Effect of electric field gradient sign on iron mossbauer spectra in amorphous materials

This paper establishes the fact that a significant asymmetry develops in ⁵⁷Fe Mössbauer spectra at high magnetic fields in amorphous materials containing iron if the electric field gradient (EFG) distribution at the iron sites is dominantly of one sign. The manner in which the symmetric quadrupole doublet develops asymmetrically into the familiar six line Zeeman pattern with increasing (spontaneous or applied) field is computed numerically for general fields, and analytically for high fields, using a broad (amorphouslike) model EFG distribution. It follows that information concerning the dominant sign (or alternatively the absence of a dominant sign) of the EFG can be obtained from iron Mössbauer spectra. Such information concerning EFG sign is potentially important evidence in a probe of the nature of the local packing (i.e. random packing vis-a-vis local crystalline unit-cell distortion) in many amorphous magnetic materials.