Optical Properties of Iron and Dilute Iron-Aluminum Alloys

摘要

An interpolation scheme for the band structure of paramagnetic iron was used to model the band structure of ferromagnetic iron. This was carried out by superimposing two paramagnetic iron band structures with a 2.2 eV energy offset to simulate the exchange splitting. This model was used to calculate the optical conductivity of ferromagnetic iron. Good agreement was achieved with that calculated by Callaway and Wang. The broad peak in the iron optical conductivity (sigma sub 1 ) at 2.5 eV is found to be due to transitions from minority-spin bands 2 and 3 to minority-spin bands 4 and 5 at locations throughout the interior of the Brillouin zone, but generally not on or near symmetry lines and points. The broad 6.0 eV peak in sigma sub 1 is found to be due to the two two-dimensional band gap minimums near the middle of the delta and lambda symmetry lines. These transitions occur in both the minority- and majority-spin band structures. Composition modulation spectroscopy was applied to iron using aluminum as a dilutant. Two characteristic features were present in the resulting delta epsilon sub 2 spectra. These were a broad negative peak at 2.5 eV and a broad positive peak at 6 eV - the same locations as the peaks in sigma sub 1 . The decrease in epsilon sub 2 at 2.5 eV is attributed to a depletion of electronic states in the host d bands. This depletion is mainly due to the valence difference between iron and aluminum. The increase in epsilon sub 2 at 6 eV is claimed to be due to band narrowing and/or the presence of a virtual bound state residing below the iron d bands. (ERA citation 12:035139)