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.Resumo IPEN-doc 23310 Hydrogen absorption effects on the physical properties of ball-milled LaNiSn intermetallic compounds2016 - ANDRE-FILHO, J.; COAQUIRA, J.A.H.; MESTNIK-FILHO, J.; CARBONARI, A.W.; NAGAMINE, L.C.C.M.A polycrystalline samples were prepared by arc melting high-purity elements under argon atmosphere. The samples were re-melted several times to ensure homogeneity. After arc-melting, the samples were annealed in vacuum at 800°C for 28h. After that, some samples were milled using a Ball milling technique. The hydrogenation was carried out by the Sievert’s method using a high purity hydrogen gas. X-ray diffraction (XRD) measurements indicate the formation of the TiNiSi-type orthorhombic structure with space group Pnma for the unmilled sample and its hydride. The milled samples show broad peaks and poor crystallinity hindering the analysis of the structural properties. One sample was milled with 10wt% of graphite. The analysis of the graphite-milled sample reveals that graphite preserves the structural properties (the sample shows better crystalline quality) and acts as a catalyst for the absorption of hydrogen. The analyses of the XRD patterns show that the structural parameters are modified after the hydrogenation. The transmission electron microscope images corroborate the XRD data. Mössbauer spectra (297K) of the unmilled LaNiSn show the presence of only one doublet inconsistency with the one symmetry site of Sn atoms in the TiNiSn-type structure. Moreover, spectra of the milled samples are better reproduced by considering three doublets. Those components were associated with Sn atoms occupying regular sites (D1), Sn atoms substituting Ni atoms (D2) and Sn atoms of some spurious phase or Sn atoms localized in the interface region of the grains (D3). The spectral area of the D1 component decreases at expenses of the other two components. However, the isomeric shift (IS) of D1 and D2 shows a constant value as the milling time is increased. The IS of the third doublet shows some fluctuating behavior likely related to its small spectral area. The quadrupole splitting (QS) of D2 component shows larger value than that of the D1 component and both show clear increasing tendency as the milling time is increased. After the hydrogenation, the IS shows an increase related to the samples before hydrogenation. However, the IS of the D1 and D2 components do not undergo a drastic change in value with the milling time. The value of the QS of D1 and D2 components show an increase with the milling time. This result has been assigned to the indirect interaction between Sn and H atoms which causes an asymmetric electron distribution around the Sn atoms.Resumo IPEN-doc 23309 Temperature anomalies of the hyperfine magnetic fields on 111Cd probe nuclei in ferro- and antiferromagnetic phases of the ordered FeRh alloys2016 - KRYLOV, V.I.; BOSCH-SANTOS, B.; CABRERA-PASCA, G.A.; CARBONARI, A.W.; SAXENA, R.N.; MESTNIK-FILHO, J.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.Artigo IPEN-doc 23077 Local structure of core−shell MnFe2O4+δ-based nanocrystals: cation distribution and valence states of manganese ions2017 - MARTINS, FERNANDO H.; SILVA, FRANCISCARLOS G.; PAULA, FABIO L.O.; GOMES, JULIANO de A.; AQUINO, RENATA; MESTNIK-FILHO, JOSE; BONVILLE, PIERRE; PORCHER, FLORENCE; PERZYNSKI, REGIME; DEPEYROT, JEROMEWe investigate the local structure of nanoparticles based on a manganese ferrite core surrounded or not by a maghemite layer obtained after hydrothermal surface treatment. Results of X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) measurements are crossed with those of infield Mössbauer spectroscopy and X-ray absorption spectroscopy (XANES/EXAFS) to study the valence state of Mn ions and the cation distribution at interstitial sites of the core−shell nanoparticle structure. Linear combination fitting of XANES data clearly indicates the existence of mixed valence states of Mn cations in the Mn ferrite phase. As a direct consequence, it induces nonequilibrium cation distributions in the nanoparticle core with the presence of a large amount of Mn cations at octahedral sites. The quantitative results of the inversion degree given by NPD, Mössbauer spectroscopy measurements, and EXAFS are in good accordance. It is also shown that both the proportions of each oxidation degree of Mn ions and their location at tetrahedral or octahedral sites of the spinel nanocrystal core can be modified by increasing the duration of the surface treatment.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 22583 Substitutional and interstitial modification of Nd5Fe172007 - MURAKAMI, R.K.; VILLAS-BOAS, V.; MESTNIK FILHO, J.; RECHENBERG, H.R.; MISSELL, F.P.Artigo IPEN-doc 22575 Time differential perturbed angular 'gamma''gamma'-correlation studies of diethylenetriaminepentaacetic acid complexes with 111In and 111mCd2001 - SHPINKOVA, L.G.; CARBONARI, A.W.; NIKITIN, S.M.; MESTNIK-FILHO, J.Resumo IPEN-doc 22170 Magnetic and transport properties along with local distortions in Bisub(2)Mnsub(4)Osub(10) and Bisub(2)Fesub(4)Osub(9) multiferroic compounds2015 - CABRERA PASCA, GABRIEL; RAMIREZ, FABIAN N.; CARBONARI, ARTUR W.; MESTNIK FILHO, JOSE; SOUZA, JOSE A.