Mössbauer Study of the FeMn Carbides (Fe_1−<i>x</i>Mn_<i>x</i>)₃C and (Fe_1.1Mn_3.9)C₂

Abstract

Abstract We have performed Mössbauer experiments on FeMn carbides having the cementite structure (Fe 1− x Mn x ) 3 C, where x ranges from 0 to 0.6, and on a Hägg carbide with the Pd 5 B 2 structure, (Fe 1.1 Mn 3.9 )C 2 , over the temperature range from 12 to 500 °K. Above the Curie temperature, the spectra exhibit a quadrupole interaction ranging from about 0.20 to 0.28 mm/s and the contributions from Fe atoms in the two types of cementite lattice sites can be identified. It is found that Mn atoms have a slight preference for “general” over “special” lattice sites in cementite. The specimens containing 0 to 20% Mn all become ferromagnetic at low enough temperatures, and the effective field decreases with Mn concentration very rapidly, extrapolating to 0 at about 34% Mn. Below T c , the quadrupole splitting decreases drastically to less than 0.05 mm/s. Most of the results seem to be consistent with a donor theory in which C donates both of its 2p electrons to the metal d‐band, giving the Fe in cementite an average electron configuration of approximately 3d 7.66 4 s 1 .