A Mössbauer spectrometry study of hyperfine magnetic fields and ordering in Fe_3Al

Calculations of the ^(57)Fe hyperfine magnetic field distribution in Fe_3Al were performed with a model that assumed the exchange polarization mechanisms depend on the magnetic moments at atom sites. Calculations with parameters from dilute alloys were in semi-quantitative agreement with experiment, but the best agreement occurred when second and third-neighbor HMF perturbations were assumed to be small. The progress of the disorder → order transformation in Fe_3Al was measured by X-ray diffractometry and Mössbauer spectrometry. Both techniques showed a transient appearance of B32-like order during the early stage of ordering at 300°C. The formation of transient B32 order is probably a kinetic phenomenon that cannot be predicted well by thermodynamics.