The Relation between Magnetic Properties and the Shape of Mössbauer Spectra

Abstract

Abstract This paper is concerned with the relation between the magnetic properties of a solid and the line shape of its Mössbauer spectrum in the presence of a magnetic hyperfine interaction. In order to observe Zeeman splitting, the natural line width must be smaller than the splitting itself, and the magnetic field at the nucleus must remain constant for a period sufficiently long to allow the nucleus to carry out a Lamor precession of about 1 rad. For paramagnetic materials the latter condition is analysed in terms of a stationary Markoff spin‐flip process; for sufficiently high spin‐flip frequencies this leads to “motional narrowing” of the Mössbauer spectrum, in agreement with experimental data. Magnetically ordered systems are treated both by the Weiss molecular field model and the spin wave model. The characteristic features exhibited by the Mössbauer spectra calculated in this way are compared with published data. One important conclusion is that the presence of a pronounced central peak in combination with hyperfine splitting does not necessarily require the coexistence of “paramagnetic” and “magnetically ordered” regions in the material.