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1.
A. W. Carbonari J. Mestnik-Filho R. N. Saxena H. Saitovitch 《Hyperfine Interactions》2001,133(1-4):77-81
Magnetic hyperfine fields (mhf) at 111Cd and 140Ce nuclei, dilutely substituting the In and Ce sites, respectively, have been measured in the intermetallic compound CeIn3 using perturbed angular correlation technique. A pure electric quadrupole interaction with an axially symmetric electric field gradient was observed at 111In(EC)111Cd probe nuclei at room temperature while a combined magnetic dipole and electric quadrupole interaction is observed below 10K. Below the ordering temperature, only a magnetic interaction is observed at 140La(–)140Ce probe. The values of mhf measured experimentally as a function of temperature are discussed in terms of critical behavior. 相似文献
2.
M. E. Mercurio A. W. Carbonari M. R. Cordeiro R. N. Saxena 《Hyperfine Interactions》2007,180(1-3):1-5
We report on the first NMR study of 73Ge nuclear spin decoherence in germanium single crystals with different abundance of the 73Ge isotope. Hahn echo decays are well fit by a superposition of two exponentials. The deviation from the single exponential is more pronounced in the more spin-diluted sample, causing long-lived echoes. We show that the decay of these echoes becomes slower with the reduction of 73Ge abundance and is therefore caused by dipole–dipole interaction, reflecting the fundamental decoherence process in the spin system. The fast decay at the beginning of the relaxation process is shown to be mainly caused by the quadrupole interaction. Our experimental findings are supported by the calculations of Hahn echo decays in the germanium crystals under study. Quite good agreement between the theory and experiment is demonstrated. 相似文献
3.
A. L. Lapolli A. W. Carbonari J. Mestnik-Filho D. M. T. Leite R. N. Saxena 《Hyperfine Interactions》2007,176(1-3):75-79
Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using 111In→ 111Cd and 140La→ 140Ce probe nuclei at the In and Gd sites, respectively. The PAC results for 111Cd show two well-defined electric quadrupole frequencies above T C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T C the measurements for 111Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by 140Ce below 100 K. 相似文献
4.
Juliana Marques Ramos Thiago Martucci Artur Wilson Carbonari Messias de Souza Costa Rajendra Narain Saxena Reiner Vianden 《Hyperfine Interactions》2013,221(1-3):129-136
Electric quadrupole interactions were studied in pure and Mn-doped powder samples and thin films of SnO2 using perturbed γγ angular correlation spectroscopy (PAC). The powder samples were prepared by Sol gel method and the thin film were prepared on the Si (100) substrate by sputtering technique using Sn in the oxygen atmosphere. The samples were characterized by x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The thickness of the film was 100 nm. The average particle size of the SnO2 powder samples was determined to be smaller than 60 nm. The radioactive 111In and 181Hf tracers were introduced in the powder samples during the sol gel chemical process. Radioactive 111In was implanted on the SnO2 thin films using the University of Bonn ion implanter (BONIS). PAC measurements were carried out in a four BaF2 detector spectrometer in the temperature range of 77–973 K for samples annealed at different temperatures. The PAC results for both nuclear probes show the presence of two electric quadrupole interactions. The major fractions in both cases correspond to the substitutional sites in the rutile phase of SnO2. The results are compared with previous PAC measurements. 相似文献
5.
F. H. M. Cavalcante M. R. Gomes A. W. Carbonari L. F. D. Pereira D. A. Rossetto M. S. Costa L. M. Redondo J. Mestnik-Filho R. N. Saxena J. C. Soares 《Hyperfine Interactions》2010,198(1-3):41-45
The hyperfine field at 181Ta lattice sites in nanostructured HfO2 thin films was studied by the Perturbed Angular Correlation (PAC) technique. Thin oxide films were deposited by Electron Beam Evaporation on a silicon substrate. The thickness of the films was ~100 nm and ~250 nm. Radioactive 181Hf nuclei were produced by neutron activation of the film samples in the Brazilian Research Reactor (IPEN IEA-R1) by the reaction 180Hf(n,γ)181Hf. PAC measurements were carried out after annealing at 1473 K. The PAC technique allows the determination of the electric field gradient (EFG) at the probe sites. 相似文献
6.
7.
C. Sena M. S. Costa G. A. Cabrera-Pasca R. N. Saxena A. W. Carbonari 《Hyperfine Interactions》2013,215(1-3):105-110
We try to envision that there might be a dark-matter world and neutrinos, especially the right-handed ones, might be coupled directly with dark-matter particles in the dark-matter world. The candidate model would be the extended Standard Model based on SU c (3) × SU L (2) × U(1) × SU f (3) × SU R (2), with the search of the detailed version through the aid of the two working rules, “Dirac similarity principle” and “minimum Higgs hypothesis”. 相似文献
8.
F.H.M. Cavalcante A.W. Carbonari R.F.L. Malavasi G.A. Cabrera-Pasca R.N. Saxena J. Mestnik-Filho 《Journal of magnetism and magnetic materials》2008,320(14):e32-e35
In the present work, the time differential perturbed angular correlation (PAC) technique was used to study the temperature dependence of electric field gradient (efg) in GdCoO3 perovskite using 111Cd and 181Ta nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the oxide lattice through chemical process during sample preparation and were found to occupy only the Co sites in GdCoO3. The efg's at 111Cd and 181Ta show temperature dependence with two different fractions each that change with temperature. In the case of 111Cd the quadrupole frequency slowly decreases, with corresponding increase of the temperature and shows a peak like structure at around 200 K and a discontinuity at 700 K. These changes have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin state and from intermediate-spin to high-spin state of Co3+ ion similar to LaCoO3 compound. Indication of a Jahn–Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out. 相似文献
9.
Carbonari A.W. Mestnik-Filho J. Attili R.N. Moralles M. Saxena R.N. 《Hyperfine Interactions》1999,120(1-8):475-478
The electric field gradient (EFG) at 111Cd nuclei dilutely substituting the cation site in bixbyite rare-earth oxides Tl2O3, Eu2O3, Lu2O3 and Tm2O3 has been measured using perturbed angular correlation technique. The 111In(EC) 111Cd probe nuclei were introduced into the samples by thermal diffusion. The experimental EFG values are compared with those
calculated using the point charge model (PCM). The results are discussed in terms of a correlation between the electric field
gradient and cation–oxygen bond length in metal oxides.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Olzon-Dionysio M. Souza S. D. Ayala A. P. Carbonari A. Longo E. 《Hyperfine Interactions》2001,136(3-8):523-528
The concentration dependence of the electric field gradient (EFG) in PZT ceramics was studied by Time Differential Perturbed
Angular Correlations (PAC) using the 181Ta radioactive probe in samples with x=0.3, 0.5 and 0.8 at room temperature. This phase presents two sites, probably related to defects close to probes, caused
by oxygen and lead vacancies. We can also state that both the paraelectric and ferroelectric phases of these systems have
two sites with different characteristics and that the high-frequency quadrupolar frequency site presents the highest fraction.
The concentration dependence revealed by our results is discussed by comparing the latter with previous PAC studies.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献