共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Kotani 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,72(3):375-384
Effect of a finite conduction-band width is studied in detail on the spectra of X-ray absorption spectroscopy (XAS) and its
X-ray magnetic circular dichroism (XMCD) at the L2,3 absorption edges of mixed valence Ce and Yb compounds in high magnetic fields.
Calculations are made with an extended single impurity Anderson model and within the leading term approximation in the 1/Nf expansion method, where Nf is the degeneracy of the 4f states.
It is shown that a model with a vanishing conduction-band width is applicable, as an approximation method, to the calculation
of XAS and XMCD spectra for realistic systems with a finite conduction-band width, if the values of the 4f level and the hybridization
strength are renormalized appropriately.
This justifies the previous calculations on general features of high-magnetic-field XAS and XMCD spectra with zero conduction-band
width.
At the same time, it is also shown that for more realistic calculations of high-magnetic-field XMCD spectra of some specific
mixed-valence Ce and Yb compounds, the present theory with a finite conduction-band width is more appropriate. 相似文献
2.
X-ray magnetic circular dichroism at rare-earth L23 absorption edges in various compounds and alloys
Theoretical interpretations of X-ray magnetic circular dichroism (XMCD) at rare-earth (called R hereafter) L23 absorption edges are reviewed using differing models, depending on the material under investigation. In the first chapter, we present an overview of recent developments for XMCD in XAS with a few general remarks, especially at R atom absorption edges. In Section 2, we first describe basic mechanism of XMCD at L23 edges of R systems, and then we essentially discuss two examples of XMCD spectra in: (i) R2Fe14B metallic compounds, with the help of a cluster model, and (ii) RFe2 Laves-phase compounds, using a tight-binding approximation for R 5d and Fe 3d conducting states. A good agreement between theory and experiment for R2Fe14B suggests that a cluster model provides a valuable method to quantitatively calculate XMCD spectra of R systems, even with quite complicated atomic arrangements. For RFe2 systems the XMCD spectral shape, especially for the L2 edge of heavy R elements, is more complicated than those of R2Fe14B systems, and this is explained by the competition of some different XMCD mechanisms. In Section 3, we focus on special series of Ce systems, related to XAS and XMCD studies at the Ce L23 edges. Two clearly differing cases are interpreted: (i) A well localized 4f1 system, i.e. CeRu2Ge2; (ii) A less localized 4f1 system, i.e. CeFe2, with a 3d partner. Then, from a more experimental point of view, we investigate the influence of substitution on the low temperature properties of CePd3 compounds, i.e. Ce(Pd1-xMnx)3 alloys where x is about 0.03, giving rise to (CePd3)8Mn ordered structure. We give another example: Ce(Pd1-xNix)3 alloys with x taken up to about 0.25. Also the Ce L23 XMCD signal measured in pure CePd3 demonstrates that in the Ce based dense Kondo materials, only the 4f1 channel yields a magnetic response. 相似文献
3.
A theoretical study is presented, with an extended single impurity Anderson model, for the crystal field effect on the X-ray
magnetic circular dichroism (XMCD) spectra at L2,3 edges of mixed-valence Ce and Yb compounds in high magnetic fields. The crystal field acting on the 4f electrons is assumed to have cubic symmetry.
Due to the competition among the effects of crystal field, mixed valency, and external magnetic field, the magnetic-field-dependence
of XMCD spectra exhibits a variety of features; for instance, the branching ratio, R(L2/L3), of L2 and L3 XMCD intensities of Ce compounds can take R(L2/L3) > 1.0 and <1.0, and that of Yb compounds can take R(L2/L3) > 0 and <0.
It is shown that the magnetic-field-dependence of the total XMCD intensity I(L2 + L3) is proportional to the magnetization curve, but that of R(L2/L3) gives more precise information on the ground state wavefunction in magnetic fields. A new and useful method to correlate
the XMCD spectra, the 4f magnetization and the ground state wavefunction is proposed and used to discuss the relation between I(L2 + L3) and the magnetization curve and that between R(L2/L3) and the ground state wavefunction. 相似文献
4.
Thermomodulation spectra were obtained near the Al L2,3 edge in Al films, using synchrotron radiation. These spectra, temperature derivatives of the absorption coefficient, completely resolve the two spin-orbit components. A fit to the shape of one component shows that broadening of the Fermi function is the dominant mechanism for the temperature dependence one-electron or many-body absorption process, is needed near the region of the “spike”. 相似文献
5.
