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1.
The contributions of spin polarization, valence correlations, and relativistic effects to the magnetic dipole constant of the hyperfine structure of the 6 S 5/2 (3d 54s 2) term in the atomic spectrum of manganese are calculated and analyzed by the configuration interaction method and in the framework of the perturbation theory.  相似文献   

2.
The hyperfine structure of the ground configurations 5d 8 6s 2 and 5d 9 6s of the stable Platin isotopes 194, 195, 196, 198 was analyzed. For the isotope 195 a complete set of the magnetic splitting constantsA is given. TheA constants of the levels 5d 8 6s 2 3 P 1 and1 D 2 were determined for the first time. From these data the electronic splitting constants a6 s=l010(10) mK, ad 3/2=57 (6) and ad 5/2=27 (2) mK could be evaluated. The effect of core polarization is discussed and a fieldκ cp=?5.6(1.0) a.u. per 5d-electron spin is found. Also the isotopic shift is determined and for the mean quadratic nuclear charge radius the valueΒδ <r 2>=0.095 (10) fm2 is derived.  相似文献   

3.
Microwave transitions between the Zeeman split doublet states 22 P 1/2 and 22 P 3/2 of7Li have been measured using the optical double resonance method. The fine structure separation was determined to bev fs=10.053.184(58) MHz. The hyperfine structure was well resolved and led to considerably improved precision of the diagonal coupling constantsa 1/2=45.914(25) MHz,a 3/2=?3.055(14) MHz,b=?0.221(29) MHz. Furthermore, the contact, spin dipolar and orbital magnetic hyperfine constants are evaluated using additional results from level crossing experiments, which are more sensitive on the non-diagonal magnetic hyperfine constanta 3/2,1/2. The results are in good agreement with recent theoretical calculations. The nuclear quadrupole moment is derived fromb to beQ(7Li)=?41(6) mbarn.  相似文献   

4.
Ultraviolet fluorescence of Nd3+ ions induced by triphotonic excitation process was studied in Nd-doped LiYF4, LiLuF4 and BaY2F8 crystals using a technique of time-resolved spectroscopy. The observed ultraviolet luminescence was due to transitions between the bottom of 4f25d configuration and 4f3 states of Nd3+ ions. Narrow emission lines superposed to the broadband emissions were observed. A detailed analysis of luminescence spectrum revealed that the narrow emissions are due to parity and spin allowed radiative transitions from the Stark levels of 4K11/2(5d) state created by the electrostatic interaction between the 5d electron and the two electrons of the 4f2 configuration. The narrow emissions are related to the high spin state (S=3/2) which gives f-f characteristics to the f-d broadband emissions. The narrow emissions superposed to the wide emission correspond to 18%, 34% and 43% of the integrated broadband emission at 262 nm observed in LiYF4, LiLuF4 and BaY2F8 crystals, respectively. Although the 5d-4f2 interaction is observed to be weaker than 5d-crystal field interaction, it is stronger enough to select only the radiative transitions from 4f25d configuration to 4f3 states that preserves the total spin S=3/2.  相似文献   

5.
The electronic structure of strontium ferrite Sr3Fe2O6 was calculated using the tight-binding linear muffin-tin orbital method (TB LMTO) in the local spin density approximation of density functional theory with Coulomb correlations correction (LSDA+U). The semiconducting character of the spectrum with charge transfer energy gap of 1.82 eV was obtained in reasonably good agreement with experimental data. The iron ions are found to be in the high spin state. The calculated value of the local spin magnetic moment of Fe3+ ion is 3.94 μB which is not typical for trivalent iron ion in the high spin state. It is shown that the strong hybridization between Fe3d and O2p orbitals favors the d6 L configuration of Fe3+ ion, where L is a hole in the oxygen p shell. The mechanism of oxygen transport in ferrite is discussed basing on the total energy calculations of the different spatial configurations of oxygen vacancies.  相似文献   

6.
7.
The hyperfine structure of the metastable states of the 6s5d configuration of135Ba and137Ba has been studied by the atomic-beam magnetic resonance (ABMR) method. The metastable barium states were populated in a plasma-discharge inside the atomic-beam oven. The atoms emerging from the ABMR-apparatus were detected by the use of a dyelaser. Compared to conventional methods this technique has the advantage of being state selective. The following magnetic dipole and electric quadrupole interaction constantsa andb have been obtained:137Ba:a(3 D 1)=?520.536 (3) MHzb(3 D 1)=17.890 (3) MHza(3D2=415.928 (3) MHzb(3D2)=25.899 (13) MHza(3D3)=456.559 (4) MHzb 3D3=47.390 (16) MHz135Ba:a 3 D 1=?465.166 (4) MHzb(3D1)=11.642 (4) MHza(3D2)=371.736(4) MHzb 3 D 2=16.745 (14) MHza(3D3)=408.038 (6) MHzb(3D3)=30.801 (24) MHz Using these constants and the earlier known ones for the1 D 2 state the hyperfine structure for the 6s5d configuration has been analyzed with an effective hyperfine hamiltonian. Hyperfine parameters obtained from the analysis have been compared with theoretical values calculated with relativistic self-consistent-field (SCF) wavefunctions. The quadrupole moments have been evaluated with the following result Q(135Ba) =0.20(3)b and Q(137Ba) = 0.34(4)b uncorrected for the quadrupole shielding.  相似文献   

8.
The contributions of the superposition of configurations ns 25d 76s+ns5d 76sn′s+ns5d 76s 2 (n=1–5, n′=7–10) to the parameters of the hyperfine structure a 5d 01 , a 5d 12 , a 5d 10 , a 6s 10 in the spectrum of the osmium atom Os I are calculated. Nonzero contributions are shown to be made only to the parameters a 5d 10 and a 6s 10 . This fact justifies the inclusion of the parameter a 5d 10 in the semiempirical analysis of experimental values of magnetic dipole constants of the hyperfine structure of the 5d 7 s configuration in the spectrum of the osmium atom. The effect of nucleus volume on the parameters of the hyperfine structure in the spectra of osmium isotopes 187Os and 189Os is estimated.  相似文献   

9.
We have studied magnetic structure and properties of Ga-substituted Pb-hexaferrites having the stoichiometry of PbFe12−xGaxO19 with x=6 (i.e., Fe:Ga=1:1). According to the neutron diffraction results, this compound is characterized by a collinear spin structure below its Curie temperature (∼325 K). Analysis of the neutron diffraction patterns further indicates that the magnetic-moment direction of Fe3+ ions located at the octahedral 2a sublattice is downward while that of the unsubstituted PbFe12O19 is upward at room temperature. With decreasing temperature, the Fe3+ magnetic moment at the octahedral 2a sublattice undergoes a reorientation to the upward direction while that of the unsubstituted PbFe12O19 remains upward down to 5 K. This selective local spin reversal at the 2a sublattice of PbFe6Ga6O19 was attributed to the weakening of the superexchange interaction between the octahedral 2a site and the tetrahedral 4fIV site upon the preferential substitution of Ga ions for Fe ions at these two neighboring sites. Comparison of the neutron diffraction results with dc magnetization responses and ac susceptibilities further indicates that the paramagnetic–ferrimagnetic transition at ∼325 K (Tc) is followed by the local spin reversal at lower temperatures.  相似文献   

10.
The magnetic structure of a geometrically frustrated system Co2Cl(OH)3 is determined by comparing the observed proton NMR spectrum with numerical calculations based on various magnetic models. The best fit is obtained with a model that the magnetic moments of Co2+ ions in the triangular plane are parallel to the principal axis of local crystal field and those of Co2+ ions in the kagome lattice plane are randomly disordered in the a-b plane, which nearly bisects the angle between the principal axis of the local field and a line pointing towards the body center of the tetrahedron. The coexistence of the ferromagnetic order in the triangular plane and the random disorder in the kagome plane is consistent with the results of measurements by Zheng et al. However, the magnetic moments of Co2+ ions are not directed towards the body center of the tetrahedron as characteristic in the “spin ice” magnetic structure. Furthermore, the Co2+ ions in the triangular plane have a smaller magnitude of magnetic moment than those in the kagome plane. Thus, our result suggests that the transition metal compound Co2Cl(OH)3 is different from the “spin ice” in magnetic structure, although it is similar to rare-earth pyrochlores in crystal structure.  相似文献   

