Mixed hyperfine interactions in amorphous materials: a model study

57Fe Moessbauer absorption profiles were calculated supposting distributions of all hyperfine parameters: hyperfine magnetic fields, isomer shifts, and electric field gradients. The effect of mixed hyperfine interactions was taken into account in all orders of perturbation theory. The shapes of the spectra were systematically studied for varying average values and widths of the hyperfine magnetic field distributions (HMFD). From the simulated spectra, the shapes of the HMFD were reconstructed using standard techniques of Moessbauer spectra processing which neglect the effects of random isomer shifts and electric field gradients. It has been shown that the reconstructed shapes of the HMFD differ qualitatively from the original single-peaked distributions and exhibit a double-peaked structure similar to the distributions found in many experiments on amorphous alloys with low iron content. A brief reveiw of various mechanisms responsible for either apparent or real double-peaked structure of HMFD has been given. (orig.)