K. Maeda 《Journal of Physics and Chemistry of Solids》1982,43(2):121-123
The wavelengths and energies of the L1, L2 and L3 absorption limits in Zr, Nb, Ru, Rh, Pd and Ag metals have been measured and some of the previous reported values have been found to be incorrect. By comparing the energies of the absorption limits with those of the Lγ1Ly, and Lβ2,15, lines and also with the binding energies obtained by XPS, the electronic transitions corresponding to the respective absorption limits have been clarified. It is concluded that (i) the end level of the electronic transition corresponding to the L1 absorption limit of Zr-Ag is the 5p-like level, and (ii) the end level corresponding to either of the L2 and L3, absorption limits of Zr-Pd is the 4d level, while that of Ag is, rather unexpectedly, the top of the 5s level. 相似文献
6.
A Adam D Billerey C Terrier K Katsumata J Magariño J Tuchendler 《Physics letters. A》1980,79(4):353-354
By performing magnetic resonance experiments in NiBr2 at high frequencies and magnetic fields, we have observed a resonance line which we relate to a helimagnetic phase, and an antiferromagnetic resonance line corresponding to an antiferromagnetic phase with strong out-of-plane anisotropy and small in-plane anisotropy. 相似文献
7.
We have carried out specific heat measurements on EuIn2P2 at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu2+ magnetic moments align ferromagnetically perpendicular to the c-axis below TC. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu2+ multiplet by internal magnetic fields. 相似文献
8.
I Davoli S Stizza A Bianconi M Benfatto C Furlani V Sessa 《Solid State Communications》1983,48(5):475-478
We have studied the local electronic structure of PdO catalysts supported on characteristic inert and quasi-inert substrate from experiment on X-ray absorption near edge structure XANES using Synchrotron radiation. From the joint analysis of L3 absorption edge and XPS core data in Pd and PdO we find that the white line in PdO XANES is an excitonic state with 0.8 eV binding energy. From the joint analysis of L3 and L1 edges the p-like and the d-like local unoccupied electronic states have been determined. The local structure of PdO catalysts is different from that of PdO crystal. Evidence for structural disorder in PdO catalysts and PdO-substrate interaction is reported. 相似文献
9.
10.
We report low temperature measurements of the C44 sound velocity of CeAl2 in magnetic fields up to 7 T. Between 5 K and 30 K the field softens C44, below 5 K a more complicated behaviour is observed. 相似文献
11.
An attempt is presented to understand the details of the lineshape of the Si L2,3 VV Auger spectrum from the (111) surface in the 7 × 7 superstructure. In the experiments we have followed the variation of the lineshape induced by adsorption of O2, H2O, CO and by bombardment with 3 keV Ar+ ions, over a range from a small perturbation of the surface to major changes in surface structure. For small perturbations from the clean surface we were able to resolve changes in the local density of states at surface silicon atoms. By unfolding the experimental spectra, effective transition densities of states result, which compare quite closely with calculated densities of states, apart from a certain enhancement of surface features in the experiments. All peaks in the experimental spectra can be explained, based on densities of states at the surface of pure Si(111) (7 × 7) (91.8 and 84.8 eV), Si(111) + adsorbed oxygen (70.6 eV), SiO2, (78.9 and 64.5 eV) and plasmon losses, at 71.0 and 57.5 eV for the clean surface. 相似文献
12.
R. Nagarajan E.V. Sampathkumaran L.C. Gupta R. Vijayaraghavan B.D. Padalia 《Physics letters. A》1981,81(7):397-398
L3 X-ray absorption spectroscopic study of Eu firmly establishes that the compound, EuPd2Si2, is a mixed valence system. It is found that the relative intensities of the absorption peaks corresponding to divalent and trivalent europium ions in EuPd2Si2 are a strong function of temperature. 相似文献
13.
The coincidence L3 and M3 photoelectron spectroscopy (PES) main lines of Cu metal are calculated by a many-body theory. There is no peak-energy shift between the singles PES main line and the coincidence one. The asymmetric narrowing of the coincidence PES main line on the low kinetic energy (KE) side is very small. This is in accord with recent experimental findings. In Cu metal, the shakeup satellite intensity is small and the main-line satellite separation energy is much larger than the core–hole lifetime width. The interference via the final-state interaction is negligible. In the PES main line, the imaginary part of the self-energy by shakeup excitations, which is very small compared to the core–hole lifetime width, decreases very slowly in linear with photoelectron KE. The branching ratio of Auger decay of a single hole state then increases very slowly in linear with photoelectron KE so that the deviation of the coincidence PES main line from the singles one is very small. The 939 eV structure seen only in the coincidence L3 PES spectrum of Cu metal is attributed to the enhancement of the inelastic peak of a smaller energy loss due to electrons of a smaller average emission depth measured in coincidence with the elastic Auger peak. The structure will not be enhanced in the singles PES spectrum. The background subtraction in the coincidence spectrum cannot be the same as that in the singles one. Such consideration is necessary before we can conclude about the asymmetric narrowing on the low KE side. A unique capability of APECS by which one can determine the photoelectron KE dependent part of the imaginary part of the self-energy is pointed out. 相似文献
14.
