Navegação por autor "CABRERA-PASCA, G.A."

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  • IPEN-DOC 24325

    DOMIENIKAN, C. ; BOSCH-SANTOS, B. ; CABRERA-PASCA, G.A.; SAXENA, R.N. ; CARBONARI, A.W. . Anomalous behavior of the magnetic hyperfine field at 140Ce impurities at La sites in LaMnSi2. AIP Advances, v. 8, n. 5, p. 055702-1 - 055702-6, 2018. DOI: 10.1063/1.5006897

    Abstract: Magnetic hyperfine field has been measured in the orthorhombic intermetallic compound LaMnSi2 with perturbed angular correlation (PAC) spectroscopy using radioactive 140La(140Ce) nuclear probes. Magnetization measurements were also carried out in this compound with MPSM-SQUID magnetometer. Samples of LaMnSi2 compound were prepared by arc melting the component metals with high purity under argon atmosphere followed by annealing at 1000°C for 60 h under helium atmosphere and quenching in water. X-ray analysis confirmed the samples to be in a single phase with correct crystal structure expected for LaMnSi2 compound. The radioactive 140La (T1/2 = 40 h) nuclei were produced by direct irradiation of the sample with neutrons in the IEA-R1 nuclear research reactor at IPEN with a flux of ∼ 1013 n cm−2s−1 for about 3 - 4 min. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. Temperature dependence of the hyperfine field, Bhf was found to be anomalous. A modified two-state model explained this anomalous behavior where the effective magnetic hyperfine field at 140Ce is believed to have two contributions, one from the unstable localized spins at Ce impurities and another from the magnetic Mn atoms of the host. The competition of these two contributions explains the anomalous behavior observed for the temperature dependence of the magnetic hyperfine field at 140Ce. The ferromagnetic transition temperature (TC) of LaMnSi2 was determined to be 400(1) K confirming the magnetic measurements.

    Palavras-Chave: cerium 140; impurities; iear-1 reactor; magnetic fields; hyperfine structure; crystal field; intermetallic compounds

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  • IPEN-DOC 23154

    BOSCH-SANTOS, B. ; CABRERA-PASCA, G.A.; SAXENA, R.N. ; FREITAS, R.S.; CARBONARI, A.W. . Characterization of magnetic phase transitions in PrMn2Ge2 compound investigated by magnetization and hyperfine field measurements. AIP Advances, v. 7, n. 5, p. 056211-1 - 056211-6, 2017. DOI: 10.1063/1.4974025

    Abstract: The magnetic properties of PrMn2Ge2 compound have been investigated by perturbed γ−γγ−γ angular correlation (PAC) spectroscopy using 111In(111Cd) as probe nuclei as well as by magnetization measurements. This ternary intermetallic compound exhibits different magnetic structures depending on the temperature. The magnetic ordering is mainly associated with the magnetic moment of 3d-Mn sublattice but at low temperatures a magnetic contribution due to ordering of the magnetic moment from 4f-Pr sublattice appears. PAC results with 111Cd probe nuclei at Mn sites show that the temperature dependence of hyperfine field Bhf(T) follows the expected behavior for the host magnetization, which could be fitted by two Brillouin functions, one for antiferromagnetic phase and the other for ferromagnetic phase, associated with the magnetic ordering of Mn ions. Magnetization measurements showed the magnetic behavior due to Mn ions highlighting the antiferromagnetic to ferromagnetic transition around 326 K and an increase in the magnetization around 36 K, which is ascribed to Pr ions ordering.

    Palavras-Chave: intermetallic compounds; magnetic properties; phase transformations; perturbed angular correlation; hyperfine structure

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  • IPEN-DOC 27768

    MACIEL, L.S. ; BURIMOVA, A. ; PEREIRA, L.F.D. ; FERREIRA, W.L. ; SALES, T.S.N. ; GONÇALVES, V.C. ; CABRERA-PASCA, G.A.; SAXENA, R.N. ; CARBONARI, A.W. . DFT-based calculations of the magnetic hyperfine interactions at Cd sites in RCd (R = rare earth) compounds with the FP-LAPW ELK code. AIP Advances, v. 11, n. 2, p. 025010-1 - 025010-4, 2021. DOI: 10.1063/9.0000161

