Mössbauer Studies of Oxygen-StabilizedEu2+in CaF2

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

“…We should mention that we initially performed exploratory 151 Eu Mössbauer measurements over a velocity range of 20 mm/s and observed a broadened resonance line centered around −11 mm/s, resembling the previous reports on an anomalous concentration dependence of the Eu 2+ isomer shift 12,13 at these low concentrations. Since the resonance line was, however, asymmetric with some additional structures apparent, in all further studies the source velocity was increased to ±35 mm/s and important additional features appeared at higher resonance velocities.…”

“…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.…”

“…Nitsche et al 12 found a very unusual temperature dependence of the Eu 2+ isomer shift in CaF 2 :1%Eu. Lambe and Schroeer 13 and Schroeer et al 14 extended the Mössbauer studies to lower concentration (0.1% to 10%) and observed an even stronger anomalous variation of the isomer shift with Eu 2+ concentration from 11.3 mm/s (0.1%) to approximately 13.4 mm/s (1%-10%). In addition, these authors reported on a very broad linewidth (up to ≈8 mm/s compared to a common experimental line-width of ≈2.5 mm/s) of the Eu 2+ absorption lines, which they attributed to spin-spin relaxation effects of paramagnetic splitting (known from the above EPR and ENDOR studies).…”

“…[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.…”

“…The anomalous shifts were speculatively attributed to oxygen neighbors of the Eu 2+ ions, with a detailed model for possible O 2− configurations. 13,14 In order to clarify the contradicting results and interpretations in these previous Mössbauer studies of CaF 2 :Eu 2+ systems, we performed the following series of 151 Eu Mössbauer studies: (i) CaF 2 :Eu 2+ with an Eu doping level of only 0.1% was studied at different temperatures between 4.2 and 295 K without an external field; (ii) CaF 2 : 0.1%Eu 2+ was studied in a relatively small external magnetic field of 0.2 T at 295 K; (iii) CaF 2 :Eu 2+ with 2% Eu was studied between 4.2 and 295 K without an external magnetic field; (iv) CaF 2 :2%Eu 2+ was studied in an external magnetic field of 0.2 T between 10 and 295 K (to elucidate the impact of an external magnetic field on the observed paramagnetic line broadening) and, in addition, in a large external field of 6 T between 2.5 and 10 K.…”