Mössbauer-Effect Study of Electronic Relaxation in the Paramagnetic Compound NH4(Fe, Al) (SO4)2·12H2O

Abstract

The Mössbauer spectra of paramagnetic ferric compounds exhibit magnetic hyperfine splittings when the electronic-relaxation rates of the ferric ions are made comparable to the precession frequency of the nucleus in the hyperfine field. This was observed in ferric ammonium alum diluted in aluminum ammonium alum, N${\mathrm{H}}_4$(Fe, Al) ${\left(\mathrm{S}{\mathrm{O}}_4\right)}_2$·12${\mathrm{H}}_2$O, as a function of iron concentration, temperature, deuteration, and external magnetic field. The effect was also observed in the corresponding potassium alums. The crystalline-field levels of the ferric ion consist of three Kramers doublets, and each doublet produces its own hyperfine pattern. In the absence of an external magnetic field, the spectrum due to the $S_z=\pm \frac{5}{2}$ doublet was completely resolved, that due to the ±0 doublet partially resolved, and that due to the ±½ doublet not resolved at all. Relaxation-time estimates are made ranging from ≈${10}^{-7\mathrm{}}$ to ≈${10}^{-10\mathrm{}}$ sec depending on the concentration, the temperature, and the particular Kramers doublet under consideration. The magnetic field produced at the nucleus by the $\pm \frac{5}{2}$ doublet was found to be -572±7 kG. The isomer shift is 0.53±0.1 mm/sec, and the quadrupole-interaction energy, $\frac{1}{4}{e}^2\mathrm{qQ}$, is equal to 0.055±0.025 mm/sec.