Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3−xO4 nanoparticles

We report a systematic study on the structural and magnetic properties of CoxFe3−xO4 magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac)3 and Co(acac)2. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < TB < 345 K for 5 < d < 13 nm) and large coercive fields (HC ≈ 1600 kA/m for T = 5 K). The smallest particles (⟨d⟩=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Neel–Arrhenius relaxation framework by including the thermal dependence of the magnetocrystalline anisotropy constant K1(T), without the need of ad-hoc corrections. This approach, using the empirical Brükhatov-Kirensky relation, provided K1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (τ0 ≈ 10−10s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener's relation between K1(T) and M(T).This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO, Project Nos. MAT2010-19326 and MAT2013-42551).Peer Reviewe

Influence of the substrate and precursor on the magnetic and magneto-transport properties in magnetite films

We have investigated the magnetic and transport properties of nanoscaled Fe3O4 films obtained from Chemical Vapor Deposition (CVD) technique using [FeIIFe2III(OBut)8] and [Fe2III(OBut)6] precursors. Samples were deposited on different substrates (i.e., MgO (001), MgAl2O4 (001) and Al2O3 (0001)) with thicknesses varying from 50 to 350 nm. Atomic Force Microscopy analysis indicated a granular nature of the samples, irrespective of the synthesis conditions (precursor and deposition temperature, Tpre) and substrate. Despite the similar morphology of the films, magnetic and transport properties were found to depend on the precursor used for deposition. Using [FeIIFe2III(OBut)8] as precursor resulted in lower resistivity, higher MS and a sharper magnetization decrease at the Verwey transition (TV). The temperature dependence of resistivity was found to depend on the precursor and Tpre. We found that the transport is dominated by the density of antiferromagnetic antiphase boundaries (AF-APB's) when [FeIIFe2III(OBut)8] precursor and Tpre = 363 K are used. On the other hand, grain boundary-scattering seems to be the main mechanism when [Fe2III(OBut)6] is used. The Magnetoresistance (MR(H)) displayed an approximate linear behavior in the high field regime (H > 796 kA/m), with a maximum value at room-temperature of \sim2-3% for H = 1592 kA/m, irrespective from the transport mechanism.Comment: 19 pages, 9 figure

Effect of temperature and copper doping on the heterogeneous Fenton-like activity of Cux_xFe3−x_{3-x}O4_4 nanoparticles

Ferrite nanoparticles serve as potent heterogeneous Fenton-like catalysts, producing reactive oxygen species (ROS) for decomposing organic pollutants. We investigated the impact of temperature and copper content on the catalytic activity of nanoparticles with different oxidation states of iron. Via solvothermal synthesis, we fabricated copper-doped magnetite (Cu$_x$Fe$_{3-x}$O$_4$) with a Fe$^{2+}$/Fe ratio ~0.33 for the undoped system. Using a microwave-assisted method, we produced copper-doped oxidized ferrites, yielding a Fe$^{2+}$/Fe ratio of ~0.11 for the undoped nanoparticles. The ROS generated by the catalyst were identified and quantified by electron paramagnetic resonance, while optical spectroscopy allowed us to evaluate its effectiveness for the degradation of a model organic dye. At room temperature, the magnetite nanoparticles exhibited the most $\cdot$OH radical production and achieved almost 90% dye discoloration in 2 hours. This efficiency decreased with increasing Cu concentration, concurrently with a decrease in $\cdot$OH generation. Conversely, above room temperature, Cu-doped nanoparticles significantly enhance the dye degradation, reaching 100% discoloration at 90$^\circ$C. This enhancement is accompanied by a systematic increase in the kinetic constants, obtained from reaction equations, with Cu doping. This study highlights the superior stability and high-temperature catalytic advantages of copper ferrite holding promise for enhancing the performance of nanocatalysts for decomposing organic contaminants.Comment: 40 pages, 11 figure

Onion-like Fe3O4/MgO/CoFe2O4 magnetic nanoparticles: new ways to control magnetic coupling between soft/hard phases

The control of the magnetization inversion dynamics is one of the main challenges driving the design of new nanostructured magnetic materials for magnetoelectronic applications. Nanoparticles with onion-like architecture offer a unique opportunity to expand the possibilities allowing to combine different phases at the nanoscale and also modulate the coupling between magnetic phases by introducing spacers in the same structure. Here we report the fabrication, by a three-step high temperature decomposition method, of Fe3O4/MgO/CoFe2O4 onio-like nanoparticles and their detailed structural analysis, elemental compositional maps and magnetic response. The core/shell/shell nanoparticles present epitaxial growth and cubic shape with overall size of (29+-6) nm. These nanoparticles are formed by cubic iron oxide core of (22+-4) nm covered by two shells, the inner of magnesium oxide and the outer of cobalt ferrite of ~1 and ~2.5 nm of thickness, respectively. The magnetization measurements show a single reversion magnetization curve and the enhancement of the coercivity field, from HC~608 Oe for the Fe3O4/MgO to HC~5890 Oe to the Fe3O4/MgO/CoFe2O4 nanoparticles at T=5 K, ascribed to the coupling between both ferrimagnetic phases with a coupling constant of =2 erg/cm2. The system also exhibits exchange bias effect, where the exchange bias field increases up to HEB~2850 Oe at 5 K accompanied with the broadening of the magnetization loop of HC~6650 Oe. This exchange bias effect originates from the freezing of the surface spins below the freezing temperature TF=32 K that pinned the magnetic moment of the cobalt ferrite shell.Comment: 39 pages, 8 figure

