Spin-Hamiltonian Parameters as a Function of Pressure-Induced and Cation-Induced Changes in Nearest-Neighbor Distance for Europium-151 in Alkaline Earth Fluorides

Abstract

The electron-paramagnetic-resonance spectra of the systems CaF 2 : 151 Eu 2+ , Srl ? 2: 151 Eu 2+ , BaF 2 : 151 Eu 2+ have been studied at a pressure of 26 kbar. These spectra were interpreted in terms of the usual phenomenological spin Hamiltonian with parameters g (spectroscopic splitting factor), h and #6 (crystalline-field parameters), and A (hyperfine splitting factor). The variations of & 4 and h with pressure were compared with their variations with cation, and a consistent interpretation of the differences was found in terms of local lattice distortions about the impurity europium ions. This model leads to the relationships ft^S -8 -8 , b%^5~1 3 -6 between the crystalline-field parameters and the nearest-neighbor distance 8.

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

“…In zero field-For very dilute CaF 2 :Eu crystals the electron-spin relaxation times are slow enough to resolve the hyperfine interaction, as shown from the ENDOR measurements on CaF 2 : 0.01%Eu at 13 K 7 or EPR studies on samples with 0.1 mol% Eu. 9 151 Eu Mössbauer studies on such dilute Eu-doped samples are difficult and time consuming because of the low Eu concentration and the resulting small resonance effects as in the present case with a CaF 2 : 0.1%Eu crystal. Using a relatively thick absorber, which reduced the normal transmission of the 21.5-keV γ rays to about 20% by photoabsorption of the CaF 2 matrix, resonance effects of ≈0.6% at 4 K [ Fig.…”

“…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.…”

Dynamic Orbit-Lattice Interactions for PbF2:Gd3+Single Crystals

“…The contributions of these two terms can be estimated by comparing the measured temperature dependence of a spin-Hamiltonian parameter with the data derived from hydrostatic [17] or uniaxial [18] EPR stress experiments. This latter method has been used in [19] for the case of the b4 spin-Hamiltonian parameter where it was found that the contribution due to the effect of thermal expansion is 88.2 ± 77.8 % of the total temperature dependence observed.…”