FERNANDO BACCI EFFENBERGER
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Artigo IPEN-doc 28161 Crystalline and magnetic properties of CoO nanoparticles locally investigated by using radioactive indium tracer2021 - SANTOS, RENATA V.; CABRERA-PASCA, GABRIEL A.; COSTA, CLEIDILANE S.; BOSCH-SANTOS, BRIANNA; OTUBO, LARISSA; PEREIRA, LUCIANO F.D.; CORREA, BRUNO S.; EFFENBERGER, FERNANDO B.; BURIMOVA, ANASTASIA; FREITAS, RAFAEL S.; CARBONARI, ARTUR W.We herein report a comprehensive investigation on the magnetic, structural, and electric properties of CoO nanoparticles with different sizes by local inspection through hyperfine interactions measured in a wide range of temperatures (10–670 K) by using radioactive 111In(111Cd) tracers with the perturbed angular correlations technique. Small cobalt oxide nanoparticles with the characteristic size of 6.5 nm have been prepared by the wet chemical route that turned out to be essential to incorporate radioactivity tracers during nucleation and growth of the particles. Nanocrystalline samples with 22.1 nm size were obtained by thermal treatments under low pressure of helium at 670 K. The hyperfine data were correlated with X-ray diffraction, ZFC–FC magnetic measurements, and transmission electron microscopy to describe the structure, magnetic properties, size, and shape of samples. An analysis of the temperature evolution of hyperfine parameters revealed that the structural distortion and the magnetic disorder in the core and on the surface layer play an important role in the magnetic behavior of CoO nanoparticles.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.Artigo IPEN-doc 21145 Síntese de nanopartículas de óxido de ferro utilizando óleo de ucuúba2015 - CORREA, BRUNO S.; SILVA, ANA P.S.; CORDEIRO, RENATO M.; MATOS, IZABELA T.; CORREA, EDUARDO L.; EFFENBERGER, FERNANDO B.; SENA, CLEIDILANE; CARVALHO JUNIOR, RAUL N.; SAIKI, MITIKO; CARBONARI, ARTUR W.Artigo IPEN-doc 20983 Sintese e caracterização de nanopartículas magnéticas de Fesub(2)Osub(4) recobertas com óleo de açai para aplicações biomédicas2015 - SILVA, ANA P.S.; CORREA, BRUNO S.; BATISTA, CAMILA R.; PINTO, RAFAEL H.H.; CORDEIRO, RENATO M.; MATOS, IZABELA T.; EFFENBERGER, FERNANDO B.; JUNIOR, RAUL N.C.; SAIKI, MITIKO; SENA, CLEIDILANE; CARBONARI, ARTUR W.