Temperature Dependence of the Hyperfine Coupling of Rare-EarthS-State Ions in Cubic Crystals

Abstract

Measurements of the hyperfine coupling constant A of CaF2:Eu 2+ were made for temperatures between 4.2 and 715°K by means of EPR techniques. It was found that | A | decreased in magnitude by approximately 2% over this temperature range. A calculation of the temperature dependence of A following Simanek and Orbach was also performed. The orbit-lattice interaction for a molecular cluster with eightfold cubic coordination was expanded in third-order spherical harmonics and normal coordinates which are antisymmetrical under inversion through the origin. This interaction was used to admix excited ns states into the ground 4/ orbitals so as to give rise to a temperature-dependent hyperfine coupling constant given by the relationGood agreement was obtained between the temperature dependence predicted by this expression and our experimental data on CaF2:Eu 2+ . However, the strength of the constant C, calculated on the basis of a nearest-neighbor point-charge model and the long-wavelength approximation, was smaller than the experimentally determined value by approximately one order of magnitude.

Phonon‐induced hyperfine interactions for 6S‐state ions in tetrahedral symmetry: Mn2+ in ZnS and ZnSe

“…Menne [4, 51, Huang and Lue [6, 71 on the basis of the point-charge niodel calculated the temperature dependence of the hyperfine coupling constant of %-state ions and %-state ions considering the acoustical and optical phonons of the entire phonon spectrum. The results obtained generalize those of Siinhek and Orbach [ Z ] and Menne et al [ 3 ] , who took into account the acoustical phonons with small wave vectors only. The obtained equations are only applicable to host lattices, in which the paramagnetic ion finds a point symmetry Oh.…”

Paramagnetic hyperfine splitting in theE151uMössbauer spectra ofCaF2:Selling1, Bielemeier2, Wortmann3 et al. 2008Phys. Rev. B3020View full textAdd to dashboardCite

“…This excludes the possibility of oxygen neighbors, which had been tentatively postulated to explain the observed "anomalous" isomer shifts in these systems. 12,13 Such regular lattice sites are also a prerequisite for the successful analysis of the paramagnetic hyperfine splitting in the ENDOR 7 and EPR studies, 8,9 as well as in the present Mössbauer spectra.…”

“…Dilute CaF 2 :Eu 2+ systems have previously been studied with paramagnetic resonance spectroscopy, [6][7][8][9] as well as 151 Eu Mössbauer spectroscopy. [10][11][12][13][14] The paramagnetic splitting of dilute Eu 2+ (0.01%) has been determined at low temperature by EPR by Baker, Bleaney, and Hayes, 6 and the hyperfine interaction has been measured by electron nuclear double resonance (ENDOR) by Baker and Williams.…”

“…7 Later the temperature and pressure dependence of these parameters have been determined. 8,9 The first 151 Eu Mössbauer studies were performed on more concentrated systems: Maletta et al 10 and Wickman et al 11 studied systems with 0.5 to 10% Eu, reporting on a very anomalous variation of the Eu 2+ isomer shift with concentration. Nitsche et al 12 found a very unusual temperature dependence of the Eu 2+ isomer shift in CaF 2 :1%Eu.…”

Phonon contribution to the hyperfine coupling constant

“…The phonons couple 4s orbitals to the 3d orbitals of Mn2+ via the orbit-lattice interaction ; then the admixed wave functions can make a nonvanishing contribution to the contact hyperfine operator. These studies were later extended [3,4] to EU~+(~S,,,) in the alkaline earth fluorides where the orbitlattice interaction produces coupling between 4f and 6s orbitals. For both Mn2+ and E u~+ the theoretical treatment of A( T ) was successful in providing a qualitative explanation for the observed decrease in the magnitude of A with increasing temperature.…”