Localization of conduction electrons in the ferromagnetic clusters AuFe

The optical-conductivity spectra of concentrated solutions Au_{1 − x} Fe _x with x = 17 and 22 at % have been measured in a frequency range of (10–33) × 10³ cm⁻¹ at room temperature. The results are analyzed together with previous optical data obtained for compounds with x = 4–12 at %. It is found that the magnetic contributions σ_magn = σ_AuFe − σ_Au to dc and low-frequency(10 cm⁻¹) conductivities for an Fe concentration below 4 at % are almost equal, while the low-frequency magnetic contribution for larger concentrations is significantly larger than the dc one. An absorption band at frequencies of 1000–3000 cm⁻¹ has been found for samples with concentrations x = 6–22 at %. The observed phenomena are attributed to the localization of electrons inside clusters containing ferromagnetically ordered iron ions.