptibility of the sample are successfully predicted by the model. Furthermore, the model reproduces the susceptibility in the applied field direction, measured for different applied field angles. In this way, it provides a simple and accurate treatment to account for the complex magnetic effects produced by dipolar interactions., Facultad de Ciencias Exactas, Instituto de Física La Plata

Element-And site-specific magnetic hysteresis-loops measurements on a zinc ferrite (ZnFe2O4) thin film were performed by X-ray magnetic circular dichroism. Results show that iron in octahedral and tetrahedral sites of spinel structure are coupled antiferromagnetically between them, and when magnetic field is applied the magnetic moment of the ion located at octahedral sites aligns along the field direction. The magnetic measurements reveal a distinctive response of the surface with in-plane anisotropy and an effective anisotropy constant value of 12.6 kJ/m3. This effective anisotropy is due to the combining effects of demagnetizing field and, volume and surface magnetic anisotropies KV =3.1 kJ/m3 and KS =16 μJ/m2. Fil: Mendoza Zélis, Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; Argentina Fil: Pasquevich, Gustavo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; Argentina Fil: Salcedo Rodriguez, Karen Lizeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina Fil: Sánchez, Francisco Homero. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina Fil: RodrÍguez Torres, Claudia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina

Iron silicides were produced by 100-keV $^{57}\mathrm{Fe}$ implantation at room temperature into Si(100), followed by 500-keV Si beam irradiation at 593 K to induce epitaxial crystallization. The iron concentration was varied between 4 and 28 at. %. The M\"ossbauer spectra associated with $^{57}\mathrm{Fe}$ probes can be described by means of a broad quadrupole interaction distribution. After thermal treatments at temperatures up to 793 K the spectra become narrower and quadrupole distribution gets closer to that of \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$. The fitted interactions are discussed in terms of those of \ensuremath{\gamma}-${\mathrm{FeSi}}_{2}$, \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$, and \ensuremath{\alpha}-${\mathrm{FeSi}}_{2}$ phases which have been observed by high-resolution transmission electron microscopy. Low-temperature measurements of \ensuremath{\gamma}-${\mathrm{FeSi}}_{2}$ precipitates prepared by the ion-beam-induced epitaxial crystallization route do not confirm the reported occurrence of magnetic ordering in this system, above 4.2 K. \textcopyright{} 1996 The American Physical Society.