    Abstract: In the work here reported, we have calculated magnetic hyperfine interactions in rare-earth (R) intermetallic compounds by using the free open-source all-electron ELK code. The RCd (R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) series was chosen as a test system because an almost complete set of experimental data on the hyperfine parameters at Cd sites was acquired through the time differential perturbed angular correlation (TDPAC) spectroscopy as previously reported. Moreover, results on magnetic hyperfine field (Bhf ) from WIEN2k code were also reported allowing a qualitative comparison analysis. We emphasize that the utilized version of ELK accounted for the contact field only. Yet, as it is the only contribution expected for Cd site in RCd compounds, the calculated Bhf values are in reasonable agreement with the experimental results. The Spin-orbit coupling when taken into account led to a decrease in deviation from experimental data. Addition, the Hubbard-like term was revealed crucial in order to make Bhf predictions for CeCd, suggesting that this behavior may be associated with a weaker 4f electron localization in Ce.

    Palavras-Chave: calculation methods; rare earths; hyperfine structure; cadmium compounds; computer codes; spectroscopy; theoretical data

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  • IPEN-DOC 26867

    CABRERA-PASCA, G.A.; BOSCH-SANTOS, B. ; BURIMOVA, A. ; CORREA, E.L. ; CARBONARI, A.W. . Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3. AIP Advances, v. 10, n. 1, p. 015223-1 - 015223-5, 2020. DOI: 10.1063/1.5130429

    Abstract: 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.

    Palavras-Chave: impurities; magnetic flux; doped materials; perturbed angular correlation; trigonal lattices; hyperfine structure; magnetic moments; cerium additions; lanthanum; thin films; manganese oxides; probes

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  • IPEN-DOC 26868

    CORREA, E.L. ; BOSCH-SANTOS, B. ; SAXENA, R.N. ; CABRERA-PASCA, G.A.; CARBONARI, A.W. . Effects of an external magnetic field on the hyperfine parameters in RE2O3 (RE = Gd, Er) nanoparticles measured by perturbed angular correlation spectroscopy. AIP Advances, v. 10, n. 1, p. 015039-1 - 015039-6, 2020. DOI: 10.1063/1.5130401

    Abstract: 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.

    Palavras-Chave: perturbed angular correlation; spectroscopy; magnetic fields; rare earths; hyperfine structure; asymmetry coefficients; thermal analysis; transmission electron microscopy; x-ray diffraction

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  • IPEN-DOC 28235

    MIRANDA FILHO, A.A. ; SALES, T.S.N. ; OTUBO, L. ; CABRERA-PASCA, G.A.; CARBONARI, A.W. . Investigation of hyperfine interactions of multiferroic oxides Bi0.85La0.15FeO3 through perturbed angular correlation spectroscopy. In: INTERNATIONAL NUCLEAR ATLANTIC CONFERENCE, November 29 - December 2, 2021, Online. Proceedings... Rio de Janeiro: Associação Brasileira de Energia Nuclear, 2021.

    Palavras-Chave: perturbed angular correlation; sol-gel process; bismuth; ferrites; ferromagnetic materials

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  • IPEN-DOC 27086

    MATOS, I.T. ; NASCIMENTO, N.M. ; CABRERA-PASCA, G.A.; EFFENBERGER, F.B. ; FREITAS, R.S.; CARBONARI, A.W. . Investigation of magnetic and structural properties of CoFe2O4 nanoparticles by measuring hyperfine interactions with 111Cd. In: INTERNATIONAL CONFERENCE ON HYPERFINE INTERACTIONS AND THEIR APPLICATIONS, February 10-15, 2019, Goa, India. Abstract... Mumbai, India: Tata Institute of Fundamental Research, 2019. p. 35-35.

    Abstract: 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.

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  • IPEN-DOC 28750

    CABRERA-PASCA, G.A.; MAGNO, J.F.; FERREIRA, W.L. ; CAMPOS, A.C. ; BOSCH-SANTOS, B.; SALES, T.S.N. ; PEREIRA, L.F.D. ; BURIMOVA, A. ; SAXENA, R.N. ; FREITAS, R.S.; CARBONARI, A.W. . Local inspection of magnetic properties in GdMnIn by measuring hyperfine interactions. In: ANNUAL CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS, 65th, November 2-6, 2020, Online. Abstract... 2020.

