Proprietes optiques et structure electronique de MnAu2
The optical spectrum of the helical antiferromagnetic compound MnAu2(tN = 90°C) has been measured, using a scanning ellipsometric method, in UHV, between 0.47 and 5.7 eV, at temperatures ranging from 88 to 700 K. Below 0.6 eV the experimental data can be fitted to a Drude-like intraband model. The maximum of the interband absorption occurs at 5.1 eV, while the onset of interband absorption may be placed at 0̃.4eV as is suggested by the rapid rise of . below 0.5 eV. In the absence of theoretical work, the analysis of the optical spectrum leads to a preliminary rough model of the electronic structure; the proposed local density of d states is represented. The 5.1eV peak is attributed to d → EF transitions (parabolic edge at 2.7 eV similar to Au), originating in the lower part of the band, associated mainly with Au sites. To account for the moment , the upper d band (mainly Mn sites) is split: the d↑ band is below EF (interband edge at 0.4eV), while the d↓ band contains 1.4 electrons. ESCA measurements tend to confirm this model. An important unusual fact is the sharp anomaly of /~ε(ω) in the infrared, around TN; attempts to correlate this with magnetic (s-d) interactions have been initiated.
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