As nanopartículas (NPs) à base de óxido de ferro, como magnetita e maguemita, têm grande destaque em diversas áreas da ciência, inclusive na medicina. Há décadas, elas são usadas na reposição de ferro para pacientes com anemia, como agentes de contraste em ressonância magnética (MRI – “Magnetic Resonance Imaging”), na entrega de agentes terapêuticos mediada ou não por gradiente de campo magnético, em terapias térmicas foto e magnetoestimuladas, entre outras. Neste artigo, apresentamos suas propriedades magnéticas. Discutimos de forma breve seu ordenamento ferrimagnético, a importância da anisotropia magnética e sua relação com a histerese magnética (modelo de Stoner-Wohlfarth) e o regime superparamagnético. As diferenças entre superparamagnetismo e paramagnetismo são enfatizadas, além da importância da estabilidade coloidal dessas nanoestruturas para aplicações biomédicas. Finalmente, diversas aplicações biomédicas são discutidas, entre elas hipertermia magnética, terapia fototérmica, imunoterapia e uma nova técnica de imagem com potencial clínico, conhecida como “Magnetic Particle Imaging” (MPI). NPs (NPs maguemita ciência medicina décadas anemia MRI Magnetic Imaging, Imaging , Imaging”) magnético magnetoestimuladas outras artigo magnéticas ferrimagnético modelo StonerWohlfarth Stoner Wohlfarth Stoner-Wohlfarth superparamagnético enfatizadas Finalmente discutidas fototérmica clínico MPI. MPI . (MPI) (MPI

Iron oxide-based nanoparticles (NPs), such as magnetite and maghemite, are highly prominent in various scientific fields, including medicine. For decades, they have been used for iron supplementation in patients with anemia, as contrast agents in magnetic resonance imaging (MRI), in the delivery of therapeutic agents mediated or not by magnetic field gradients, and in photo- and magneto-stimulated thermal therapies, among other applications. In this article, we present their magnetic properties. We briefly discuss their ferrimagnetic ordering, the importance of magnetic anisotropy and its relation to magnetic hysteresis (Stoner-Wohlfarth model), and the superparamagnetic regime. The differences between superparamagnetism and paramagnetism are emphasized, as well as the importance of the colloidal stability of these nanostructures for biomedical applications. Finally, various biomedical applications are discussed, including magnetic hyperthermia, photothermal therapy, immunotherapy, and a new imaging technique with clinical potential known as Magnetic Particle Imaging (MPI). oxidebased oxide based NPs, NPs , (NPs) maghemite fields medicine decades anemia MRI, MRI (MRI) gradients photo magnetostimulated magneto stimulated therapies article properties ordering StonerWohlfarth Stoner Wohlfarth model, model model) regime emphasized Finally discussed hyperthermia therapy immunotherapy MPI. MPI . (MPI) (NPs (MRI (MPI

Resumen En la última década los nanomateriales magnéticos se han utilizado ampliamente en el campo de la química, la física, la ingeniería y la medicina debido a sus propiedades ópticas, magnéticas y de conducción, y como agentes de contraste en resonancia magnética. Se ha evaluado su influencia en el tratamiento de tumores cancerosos y está despertando gran interés en sistemas de reparación ambiental como absorbentes magnéticos que atrapan partículas de metal y algunos contaminantes. En este estudio se analizó la influencia de los parámetros de proceso en la obtención de nanopartículas magnéticas bajo tres métodos de síntesis química. La caracterización morfológica se hizo por microscopía electrónica de barrido (SEM), su composición elemental se estudió mediante espectroscopia de energía dispersiva de rayos x (EDS), y su estructura, mediante difracción de rayos x (XRD). Los resultados evidenciaron una gran influencia del método de obtención, como se reflejó en la variabilidad del tamaño de las nanopartículas. Es de resaltar la obtención de partículas a escala nanométrica, con predominancia de estructuras Fe3O4 (magnetita) y Fe2O3 (maghemita), lo cual supondría propiedades de superparamagnetismo que abrirían el camino a un amplio abanico de aplicaciones futuras con su producción a bajo costo y de fácil acceso.

Abstract In the last decade, magnetic nanomaterials have been widely used in the fields of chemistry, physics, engineering, and medicine due to their optical, magnetic, and conductive properties, and as contrast agents in magnetic resonance. Their influence in the treatment of cancerous tumors has been evaluated and has sparked great interest in its use in environmental repair systems such as magnetic absorbers that trap metal particles and some contaminants. Here we analyze the influence of process parameters to obtain magnetic nanoparticles under three chemical synthesis methods. Its morphological characterization was performed by scanning electron microscopy (SEM), its elemental composition by energy dispersive spectroscopy (EDS), and its structure by x-ray diffraction (XRD). Our results showed that the obtention method had a great influence as evidenced by the variability in nanoparticle sizes. It is worth highlighting that we obtained particles at a nanometric scale, especially Fe3O4 (magnetite) and Fe2O3 (maghemite) structures, with potential superparamagnetism properties that could open a wide range of future applications for the production of these materials at low cost and easy access.

