Magnetic Hyperfine Structure Research Articles

Hyperfine structure constant of the neutron halo nucleus (11)Be(+).

The hyperfine splittings of ground state Be+11 have been measured precisely by laser-microwave double resonance spectroscopy for trapped and laser cooled beryllium ions. The ions were produced at relativistic energies and subsequently slowed down and trapped at mK temperatures. The magnetic hyperfine structure constant of Be+11 was determined to be A11=-2677.302 988(72) MHz from the measurements of the mF-mF'=0-0 field independent transition. This measurement provides essential data for the study of the distribution of the halo neutron in the single neutron halo nucleus Be11 through the Bohr-Weisskopf effect.

Macroscopic quantum effects observed in Mössbauer spectra of antiferromagnetic nanoparticles

The 57Fe Mossbauer spectra of antiferromagnetic nanoparticles have been measured for almost half a century and often displayed a specific (non-superparamagnetic) temperature evolution of the spectral shape which looks like a quantum superposition of well-resolved magnetic hyperfine structure and single line or quadrupolar doublet of lines with the temperature-dependent partial spectral areas. We have developed a quantum-mechanical model for describing thermodynamic characteristics of an ensemble of ideal and “uncompensated” antiferromagnetic nanoparticles with uniaxial magnetic anisotropy in the first approximation of slowly relaxing macrospins of magnetic sublattices. This model allows one to qualitatively describe the macroscopic quantum effects observed in the Mossbauer spectra and to clarify principally the difference in thermodynamic properties of ferromagnetic and antiferromagnetic particles revealed in spectroscopic measurements.

Relativistic effects on the hyperfine structures of2p4(3P)3p2Do,4Do, and4Poin19F i

The hyperfine interaction constants of the 2p4(3P)3p 2Do_{3/2,5/2}, 4Do_{1/2-7/2} and 4Po_{1/2-5/2} levels in neutral fluorine are investigated theoretically. Large-scale calculations are carried out using the multiconfiguration Hartree-Fock (MCHF) and Dirac-Hartree-Fock (MCDHF) methods. In the framework of the MCHF approach, the relativistic effects are taken into account in the Breit-Pauli approximation using non relativistic orbitals. In the fully relativistic approach, the orbitals are optimized using the Dirac-Coulomb Hamiltonian with correlation models inspired by the non relativistic calculations. Higher-order excitations are captured through multireference configuration interaction calculations including the Breit interaction. In a third (intermediate) approach, the Dirac-Coulomb-Breit Hamiltonian matrix is diagonalized in a relativistic configuration space built with non relativistic MCHF radial functions converted into Dirac spinors using the Pauli approximation. The magnetic dipole hyperfine structure constants calculated with the three relativistic models are consistent and reveal unexpectedly large effects of relativity for 2Do_{5/2}, 4Po_{3/2} and 4Po_{5/2}. The agreement with the few available experimental values is satisfactory. The strong J-dependence of relativistic corrections on the hyperfine constants is investigated through the detailed analysis of the orbital, spin-dipole and contact relative contributions calculated with the non relativistic magnetic dipole operator.

Hyperfine structure investigations of atomic niobium with optogalvanic and laser-induced fluorescence spectroscopy in the near-infrared wavelength range

Aims. The aim of this work is to increase the amount of hyperfine structure data of atomic niobium (Nb I), which is needed for astrophysicists for the detailed analysis of new stellar spectra. Particular emphasis was placed on the investigation of energy levels with unknown hyperfine structure constants. Methods. The hyperfine structure in the spectrum of Nb I was studied using laser-induced fluorescence spectroscopy and laser optogalvanic spectroscopy with a tuneable single-mode cw Ti:Sa laser in the wavelength range from 750 nm to 865 nm. The Nb atoms were produced and excited in a liquid-nitrogen-cooled hollow-cathode plasma. Results. We measured and analysed 81 spectral lines, 19 of which are not previously known from the literature. In total, the magnetic dipole hyperfine structure constants A were determined for 28 energy levels of even and 53 energy levels of odd parity. The electric quadrupole hyperfine structure constants B were only determined in a few cases, when the spectra were clearly resolved and/or when a level was found from several transitions. The magnetic dipole hyperfine structure constants A of 13 even and 11 odd levels as well as the electric quadrupole hyperfine structure constants B of 13 even and 17 odd levels are presented for the first time. For the other levels, improved values of hyperfine structure constants are given. Conclusions. The hyperfine structure can have a significant effect on stellar absorption line profiles, and the corresponding abundances can be substantially overestimated if these effects are not taken into account. Therefore, a detailed consideration of the hyperfine structure is important for stellar abundance determinations. The present work substantially increases the knowledge of hyperfine structure of Nb, which plays an important role in investigating the nucleosynthesis of heavy elements.

The second spectrum of niobium: I. Accurate fine structure study of even-parity levels

For the first time, a parametric analysis of the fine and hyperfine structure for even-parity levels of Nb II, involving 17 configurations, has been performed. The interpretation has been carried out based on a linked-parameter method of level-fitting calculations in a large multiconfiguration basis. The sets of fine structure parameters, the leading eigenvector percentages of levels, as well as their calculated magnetic Landé g-factors are newly given. Furthermore, we confirm on the whole the validity of the attributions to term designations, previously proposed. The single-electron hyperfine structure parameters are determined in their entirety for 93Nb II for the model space (4d + 5s)4 with a good accuracy and confirmed by ab initio calculations. Finally, a complete list of the predicted magnetic hyperfine structure constants A of all levels of this model space was generated.

Reexamination of nuclear quadrupole moments in39−41K isotopes

Nuclear quadrupole moments ($Q$'s) in three isotopes of the potassium atom (K) with mass numbers 39, 40, and 41 are evaluated more precisely in this work. The $Q$ value of ${}^{39}$K is determined to be 0.0614(6) $b$ by combining the available experimental result of the electric quadrupole hyperfine structure constant ($B$) with our calculated $B/Q$ result of its $4{P}_{3/2}$ state. Furthermore, combining this $Q$ value with the measured ratios $Q$(${}^{40}$K)$/Q$(${}^{39}$K) and $Q$(${}^{41}$K)$/Q$(${}^{39}$K), we obtain $Q$(${}^{40}$K)$=\ensuremath{-}0.0764(8)\phantom{\rule{4pt}{0ex}}b$ and $Q$(${}^{41}$K)$=0.0747(7)\phantom{\rule{4pt}{0ex}}b$, respectively. These results disagree with the sub-1$%$ accuracy standard values recently quoted by Pyykk\"o [Mol. Phys. 106, 1965 (2008)]. The calculations were carried out by employing the relativistic coupled-cluster theory at the single, double, and involving important valence triple approximation. The accuracies of the calculated $B/Q$ results can be viewed on the basis of comparison between our calculated magnetic dipole hyperfine structure constants ($A$'s) with their corresponding measurements for many low-lying states. Both $A$ and $B$ results in a few more excited states are presented. Also, we find that the latest reported experimental hyperfine structure constant results for the $4P$ states in ${}^{39}$K are inconsistent with our calculations.

Correlation effects in Yb+and implications for parity violation

Calculation of the energies, magnetic dipole hyperfine structure constants, $E$1 transition amplitudes between the low-lying states, and nuclear spin-dependent parity-nonconserving amplitudes for the ${}^{2}{S}_{1/2}\ensuremath{-}{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2,5/2}$ transitions in ${}^{171}$Yb${}^{+}$ ion is performed using two different approaches. First, we carried out many-body perturbation theory calculation considering Yb${}^{+}$ as a monovalent system. Additional all-order calculations are carried out for selected properties. Second, we carried out configuration interaction calculation considering Yb as a 15-electron system and compared the results obtained by two methods. The accuracy of different methods is evaluated. We find that the monovalent description is inadequate for evaluation of some atomic properties due to significant mixing of the one-particle and the hole-two-particle configurations. Performing the calculation by such different approaches allowed us to establish the importance of various correlation effects for Yb${}^{+}$ atomic properties for future improvement of theoretical precision in this complicated system.

Relaxation Mössbauer Spectroscopy of Iron Oxides Nanoparticles in Superferrimagnetic Regime

Film composites based on magnetite Fe3O4 nanoparticles in the polyvinyl alcohol (PVA) matrix and the dried ferrofluid ARA-250 (Chemicell GmbH, Germany) were studied at temperatures 78-300 K by Mössbauer spectroscopy and magnetic measurements in magnetic fields H < 5 kOe. The Mössbauer spectra taken in magnetic fields show essential restoration of the magnetic hyperfine structure characteristic for the nanoparticles. The experimental Mössbauer spectra have been analyzed within the recently developed three-level [ and multi-level [ relaxation models of magnetic dynamics in an ensemble of single-domain particles. These models take into account the precession and diffusion of particles uniform magnetization as well as the particles size distribution and interparticle interactions.

Measurements of hyperfine structure in 51V II

We have applied fast-ion-beam laser-fluorescence spectroscopy to measure the magnetic dipole hyperfine structure (hfs) constants of 24 even levels and 31 odd levels in 51V II. These are the first published data for hfs in this ion. These results will be very useful for the measurement of stellar photospheric abundances, studies of the history of nucleosynthesis and the testing of models of stellar interiors. The rather large hyperfine splittings in 51V II significantly affect the saturation and width of absorption lines, and this must be taken into account in order to derive accurate abundances and stellar rotation and micro- and macro-turbulence parameters, as well as to help determine if line blending is occurring.

On the mechanism of the temperature evolution of the symmetric magnetic hyperfine structure of Mössbauer spectra of magnetic nanoparticles to the quadrupole doublet of lines

The multilayer relaxation model of Mossbauer spectra of an ensemble of single-domain particles has been generalized to the case of the presence of the electric field gradient on nuclei with a chaotic orientation of its principal axes. The generalized model makes it possible to take into account the physical mechanisms of the formation of the hyperfine structure of the spectra in the real situation and to numerically describe the qualitative features of the temperature evolution of the spectra from symmetric magnetic sextet to the quadrupole doublet of lines, which is observed in most experimental spectra of 57Fe nuclei in magnetic nanoparticles.

Hyperfine structure study of atomic niobium with enhanced sensitivity of Fourier transform spectroscopy

In an experimental setup with a high-resolution Fourier transform (FT) spectrometer and a hollow-cathode discharge, bandpass interference filters are used to enhance the sensitivity. This extension leads to an improvement of the signal-to-noise ratio in the spectrum of atomic niobium by a factor of up to 10 compared to FT spectra measured previously without filters (see Kröger et al 2010 Astron. Astrophys. 516 A70). Several additional spectral lines with low intensity have been observed. Additionally, in some intense lines, blends become visible due to the better signal-to-noise ratio. The hyperfine structure of 51 lines recorded in the wavelength range from 415 to 670 nm is analysed or re-analysed and magnetic dipole hyperfine structure constants A of 8 levels of even parity and 43 levels of odd parity are determined. Improvement of sensitivity of FT spectroscopy in the visible wavelength range enabled the determination of new hyperfine structure constants A for two energy levels of even parity, which fill the last gaps for energetically low-lying levels below 14 000 cm−1. Additionally, ten new A constants for energetically higher lying levels of odd parity as well as several improved A values have been obtained.

Mössbauer analysis of high-energy mechanical-milled sand fraction of a magnetic soil developing on basalt

A sample of the coarse sand fraction from the soil material of the A-horizon (0–0.2 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 Mossbauer 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.

57Fe and 151Eu Mössbauer spectroscopy and magnetization studies of Eu(Fe0.89Co0.11)2As2 and Eu(Fe0.9Ni0.1)2As2

The superconducting compound Eu(Fe0.89Co0.11)2As2 and the normal conducting compound Eu(Fe0.9Ni0.1)2As2 were studied by 151Eu and 57Fe Mössbauer spectroscopy (MS) and magnetometry at temperatures ranging from 5 to 297 K. The 151Eu MS studies showed that in both compounds, the europium magnetic moments order helically (at TM=18 and 20 K, respectively) with a tilting angle of about 36° to the c-axis, whereas in pure EuFe2As2 where the Fe is magnetically ordered, they order perpendicular to the c-axis. We concluded that this change is due to the disappearance of iron magnetism in the mixed compounds. Although the iron ions are nonmagnetic in both the superconducting and the normal conducting compound, 57Fe MS studies display, at 5 K, magnetic hyperfine structure due to transferred magnetic hyperfine fields (∼1 T) from the magnetically ordered Eu sublattice.

Fock-space relativistic coupled-cluster calculations of two-valence atoms

We have developed an all-particle Fock-space relativistic coupled-cluster method for two-valence atomic systems. We then describe a scheme to employ the coupled-cluster wave function to calculate atomic properties. Based on these developments we calculate the excitation energies, magnetic hyperfine structure constants, and electric dipole matrix elements of Sr, Ba, and Yb. Furthermore, we calculate the electric quadrupole hyperfine structure constants and the electric dipole matrix elements of ${\mathrm{Sr}}^{+}$, ${\mathrm{Ba}}^{+}$, and ${\mathrm{Yb}}^{+}$. For these we use the one-valence coupled-cluster wave functions obtained as an intermediate in the two-valence calculations. We also calculate the magnetic dipole hyperfine structure constants of ${\mathrm{Yb}}^{+}$.