11.
Iron can be easily introduced in BaVS3 and V5S8. It is located at the vanadium sites and has been used as a probe to analyse by Mössbauer effect the magnetic properties of its surrounding matrix. The electronic state of iron in this matrix has also been studied. It was found that in BaVS3, the iron is in a low spin Fe3+ configuration (S = 12). In V5S8 at 4.2 K, the iron is in low spin Fe2+ configuration (S = 0). The rapid decrease of quadrupole splitting observed between 50 and 200 K is attributed to a thermally activated change in electronic structure. The high temperature configuration (above 200 K) seems to be neither pure low spin Fe3+ nor high spin Fe2+, but a mixture of configurations fluctuating at a rate which is faster than the characteristic time of Mössbauer measurements.  相似文献   

12.
Tetragonal paramagnetic centers with spin S = 7/2 were detected in x-ray-irradiated BaF2: Fe (cFe ≈ 0.002 at. %) crystals using the EPR method. Electronic transitions between the |±1/2〉 states of a Kramers doublet were observed in the X and Q ranges. In the EPR spectra of the tetragonal centers, a ligand hyperfine structure (LHFS) was observed corresponding to the interaction of the electron magnetic moment of the tetragonal center with eight equivalent ligands. The large spin moment, significant anisotropy of the magnetic properties, and the characteristic LHFS indicate that the tetragonal center is a Fe1.5+?Fe1.5+ dimer in which the two iron ions are bound via superexchange interaction. It is assumed that, before crystal irradiation, this dimer was in the Fe3+(3d5)?Fe+(3d7) state.  相似文献   

13.
The electron-energy structure of CrS and CoS monosulfides at a temperature of 0 K is investigated theoretically using the augmented plane wave approach in combination with the WIEN2k program code. Computations of the total and partial densities of electron states are performed in the LDA + U approximation with allowance for the antiferromagnetic ordering of magnetic moments of 3d-metal atoms. In our models, the optical forbidden band gap E g in the CrS compound emerges in the monoclinic crystal structure but is missing from the NiAs structure. For the CoS compound in the NiAs structure, computations of the electron-energy structure are performed for both the highand low-spin configurations of the Co atom’s 3d 7 shell. The optically forbidden E g band gap appears in the high-spin configuration with strong correlations of d-electrons, while CoS remains a conductor in the low-spin configuration.  相似文献   

14.
We report a comparative study of the electronic structure and magnetic properties of two cobalt compounds Co3O4 and Co3S4, through first-principles Hubbard-U calculations. Our results indicate that Co3O4 and Co3S4 have similarities in crystal structure (normal spinel), magnetic order (antiferromagnetism), Co spin configuration (high spin Co2+ and low spin Co3+), and comparable band-gap energy. However, the U-dependence on electronic structure in two materials are different from each other. With a change in the applied U values, the band dispersion and the type of band gap are significantly changed in Co3O4, while the band-gap energy only is affected in Co3S4.  相似文献   

15.
We report the temperature dependence of susceptibility for various pressures, magnetic fields and constant magnetic field of 5 T with various pressures on La2−2xSr1+2xMn2O7 single crystal to understand the effectiveness of pressure and magnetic field in altering the magnetic properties. We find that the Curie temperature, Tc, increases under pressure (dTc/dP=10.9 K/GPa) and it indicates the enhancement of ferromagnetic phase under pressure up to 2 GPa. The magnetic field dependence of Tc is about 26 K for 3 T. The combined effect of pressure and constant magnetic field (5 T) shows dTc/dP=11.3 K/GPa and the peak structure is suppressed and broadened. The application of magnetic field of 5 T realizes 3D spin ordered state below Tc at atmospheric pressure. Both peak structure in χc and 3D spin ordered state are suppressed, and changes to 2D-like spin ordered state by increase of pressure. These results reveal that the pressure and the magnetic field are more competitive in altering the magnetic properties of bilayer manganite La1.25Sr1.75Mn2O7 single crystal.  相似文献   

