JOSE MESTNIK FILHO
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Resumo IPEN-doc 27307 Investigation of local magnetic properties of CeCd as a function of the unit cell volume by means of first principles calculations2019 - PEREIRA, L.F.; SCALISE, L.M.; MESTNIK-FILHO, J.; FERREIRA, W.L.; GONÇALVES, V.C.; CARBONARI, A.W.In the work here reported magnetic hyperfine field (Bhf) at Cd site as well as the cerium magnetic moment (m-Ce) were calculated from simulation of the CeCd compound in many different unit cell volumes. Results are compared with the experimental values of Bhf (5.10 T) obtained with Perturbed Angular Correlation spectroscopy measurements [1] and m-Ce from magnetization measurements. The electronic structure calculations of the CeCd cubic cells (under normal conditions the space group is Pm-3m) were performed using density functional theory implemented on ELK and WIEN2k codes with “full-potential linearized augmented plane wave” method and the local density or generalized gradient approximations to estimate exchange-correlation energy. Three methodologies were carried out in our simulations: just spin polarized (SP); spin-orbit coupling (SO); and, SO plus ad hoc U parameter to treat the strong correlation in the cerium 4f shell. The cell energy (CE), m-Ce and Fermi-contact contribution (BFc) of Cd-Bhf from electrons (labelled core and valence) inside the atomic spheres and others quantities were calculated for volume fractions varying from -14% to 5% of the experimental unit cell volume, in steps of 1%. The smallest energy and bestest Cd-Bhf agreement were reached when the volume is compressed by 12%. Results are discussed in terms of Ce-4f electron (de)localization and its strong correlation as well as hybridization effects between Cd and Ce observed through density of states plots to understand the dependence of Cd-BFc with the compression and relaxation of the cell. A brief comparison of Cd-BFc for 3 the methodologies and m-Ce and Cd-BFc versus volume (SP calculation) from WIEN2k are presented.Resumo IPEN-doc 27093 Insights into anomalous magnetic hyperfine field at Ce impurity in LaMn2X2 (X=Si, Ge)2019 - PEREIRA, LUCIANO F.D.; MESTNIK-FILHO, JOSE; CABRERA-PASCA, GABRIEL A.; BOSCH-SANTOS, BRIANNA; FERREIRA, WANDERSON L.; GONÇALVES, VITOR C.; SCALISE, LEVY; GENEZINI, FREDERICO A.; SAXENA, RAJENDRA N.; CARBONARI, ARTUR W.The LaMn2X2 (X=Si, Ge) intermetallic compounds doped with cerium exhibit the interesting physical effects that are typical of the REMn2X2 (RE=rare earth) series (such as magnetocaloric, superconductivy) or are originated from cerium in specific electronic environment (e.g. Kondo, intermediate valence, strongly correlated electron). Recently, the magnetic hyperfine field (mhf) at 140Ce-doped LaMn2(Si(1-x)Gex)2 was determined by perturbed gamma-gamma angular correlation spectroscopy. The 140Ce mhf follow the host magnetization in LaMn2Si2, while in LaMn2(Si(1-x)Gex)2 (with x = 0.2 up to 1), it has anomalous behaviour, which was associated with 4f cerium mhf contribution. In this work, first principles band structure simulations were used to improve the understanding of the distance role (generated by interchange of Si and Ge) on mhf cerium contribution.Resumo IPEN-doc 23311 First-principles calculations of the magnetic hyperfine field at Cd sites in RECd (RE = rare-earth element)2016 - PEREIRA, LUCIANO F.; MESTNIK-FILHO, JOSE; CARBONARI, ARTUR; CAVALCANTE, FABIO; LEITE-NETO, OSMARBinary magnetic compounds based on rare-earth (RE) elements of the type REX, where X is a transition metal, with the simplest stoichiometry and crystalline cubic structure, are isostructural systems with different RE constituents, which differ only slightly in the crystallographic properties, but strongly in the magnetic properties. They thus offer excellent conditions for the