Correlations among hyperfine parameters in amorphous metal systems: Mössbauer linewidth asymmetries and fluctuation hyperfine correlation functions

The microscopic correlations among hyperfine parameters in amorphous metal systems appear in the Mössbauer linewidth asymmetries. The fluctuation hyperfine correlation functions can be derived using the formalism of Lines, Eibschutz and coworkers. This approach has been reviewed in detail in this paper. A quantitative estimate of the role of the anisotropic component of the hyperfine field toward linewidth asymmetries is presented. It is stressed that contrary to earlier claims, this approach does not give a correct measure of the variance of quadrupole splitting. It is not, therefore, possible to pass judgement on the validity of a linear correlation between quadrupole splitting and hyperfine field or quadrupole splitting and isomer shift. The experimental evidence against a linear correlation between the hyperfine field and the isomer shift, however, remains valid. A simple procedure for checking the validity of a linear correlation between the isomer shift and the magnitude of the quadrupole splitting is suggested. Critical comments on the method of analysis are given.