NATALIA MARTINS DO NASCIMENTO
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Resumo IPEN-doc 27086 Investigation of magnetic and structural properties of CoFe2O4 nanoparticles by measuring hyperfine interactions with 111Cd2019 - MATOS, I.T.; NASCIMENTO, N.M.; CABRERA-PASCA, G.A.; EFFENBERGER, F.B.; FREITAS, R.S.; CARBONARI, A.W.Because their ability of magnetic nanoparticles (MNP) to become magnetized when exposed to an external magnetic field, which make them good candidates for biomedical applications [1]. The investigation of the magnetic and structural properties by techniques with atomic resolution, such as those based on hyperfine interactions, is, therefore, greatly useful in the study of MNP. In this work, hyperfine interactions in nanoparticles of CoFe2O4 were investigated by perturbed γ-γ angular correlation (PAC) spectroscopy using 111Cd as probe nuclei in the temperature range from 50 K to 850 K. Samples of CoFe2O4 were prepared by thermal decomposition [2]. Magnetic measurements results show a blocking temperature of 210 K and a superparamagnetic behavior at 300 K. MET measurements show that particles present well-monodispersed spherical shape with average size of 7 nm. XRD results show that samples crystallize in a single phase with the expected spinel structure. PAC spectra were fitted by a model considering two site fractions occupied by the probe nuclei. One were characterized by a single well-defined Larmor frequency with site fraction population of 47%, which was assigned to probe nuclei substituting cation sites in the core region of the particles. The other was characterized by a broad distribution quadrupole frequency with population of 53% corresponding to probe nuclei at distorted cation sites in the shell region of the particles. This assignment agrees with an expected shell/core volume ratio for particles with a diameter of 7 nm. Hyperfine measurements also show that the magnetic hyperfine field (Bhf) is 12.6 T at 10 K in the saturated region and the temperature dependence of Bhf indicate that the transition temperature is around 900 K.Resumo IPEN-doc 24605 Production and study of nanoparticles magnetic properties by hyperfine interactions2017 - NASCIMENTO, N.M.; CORREA, E.L.; BOSCH-SANTOS, B.; MATOS, I.T.; CABRERA-PASCA, G.A.; CARBONARI, A.W.In the past years nanotechnology was highlighted as a quick growing field, with many applications in science and technology including information storage, drug delivery and medical images, in which gadolinium-based nanoparticles (NPs) have been studied as contrast agent for magnetic resonance image. On the other hand erbium oxide NPs present potential for many applications due to their optical, electrical and photoluminescence properties, and can be used in display monitors, carbon nanotubes for "green" chemistry and in bioimaging, and iron-based NPs have been studied for application in hyperthermia due to its superparamagnetic properties. At the Hyperfine Interactions Laboratory (LIH) NPs are synthesized by thermal decomposition and co-precipitation. Structural characterization is made using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and magnetic properties are studied by magnetization, both at partner laboratories, and perturbed angular correlation (PAC) spectroscopy using 111In(111Cd) as probe nuclei at LIH. PAC spectroscopy is based on the angular correlation between nuclear radiations emitted by radioactive probe nuclei, which is a well-established method in nuclear spectroscopy. Perturbation occurs in this correlation by electromagnetic interactions external to the nucleus when it is inserted in a material, which can provide information on the electronic distribution of the neighborhood. In this work, an important material was investigated by PAC spectroscopy using 111In, which decays to 111Cd by electron capture, as probe nuclei. Results have shown that NPs produced by thermal decomposition present narrow size distribution, with average size of 5 nm. On the other hand, results related to NPs produced by co-precipitation have shown that NPs don’t have a homogeneity in size and shape distribution.