Resumo Apresentamos um software desenvolvido com o objetivo de proporcionar um melhor entendimento acerca do comportamento de sistemas superparamagnéticos sujeitos a campos magnéticos externos, sem a necessidade de conhecimento prévio em programação. O simulador reproduz o comportamento da magnetização em função de diversas variáveis, tais como temperatura, magnetização de saturação e diâmetro médio dos momentos magnéticos. O problema é abordado de forma simplificada através da função de Langevin. Nosso trabalho busca auxiliar no estudo de materiais magnéticos nanoestruturados, normalmente de difícil abordagem experimental no âmbito do ensino, assim também servindo de base para futuros pesquisadores da área.

Abstract We introduce a software aimed to provide with a better understanding over the behavior of superparamagnetic systems under external magnetic fields that does not require previous knowledge in coding. Our simulator generates the magnetization behavior according to many variables such as temperature, saturation magnetization, and the average diameter of the magnetic moment. The problem is tackled in a very simple way via the Langevin function. Our work ultimately seeks to assist learning in nanostructured magnetic materials, quite often a bit hard to grasp by many students, thereby also being of use for prominent researchers in the field.

In this paper the synthesis of the LaBiFe2O6 material by the modified Pechini method is reported. Structural, morphologic, magnetic and optic experimental studies were performed. Rietveld refinement of x-ray diffraction patterns revealed that LaBiFe2O6 crystallizes in an orthorhombic perovskite structure (space group Pnma, # 62). Scanning electron microscopy images showed the nanometric feature of grains. X-ray dispersive spectroscopy permitted to infer the obtaining of the LaBiFe2O6 expected stoichiometry. Results of magnetic susceptibility as a function of temperature and field magnetization evidenced mixed ferromagnetism and superparamagnetism behavior at T=300 K. Mössbauer spectroscopy supported the superparamagnetic and ferromagnetic responses as a result of the nanogranular morphology and anisotropy effects. Spectrum of diffuse reflectance suggest that this material behaves as a semiconductor with energy gap Eg=2.13 eV.

This work has focused on the synthesis of three nanosystems composed of superparamagnetic iron oxide nanoparticles (SPIONs) coated either with a carboxylate platinum(IV) complex (PD = cis,cis,trans-[Pt(NH3)2Cl2(HOOCCH2CH2COO)(OH)]) or with platinum(II) complex functionalized dextrans (DexPt1 = [Pt(Dex-NH2)Cl3] and DexPt2 = [Pt(Dex-NH2)(NH3)2(H2O)]). All nanosystems have shown superparamagnetic behavior. Powder X-ray diffraction (XRD) has confirmed that the SPIONs were iron oxide phase and transmission electron microscopy (TEM) has shown average size of 6 nm (M6). Characterization of the nanosystems by inductively coupled plasma atomic emission spectroscopy (ICP AES) has revealed the presence of platinum on their surface (M6@PD, 0.54 mmol g-1 of Fe and M6@CA@DexPt1-2, 0.32-1.20 mmol g-1 of Fe); infrared spectroscopy (IR) and thermogravimetric and differential thermal analyses (TG-DTA) have confirmed the presence of dextran. Furthermore, the colloidal properties of these nanosystems (M6@PD and M6@CA@DexPt1-2) have been evaluated in water and in PBS buffer. Although M6@PD has shown good colloidal dispersion in water in the pH range of 2.0-8.0, the system underwent rapid agglomeration in PBS buffer. The M6@CA@DexPt1-2 nanosystems have exhibited improved colloidal behavior both in water and in PBS, where hydrodynamic sizes were kept below 100 nm over a large pH range (2.0-12.0). Furthermore, the latter systems have displayed isoelectric points below pH 5.0 and low surface charges at pH 7.0 (ζ-potential = -10 mV) and therefore PBS did not affect their colloidal stability.

A large scale direct hydrothermal method has been used to prepare face-centered cubic (FCC) Co/C nanocapsules with a core of FCC-Co nanoparticles and a shell of amorphous C. The size distribution is 5-20 nm. The TB of FCC-Co/C nanocapsules is determined as 85 K, indicating that FCC-Co/C nanocapsules are superparamagnetic at 300 K. For FCC-Co/C nanocapsules-paraffin composite, an optimal reflection losbs (RL) of -33.4 dB is observed at 9.6 GHz for the 2.6 mm thick layer. RL values exceeding –20 dB in the 7.4 –15 GHz range are obtained by choosing an appropriate absorption-layer thickness between 1.7 and 3.3 mm. The good microwave absorbing properties of FCC-Co/C nanocapsules is considered to result from the excellent synergetic effect of the multi-dielectric relaxation loss and the multi-magnetic resonance loss. Quantitative calculation demonstrated that not only RL peak position but also the number of the peaks are determined by the quarter-wavelength cancellation model.