A physiologically based pharmacokinetic model to predict the superparamagnetic iron oxide nanoparticles (SPIONs) accumulation in vivo

AbstractSuperparamagnetic iron oxide nanoparticles (SPIONs) have been identified as a promising material for biomedical applications. These include as contrast agents for medical imaging, drug delivery and/or cancer cell treatment. The nanotoxicological profile of SPIONs has been investigated in different studies and the distribution of SPIONs in the human body has not been fully characterized. The aim of this study was to develop a physiologically-based pharmacokinetic (PBPK) model to predict the pharmacokinetics of SPIONs. The distribution and accumulation of SPIONs in organs were simulated taking into consideration their penetration through capillary walls and their active uptake by specialized macrophages in the liver, spleen and lungs. To estimate the kinetics of SPION uptake, a novel experimental approach using primary macrophages was developed. The murine PBPK model was validated against in vivo pharmacokinetic data, and accurately described accumulation in liver, spleen and lungs. After validation of the murine model, a similar PBPK approach was developed to simulate the distribution of SPIONs in humans. These data demonstrate the utility of PBPK modeling for estimating biodistribution of inorganic nanoparticles and represents an initial platform to provide computational prediction of nanoparticle pharmacokinetics.</jats:p

The Brazilian Registry of Adult Patient Undergoing Cardiovascular Surgery, the BYPASS Project: Results of the First 1,722 Patients

Objective: To report the early results of the BYPASS project - the Brazilian registrY of adult Patient undergoing cArdiovaScular Surgery - a national, observational, prospective, and longitudinal follow-up registry, aiming to chart a profile of patients undergoing cardiovascular surgery in Brazil, assessing the data harvested from the initial 1,722 patients. Methods: Data collection involved institutions throughout the whole country, comprising 17 centers in 4 regions: Southeast (8), Northeast (5), South (3), and Center-West (1). The study population consists of patients over 18 years of age, and the types of operations recorded were: coronary artery bypass graft (CABG), mitral valve, aortic valve (either conventional or transcatheter), surgical correction of atrial fibrillation, cardiac transplantation, mechanical circulatory support and congenital heart diseases in adults. Results: 83.1% of patients came from the public health system (SUS), 9.6% from the supplemental (private insurance) healthcare systemsand 7.3% from private (out-of-pocket) clinic. Male patients comprised 66%, 30% were diabetics, 46% had dyslipidemia, 28% previously sustained a myocardial infarction, and 9.4% underwent prior cardiovascular surgery. Patients underwent coronary artery bypass surgery were 54.1% and 31.5% to valve surgery, either isolated or combined. The overall postoperative mortality up to the 7th postoperative day was 4%for CABG was 2.6%, and for valve operations, 4.4%. Conclusion: This first report outlines the consecution of the Brazilian surgical cardiac database, intended to serve primarily as a tool for providing information for clinical improvement and patient safety and constitute a basis for production of research protocols.Univ Fed Sao Paulo UNIFESP EPM, Hosp Sao Paulo, Sao Paulo, SP, BrazilHosp Caridade Sao Vicente Paulo, Jundiai, SP, BrazilInst Med Integral Prof Fernando Figueira IMIP, Recife, PE, BrazilHosp Base FUNFARME & FAMERP, Sao Jose Do Rio Preto, SP, BrazilIMC, Sao Jose Do Rio Preto, SP, BrazilIrmandade Santa Casa Sao Paulo INCT HPV, Fac Ciencias Med Santa Casa Sao Paulo, Sao Paulo, SP, BrazilFundacao Univ Cardiol, Inst Cardiol Rio Grande do Sul, Porto Alegre, RS, BrazilInst Coracao Natal, Natal, RN, BrazilInst Cardiol Dist Fed, Brasilia, DF, BrazilUniv Fed Maranhao HU UFMA, Univ Hosp, Sao Luis, MA, BrazilHosp Evangelico, Cachoeiro De Itapemirim, ES, BrazilHosp Coracao Sergipe, Aracaju, SE, BrazilHosp Nossa Senhora Salete, Inst Cirurgia Cardiovasc ICCV, Cascavel, PR, BrazilHosp Wilson Rosado, Mossoro, RN, BrazilHosp Bosque Saude, Sao Paulo, SP, BrazilHosp Univ Santa Maria, Santa Maria, RS, BrazilHosp Coracao HCor, Sao Paulo, SP, BrazilHosp Coracao IP HCor, Ins Pesquisa, Sao Paulo, SP, BrazilInst Coracao InCor, Sao Paulo, SP, BrazilUniv Fed Sao Paulo UNIFESP EPM, Hosp Sao Paulo, Sao Paulo, SP, BrazilWeb of Scienc

