Redistribution of the conduction band density of states near ferromagnetic saturation in EuS

Abstract

We report new absorption measurements on (100) textured EuS films in the 4f7→4f65dt2g transition energy range. For low fields (H<0.2T) the whole absorption peak shifts continuously to lower energies between 70 K and 5 K. If the magnetic field is increased at T=5.5 K so as to saturate the sample, a striking change of the spectrum is observed. The absorption increases in the low energy part of the peak, while it diminishes at higher frequencies, leading to the appearance of a pronounced shoulder in the spectrum. A new theoretical approach is presented, which indicates that the conduction band splits into 12 quasiparticle bands due to the exchange interaction. The spectral weights of these subbands are strongly dependent on the magnetization 〈Sz〉 of the f-system and on the population of the conduction band. A numerical estimate for the 〈Sz〉 dependence of the spectral weights of these subbands agrees qualitatively with the observed behavior of the absorption spectrum of EuS.