Time-dependent effects using selective-excitation double-Mössbauer techniques with application toα−Fe2O3

Selective-excitation double-Mössbauer (SEDM) experiments have been done using powdered scatterers of iron and $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$. In addition, calculations have been made to predict the SEDM line shape. These calculations included Rayleigh, incoherent electronic, and thickness effects. The scatterer was assumed to have a six-line Mössbauer transmission spectrum. SEDM line shapes are calculated for both static and dynamic ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclear environments. Results for static SEDM line shapes involving one transition show that the scattered radiation consists of a single peak located at the excitation energy for scatterer thicknesses $\beta >20\mathrm{}$. This is not true in the dynamic case. SEDM procedures are shown to be superior to ordinary Mössbauer transmission experiments in determining time-dependent effects in certain cases. We have applied these methods to study the Morin transition in $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$. Our results show that each iron nucleus is in a fluctuating hyperfine field. The values of the relaxation times at 263.5, 261, 259.5, and 258.5 K are (1.1 ± 0.2) × ${10}^{-7\mathrm{}}$, (2.3 ± 0.4) × ${10}^{-7\mathrm{}}$, (2.9 ± 0.6) × ${10}^{-7\mathrm{}}$, and (4.3 ± 0.9) × ${10}^{-7\mathrm{}}$ sec.