Hyperfine structures of Mössbauer spectra of trivalent 167Er and 151Eu in an hydroxide host

Abstract

The hyperfine energy levels of 167Er in Er(OH)3 have been deduced using the crystal field parameters and wave functions obtained from an analysis of the experimental results of magnetic susceptibilities, their anisotropies, and optical absorption spectra of pure Er(OH)3. The hyperfine splitting of the energy levels corresponding to the ground (Ig =7/2) and first excited (Ie =9/2) 79.32-keV nuclear manifolds of 167Er in Er(OH)3 are 0.124 and 0.152 cm−1, respectively. The expected Mössbauer spectra were also predicted. No experimental data is available for comparison. The width of Mössbauer spectra for 166Er in Er(OH)3 was found to be 10.56 mm/s, which is close to the reported value. The Mössbauer spectra of 151Eu(OH)3 was studied between 300 and 4.2 K and the results were compared with the spectra calculated using similar magnetic and optical data of Eu(OH)3. The observed isomer shift (with respect to EuF3) remained temperature independent, having a value of 1.04±0.02 mm/s. The nuclear specific heat (Chf) was calculated for the 151Eu isotope in Eu(OH)3 and it showed a peak at about 0.9 mK. It was observed that Chf varied as 1/T2 between 1 K and 10 mK, which is a property that may be utilized in millikelvin thermometry.

A study on crystal field effect and single ion anisotropy in pyrochlore europium titanate (Eu2Ti2O7)

“…1a. In EuT, K ⊥ is found to be greater than K || for the entire temperature range, which implies that singlet µ J = 0 level of the 7 F 1 multiplet lies below the doublet µ J = ±1 level [24]. This is consistent with the observed spectra of EuT [19].…”

“…These values agree well with those obtained experimentally [20,22]. The hyperfine splittings of the ground (I g = 5/2) and the excited nuclear level (I e = 7/2) are found to be 153 and 194 MHz respectively which are large compared to reported values in other Eu 3+ compounds [24,35]. Using the best fitted CF energy eigenvalues and wave functions, thermal variations of K || , and K ⊥ and SIA are computed as shown in Fig.…”

“…1a). Generally it is observed that for Eu 3+ compounds,K versus T curve attains a constant valueK MAX below a characteristic temperature (T MAX ) and the values of K MAX and T MAX depend primarily on the separation between 7 F 0 and CF levels of 7 F 1,2 [24]. Thus values of K MAX and T MAX act as additional constraints for selecting CF parameters accurately.…”

“…1a) and the accuracy of the results is ∼0.5%. At room temperature (RT),K has a value of 5100 × 10 −6 emu/ion which is greater than values found in several other Eu 3+ compounds, viz.,K being 4350, 4335, 4348, 4538 in units of 10 −6 emu/ion, respectively for EuF 3 [31], Eu-bromate [23], Eu(OH) 3 [24] and Eu mixed oxides [32]. On cooling,K increases quite rapidly between 300 and 180 K and follow a Curie-Weiss type of behaviourK = 0.461/(T − 85) emu K/ion.…”

“…Furthermore, inspection of the CF pattern of the spectra of EuT [19] revealed that a planer anisotropy is expected in EuT as in YbT. Because of the large CF splitting of the 7 F 1 term in EuT, it is expected to have a large SIA and as in other Eu 3+ compounds SIA is to exhibit a unique thermal characteristic [23,24]. This encouraged us to study the SIA characteristic of EuT.…”