Volume effect and electron band modification in α-Fe by substitutional impurities

Abstract

Systematic investigation of the various impurities influence on the electron and electron spin density on the iron nucleus has been undertaken for impurities dissolved randomly on the regular iron sites in the ferromagnetic BCC iron. The average electron and spin density on the iron nucleus is affected by the volume effect caused by solution of the impurity and by the conduction band modification due to the same impurity. It was attempted to correct data for the volume effect by using information obtained by ab initio calculations of the hyperfine field B and electron density ρ in pure iron versus varying lattice constant a. It was found that ∂ B / ∂ a = 33 ( 3 ) T A ˙ − 1 and ∂ ρ / ∂ a = − 5.2 ( 1 ) el . a . u . − 3 A ˙ − 1 . Mössbauer data were used to evaluate hyperfine parameters versus particular impurity concentration c, while the corresponding lattice constant evolution was obtained from the X-ray diffraction data. Hence, it was possible to make volume correction by using above slopes obtained in calculations. It was found that for all d impurities one has the linear correlation between volume corrected hyperfine field variation ( dB/ dc) b and corresponding electron density variation ( dρ/ dc) b . The slope for the above correlation amounts to (∂ ρ/∂ B) b = −0.031(3) el. a.u. −3 T −1. A linear correlation between the out of the core electrons N e of the impurity and electron density on the iron nucleus was found with the slope −0.0038(7) a.u. −3 at.% −1 for all d impurities and −0.0072(3) a.u. −3 at.% −1 for the s–p impurities of the fourth period.