Magnetic Fluid Hyperthermia: focusing on the absorption power mechanisms and its influence for in vitro experiments

Resumen del trabajo presentado a la 9th International Conference on Fine Particle Magnetism, celebrada en Gaithersburg (USA) del 13 al 17 de junio de 2016.Magnetic Hyperthermia has received great attention in the last decade, being one of the most promising applications of magnetic nanoparticles in biomedicine. Despite several studies were performed and published, including in vitro, in vivo and clinical studies, a better comprehension of the physical mechanisms of power absorption are needed, especially when the nanoparticles are in the biological conditions. In this work, we focused in the design of magnetite nanoparticles looking for a controlled heating in vitro hyperthermia experiments. The experiments were perfonned in BV2 cell lineage with magnetite nanoparticles coated with DEXTRAN and mPEG2000 (Fig. 1, left). In order to understand deeply the results, an intense study on the mechanisms involved in the Power Absorption of nanoparticles in an alternating magnetic field was previously perfonned, together with the magnetic and morphological characterization of the nanoparticles. In addition, the toxicity and cell uptake of the nanoparticles with both coatings were studied for this cellular model. lnterestingly, we obtain cell death induced without an overheating (Temperature < 38 oC) after 6 hours, probably induced by cell stress promoted by the nanoparticles in the hyperthermia experiment. The SP A obtained from the experiments were interpreted and simulated in terms of our previous experimental and theoretical hyperthermia studies for ferrofluid.Peer Reviewe

Relaxation time diagram for identifying heat generation mechanisms in magnetic fluid hyperthermia

et al.We present a versatile diagram to envisage the dominant relaxation mechanism of single-domain magnetic nanoparticles (MNPs) under alternating magnetic fields, as those used in magnetic fluid hyperthermia (MFH). The diagram allows estimating the heating efficiency, measured by the Specific Power Absorption (SPA), originated in the magnetic and viscous relaxation times of single-domain MNPs for a given frequency of the ac magnetic field (AFM). The diagram has been successfully applied to different colloids, covering a wide variety of MNPs with different magnetic anisotropy and particle size, and dispersed in different viscous liquid carriers. From the general diagram, we derived a specific chart based on the Linear Response Theory in order to easily estimate the experimental condition for the optimal SPA values of most colloids currently used in MFH.The authors are grateful to the CONICET-Argentina. The authors would also like to acknowledge the use of the Servicio General de Apoyo a la Investigación–SAI, Universidad de Zaragoza. This work was supported partially from the Argentinean agencies ANPCyT (PICT2007-832), CONICET (PIP2008-1333), and UNCuyo grants. This work also was supported from Diputación General de Aragón (DGA) and Ministerio de Economia y Competitividad (MINECO, Project MAT2010-19326)-Spain.Peer Reviewe

Effect of Thermal Fluctuations in FMR Experiments in Uniaxial Magnetic Nanoparticles: Blocked vs. Superparamagnetic Regimes

We present ferromagnetic resonance (FMR) experiments on two low-interacting nanoparticle systems: Fe3O4 and CoFe2O4 corresponding to low- and high-anisotropy cases, respectively. The spectra have been interpreted in terms of a phenomenological model which applies to the FMR of nanoparticles. The model includes the effect of thermal fluctuations in the FMR covering the range from the superparamagnetic (low-anisotropy-high-temperature) regime to the high-anisotropy-low-temperature situation. We have been able to explain several simultaneous features observed in the FMR spectra of a system of anisotropic nanoparticles when lowering the temperature that include: a decrease of the resonance field with a simultaneous linewidth increase and intensity reduction. These effects had been previously attributed to the existence of a ‘‘blocking-temperature’’ in the FMR. Our interpretation, however, shows that in a magnetic system with easy axes this FMR response originates in the temperature dependence of the dispersion relation. Also, applying the present model to the FMR within the hysteresis cycle it is possible to reproduce the irreversibilities occurring in the resonance spectra. Comparison of FMR and magnetization measurements show that the characteristic FMR time is not related to the inverse microwave frequency.Fil: de Biasi, Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); ArgentinaFil: Lima Jr., Enio. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); ArgentinaFil: Ramos, Carlos A.. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); ArgentinaFil: Butera, Alejandro Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); ArgentinaFil: Zysler, Roberto Daniel. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentin