Magnetic hyperfine splitting in mössbauer spectra of microcrystals

Below the superparamagnetic blocking temperature of a microcrystal the magnetization direction is in general not fixed, but fluctuates in directions close to an easy direction of magnetization. Such fluctuations (collective magnetic excitations) result in a reduction in the magnetic splitting of the Mössbauer spectrum. A low-temperature approximation for this reduction is derived for microcrystals with arbitrary magnetic energy. Moreover, explicit expressions are presented for particles with special types of magnetic anisotropy and for particles exposed to external magnetic fields. The reduction in the magnetic hyperfine field has its maximum value just below the blocking temperature but does not exceed 5–15% in isolated particles with uniaxial anisotropy in zero applied magnetic field. However, ferro- and ferrimagnetic particles, exposed to external magnetic fields, and particles for which exchange anisotropy is predominant, may exhibit any magnetic hyperfine splitting between zero and the saturation value. It is shown that in special cases an assembly of microcrystals in close contact with each other may behave like a spin-glass. We discuss how studies of the magnetic hyperfine splitting ofMössbauer spectra of microcrystals give information of the particle size and the prevailing magnetic anisotropies.     

O(alpha(3) lnalpha) corrections to muonium and positronium hyperfine splitting

We compute O(alpha(3)lnalpha) relative corrections to the ground-state hyperfine splitting of a QED two-body bound state with different masses of constituents. The general result is then applied to muonium and positronium. In particular, a new value of the muon-to-electron mass ratio is derived from the muonium ground-state hyperfine splitting.     

Order alpha(7)ln(1/alpha) contribution to positronium hyperfine splitting

The logarithmically enhanced alpha(7)ln(1/alpha) contribution to the hyperfine splitting of the positronium ground-state energy levels is calculated in the framework of dimensionally regularized nonrelativistic quantum electrodynamics. The correction is negative and amounts to about 1/3 of the leading logarithmic alpha(7)ln (2)(1/alpha) one. The discrepancy between the experimental measurements and the theoretical prediction is reduced.     

“Recoil”-effect-induced contribution of order mα 6 to the hyperfine splitting of the positronium ground state

The recoil-effect-induced part of the mα ⁶ contribution to the hyperfine splitting of the positronium ground state is calculated. The method employed is based on noncovariant perturbation theory within QED. The result is 0.381(6)mα ⁶, which agrees well with the results of previous studies. This means that it deviates sizably from experimental data.     

Enhanced Sensitivity to Variation of m(e)/m(p) in molecular spectra

We propose new experiments with high sensitivity to a possible variation of the electron-to-proton mass ratio mu identical with m(e)/m(p). We consider a nearly degenerate pair of molecular vibrational levels, each associated with a different electronic potential. With respect to a change in mu, the change in the splitting between such levels can be large both on an absolute scale and relative to the splitting. We demonstrate the existence of such pairs of states in Cs2, where the narrow spectral lines achievable with ultracold molecules make the system promising for future searches for small variations in mu.     

NMR-ON on196,197m,198,198m,200mAu in Fe and Ni

The zero-field hyperfine splitting frequencies of a series of Au isotopes in Fe and Ni have been determined with nuclear magnetic resonance on oriented nuclei. The results are:. For¹⁹⁸Au(2^–) in Fe the quadrupole splitting could be resolved. The results are ¦g_NB_HF/h|=259.48 (3) MHz and e²qp/h=–2.08(4) MHz. Our measurements show that most hyperfine splittings published on these isotopes have been incorrect. The quadrupole splitting of¹⁹⁸AuFe disagrees in magnitudeand sign from the value reported by single-passage NMR on oriented nuclei. The following nuclear quantities are deduced: (^197mAu,11/2^–)=5.98(9) _N; (^198mAu, 12^–)=5.85(9) _N; (^200mAu, 12^–)=5.90(9) _N; Q(¹⁹⁸Au,2^–)/Q(¹⁹⁹Au, 3/2⁺)=1.37(3). Our measurements show further that the non-contact hyperfine field for Au in Ni is smaller than assumed previously, and that the magnetic hyperfine splitting frequency of¹⁹⁷AuFe known from NMR is inconsistent with the magnetic hyperfine splitting frequencies of^{198, 199}AuFe.     

