Calculation of the magnetic dipole constant of the hyperfine structure of the 6 S 5/2(3d 54s 2) term in the atomic spectrum of manganese

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.     

Eine Hyperfeinstruktur-Analyse der Grundkonfigurationen 5d 8 6s 2 und 5d 9 6s des Pt-I Spektrums

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 a_{6 s}=l010(10) mK, a_{d 3/2}=57 (6) and a_{d 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.     

Fine and hyperfine structure of the 22 P term of7Li; determination of the nuclear quadrupole moment

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.     

Luminescence study of the 4f5d configuration of Nd in LiYF4, LiLuF4 and BaY2F8 crystals

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 ⁴K_11/2(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.     

Electronic structure and properties of strontium ferrite Sr3Fe2O6

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 μ_B 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.     

Hyperfine-structure investigation in the 6s5d configuration of135Ba and137Ba

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.     

Hyperfine structure of the atomic osmium spectrum: Superposition of configurations and the effect of nucleus volume

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.     

Local spin reversal and associated magnetic responses in Ga-substituted Pb-hexaferrites

We have studied magnetic structure and properties of Ga-substituted Pb-hexaferrites having the stoichiometry of PbFe_12−xGa_xO₁₉ 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 4f_IV 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 (T_c) is followed by the local spin reversal at lower temperatures.     

Magnetic structure of geometrically frustrated compound Co2Cl(OH)3 determined by proton NMR

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.     

Mössbauer and magnetic studies of BaVS3 and V5S8 doped with 57Fe

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 $\text{(S =}\text{1}\text{2}\text{)}$. 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.     

EPR study of impurity iron ion clusters in BaF<Subscript>2</Subscript> crystals

Tetragonal paramagnetic centers with spin S = 7/2 were detected in x-ray-irradiated BaF₂: Fe (c_Fe ≈ 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 Fe^1.5+?Fe^1.5+ 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.     

First-principles study of antiferromagnetic cobalt spinels

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.     

Aspects of simulating metal-insulator transitions in CrS and CoS

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.     

Effect of pressure and magnetic field on bilayer La1.25Sr1.75Mn2O7 single crystal

We report the temperature dependence of susceptibility for various pressures, magnetic fields and constant magnetic field of 5 T with various pressures on La_2−2xSr_1+2xMn₂O₇ single crystal to understand the effectiveness of pressure and magnetic field in altering the magnetic properties. We find that the Curie temperature, T_c, increases under pressure (dT_c/dP=10.9 K/GPa) and it indicates the enhancement of ferromagnetic phase under pressure up to 2 GPa. The magnetic field dependence of T_c is about 26 K for 3 T. The combined effect of pressure and constant magnetic field (5 T) shows dT_c/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 T_c at atmospheric pressure. Both peak structure in χ_c 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 La_1.25Sr_1.75Mn₂O₇ single crystal.     

Ground state of BaCoS2 as a set of energy-degenerate orbital-ordered configurations of Co2+ ions

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 = 2.32μ_B 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.     

Relaxationsphänomene in Mössbauerspektren von magnetisierten paramagnetischen Substanzen

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.     

Ferromagnetic half-metallic characteristic in bulk Ni0.5M0.5O (M=Cu,Zn and Cd): A GGA+U study

Ferromagnetic half metallicity with a high spin polarization of 100% was predicted in the bulk Ni_0.5Cu_0.5O using density-functional theory method. The band gap of majority spin is 3.45 eV for Ni_0.5Cu_0.5O. The density of states of minority spin at the Fermi level are mainly from Cu 3d and O 2p in the Ni_0.5Cu_0.5O. The magnetic moments are from Ni 3d states. Ni_0.5Zn_0.5O and Ni_0.5Cd_0.5O systems are ferromagnetic insulators, but the magnetic moment of Ni²⁺ ions is enhanced by the Zn and Cd incorporation. Therefore, Ni_0.5Cu_0.5O is the potential candidate for spintronics devices because of the predicted high spin polarization.     

Mössbauer study of antiferromagnetic CuFeO2

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, CuFe_0.98Al_0.02O₂ powder with a noncollinear spin structure was fitted with 4-sextet at 4.2 K.     

Hyperfine interactions in Sc<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript>x</Subscript>Fe<Subscript>2</Subscript> cubic Laves alloys

Effects of hybridization of 3d bands of iron with 3d bands of scandium and 4d bands of yttrium in Sc_1?xY_xFe₂ 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 Sc_1?xY_xFe₂ alloys.