Síntese, caracterização e magnetohipertermia de ferritas de manganês Mn1-xAxFe2O4 dopadas com cobre, magnésio ou cobalto

• Autor(a) principal: Araújo, Marcus Vinicíus
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/7742
• topic: Nanomagnetismo; Nanopartículas magnéticas; Hipertermia magnética; Nanomagnetism; Magnetic nanoparticles; Magnetic hyperthermia; FISICA::FISICA GERAL

Nanoparticles based on Mn-ferrite, Mn1−xAxFe2O4, doped with copper, magnesium and cobalt (A = Cu, Mg ou Co) were synthesized by hydrothermal method under pressure, with X varying from 0 to 0, 5. Magnetic fluids stable in physiological conditions were obtained surface-coating the nanoparticle with citric acid. X-ray diffraction confirmed the spinel structure. Energy dispersive spectroscopy (EDS) confirmed the success of the synthesis of the mixed ferrite, where the element composition agreed with the value expected within an error of 10%. Transmission electron microscopy showed sphericalshaped nanoparticles, while magnetization data at room temperature allowed the analysis of the coercivity field (Hc) and the saturation magnetization (Ms). Ms decreased with the increase of X for the Cu and Mg doped samples, while the opposite effect was observed for Co doped nanoparticles. Hc increased the higher the X value for all the samples. The effect on the Cu and Mg-doped ferrites are explained by the increase in particle size. However, the Co-doped samples, showed a diameter increasing the higher X, but Hc also increased. In this case the Hc behavior is explained by the increase concentration of Co and its effect on the magnetic anisotropy which increases for higher Co content. The magnetic hyperthermia efficiency of the magnetic fluids, for all samples, were investigated in a field amplitude ranging from 50 Oe to 170 Oe and frequencies from 110 kHz up to 990 kHz. The hyperthermia efficiency decreased with X increasing, considering the case of 130Oe and 333 kHz, which indicates that at this experimental condition undoped Mnferrite nanoparticles are better for hyperthermia. In most of the samples it was observed that the efficiency scaled with the square of the field amplitude, which is in accordance with Linear Response Theory (LRT). In addition, the hyperthermia frequency dependence study showed a saturation effect, for some samples, at a frequency higher than 600 kHz. The experimental data as function of frequency were susccessfully curve fitted with the LRT model using 2 free parameters related to the effective relaxation time ( ef ) and the equilibrium susceptibility ( 0). In particular, for theMn-ferrite sample for a field of 130Oe it is found ef = 5, 2 · 10−7s and 0 = 0, 028. The value of ef can be explained using an effective magnetic anisotropy value of 2·105 erg/cm3. The value is one order of magnitude higher than the bulk value, and allowed one to estimate the surface anisotropy contribution to in the order of 0, 04 erg/cm2. On the other hand, a linear chain formation model, for this sample consisted of a trimer (3 nanoparticles), can also explain the increase of the effective anisotropy. Moreover, we found a 0 value lower than the estimated Langevin susceptibility. In order to explain this, a new model, valid in the linear regime, was developed considering the contribution from blocked nanoparticles. Indeed, the analysis of hyperthermia data using this model indicates that the contribution to heat generation spans from 34.7% of the nanoparticles for a field of 110 Oe up to 52.5% at 170 Oe.