On the hyperfine structure of neutral muonic helium

The ground state hyperfine splitting of the neutral muonic helium atom has been (re)calculated to be equal to 4,493.3 Mhz.     

自由基-三重态对化学诱导动态电子极化强度的全哈密顿计算(英文)

基于考虑含E(S2Tξ-S2Tη)项的相互作用全哈密顿,利用密度矩阵运动方程,对自由基-三重态对机理的CIDEP强度进行了详细的理论计算.计算结果表明:四重态母体自由基-三重态机理(QP-RTPM)和二重态母体自由基-三重态机理(DP-RTPM)分别使稳定自由基形成发射+发射/吸收(E+E/A)和吸收+吸收/发射(A+A/E)型多重性极化,其中净E(A)极化由零场分裂相互作用产生,超精细相关E/A(A/E)极化由超精细相互作用产生.另外,零场分裂相互作用项E(S2Tξ-S2Tη),使稳定自由基的净极化减弱     

A non-perturbative approach to hyperfine splitting

A hyperfine energy splitting for atomic hydrogen is calculated in a non-perturbative manner for a finite width contact interaction. A close agreement between this result and first order perturbation theory is obtained.     

Calculation of the hyperfine structure of heavy H and Li like ions

The present status of calculations of the hyperfine splitting and the transition probability between the hyperfine splitting components in hydrogen and lithium like ions is discussed. The results of the calculations are compared with recent experimental data. A special attention is focused on the hyperfine splitting in hydrogen like lead and lithium like bismuth. It is shown that the theoretical prediction for the ground state hyperfine splitting in lead based on the single particle nuclear model for the Bohr-Weisskopf effect is in fair agreement with experiment. The theoretical prediction for the ground state hyperfine splitting in lithium like bismuth is improved due to more accurate calculations of the interelectronic interaction, QED, and nuclear corrections. This revised version was published online in August 2006 with corrections to the Cover Date.     

On interpretation of EPR spectrum of free radicals in γ-irradiated methanol

Some authors interpret the EPR spectrum in-irradiated methanol at 77K either by the radical H₂OH or by ⁺ H₂. In order to contribute to this question we have calculated the values of the hyperfine splitting constants of this EPR spectrum as a function of the valence angle H-C-H in a CH₂ fragment. The comparison of the experimental and calculated values of the hyperfine splitting constant and a discussion of the possible valence angles leads us to the conclusion that the EPR spectrum in irradiated methanol originates from the radical H₂OH.The author thanks J. Teplý for valuable remarks which helped this work.     

Magnetic moments and hyperfine fields at Fe in 3d-transition metals

The magnetic moments and hyperfine fields at Fe sites in 3d-transition metals are calculated using the first principle discrete variational method in local density approximation. Although a large positive moment is retained at each Fe site, the hyperfine fields varied from large negative to large positive values. It is concluded that the absence of Mössbauer magnetic splitting does not necessarily imply the absence of local magnetic moments.     

Radiative and interelectronic-interaction corrections to the hyperfine splitting in highly charged B-like ions

The ground-state hyperfine splitting values of high-Z boronlike ions are calculated. Calculation of the interelectronic-interaction contribution is based on a combination of the 1/Z perturbation theory and the large-scale configuration-interaction Dirac-Fock-Sturm method. The screened QED corrections are evaluated utilizing an effective screening potential approach. Total hyperfine splitting energies are presented for several B-like ions of particular interest: ⁴⁵Sc¹⁶⁺, ⁵⁷Fe²¹⁺, ²⁰⁷Pb⁷⁷⁺, and ²⁰⁹Bi⁷⁸⁺. For lead and bismuth the experimental values of the 1s hyperfine splitting are employed to improve significantly the theoretical results by reducing the uncertainty due to the nuclear effects.     

