The Mossbauer effect provides an ideal and sometimes unique method for isolating and studying certain properties of a lattice. The method is discussed and illustrated by a detailed study of metallic iron from 4°K to 1300°K. The temperature shift (1, 2) observed in the M ω ssbauer spectrum of metallic Fe 57 is due chiefly to relativistic time dilation. In the low-temperature region the variation is nonlinear and compatible with a Debye temperature θ = 400°K, although θ is not strictly independent of temperature. The zero-point root-mean-square velocity in the lattice and the lattice specific heat may be derived from the data. At high temperatures, the classical limit (1/ E ) ∂ E /∂ T = 3 k /2 Mc 2 for the relativistic shift is attained and perhaps exceeded. Disagreement with the classical limit would indicate a temperature variation in the isomer shift. (3) At the Curie point and at the transition from α to γ iron, discontinuities are observed in the temperature shift. These discontinuities are too great to be attributed to the relativistic shift. If attributed to the isomer shift, they indicate that the electron density at the nucleus increases at the transitions from the ferromagnetic to the paramagnetic state and from α to γ iron. The strength of the Mossbauer absorption, determined as a function of temperature, is compatible with a Debye temperature that falls from about 400°K to 300°K in passing from low to high temperatures over the range studied. In principle, root-mean-square displacements in the lattice may be computed as a function of the temperature. Measurements on the internal field at the nucleus show that the polarizability of s -electrons is slightly temperature dependent.
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Jan 1, 1967
I B Bersuker + 2
