Determination of the blocking temperature of magnetic nanoparticles: The good, the bad, and the ugly

A numerically solved two-level Stoner-Wohlfarth model with thermal agitation is used to simulate Zero Field Cooling (ZFC)-Field Cooling (FC) curves of monosize and polysize samples and to determine the best method for obtaining a representative blocking temperature TB value of polysize samples. The results confirm a technique based on the T derivative of the difference between ZFC and FC curves proposed by Micha et al. (the good) and demonstrate its relation with two alternative methods: the ZFC maximum (the bad) and the inflection point (the ugly). The derivative method is then applied to experimental data, obtaining the TB distribution of a polysize Fe3O4 nanoparticle sample suspended in hexane with an excellent agreement with TEM characterization

Oxygen-vacancy-induced local ferromagnetism as a driving mechanism in enhancing the magnetic response of ferrites

This work probes the relevance of oxygen vacancies in the formation of local ferromagnetic coupling between Fe ions at octahedral sites in zinc ferrites. This coupling gives rise to a ferrimagnetic ordering with the Curie temperatures above room temperature in an otherwise antiferromagnetic compound. This conclusion is based on experimental results from x-raymagnetic circular dichroismmeasurements at the Fe L2,3 edges and magnetization measurements performed on zinc ferrites, nanoparticles, and films, with different cation distributions and oxygen vacancy concentrations. Our observations are confirmed by density-functional-theory calculations and indicate that the enhanced ferrimagnetic response observed in some nominally nonmagnetic or antiferromagnetic ferrites can be taken as a further example of the defect-induced magnetism phenomenon.Fil: RodrÍguez Torres, Claudia Elena. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. 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; ArgentinaFil: Pasquevich, Gustavo Alberto. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. 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; ArgentinaFil: Mendoza Zélis, Pedro. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. 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; ArgentinaFil: Golmar, Federico. CIC Nanogune; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pérez, Silvia Inés. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Nayak, Sanjeev K.. Martin Luther University Halle-Wittenberg; AlemaniaFil: Adeagbo, Waheed A.. Martin Luther University Halle-Wittenberg; AlemaniaFil: Hergebert, Wolfram. Martin Luther University Halle-Wittenberg; AlemaniaFil: Hoffmann, Martin. Martin Luther University Halle-Wittenberg; Alemania. Institut Max Planck of Microstructure Physics; AlemaniaFil: Ernst, Arthur. Institut Max Planck of Microstructure Physics; AlemaniaFil: Esquinazi, P.. University of Leipzig; AlemaniaFil: Stewart, Silvana Jacqueline. 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 Ciencias Exactas. Departamento de Física; Argentin

Dipolar interactions among magnetic dipoles of iron oxide particles dispersed in mili-size hydrogel beads

The recently published Mean Field Interacting Superparamagnet Model (MFISP model), which introduces the effective demagnetizing factor NE, is tested in specimens having a random-like spatial distribution of magnetic nanoparticles, where different hierarchies of clustering are present. These specimens are ferrogel PVA/iron oxide beads synthesized by a one-pot route, having spheroidal shapes and sizes of about 1 mm, and chain and disk-like arrays (superstructures) of beads. Raman analyses indicated that magnetic nanoparticles are composed by a mixture of magnetite and maghemite. Beads swell 208% by hydration in about 40 min. The increase of the ac susceptibility as a function of hydration time closely reflects the effect of bead swelling, in agreement with the expected diminution of dipole–dipole interactions. Measured susceptibility is analyzed in terms of the susceptibility ? of non-interacting particles and the effective demagnetizing factor NE of the specimen, which depends on swelling. The Specific Absorption Rate of electromagnetic power by the beads grows with the hydration time in agreement with ac susceptibility behavior. For long hydration times susceptibility and high field magnetization decrease. This is explained by the occurrence of oxidation of magnetite/maghemite to hematite. Isothermal magnetization experiments are performed on each superstructure in two perpendicular principal directions each. Results are consistently described with the MFISP model by considering two hierarchies of clustering: beads themselves and clusters within the beads. From the whole set of experiments, it is possible to estimate values for the volume fractions of particles in clusters and clusters in beads, given by xpc=0.46(15) and xcb=0.16(5). The susceptibility of non-interacting particles, ?=13(4), is also obtained, which results about five times larger than the measured (apparent) one. The MFISP model proves to be a convenient and efficient tool for the analysis of magnetization studies of complex 3d dispersions of magnetic nanoparticles, allowing an experimental determination of relevant physical information, otherwise not accessible by magnetic measurements. © 2020 Elsevier B.V

