Hard x-ray absorption and magnetic circular dichroism spectroscopy have been applied to study the consequential changes of the local environment around Fe atoms and their orbital polarizations in 40 nm thick ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ thin films along the order-disorder $\left(B2\to A2\right)$ phase transition initiated by 20-keV ${\mathrm{Ne}}^{+}$ ion irradiation with fluences of $(0.75–6)\times {10}^{14}\text{ions}{\mathrm{cm}}^{-2}$. The analysis of the extended x-ray absorption fine structure spectra measured at the Fe K edge at room temperature revealed an increased number of Fe-Fe nearest neighbors from 3.47(7) to 5.0(1) and $\sim 1\%$ of volume expansion through the transition. The visualization of the Fe and Al nearest-neighbor rearrangement in the first coordination shell of Fe absorbers via the transition was carried out by wavelet transformations. The obtained changes in Fe coordination are evidently reflected in the x-ray magnetic circular dichroism spectra which show an increased orbital magnetic moment of Fe atoms and a pronounced magnetic multielectronic excitations peak at $\sim 60$ eV above the edge. The amplitudes of both peaks demonstrated similar dependencies on the irradiation fluence. The results of self-consistent density functional calculations on relaxed ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ model structures for the ordered $\left(B2\right)$ and the disordered $\left(A2\right)$ phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.

• Received 11 February 2017
• Revised 19 June 2018

DOI:https://doi.org/10.1103/PhysRevB.98.024101