separation of the magnetic from other solid-state parameters and permit the magnetism studies. However, in most RE compounds and, particularly when X=Cd, details of the magnetic structure at an atomic scale are not available mainly because is not possible to use neutron diffraction to investigate them. In this paper, the magnetic hyperfine field (mhf) at Cd sites in RECd compounds was studied by first-principles calculation. These compounds crystalizes in the CsCl prototype cubic structure (Pm-3m space-group) and order ferromagnetically below the Curie temperature with exception of PrCd, which presents antiferromagnetism. Recently, it was observed an unexpected transition in the mhf at 111Cd in DyCd below 40 K, when mhf vanishes [1]. We have used the density functional theory framework with full potential Augmented Planes Waves plus local orbitals (APW+lo) method embodied in the WIEN2k code to simulate electronic structures of the ferromagnetic and antiferromagnetic crystal cells in these compounds. For the exchange-correlation effects we chose local density approximation. The mhf at Cd sites and the formation energy were calculated for each compound as well as the density of states were obtained. Results of mhf are in very good agreement (less than 10%) with the experimental values previously reported [1]. Interestingly, for DyCd the energy for the formation of the antiferromagnetic ordering with (π, π, 0) structure is smaller than that for the ferromagnetic and others possible antiferromagnetic phases. As far as we know, it is the first time that such an excellent agreement between the calculated and experimental mhf at Cd sites is observed. Moreover, this results is even more important because the calculations were fully variational without the use of the Hubbard model which takes into account the on-site correlation of 4f electrons.Artigo IPEN-doc 22670 Magnetic hyperfine interactions on Cd sites of the rare-earth cadmium compounds RCd (R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)2016 - CAVALCANTE, F.H.M.; LEITE NETO, O.F.L.S.; SAITOVITCH, H.; CAVALCANTE, T.P.D.; CARBONARI, A.W.; SAXENA, R.N.; BOSCH-SANTOS, B.; PEREIRA, L.F.D.; MESTNIK-FILHO, J.; FORKER, M.This paper reports the investigation of the magnetic hyperfine field Bhf in a series of rare-earth (R) cadmium intermetallic compounds RCd and GdCd2 measured by perturbed angular correlation (PAC) spectroscopy using 111In/111Cd as probe nuclei at Cd sites as well as first-principles calculations of Bhf at Cd sites in the studied compounds. Vapor–solid state reaction of R metals with Cd vapor and the 111In radioisotope was found to be an appropriate route of doping rare-earth cadmium compounds with the PAC probe 111In/111Cd. The observation that the hyperfine parameters depend on details of the sample preparation provides information on the phase preference of diffusing 111In in the rare-earth cadmium phase system. The 111Cd hyperfine field has been determined in the compounds RCd for the R constituents Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, in several cases as a function of temperature. For most R constituents, the temperature dependence Bhf (T ) of 111Cd:RCd is consistent with ferromagnetic order of the compound. DyCd, however, presents a remarkable anomaly: a finite magnetic hyperfine field is observed only in the temperature interval 35 K T 80 K which indicates a transition from ferromagnetic order to a spin arrangement where all 4f -induced contributions to the magnetic hyperfine field at the Cd site cancel. First-principles calculation results for DyCd show that the (π, π, 0) antiferromagnetic configuration is energetically more favorable than the ferromagnetic. The approach used in the calculations to simulate the RCd system successfully reproduces the experimental values of Bhf at Cd sites and shows