Consideration of the spin density of conduction electrons in the formation of a hyperfine interaction field on 57Fe cores in disordered Fe x Cr1 − x alloys

Mossbauer spectra of quenching-disordered FexCr1−x alloys were measured over a wide range of chromium concentrations (0.9–45 at %), and a detailed analysis of their hyperfine structure was performed. Considering the known data that chromium atoms have an all but negligible perturbation effect on the magnetic moments of matrix atoms, it was concluded that the RKKY polarization of conduction electrons plays a leading part in the formation of the hyperfine magnetic structure of FeCr alloys. It is necessary to take into account the Zener effect.

The magnetic hyperfine structure in the rotational spectrum of H 2CNH

The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64–172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the 14N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters.

Hyperfine structure measurements of neutral niobium with Fourier transform spectroscopy

Aims. We report on experimental studies of hyperfine structure splitting of neutral niobium.Methods. We used high-resolution Fourier transform spectroscopy to record a spectrum of niobium produced with a hollow cathode discharge lamp in the range of wavenumbers from 10 000 cm-1 to 30 000 cm-1 .Results. The magnetic dipole hyperfine structure constants A were determined for the 109 levels of odd parity by analyzing the profiles of 224 spectral lines. The A values of 57 of these level are reported for the first time.

High sensitivity CRDS of the a1Δ g− X3Σg− band of oxygen near 1.27 μm: Extended observations, quadrupole transitions, hot bands and minor isotopologues

The CW-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of the a 1Δ g– X 3 Σ g − band of oxygen near 1.27 μm. The spectra were obtained between 7640 and 7917 cm −1 with “natural” oxygen and with a sample highly enriched in 18O. The absolute intensities of 376 and 643 oxygen transitions were measured in the two spectra. They include the a 1Δ g− X 3 Σ g − (0–0) bands of 16O 2, 16O 18O, 16O 17O, 17O 18O and 18O 2. The (0–0) bands of 16O 2 and 18O 2 show weak quadrupole transitions with line intensities ranging from 1×10 −30 to 1.9×10 −28 cm/molecule. They are accompanied by the a 1Δ g− X 3 Σ g − (1–1) hot bands, which are reported for the first time. The line profiles of the transitions of the 16O 17O and 17O 18O isotopologues were observed to be broadened due to an unresolved magnetic hyperfine structure. Accurate spectroscopic parameters of the different energy levels involved in the observed bands were derived from a global fit of the observed line positions, combined with microwave and Raman measurements available in the literature.

Super-ferrimagnetism of magnetite nanoparticles in a weak magnetic field

Film composites based on the magnetite Fe3O4 nanoparticles in the polyvinyl alcohol matrix were studied by means of the Mössbauer spectroscopy in a weak magnetic field, mainly at room temperature. The Mössbauer spectra in the absence of a magnetic field show a superposition of minor (poor-resolved) magnetic hyperfine structure and major collapsed spectrum typical for superparamagnetic particles. Such a pattern evidences for the mean particles size (<D> ≈ 4 nm) being close to the 'blocking' size for this material at a given temperature. The spectra taken in a weak (0.34 T) magnetic field show almost complete restoration of the magnetic hyperfine structure characteristic for the nanoparticles of the kind. The experimental Mössbauer spectra have been analyzed within the recently developed three-level relaxation model of magnetic dynamics in an ensemble of single-domain particles. This model takes into account the precession and diffusion of particle's uniform magnetization as well as the particles size distribution.

Accommodation stresses and structural-phase transitions in Fe-Ni alloys upon compression in Bridgman anvils

Mossbauer spectroscopy was used to study polymorphic phase transitions in iron and Fe-Ni (15, 25, 32 at % Ni) alloys in situ in Bridgman anvils under a quasi-hydrostatic compression to 25 GPa. A connection has been established between the type of polymorphism and degree of transformations on the one hand and the hyperfine parameters, magnetic texture, and stresses in the structure of the initial and resultant phases on the other hand. In iron and in the Fe-15 % Ni alloy, a baroelastic change in the direction of the magnetic texture of the phase has been revealed, which is caused by the appearance of oriented accommodation stresses between the and phases. In the range of compositions of 15–25 at % Ni, the appearance of a hyperfine magnetic structure of spectra of the high-pressure phase has been found.