EDUARDO DE LIMA CORREA

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Magnetic and structural properties of the intermetallic Ce(1−x)LaxCrGe3 series of compounds
2021 - BOSCH-SANTOS, B.; CABRERA-PASCA, G.A.; CORREA, E.L.; CORREA, B.S.; SALES, T.N.S.; MOON, K-W.; DENNIS, C.L.; HUANG, Q.; LEAO, J.B.; LYNN, J.W.; CARBONARI, A.W.
The Ce(1−x)LaxCrGe3 (x = 0, 0.19, 0.43, 0.58, and 1) intermetallic compound system has been investigated by magnetization measurements and neutron scattering techniques to determine the effect of La doping on the magnetic ordering and exchange interaction between Cr ions. The structural and magnetic characterization in this series was first verified by x-ray diffraction and bulk magnetization measurements. The samples exhibit the known hexagonal perovskite structure (P63/mmc space group) and have a single magnetic phase according to magnetizationmeasurements. In this paper, the ferromagnetic ordering temperature for Cr evolves smoothly from a range of 68 K to 77 K for CeCrGe3 to a range of 91 K to 96 K for LaCrGe3 as La replaces Ce. Magnetization results indicate the formation of domain walls below the transition temperature for all Ce(1−x)LaxCrGe3 systems investigated. Neutron results indicate ordered magnetic Cr moments aligned along the c axis for the x = 1 LaCrGe3 system, as well as for x = 0.19, 0.43, and 0.58, which contrasts with the x = 0 CeCrGe3 where the moments order in the ab plane.
High-saturation magnetization in small nanoparticles of Fe3O4 coated with natural oils
2020 - CORRÊA, BRUNO S.; COSTA, MESSIAS S.; CABRERA-PASCA, GABRIEL A.; SENA, CLEIDILANE; PINTO, RAFAEL H.H.; SILVA, ANA P.S.; CARVALHO JUNIOR, RAUL N.; ISHIDA, LINA; RAMON, JONATHAN G.A.; FREITAS, RAFAEL S.; SAIKI, MITIKO; MATOS, IZABELA T.; CORRÊA, EDUARDO L.; CARBONARI, ARTUR W.
The enhancement of nanoparticle’s magnetic properties with a suitable coating is the main tool to increase their potential as an effective candidate for applications in different areas, especially in biomedicine. In the work here reported, Fe3O4 nanoparticles coated with natural oils were synthesized by iron (III) acetylacetonate thermal decomposition and the effects of the coating on the magnetic properties of these particles have been investigated. The oils were extracted from three Amazon fruits seeds: açaí, ucuúba, and bacaba by CO2 supercritical extraction process, and the relative percentage composition of fatty acids were determined by gas chromatography. A systematic study of crystalline, morphological, and magnetic properties revealed a saturation magnetization (Ms) enhancement and high values of the anisotropy constant for Fe3O4 samples when coated with açaí and ucuúba oils, which present a large percentage of saturated total fatty acid. Our results indicate that nanoparticles with sizes smaller than around 5 nm present Ms values as high as that found for bulk Fe3O4 and, consequently, much higher than Ms values for nanoparticles usually coated with oleic acid. The nuclear techniques neutron activation analysis and perturbed angular correlations were used to better characterize the nanoparticles.
Effects of an external magnetic field on the hyperfine parameters in RE2O3 (RE = Gd, Er) nanoparticles measured by perturbed angular correlation spectroscopy
2020 - CORREA, E.L.; BOSCH-SANTOS, B.; SAXENA, R.N.; CABRERA-PASCA, G.A.; CARBONARI, A.W.
In order to understand the interaction mechanisms in RE2O3 (RE=Gd, Er) nanoparticles (NPs), Perturbed Angular Correlation (PAC) spectroscopy, a local technique, plus external magnetic field, was used to elucidate local interactions and possible mapping of the different contribution in these compounds. NPs were synthesized by thermal decomposition and characterized by transmission electron microscopy and X-ray diffraction. PAC measurements were performed using 111In(111Cd) as probe nuclei, with and without the application of an external magnetic field (EMF) of 0.5 T in different temperatures (50 K, 100 K, 200 K, 300 K). Results show that the hyperfine magnetic field is almost zero when the probe is located at the symmetric site, and ∼4 T and ∼5 T for Gd2O3 and Er2O3, respectively, when the probe occupies the asymmetric field.
Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3
2020 - CABRERA-PASCA, G.A.; BOSCH-SANTOS, B.; BURIMOVA, A.; CORREA, E.L.; CARBONARI, A.W.
LaMnO3+δ is a complex oxide, which, depending on the oxygen excess concentration, presents different crystalline structure and interesting magnetic and electric properties such as colossal magnetoresistance, polaron dynamics, multiferroic behavior, and charge-orbital ordering. This complexity requires different characterization techniques to draw a picture as complete as possible allowing a good understanding of these phenomena. Here, we have used the perturbed angular correlation (PAC) technique to measure hyperfine interactions at La and Mn sites of LaMnO3+δ(δ ∼0.15) using 140Ce and 111Cd at La sites as probe nuclei in order to investigate within an atomic scale the magnetic and electric interactions in this compound. The results show that 111Cd nuclei occupy highly symmetric local sites in agreement with a rhombohedral structure. The magnetic hyperfine field (Bhf ) measured with 111Cd at La sites is very small (Bhf = 0.40 T) due to the supertransferred magnetic field from Mn neighbors through oxygen orbitals. On the other hand, 140Ce nuclei at La sites present a saturation field of around 3.7 T much higher than that expected for La sites (due to the weak transfer field by superexchange mechanism). In addition, for temperature range above the magnetic ordering (200-300 K) a dynamic hyperfine interaction was observed characterized by the attenuation parameter λ(T) whose temperature dependence allowed to determine the activation energy (Ea) associated to charge transfer. The polarization of the 4f -electron of Ce impurities affects the local magnetic field at impurity sites as well as the Ea.
Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites
2019 - BOSCH-SANTOS, B.; NASCIMENTO, N.M.; SAIKI, M.; CORREA, E.L.; SALES, T.S.N.; PEREIRA, L.F.D.; CABRERA-PASCA, G.A.; SAXENA, R.N.; SCHELL, J.; CARBONARI, A.W.
Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol- Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.
Influence of the vials radioactive residue in Nuclear Medicine procedure applied to a new “in situ” activimeter calibration methodology
2019 - KUAHARA, L.T.; CORREA, E.L.; CARNEIRO, R.C.G.; BEZERRA, R.R.L.; POTIENS, M.P.A.
In this study we present a new “in situ” calibration methodology establishment for activimeters – i.e., this equipment calibration can be made at the hospital and/or the nuclear medicine service (NMS) – and also the importance of considering vials radioactive residue when generating the calibration coefficient in terms of activity (NA). For the calibration, two methods are presented here: in the first, 99mTc sample activity (AC) is measured in the NMS. Then it is sent to the Instruments Calibration Laboratory (LCI/IPEN) where the reference activity (AR) is obtained under controlled conditions in a reference vial. After geometry and residue corrections, NA is calculated. In the second method, AR is obtained at the LCI, then 99mTc sample is sent to the hospital/NMS, where AC is measured and NA calculated. Calibration methodologies were applied to three NMS and to four equipment belonging to the radiopharmaceutical production facility (CR) at the Nuclear and Energy Research Institute (IPEN). Both methodologies were tested with and without residual activity corrections under controlled conditions. Variations of up to 4% were obtained.
Synthesis and atomic scale characterization of Er2O3 nanoparticles
2018 - CORREA, EDUARDO L.; BOSCH-SANTOS, BRIANNA; FREITAS, RAFAEL S.; POTIENS, MARIA da P.A.; SAIKI, MITIKO; CARBONARI, ARTUR W.
In the investigation reported in this paper a modified thermal decomposition method was developed to produce very small Er2O3 nanoparticles (NPs). Particles structure, shape and size were characterized by x-ray diffraction and transmission electron microscopy which showed that the synthesis by thermal decomposition under O2 atmosphere produced very small and monodisperse NPs, allowing the investigation of finite-size and surface effects. Results of magnetization measurements showed that the smallest particles present the highest values of susceptibility that decrease as particle size increases. Specific heat measurements indicate that the sample with the smallest NPs (diameter ∼5 nm) has a Néel temperature of 0.54 K. The local structure of particles was investigated by measurements of hyperfine interactions with perturbed angular correlation spectroscopy using 111Cd as probe nuclei replacing the cationic sites. Results showed that the relative population of sites 8b increases in both the core and surface layer of particles.