Evaluation of asymmetric Mössbauer spectra of a Fe-41.3 at.% Ni invar alloy

Following a model of Billard and Chamberod the asymmetric Mössbauer spectra of a Fe-41.3 at.% Ni invar alloy have been quantitatively interpreted. In the temperature range from about 77 K up to the Curie temperature for each spectrum four parameter values have been obtained. These are the mean hyperfine field H₀, the magnetic field difference h₁ caused by the isotropic contribution of one first Fe-neighbour atom, the corresponding anisotropic difference h₂ and the strength of the anisotropic quadrupole interaction w. A physical interpretation of these parameters and their temperature dependence has been worked out. The last parameter shows an especially unexpected dependence which is strongly connected with the thermal expansion of the lattice. A mechanism seems to exist by which small changes of the lattice constant cause an enhanced variation of w.