In this paper, polyacrylamide (PAM)-modified magnetite (Fe3O4) nanoparticles were prepared by in situ polymerization in aqueous solution. The particle size, morphology, crystal phase and magnetic properties were measured utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. The size distribution and stability of the nano-particles in aqueous solution were evaluated using the laser particle size analyzer and ultraviolet-visible spectroscopy (UV-vis). The influences of the dose of acrylamide (AM) and the pH value on the particle size and stability were also examined. The results showed that the Fe3O4 nanoparticles possessed superparamagnetic property and super dispersion stability in aqueous solution after PAM modification.

O objetivo deste Account é fornecer uma visão geral de nossas atividades atuais de pesquisa, as quais envolvem a síntese e modificação de nanomateriais superparamagnéticos para aplicação na área de separação magnética e catálise. Primeiramente, uma introdução ao magnetismo e à separação magnética é feita. Em seguida, estratégias sintéticas que têm sido desenvolvidas para gerar nanopartículas superparamagnéticas revestidas esfericamente por sílica e outros óxidos, com destaque a sistemas bem caracterizados e preparados por metodologias que geram amostras de elevada qualidade e que, a princípio, podem ser produzidas em maior escala, são discutidas. Uma série de catalisadores magneticamente recuperáveis preparados em nosso grupo de pesquisa pela combinação única de suportes superparamagnéticos e nanopartículas metálicas é destacada. Este Account é concluído com observações pessoais e perspectivas neste campo de pesquisa.

The aim of this Account is to provide an overview of our current research activities on the design and modification of superparamagnetic nanomaterials for application in the field of magnetic separation and catalysis. First, an introduction of magnetism and magnetic separation is done. Then, the synthetic strategies that have been developed for generating superparamagnetic nanoparticles spherically coated by silica and other oxides, with a focus on well characterized systems prepared by methods that generate samples of high quality and easy to scale-up, are discussed. A set of magnetically recoverable catalysts prepared in our research group by the unique combination of superparamagnetic supports and metal nanoparticles is highlighted. This Account is concluded with personal remarks and perspectives on this research field.

Fe10Ag90 granular alloys have been prepared using a sol-gel process, sintered at 300 °C and annealed at temperatures between 400 °C and 700 °C. The mean size of the iron particles, obtained from X-ray diffraction, is 30.0 ± 0.7 nm. Due to the existence of a distribution of particle sizes in these samples, both blocked (BL) and superparamagnetic (SPM) particles are present simultaneously, as confirmed by magnetization measurements at room temperature. AC susceptibility measurements as a function of temperature reveal a magnetic phase transition at about 770 °C, indicating the presence of particles exhibiting bulk behavior, in the samples annealed above 550 °C. The presence of these particles has been attributed to an atomic diffusion process between the grains, forming bulk-like multiple-domain Fe particles having Curie temperatures near that of bulk alpha-Fe phase (T C = 770 °C).

Some fundamentals of Mössbauer spectroscopy and of fluctuating magnetic hyperfine interactions are reviewed. An expression for calculation of spin-phonon interaction transition probabilities on the ground of a Debye model is given. Basic ideas of superparamagnetism and classical results for low-temperature relaxation rates are presented. A theory of superparamagnetism based on spin-phonon interaction is introduced. It is shown how to calculate from this Mössbauer spectra taking all spin-levels into account. Experimental spectra of ferrofluids are compared with simulated spectra and found in good accordance.

Granular systems composed by nanostructured magnetic materials embedded in a non-magnetic matrix present unique physical properties that depend crucially on their nanostructure. In this work, we have studied the structural and magnetic properties of NiZn-ferrite nanoparticles embedded in SiO2, a granular system synthesized by sol-gel processing. Samples with ferrite volumetric fraction x ranging from 6% to 78% were prepared, and characterized by X-ray diffraction, Mössbauer spectroscopy and vibrating sample magnetometry. Our results show the formation of pure stoichiometric NiZn-ferrite in the SiO2 matrix for x < 34%. Above these fraction, our samples presented also small amounts of Fe2O3. Mössbauer spectroscopy revealed the superparamagnetic behaviour of the ferrimagnetic NiZn-ferrite nanoparticles. The combination of different ferrite concentration and heat treatments allowed the obtaintion of samples with saturation magnetization between 1.3 and 68 emu/g and coercivity ranging from 0 to 123 Oe, value which is two orders of magnitude higher than the coercivity of bulk NiZn-ferrite.