Shell model analysis of the magnetic hyperfine splitting in muonic thallium

The magnetic hyperfine splitting of the ground and first excited state in muonic²⁰³Tl and²⁰⁵Tl is calculated on the basis of the shell model with configuration mixing. Fair agreement with the recently measured ground state splitting is found.     

Correlations among hyperfine parameters in amorphous metal systems: Mössbauer linewidth asymmetries and fluctuation hyperfine correlation functions

The microscopic correlations among hyperfine parameters in amorphous metal systems appear in the Mössbauer linewidth asymmetries. The fluctuation hyperfine correlation functions can be derived using the formalism of Lines, Eibschutz and coworkers. This approach has been reviewed in detail in this paper. A quantitative estimate of the role of the anisotropic component of the hyperfine field toward linewidth asymmetries is presented. It is stressed that contrary to earlier claims, this approach does not give a correct measure of the variance of quadrupole splitting. It is not, therefore, possible to pass judgement on the validity of a linear correlation between quadrupole splitting and hyperfine field or quadrupole splitting and isomer shift. The experimental evidence against a linear correlation between the hyperfine field and the isomer shift, however, remains valid. A simple procedure for checking the validity of a linear correlation between the isomer shift and the magnitude of the quadrupole splitting is suggested. Critical comments on the method of analysis are given.     

Electronic structure of the F-centre in sodalite

The electronic structure of the F-centre in sodalite has been studied by means of the multiple scattering MSXα method. The first absorption peak and the hyperfine splitting constant have been calculated and compared with corresponding experimental values. The results are satisfactory both for the absorption line and the hyperfine constant when the ionic radii are used.     

Evolution from quasielastic to deep-inelastic transfer in the system132Xe+natFe§

The pronounced isotope shift of⁸⁷Sr versus⁸⁷Sr observed recently in 5sns¹S₀ Rydberg states reflects the singlet-triplet mixing solely caused by magnetic hyperfine interaction. Using semiempirical estimates for the hyperfine coupling constant a_{5 s} and the singlet-triplet splitting ΔE_ST (n) excellent agreement between experimental and calculated values is obtained.     

Rubidium and proton ENDOR on ion pairs in solution

The E.S.R. spectrum of the o-dimesitoylbenzene anion-alkali cation radical shows unusually large isotropic alkali hyperfine splitting constants. We report a solution ENDOR study of this radical in which both alkali (^85,87Rb) and proton ENDOR spectra were recorded. Both the alkali and proton intensities showed a strong dependence on the metal ion nuclear spin quantum number of the E.S.R. line being saturated. This dependence is attributed to strong flip-flop cross-relaxation induced by modulation of the isotropic alkali hyperfine splitting. The powder E.S.R. spectrum of the complex reveals a small anisotropy of the Rb hyperfine splitting tensor. This indicates a small metal non-s-contribution to the half-filled molecular orbital, which is consistent with the observed relaxation behaviour and the small g shift. The intensity variations in the alkali and proton ENDOR spectra were used to determine the relative signs of all hyperfine splitting constants, and the absolute signs of the hyperfine splitting constants are deduced from a model of the structure of the complex.     

Analysis of hyperfine interactions in NMR studies of Pr skutterudites

The splitting of NMR signal, which is analyzed in terms of the invariant hyperfine coupling between the nuclear spin and the multipolar moments of magnetic ions, gives important information about the multipolar ordering. The NMR splitting of P nuclei is analyzed for the low-temperature phase of PrFe₄P₁₂, whose nature has been controversial. Two scenarios are examined: one is a modulation of the hyperfine coupling caused by the antiferro-quadrupole (AFQ) ordering; another is the hyperfine coupling due to a monopole-type ordering.     

Self-energy correction to the hyperfine splitting of the 1 s and 2 s states in hydrogenlike ions

The one-loop self-energy correction to the hyperfine splitting of the 1 s and 2 s states of hydrogenlike ions is calculated for both point and finite nuclei. The results of the calculation are combined with other corrections to find the ground state hyperfine splitting in lithiumlike ²⁰⁹Bi⁸⁰⁺ and ¹⁶⁵Ho⁶⁴⁺. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 19–22 (10 July 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.