    Abstract: GdMn2 is a member of a series of Laves phase containing a rare-earth element and a magnetic 3dtransition metal with very peculiar magnetic properties[1]. Doping with a non-magnetic element such as indium affects these properties[2,3]. GdMnIn is reported to crystalize in the hexagonal MgNi2-type structure presenting a spin-glass behavior with no magnetic order attributed to the triangular spin frustration of magnetic ions[3]. The observed absence of long-range interactions by magnetization measurements along with the almost impossible measurements with neutron diffraction due to the presence of Gd with very high neutron absorption cross section makes the investigation of local exchange interactions in this compound very difficult. In the present work, measurements of hyperfine interactions at In sites using 111In(111Cd) probe nuclei were carried out by perturbed angular correlations (PAC) technique to investigate the local magnetic exchange in GdMnIn compound. Results displayed in Fig. 1 for the behavior of the major component (Vzz) of the electric field gradient (efg) tensor and the distribution of electric quadrupole frequency () show a strong instability of the electronic environment of In sites when temperature decreases indicating a Mn-In disorder. The weak magnetic hyperfine field at In sites also shown in Fig.1 with an anomalous temperature dependence below around 140 K along with the increase in the angle between Bhf and Vzz directions suggest a weak long-range exchange interaction.

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  • IPEN-DOC 27552

    CABRERA-PASCA, G.A.; MAGNO, J.F.; FERREIRA, W.L. ; CAMPOS, A.C. ; BOSCH-SANTOS, B. ; SALES, T.S.N. ; PEREIRA, L.F.D. ; BURIMOVA, A. ; SAXENA, R.N. ; FREITAS, R.S.; CARBONARI, A.W. . Local inspection of magnetic properties in GdMnIn by measuring hyperfine interactions. AIP Advances, v. 11, n. 1, p. 015322-1 - 015322-6, 2021. DOI: 10.1063/9.0000037

    Abstract: GdMnIn is reported to crystallize in the hexagonal MgNi2-type structure presenting a spin-glass behavior with no magnetic order attributed to the triangular spin frustration of magnetic ions. In the present work, FC-ZFC magnetization, specific heat and AC susceptibility measurements along with the local magnetic exchange measured by hyperfine interactions at In sites are used to investigate the magnetic behavior in GdMnIn compound. The ZFC-FC magnetization curves exhibit an inflection which was ascribed to the antiferromagnetic transition at TN= 145 K. These curves also give an indication of thermomagnetic irreversibility at 118 K, which along with the absence of inflection in specific heat results might be associated to spin-glass behavior. Results of AC susceptibility and magnetic hyperfine field measured using 111In(111Cd) probe nuclei carried out by perturbed angular correlations (PAC) technique did not show evidence of spin-glass behavior. The thermomagnetic irreversibility in FC-ZFC curves along with results of hyerfine interactions suggest the presence of magneto-crystalline anisotropy effects and a weak long-range coupling in GdMnIn.

    Palavras-Chave: magnetic properties; hyperfine structure; angular correlation; perturbed angular correlation; spin glass state; magnetization; gadolinium; manganese; indium

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  • IPEN-DOC 28168

    FERREIRA, W.L. ; PEREIRA, L.F.D. ; LEITE NETO, O.F.S. ; MACIEL, L.S. ; GONÇALVES, V.C. ; SAXENA, R.N. ; CARBONARI, A.W. ; COSTA, M.S.; CABRERA-PASCA, G.A.. Locally symmetric oxygen vacancy around Cd impurities in CeO2. Physical Review B, v. 104, n. 3, p. 035146-1 - 035146-11, 2021. DOI: 10.1103/PhysRevB.104.035146

    Abstract: A detailed investigation of the electronic structure in the neighborhood of Cd impurities in CeO2 has been performed by ab initio calculations to elucidate the interplay between the oxygen vacancies and electric quadrupole interactions. The quadrupole frequency related to the major component of the electric-field gradient (EFG) at impurities sites from its neighboring charge density as well as its symmetry were calculated by simulating oxygen vacancies at oxygen nearest neighbor of Cd. Results show a very good agreement with experimental hyperfine interactions measurements at the 111Cd nucleus replacing Ce at CeO2. A systematic mapping of oxygen vacancies in CeO2 supercells was proposed within the framework of density-functional theory using the WIEN2K code focusing on the electronic distribution in the vicinity of Cd impurities. Results show that the calculated values of EFG crucially depend on impurity-vacancy complex position and the striking axial symmetry observed when an oxygen monovancy is at the nearest neighborhood of Cd is explained by a rearrangement of its p orbitals.

