Preferred site occupation of 3d atoms in NixFe4−xN(x=1 and 3) films revealed by x-ray absorption spectroscopy and magnetic circular dichroism

Abstract

X-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism measurements were performed at the Ni and Fe ${L}_{2,3}$ absorption edges for $\mathrm{N}{\mathrm{i}}_{x}\mathrm{F}{\mathrm{e}}_{4\ensuremath{-}x}\mathrm{N}\phantom{\rule{4pt}{0ex}}(x=1$ and 3) epitaxial films. Spectral line-shape analysis and element-specific magnetic moment evaluations are presented. Shoulders at approximately 2 eV above the Ni ${L}_{2,3}$ main peaks in the XAS spectrum of $\mathrm{N}{\mathrm{i}}_{3}\mathrm{FeN}$ were interpreted to originate from hybridization of orbitals between Ni $3d$ at face-centered (II) sites and N $2p$ at body-centered sites, while such features were missing in $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ film. Similar shoulders were observed at Fe ${L}_{2,3}$ edges in both films. These results indicate that the orbitals of Ni atoms did not hybridize with those of N atoms in the $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ film. Hence, Ni atoms preferentially occupied corner (I) sites, where the hybridization was weak because of the relatively long distance between Ni at I sites and N atoms. The relatively large magnetic moment deduced from sum-rule analysis of $\mathrm{NiF}{\mathrm{e}}_{3}\mathrm{N}$ also showed a good agreement with the presence of Ni atoms at I sites.