Magnetic nanocomposites based on shape memory polyurethanes

CNPEN - CENTRO NACIONAL DE PESQUISA EM ENERGIA E MATERIAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOShape memory composites based on a commercial segmented polyurethane and magnetite (Fe3O4) nanoparticles (MNPs) were prepared by a simple suspension casting method. The average sizes of individual magnetic particles/clusters were determined by TEM microscopy and corroborated from SAXS patterns. The magnetization properties of selected samples were evaluated using zero field cooling/field cooling (ZFC/FC) measurements and magnetization loops obtained at different temperatures. The results showed that magnetization at high field (20 k Oe) and coercitivity measured at 5 K increase with magnetite content and that all the composite films exhibit superparamagnetic behavior at 300 K. The specific absorption rate (SAR) of the nanocomposites was calculated by experimentally determining both the specific heat capacity and the heating rate of the films exposed to an alternant magnetic field. All nanocomposites were able to increase their temperature when exposed to an alternant magnetic field, although the final temperature reached resulted dependent of the MNPs concentration. What is more, a fast and almost complete recovery of the original shape of the nanocomposites containing more than 3 nominal wt.% MNP was obtained by this remote activation applied to the previously deformed samples.109815CNPEN - CENTRO NACIONAL DE PESQUISA EM ENERGIA E MATERIAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCNPEN - CENTRO NACIONAL DE PESQUISA EM ENERGIA E MATERIAISFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOME -223452011-12356303236/2017-5Agências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

Small-angle X-ray scattering to quantify the incorporation and analyze the disposition of magnetic nanoparticles inside cells

Access to detailed information on cells loaded with nanoparticles with nanoscale precision is of a long-standing interest in many areas of nanomedicine. In this context, designing a single experiment able to provide statistical mean data from a large number of living unsectioned cells concerning information on the nanoparticle size and aggregation inside cell endosomes and accurate nanoparticle cell up-take is of paramount importance. Small-angle X-ray scattering (SAXS) is presented here as a tool to achieve such relevant data. Experiments were carried out in cultures of B16F0 murine melanoma and A549 human lung adenocarcinoma cell lines loaded with various iron oxide nanostructures displaying distinctive structural characteristics. Five systems of water-dispersible magnetic nanoparticles (MNP) of different size, polydispersity and morphology were analyzed, namely, nearly monodisperse MNP with 11 and 13 nm mean size coated with meso-2,3-dimercaptosuccinic acid, more polydisperse 6 nm colloids coated with citric acid and two nanoflowers (NF) systems of 24 and 27 nm in size resulting from the aggregation of 8 nm MNP. Up-take was determined for each system using B16F0 cells. Here we show that SAXS pattern provides high resolution information on nanoparticles disposition inside endosomes of the cytoplasm through the structure factor analysis, on nanoparticles size and dispersity after their incorporation by the cell and on up-take quantification from the extrapolation of the intensity in absolute scale to null scattering vector. We also report on the cell culture preparation to reach sensitivity for the observation of MNP inside cell endosomes using high brightness SAXS synchrotron source. Our results show that SAXS can become a valuable tool for analyzing MNP in cells and tissues.This work was supported by Conicet PIP 0897 and 567, UNLP x807 and UBACYT 20020130100673A and we kindly thank Brazilian Synchrotron Light Laboratory (Proposals: SAXS1-14429, SAXS2-22014, SAXS1-20160237, Campinas-Brazil, Universidad Nacional de La Plata-Argentina, and CONICET-Argentina. We thanks Maria del Puerto Morales for usefull discussion. The group of IFLP thanks Instituto de Investigaciones Bioquímicas de La Plata INIBIOLP Patología B - CONICET for allowing the use of cell culture lab, help in cell culture handling and kind suggestions on biological issues and Y-TEC S. A. for the use of TEM TALOS F200X under the supervision of A. Floridia and A. Caneiro. M. E. F. Brollo acknowledges the Brazilian agency CNPq for the grant [232947/2014-7] within the Science without Borders program A.R acknowledges financial support from the Spanish Ministry of Science and Innovation through the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (CEX2019-000917-S). M. B. Fernández van Raap, P. C. Setton-Avruj and P. Mendoza Zélis, are members of CONICET, and P. A. Soto is a fellow of CONICET, Argentina.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe