X-rayL2,3resonant Raman scattering from NiO: Spin flip and intermediate-state relaxation

Abstract

We present measurements of x-ray resonant Raman scattering from NiO with ${\mathrm{L}}_{2,3}$ excitation and calculations in an ionic model based on the process (${2\mathrm{p}}^{6}$${3\mathrm{s}}^{2}$${3\mathrm{d}}^{8}$)\ensuremath{\rightarrow}(${2\mathrm{p}}^{5}$${3\mathrm{s}}^{2}$${3\mathrm{d}}^{9}$)\ensuremath{\rightarrow}(${2\mathrm{p}}^{6}$${3\mathrm{s}}^{1}$${3\mathrm{d}}^{9}$). The agreement between theory and experiment is good from below threshold up to 2.5--3 eV above threshold. By comparing theory and experiment, we show the effect of crystal-field splitting and the contribution bringing the ${\mathrm{Ni}}^{2+}$ triplet ground state to a singlet final state with excitation above the ${\mathrm{L}}_{3}$ edge. When the excitation energy exceeds the ${\mathrm{L}}_{3}$ threshold by about 3 eV, we present evidence that the intermediate state in the scattering can also relax to a state similar to that created with threshold excitation. We suggest d-d excitation and electron-hole pair excitation as the origin of this relaxation.