16.
The linear muffin-tin orbital method in the local density approximation (LDA + U) explicitly considering Coulomb correlations has been applied to calculate the electronic structure, magnetic moments, and parameters of the Heisenberg exchange interaction for cobalt ions in BaCoS2. Five solutions close in total energy with various orbital ordering of Co2+ ions and almost identical spin magnetic moments μ = 2.32μB of the Co2+ ion 3d-shell have been found. The BaCoS2 ground state can be considered as a set of energy-degenerate orbital-ordered configurations of Co2+ ions in the high-spin state.  相似文献   

17.
The Mössbauer spectra of partly magnetized FeNH4(SO4)2·12 H2O show a broadening and a shift of the hyperfine structure lines, reflecting the paramagnetic spin fluctuations. These fluctuations and their influence on the γ-spectrum may be treated in a spin wave model without introducing phenomenological parameters. By means of a simple diagram technique we get a line broadening γ and line shift δ, proportional to second and third order polynomials of the magnetization and to ∫g 2 dΩ and ∫g 3 dΩ, respectively.g(Ω) is the frequency spectrum of spin waves. The values of the two frequency integrals, as deduced from the measured Mössbauer data γ and δ of ferric alum, are in reasonable agreement with the results obtained from the calculated spin wave spectrum, assuming pure magnetic dipole-dipole coupling (long wave length approximation of Holstein-Primakoff). A small contribution of non-magnetic dipole-dipole interaction (van Vleck) cannot be excluded.  相似文献   

18.
We have studied the magnetic spin structure of antiferromagnetic CuFeO2 by X-ray diffraction (XRD) and Mössbauer spectroscopy. Its crystal structure determined by XRD analysis was a rhombohedral structure (space group R-3m) and lattice constants a0 and c0 were 3.0333 and 17.1595 Å, respectively. In spite of 4-Fe sublattices in a delafossite CuFeO2, its Mössbauer spectra were analyzed with 1-set (6-Lorentzian lines) below 10 K due to the collinear-commensurate spin structure, but the spectra were fitted with 4-sextet above 10 K due to the incommensurate spin structure. This phenomenon was attributed to the spin–lattice relaxation effect. Magnetic Néel temperature was also determined at 18 K, which corresponded to the high-spin Fe3+ valance state. On the other hand, CuFe0.98Al0.02O2 powder with a noncollinear spin structure was fitted with 4-sextet at 4.2 K.  相似文献   

19.
Ferromagnetic half metallicity with a high spin polarization of 100% was predicted in the bulk Ni0.5Cu0.5O using density-functional theory method. The band gap of majority spin is 3.45 eV for Ni0.5Cu0.5O. The density of states of minority spin at the Fermi level are mainly from Cu 3d and O 2p in the Ni0.5Cu0.5O. The magnetic moments are from Ni 3d states. Ni0.5Zn0.5O and Ni0.5Cd0.5O systems are ferromagnetic insulators, but the magnetic moment of Ni2+ ions is enhanced by the Zn and Cd incorporation. Therefore, Ni0.5Cu0.5O is the potential candidate for spintronics devices because of the predicted high spin polarization.  相似文献   

20.
Effects of hybridization of 3d bands of iron with 3d bands of scandium and 4d bands of yttrium in Sc1?xYxFe2 cubic Laves alloys (0≤x≤1) are studied by the nuclear magnetic resonance method. The concentration dependences of the lattice parameters a, saturation magnetization σ, and hyperfine fields at the 57Fe, 45Sc, and 89Y nuclei—as well as the 27Al impurity nuclei, whose atoms substitute iron atoms in the lattices of these alloys—are measured. The “local” and “induced” contributions to hyperfine fields at the 57Fe nuclei are separated and the magnetic moments at iron atoms are estimated. It is found that the hybridization effect leads to the formation of magnetic moments at Sc and Y atoms (whose direction is opposite to the direction of the magnetic moment at iron atoms) and is responsible for the ferrimagnetic structure in Sc1?xYxFe2 alloys.  相似文献   

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