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

Abstract

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.