EDUARDO DE LIMA CORREA

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Effects of an external magnetic field on the hyperfine parameters in RE2O3 (RE = Gd, Er) nanoparticles measured by perturbed angular correlation spectroscopy
2019 - CORREA, E.; BOSCH-SANTOS, B.; SAXENA, R.N.; CABRERA-PASCA, G.; CARBONARI, A.W.
The RE2O3 (RE = rare-earth) oxides present three different structures depending on the RE ionic radii: hexagonal (A-type), monoclinic (B-type) or cubic (C-type). In the latter, RE ions occupy two non-equivalent cation sites: asymmetric 24d sites and symmetric 8b sites. Gd2O3 and Er2O3 crystallize in this structure and have a paramagnetic behavior, although Er2O3 also orders antiferromagnetically below 4 K. Due to the high magnetic moment of Gadolinium ions, Gd3+ chelates have been used as a contrast agent for magnetic resonance imaging[1]. An investigation of the localized magnetic moment behavior on Gd and Er sites in Gd2O3 and Er2O3 nanoparticles (NPs), within an atomic resolution, under the influence of an external magnetic field (EMF), is very necessary mainly because the high neutron absorption cross-section of Gd prevents the use of neutron diffraction[ 2]. In this paper, hyperfine interactions, measured by Perturbed Angular Correlation (PAC) spectroscopy using 111In→111Cd as probe nuclei, were used to investigate the behavior of each RE site in Gd2O3 and Er2O3 NPs with and without the application of an EMF of 0.5 T. NPs were synthesized by thermal decomposition and characterized by transmission electron microscopy and X-ray diffraction. Results show that the contribution of RE atoms at 24d sites is invariant with temperature whereas the contribution from RE atoms at 8b sites is so that the hyperfine magnetic field (Bhf) increases in Er2O3 and decreases in Gd2O3 when temperature decreases indicating an opposite alignment of Gd magnetic moments at the 8b symmetric sites.
Hyperfine interactions measurements in bismuth tri-iodide (BiI3) by time differential perturbed angular correlation spectroscopy (TDPAC)
2019 - SANTOS, R.A.; SANTOS, B.B.; CORREA, E.L.; PEREIRA, L.F.D.; SCHELL, J.; CORREIA, J.G.M.; LUPASCU, D.C.; SCHAAF, P.; HOFSAESS, H.C.; SAXENA, R.N.; CARBONARI, A.W.
Bismuth tri-iodide (BiI3) is a material of great interest in applications such as solar cells and semiconductor detectors. In the work reported here, bulk samples of BiI3 were characterized by time differential perturbed angular correlation spectroscopy (TDPAC) at different temperatures using 111mCd (111Cd) and 111In (111Cd) as radioactive probes, inserted by implantation at ISOLDE/CERN and by thermal diffusion at IPEN, respectively. TDPAC measurements were used to investigate the hyperfine interactions at Bi sites in the crystalline structure of BiI3. The hyperfine parameters obtained were analyzed to elucidate the electrical properties expected for the mentioned technological applications. The optimal temperatures for annealing after the implantation (300°C and 320°C) were determined, allowing to observe the perturbation pattern R(t). Measurements show that the incidence of UV light at 350–363nm wavelength has an effect on the electronic structure around the Cd probe nuclei located near the surface of samples.
Hyperfine interactions in Gd2Ti2O7 pyrochlore
2019 - PEREIRA, LUCIANO F.D.; FERREIRA, WANDERSON L.; GONÇALVES, VITOR C.; SCALISE, LEVY; GENEZINI, FREDERICO A.; CORREA, EDUARDO L.; SAXENA, RAJENDRA N.; CARBONARI, ARTUR W.
The cubic pyrochlore structure of the RE2Ti2O7 (R= rare earth) form is highly geometrically frustrated antiferromagnets and Gd2Ti2O7 is particularly interesting due to the fact gadolinium has a large magnetic moment and its orbital momentum is zero. Up to nowadays, a few investigations of the local structure on Gd2Ti2O7 using hyperfine interactions techniques were made. Namely, the magnetic hyperfine interaction at Gd previously reported from Mossbauer effect spectroscopy with 155Gd [1] and perturbed angular correlation (PAC) have used to reach electric field gradient at 111mCd and 111In probe nuclei [2]. However, these studies are lacking in interpretation, so first principles calculations may led to the elucidation of the electronic structure at the specific crystalline site. Then, Gd2Ti2O7 single and doped-Cd cell simulations have performed with full potential linearized augmented plane waves methods and generalized gradient approximation from Perdew-Burke-Ernzerhorf within the WIEN2k code. Electric field gradient and magnetic hyperfine components were evaluated.
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.
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.