Reflectivity spectra of NiCl2and NiBr2crystals

Abstract

Quasi normal-incidence reflectivity measurements in the 2-11 eV region at 300 and 80K are reported for the magnetic insulators NiCl₂ and NiBr₂. The data has been discussed in relation to a possible energy-band scheme. The authors conclusions can be summarized as follows: the peaks up to approximately=7.7 eV in NiCl₂ and up to approximately=7 eV in NiBr₂ are due to a charge transfer process from the p states of the halogen (valence band) to the localized d states of the Ni²⁺ ion; the structures at higher energies are probably due to excitonic and band-to-band transitions (halogen p states to metal s states).