Observation of nitrogen polarization in $Fe–N$ using soft x-ray magnetic circular dichroism

X-ray magnetic circular dichroism (XMCD) measurements were performed on epitaxial iron nitride thin films at the nitrogen $K$ and at the Fe $LIII$ and $LII$ absorption edges. The iron nitride samples measured with XMCD consist primarily of $γ′$ phase with no observed enhancement on their magnetic moment as compared to that of pure Fe. The XMCD difference signal between left and right elliptically polarized x rays shows a small effect in the $10−5$ range at the $N$ edge, indicative of the possible polarization of nitrogen in the $γ′$ $Fe–N$ samples. XMCD spectra collected with higher energy resolution reveal the presence of multiple components in the Fe $LIII$ absorption edge that are related to different environments for the Fe atoms, i.e., near neighbors or next near neighbors to the $N$ sites. Finally element specific hysteresis loops were also recorded at the N and Fe absorption edges using the difference signal in various incident beam angle geometries.