    Palavras-Chave: electric fields; cadmium; cerium oxides; x-ray spectra

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  • IPEN-DOC 28524

    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. . Magnetic and structural properties of the intermetallic Ce(1−x)LaxCrGe3 series of compounds. Physical Review Materials, v. 5, n. 11, p. 114406-1 - 114406-11, 2021. DOI: 10.1103/PhysRevMaterials.5.114406

    Abstract: 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.

    Palavras-Chave: magnetic properties; intermetallic compounds; magnetization; neutron dosimetry

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  • IPEN-DOC 26466

    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. . Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites. AIP Advances, v. 9, n. 3, p. 035245-1 - 035245-5, 2019. DOI: 10.1063/1.5080094

    Abstract: 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.

    Palavras-Chave: magnetic fields; spectroscopy; perturbed angular correlation; transmission electron microscopy; perovskite; cerium alloys; impurities; polycrystals; lanthanum

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  • IPEN-DOC 26772

    BOSCH-SANTOS, B. ; NASCIMENTO, N. ; SAIKI, M. ; CORREA, E.L. ; SALES, T.S. ; PEREIRA, L.F. ; CABRERA-PASCA, G.A.; CARBONARI, A.W. . Magnetic field at Ce impurities in La sites of LaBaMn2O6 double perovskites. In: JOINT MMM-INTERMAG CONFERENCE, January 14-18, 2019, Washington, DC, USA. Abstract... Melville, NY, USA; Piscataway, NJ, USA: AIP Publishing; IEEE Magnetics, 2019. p. 759-760.

    Abstract: Magnetic behavior in LaBaMn2O6 double perovskite compounds has been investigated with various techniques, due to the rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine field at the 140Ce nucleus of Ce impurities occupying La sites. The radioactive 140La nuclei with a half-life of 40.8 h were produced by direct activation of natural La present in the samples through the irradiation with neutrons in the IEA-R1 nuclear research reactor of IPEN. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. 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. This phase occurs due to an oxygen deficiency. The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites, which can be ascribed to the contribution of 4f band of Ce to Bhf at low temperatures due to the increase in its localized character.

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  • IPEN-DOC 24375

    BOSCH-SANTOS, B. ; CABRERA-PASCA, G.A.; SAXENA, R.N. ; BURIMOVA, A.N. ; CARBONARI, A.W. . Magnetic interactions at Ce impurities in REMn2Ge2 (RE = La, Ce, Pr, Nd) compounds. Physica B: Condensed Matter, v. 536, p. 137-141, 2018. DOI: 10.1016/j.physb.2017.10.047

    Abstract: In the work reported in this paper, the temperature dependence of the magnetic hyperfine field (Bhf) at 140Ce nuclei replacing Pr atoms in PrMn2Ge2 compound was measured by the perturbed angular correlation technique to complete the sequence of measurements in REMn2Ge2 (RE = La, Ce, Pr, Nd). Results show an anomalous behavior different from the expected Brillouin curve. A model was used to fit the data showing that the Ce impurity contribution (Bimp hf ) to Bhf is negative for NdMn2Ge2 below 210 K. The impurity contribution (Bimp hf ) at 0 K for all compounds is much smaller than that for the free Ce3+, showing that the 4f band of Ce is more likely highly hybridized with 5d band of the host. Results show that direction of the localized magnetic moment at Mn atoms strongly affects the exchange interaction at Ce impurities.

    Palavras-Chave: cerium 140; cerium ions; exchange interactions; germanium; impurities; magnetic moments; magnetization; neodymium compounds; perturbed angular correlation; temperature dependence

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  • IPEN-DOC 29751

    CORREA, E.L. ; BOSCH-SANTOS, B.; SALES, T.S.N. ; CABRERA-PASCA, G.A.; CORREA, B.S. ; CARBONARI, A.W. ; OLESHKO, V.P.; DENNIS, C.L.. Magnetic properties of Er-doped Fe3O4 nanoparticles studied by perturbed angular spectroscopy. In: RIVAS, MONTSERRAT (Ed.); BLANCO, JESUS A. (Ed.); GORRIA, PEDRO (Ed.) INTERNATIONAL CONFERENCE ON FINE PARTICLE MAGNETISM, 10th, May 26-31, 2019, Gijón, Spain. Proceedings... 2019. p. 133-133.

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  • IPEN-DOC 24605

    NASCIMENTO, N.M. ; CORREA, E.L. ; BOSCH-SANTOS, B. ; MATOS, I.T. ; CABRERA-PASCA, G.A.; CARBONARI, A.W. . Production and study of nanoparticles magnetic properties by hyperfine interactions. In: 60 YEARS OF IEA-R1: INTERNATIONAL WORKSHOP ON UTILIZATION OF RESEARCH REACTORS, November 28 - December 01, 2017, São Paulo, SP. Abstract... São Paulo, SP: Instituto de Pesquisas Energéticas e Nucleares, 2017. p. 81-81.

    Abstract: 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.

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  • IPEN-DOC 23107

    SALES, T.S.N. ; CAVALCANTE, F.H.M.; BOSCH-SANTOS, B. ; PEREIRA, L.F.D. ; CABRERA-PASCA, G.A.; FREITAS, R.S.; SAXENA, R.N. ; CARBONARI, A.W. . Stable tetragonal phase and magnetic properties of Fe-doped HfO2 nanoparticles. AIP Advances, v. 07, n. 05, p. 056315-1 - 056315-6, 2017. DOI: 10.1063/1.4976583

    Abstract: In this paper, the effect in structural and magnetic properties of iron doping with concentration of 20% in hafnium dioxide (HfO2) nanoparticles is investigated. HfO2 is a wide band gap oxide with great potential to be used as high-permittivity gate dielectrics, which can be improved by doping. Nanoparticle samples were prepared by sol-gel chemical method and had their structure, morphology, and magnetic properties, respectively, investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD), and magnetization measurements. TEM and SEM results show size distribution of particles in the range from 30 nm to 40 nm with small dispersion. Magnetization measurements show the blocking temperature at around 90 K with a strong paramagnetic contribution. XRD results show a major tetragonal phase (94%).

    Palavras-Chave: nanoparticles; doped materials; hafnium oxides; magnetic properties; iron oxides; phase stability; tetragonal lattices

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  • IPEN-DOC 24523

    CABRERA-PASCA, G.A.; CARBONARI, A.W. . Study of nanoparticles and nanowires by PAC spectroscopy. In: 60 YEARS OF IEA-R1: INTERNATIONAL WORKSHOP ON UTILIZATION OF RESEARCH REACTORS, November 28 - December 01, 2017, São Paulo, SP. Abstract... São Paulo, SP: Instituto de Pesquisas Energéticas e Nucleares, 2017. p. 09-09.

    Abstract: Nanoparticles, nanowires and other low-dimensional nanostructures have received considerable attention due their unique physical properties and also for their promising applications. These nanostructures have contributed to the development of emerging technologies in addition to assisting the progress of nanoscience. Nanoscience is an emerging interdisciplinary area that hopes to have broad implications in many fields such as: materials science, medicine, electronics, optics, etc. The potential applications of these nanostructures depend strongly on their quality, diameter, density, and chemical composition and their crystal structure, therefore, must be precisely controlled. However, the control of the size and morphology of nanostructured materials is not always an easy task and sometimes become challenging. On the other hand, in order to understand the properties derived from the dimensionality of these nanosystems, different techniques have been used. The choice of each technique or methodology depends on several factors including the facility implementation on research laboratories. In this way, we believe that the analysis taking into account the correlation between different techniques would allow an improvement of the projection of future technologies. For these reason, in recent years we have carried out studies on nanostructured systems using the Perturbed Angular Correlation spectroscopy to obtain a local view of these system. Particularly, our studies have focused on Fe3O4 and CoO nanoparticles, which were synthesized by the thermal decomposition method. The choice of this synthesis method was due of their feasible for production in large-scale with high-quality of nanoparticles and also due of feasible to incorporate the nuclear probe. Also, we have studied hyperfine parameter of the hierarchically structured nanowires on the microtubule of ZnO and CuO obtained by thermal oxidation process by simply heating a high purity metal. These measurements are correlated with X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and magnetic measurements using a SQUID magnetometer.

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  • IPEN-DOC 27751

    SALES, T.S.N. ; BURIMOVA, A. ; RODRIGUES, P.S. ; MATOS, I.T. ; CABRERA-PASCA, G.A.; SAXENA, R.N. ; PEREIRA, L.F.D. ; OTUBO, L. ; CARBONARI, A.W. . Synthesis and characterization of Fe3O4-HfO2 nanoparticles by hyperfine interactions measurements. AIP Advances, v. 11, n. 1, p. 015047-1 - 015047-4, 2021. DOI: 10.1063/9.0000235

    Abstract: Nanoparticles (NPs) that combine biocompatibility and enhanced physical characteristics for biomedical applications are currently an area of intense scientific research. Hafnium oxide NPs are an innovative approach in the anticancer treatment by radiotherapy due to their low toxicity and enhancement of local dose in the tumor reducing the total radiation dose for the patient. The combination of this property with the excellent magnetic hyperthermia performance of Fe3O4 NPs can produce a promising nanomaterial for cancer therapy. In this work, we attempted to synthesize nanoscale samples of HfO2 doped with nominal 10 at.% Fe, and Fe3O4 doped with Hf at 10 at.% level using simple chemical routes. The crystal structure of the samples was characterized by X-ray diffraction. The material was irradiated with neutrons in a research reactor, the nuclear reaction 180Hf(n, γ)181Hf yielding the probe nucleus 181Hf(181Ta) used in the perturbed angular correlations experiments to measure hyperfine interactions. Despite their immediate response to the external magnetic field, at local level both samples showed only electric quadrupole interaction typical of the monoclinic hafnia indicating that Fe replaces Hf in HfO2 NPs, but, rather than substituting Fe, Hf enters magnetite in the form of HfO2 clusters. Transmission Electron Microscopy was exploited to study the morphology of these complex systems, as well as to localize hafnia clusters and understand the nature of their coupling to Fe3O4 specks.

    Palavras-Chave: nanoparticles; magnetite; transmission electron microscopy; hafnium oxides; radiotherapy; synthesis; composite materials

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  • IPEN-DOC 23309

    KRYLOV, V.I. ; BOSCH-SANTOS, B. ; CABRERA-PASCA, G.A. ; CARBONARI, A.W. ; SAXENA, R.N. ; MESTNIK-FILHO, J. . Temperature anomalies of the hyperfine magnetic fields on 111Cd probe nuclei in ferro- and antiferromagnetic phases of the ordered FeRh alloys. In: TEMST, KRISTIAAN (Ed.); VANTOMME, ANDRE (Ed.); COTTENIER, STEFAAN (Ed.); PEREIRA, LINO (Ed.) INTERNATIONAL CONFERENCE ON HYPERFINE INTERACTIONS AND THEIR APPLICATIONS, July 3-8, 2016, Leuven, Belgium. Abstract... Leuven, Belgium: Instituut voor Kern- en Stralingsfysica, 2016.

    Abstract: FeRh ordered alloy crystallizes in the bcc B2 structure [1], presents first order phase transition from antiferromagnetic (AF) ordering at low temperature to ferromagnetic (F) state above 350 K [2], and shows significant magnetocaloric effect near RT [3]. Recently, FeRh alloy has also been considered as an interesting material for spintronics applications [4]. In the AF state, FeRh has compensated AFII-type magnetic structure with μFe=3.3 μB and μRh=0. In the F state of FeRh both Fe and Rh atoms have magnetic moments of μFe=3.2 μB and μRh=0.9 μB, respectively [5]. The Fe – Rh compounds were studied by Mössbauer spectroscopy (MS) on 57Fe [6, 7] and 119Sn probe nuclei [8]. In this work, we have, for the first time, investigated the HFs for 111Cd probe atoms in two FeRh samples of different composition by perturbed γ-γ angular correlation (PAC) spectroscopy in the range from 40 K to a temperature above the TC. The alloy Fe0.48Rh0.52 (A1 sample) is AF at low temperatures. At the temperature Tt = 345 K the first order phase transition is observed, and this compound becomes F at the temperatures lower than TC = 685 K. The alloy Fe0.52Rh0.48 (A2 sample) is only ferromagnetic below TC = 800 K. It was established that in both alloys 111Cd probes substitute only Fe ions. The HFs values extrapolated to 0 K were found to be B1(0) =8.70(5) T and B2(0) =5.53(5) T for AF and F ordering of A1 and A2 samples, respectively. The HF in the AF state is almost 60% higher than the HF in the F alloy. The dependences B1 (T) and B2 (T) show anomalous behavior. At Tt = 345 K, phase transition AF-F is accompanied by a sharp decrease in the HF at 111Cd probe nuclei. Earlier, an increase of the corresponding HFs was observed for 57Fe atoms and 119Sn impurity atoms in the region of AF-F transition by MS in [6] and [8]. Analysis of B1(T) and B2(T) has allowed to obtain the temperature dependences of the competing contributions BFe (T) and BRh (T) to the HFs on 111Cd probe nuclei in FeRh alloys.

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