Raman scattering by phonons and magnons in Ni_cMg_1-cO solid solutions

The Raman scattering by phonons and magnons was studied at room temperature in polycrystalline solid solutions Ni_cMg_1-cO and pure NiO. The experimental Raman spectrum of NiO consists of six well resolved bands, whose origin is due to the disorder-induced one-phonon scattering (bands at 400 and 500 cm^-1), two-phonon scattering (bands at 750, 900 and 1100 cm^-1) and two-magnon scattering (band at 1500 cm^-1). In Ni_cMg_1-cO solid solutions, a relative increase of one-phonon scattering is observed upon a dilution of nickel oxide by magnesium ions: at room temperature, the two-magnon band becomes invisible for c<0.7, whereas the two-phonon contribution disappears at c<0.5. Such behaviour is explained by disorder-induced effect, caused by chemical substitution and off-centre displacement of nickel ions.