An ab-initio calculation of magnetic resonant x-ray scattering spectra in NiO

TL;DR

This study uses ab-initio calculations to accurately reproduce and analyze the magnetic resonant x-ray scattering spectra in NiO, revealing the roles of orbital polarization and spin-orbit interaction in the spectral features.

Contribution

It demonstrates the effectiveness of ab-initio band-structure calculations in explaining magnetic resonant x-ray scattering spectra and clarifies the origins of spectral peaks in NiO.

Findings

Main-edge peak reflects $4p$ orbital polarization induced by spin polarization.

Pre-edge peak is a direct measure of unoccupied $3d$ orbital polarization.

The spectra are well reproduced by including orbital polarization and spin-orbit effects.

Abstract

We investigate the magnetic resonant x-ray scattering spectra around the $K$ edge of Ni in antiferromagnetic NiO using an \textit{ab-initio} band-structure calculation based on the density-functional theory. By taking account of orbital polarization through the spin-orbit interaction, we reproduce well the spectra obtained experimentally, thus demonstrating the usefulness of the \textit{ab-initio} calculation. It is shown that the main-edge peak, which mainly comes from the dipolar ($1s \to 4p$) transition, is a direct reflection of the orbital polarization of the $4p$ states. It is clarified that the $4p$ orbital polarization is mainly induced from the spin polarization on the $4p$ states by the spin-orbit interaction. The 3d orbital polarization at neighboring Ni sites gives rise to only a minor contribution to the $4p$ orbital polarization through a $p$-$d$ mixing. It is also shown that the pre-edge peak, which mainly originates from the quadrupolar ($1s \to 3d$) transition, is a direct reflection of the orbital polarization of the unoccupied 3d states. It shows a Fano-type antiresonant dip due to interference with the nonresonant contribution, in agreement with the experimental result.