TmPd2Si2 and YbPd2Si2 : a Mössbauer effect study of crystal fields and intermediate valence

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Abstract
We report and compare Mössbauer effect measurements on 169Tm in TmPd2Si2 and on 170Yb both diluted into the TmPd2Si2 and in YbPd2Si2. For Tm the data is interpreted in terms of a Tm3+ charge state and the crystal field parameters, the magnetic ordering temperature and the paramagnetic relaxation rates are obtained. The results on Yb in both the dilute and concentrated cases show no evidence of any magnetic character. The thermal variation of the quadrupole hyperfine interaction is treated in terms of intermediate valence Yb within the interconfiguration fluctuation model and yields a hybridization width of approximately the same size as the expected total energy splitting of the Yb3+ 2F 7/2 configuration (∼ 100 K). The intermediate valence behaviour is observed on Yb in both the dilute and concentrated samples. In an appendix we give the theoretical line shapes, calculated in the slow electronic relaxation limit, for a Tm3+ ground state non-Kramers doublet whose degeneracy is lifted by the crystal field. This analysis predicts absorption lines at Doppler velocities in excess of ± 100 cm/s