Abstract
The Mössbauer absorption spectra of have been measured in the rare-gas matrices argon, krypton, and xenon with iron atomic concentrations from 0.3 to 3% and matrix temperatures between 1.45 and 20.5 K. All of the spectra show an absorption line with an isomer shift of mm/sec with respect to an iron foil at 300 K. This isomer shift is independent of rare-gas matrix, iron concentration, and matrix temperature. This line is ascribed to an isolated atom (monomer) with an atomic configuration of . The measured isomer shift gives a new calibration point in the isomer-shift-versus-electron-density plot for . The observed temperature dependence of the monomer linewidth shows that the direct phonon process is dominant in the spin-lattice relaxation mechanism. Spin-lattice relaxation times of the order of 2.5 × sec are obtained by assuming a hyperfine field of 1.1 × Oe at the nucleus due to an iron atom with unquenched orbital momentum. From the temperature dependence of the Mössbauer factor, the Mössbauer temperatures in the Debye model are calculated and compared with the values expected from specific-heat measurements. The Mössbauer spectra show, in addition to the monomer absorption line, a pair of narrow lines ( mm/sec), which is intensified with increasing iron concentrations. These lines can be interpreted as the result of the quadrupole splitting of the excited state of in the axial field produced by an iron nearest neighbor (dimer). The measured quadrupole splitting is mm/sec, and the isomer shift for the dimer is mm/sec, corresponding to an effective atomic configuration of with . For in krypton and xenon, the measured dimer/monomer ratio is that which one would expect from probability considerations, but in argon it is a factor of approximately 3 higher than expected.
- Received 2 June 1971
DOI:https://doi.org/10.1103/PhysRevB.4.3787
©1971 American Physical Society