that the main contribution to Bhf comes from the valence electron polarization. The de Gennes plot of the hyperfine field Bhf of 111Cd:RCd vs the 4f -spin projection (g − 1)J reflects a decrease of the strength of indirect 4f -4f exchange across the R series. Possible mechanisms are discussed and the experimental results indicate that the indirect coupling is provided by the intra-atomic 4f -5d exchange and interatomic 5d-5d interaction between the spin-polarized 5d electrons of neighboring R atoms. The ratio of the hyperfine fields of GdCd and GdCd2 scales with the number of nearest Gd neighbors. In the paramagnetic phases of the RCd compounds, the PAC spectra indicate the presence of a broad distribution of weak quadrupole interactions suggesting a perturbation of the cubic CsCl symmetry of the Cd site, most probably due to chemical disorder of the R and Cd sublattices. A substantial interchange of R and Cd atoms is also reflected in the temperature dependence of the linewidth of the magnetic hyperfine interaction in the magnetically ordered phase of RCd and GdCd2. Its critical increase towards the order temperature is evidence for a distribution of the order temperature with a width of about 10 K.Artigo IPEN-doc 21733 A method to determine contributions to the hyperfine field at Ce probes in magnetic host: Application to Ce impurities at RE sites in REAg (RE=Gd, Tb, Dy, Ho) compounds2016 - CAVALCANTE, F.H.M.; PEREIRA, L.F.D.; CARBONARI, A.W.; MESTNIK-FILHO, J.; SAXENA, R.N.Artigo IPEN-doc 21223 Charge distribution and hyperfine interactions in the vicinity of impurity sites in Insub(2)Osub(3) doped with Fe, Co and Ni2015 - SENA, C.; COSTA, M.S.; MUNOZ, E.L.; CABRERA PASCA, G.A.; PEREIRA, L.F.D.; MESTNIK FILHO, J.; CARBONARI, A.W.; COAQUIRA, J.A.H.Resumo IPEN-doc 20677 First principles calculation of the Cd-doped ZrInsub(2): a study of electronic properties and electric field gradients2014 - PEREIRA, L.F.D.; CAVALCANTE, F.H.M.; BAGGIO-SAITOVITCH, E.; FONTES, M.B.; SAINTOVITCH, H.; MESTNIK FILHO, J.; CARBONARI, A.W.Artigo IPEN-doc 10586 Determinacao do campo hiperfino magnetico em nucleos de sup(148)Ce substituindo Gd em GdAg por electroscopia de correlacao angular perturbada2005 - PEREIRA, L.F.D.; MESTNIK FILHO, J.; CAVALCANTE, F.H.M.; CARBONARI, A.W.Artigo IPEN-doc 16267 Magnetic field at sup(140)Ce in Dy sites in DyX (X=Cu, Ag) compounds studied by perturbed angular correlation spectroscopy2007 - CARBONARI, A.W.; CAVALCANTE, F.H.M.; PEREIRA, L.F.D.; CABRERA PASCA, G.A.; MESTNIK FILHO, J.; SAXENA, R.N.Artigo IPEN-doc 10786 Investigation of the local magnetism at rare-earth sites in RAg(R=rare-earth) intermetallic compounds using perturbed gamma-gamma angular correlation spectroscopy2005 - CAVALCANTE, F.H.M.; CARBONARI, A.W.; MESTNIK FILHO, J.; PEREIRA, L.F.D.; SAXENA, R.N.; OLIVEIRA, A.J.A.; SOUZA, P.E.N.; SANTOS, A.O.Time differential perturbed gamma-gamma angular correlation (TDPAC) technique was used to measure the magnetic hyperfine field (mhf) at rare earth sites in intermetallic compounds RAg (R = Dy, Gd, Ho, Nd, Tb) in order to study the behavior of the mhf with 4f-electron density variation. 140Ce was used as probe nuclei in the TDPAC measurements, which was carried out in the temperature range of 10 K to 300 K. The results of the temperature dependence of the mhf show a standard antiferromagnetic behavior below the magnetic order temperature but, for lower temperatures, it was observed a sharp deviation from the expected Brillouin-like behavior with an increase of the mhf values. The values of the mhf for each compound at the lowest temperature just above the deviation were compared to the respective projection of the rare-earth spin on the total angular momentum J. The results showed to follow a similar behavior when compared to those for the magnetic moment of the compounds.