We have investigated the 5d-4f interband and the intra-4f photoluminescence of Eu3S4. An anomalous shift of the interband luminescence can be explained by temperature dependent valence fluctuations. The ferromagnetic ordering of Eu3S4 is also verified. 相似文献
15.
Ö. Sö?üt 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,97(3):388-394
The Coster-Kronig (CK) enhancement effect was measured for L3 subshell X-rays using the experimental Lα X-ray production cross-section, the fraction of Lα X-rays, L3 subshell fluorescence yields and L3 subshell photoionisation cross-section. The samples were excited by gamma-rays with 59.5 keV energy from a 75 mCi radioisotope source and L X-rays emitted from samples were counted by a Si(Li) detector with resolution 155 eV at 5.96 keV. Variation of enhancement effect of CK transition of L3 X-rays of La and Ce compounds was measured to be more than that of Ba. Ba has a partially filled 6s orbital whereas La and Ce have partially filled 5d and 4f orbitals, respectively. 相似文献
16.
We have measured on the CeSn3 compound, the expansion coefficient between 80 and 800 K at normal pressure, the isothermal compressibility in the 0–8 GPa pressure range at room temperature and the heat capacity at constant pressure in the 60–300 K temperature range. The experimental data were compared with those previously found for the isomorphous LaSn3 phase, assumed as a proper reference material for the study of the intermediate valency states in CeSn3. Both the thermal expansion (3α) and the isothermal compressibility (k) of CeSn3 show behaviours quite different from those of LaSn3: for instance, in the standard conditions, 3α is 55 × 10?6K?1for CeSn3 and 38 × 10?6K?1for LaSn3; k is 15 × 10?12 Pa?1 and 12 × 10?12 Pa?1 respectively for CeSn3 and LaSn3. The thermal behaviour of the molar specific heat at constant pressure of CeSn3 is similar to that of LaSn3 for temperatures lower than 50 K. In the 70–300 K temperature range, the heat capacity of CeSn3 is clearly higher than that of LaSn3, ΔCp being maximum near 150 K. The analysis of the calorimetric data show that the electronic coefficient γ of CeSn3 is temperature dependent: its value varies from 53 mJ K?2 mole?1 at low temperature 24 mJ K?2 mole?1 at 300 K. 相似文献
17.
The complex network theory is a way to investigate the complex systems with minimum
information about their entities and corresponding interactions. There is a growing
interest to studying the earthquake phenomena by the method of networks. Several network
features characterize the complexity of seismic events. Unfortunately they depend on how
we construct the network. Here we study the role of cell size or in other word the
resolution on the network properties for the Iran’s seismic data. We have found that all
the network topological features vary as a power of the resolution. Furthermore by
increasing the resolution, the networks become random and uncorrelated. 相似文献
18.
W.J. Ren J.L. Yang B. Li D. Li X.G. Zhao Z.D. Zhang 《Physica B: Condensed Matter》2009,404(20):3410-3412
The structural, magnetic and magnetostrictive properties of Sm1−xCexFe2 (0≤x≤1) Laves compounds have been investigated. The magnetostriction coefficient λ111 and the anisotropy of the Sm1−xCexFe2 compounds decrease with increasing Ce content. The decreasing of anisotropy results in an enhancement of the anisotropic magnetostriction at low magnetic fields for the compounds with a small amount of Ce substituted for Sm. 相似文献
19.
Kenji Yoshii Yasuhiro Yoneda Ignace Jarrige Tatsuo Fukuda Yasuo Nishihata Chikashi Suzuki Yoshiaki Ito Takahito Terashima Shinzo Yoshikado Sei Fukushima 《Journal of Physics and Chemistry of Solids》2014
We have studied the electronic properties of the ferroelectric barium titanate BaTiO3 using two complementary bulk-sensitive spectroscopic probes, resonant X-ray emission spectroscopy (RXES) and X-ray absorption spectroscopy in the partial fluorescence mode (PFY-XAS) at the Ba-L3 and Ti-K absorption edges. Contrary to a previous study, we found no fine structure in the pre-edge area of the PFY-XAS spectrum at the Ba-L3 edge, and no temperature-induced spectral change was observed between room temperature and 150 °C. This result is not supportive of the possible presence of the displacement around Ba2+ at the Curie temperature. RXES spectra were measured at the Ti-K edge for BaTiO3, along with SrTiO3 and La-doped metallic SrTiO3. The photon energy of the emission peak is found to be nearly constant throughout the absorption edge for all three compounds. We deduce the Ti 3d states to have a delocalized character, in contrast with the Ba 5d states, a property which is consistent with the proposed scenario of the formation of electric dipoles in BaTiO3. 相似文献
20.
He II photoelectron spectra of La, Ce and Yb show features which cannot be explained in terms of single electron excitations.
It is proposed that these are due to formation of electron-hole paris.
Communication No. 227. 相似文献