排序方式: 共有39条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Jos�� Fl��vio Marcelino Borges Marlon Luiz Hneda Andr�� Maur��cio Brinatti Jo?o Batista Marimon da Cunha Jadir Aparecido Rosa Jos�� Domingos Fabris 《Hyperfine Interactions》2011,203(1-3):9-15
A sample of the coarse sand fraction from the soil material of the A-horizon (0?C0.2 m from the soil surface) of a dusky red magnetic Oxisol was submitted to high-energy mechanical milling for different times. This assay aimed mainly at (a) monitoring the individualization of strongly aggregated mineral particles, and (b) measuring the effect of the milling pressure on the mineralogy changes of the material. These data are also intended to experimentally subside any physical model describing the mechanical behavior of the superficial soil layer that is subjected to intensive machine management, in agriculture fields. Powder X-ray data reveal that some mineralogical phases, notably gibbsite, disappear soon after the first few hours milling. The 298 K-transmission Mössbauer spectrum for the non-milled sand sample shows a qualitatively typical pattern for the sand fraction of basalt derived soils, with magnetically ordered sextets, assignable mainly to hematite and maghemite, and an intense central (super)paramagnetic Fe3?+? doublet. For the milled samples, spectra revealed progressive spectral reduction of the magnetic hyperfine structure, with concomitant increase of relative subspectral areas due to (super)paramagnetic phases, as the milling time increased. This result is consistent with the reduction of measured saturation magnetization, from 4.96(8) J T???1 kg???1, for the non-milled sample, to 3.26(7) J T???1 kg???1, for the sample milled for 8 hours. 相似文献
6.
P. Bonville J. A. Hodges F. Hulliger P. Imbert G. Jéhanno J. B. Marimon Da Cunha H. R. Ott 《Hyperfine Interactions》1988,40(1-4):381-384
170Yb Mössbauer measurements show that the heavy electron compound YbAs undergoes a first order paramagnetic-antiferromagnetic transition centered at TN=0.58K. The saturated 4f-shell magnetic moments are reduced by 47% relative to the value predicted by a crystal field model. A study of the line shapes below TN in the presence of an external field shows that the RKKY exchange energy is about 20 times bigger than kB TN. These results show that YbAs presents a magnetic order frustrated by the Kondo effect.supported by CNPq 相似文献
7.
Conservative methods for the Toda lattice equations 总被引:1,自引:0,他引:1
We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings. 相似文献
8.
Valdecir Biondo Suzana Nóbrega de Medeiros Andrea Paesano Luis Ghivelder Bachir Hallouche João Batista Marimon da Cunha 《Solid State Sciences》2009,11(8):1444-1450
The Fex(Cr2O3)1?x system, with 0.10 ≤ X ≤ 0.80, was mechanically processed for 24 h in a high-energy ball-mill. In order to examine the possible formation of iron–chromium oxides and alloys, the milled samples were, later, thermally annealed in inert (argon) and reducing (hydrogen) atmospheres. The as-milled and annealed products were characterized by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and magnetization. The as-milled samples showed the formation of an Fe1+YCr2?YO4?δ nanostructured and disordered spinel phase, the α1-Fe(Cr) and α2-Cr(Fe) solid solutions and the presence of non-exhausted precursors. For the samples annealed in inert atmosphere, the chromite (FeCr2O4) formation and the recrystallization of the precursors were verified. The hydrogen treated samples revealed the reduction of the spinel phase, with the phase separation of the chromia phase and retention of the Fe–Cr solid solutions. All the samples, either as-milled or annealed, presented the magnetization versus applied field curves typical for superparamagnetic systems. 相似文献
9.
J. A. Hodges P. Imbert G. Jéhanno J. B. Marimon Da Cunha J. P. Sanchez 《Hyperfine Interactions》1988,42(1-4):1225-1226
For the high Tc compound YbBa2Cu3O7−x, Mossbauer absorption measurements show that magnetic ordering occurs within the Yb3+ sublattice at 0.35K (μsat=1.7μB). For ErBa2Cu3O7−x the Er3+ sublattice orders at 0.7K (μsat=4μB). Measurements on57Fe diluted into YBa2Cu3O7−x shows that no ordered magnetic moments exist within the Cu sublattices down to at least 4.2K.
Instituto de Fisica, Porto-Alegre, Brasil (supported by CNPq) 相似文献
10.