Local probe of irradiation-induced structural changes and orbital magnetism in Fe60Al40 thin films via an order-disorder phase transition

Abstract

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 Fe 60 Al 40 thin films along the order-disorder (B2 → A2) phase transition initiated by 20-keV Ne + ion irradiation with fluences of (0.75-6) ×10 14 ions 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 ∼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 ∼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 Fe 60 Al 40 model structures for the ordered (B2) and the disordered (A2) phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.

Al-driven peculiarities of local coordination and magnetic properties in single-phase Alx-CrFeCoNi high-entropy alloys

“…It not only offers the possibility to visualize the contributions depending on a particular backscatter but for instance, it allows also to distinguish contributions from light and heavy backscattering elements. The theoretical background of WT analysis and some cases of its application could be found elsewhere [48][49][50][51][52].…”

Magnetic response of FeRh to static and dynamic disorder

“…Nevertheless, the increase of the open volumes is consistent with the increased static disordering observed in the ion-irradiated films, as determined from the EXAFS measurements.DiscussionFrom the performed EXAFS measurements it is evident, that a change in the chemical composition of the nearest neighbour shell upon ion irradiation is not detected. A variation of the chemical composition can give rise to the onset of Fe-rich regions due to intermixing and would lead to changes in the relative intensity of the different features in the Fourier transform, as it is present for example in ion irradiated Fe 60 Al 40 thin films 27. This is in contrast to XRD measurements,24 where intermixing was suggested due to a decrease of the long-range order parameter S with rising ion irradiation fluence.…”

Evolution of the magnetic hyperfine field profiles in an ion-irradiated Fe60Al40 film measured by nuclear resonant reflectivity

“…A very small increase in the film thickness ($0.5 nm) due to the irradiation is revealed by the change in the oscillation frequency. The result corresponds to the $1% increase in the lattice parameter determined by X-ray diffraction (Liedke et al, 2015;Ehrler et al, 2020;La Torre et al, 2018). The peculiarities of the oscillation shapes characterize the top and bottom interfaces.…”

“…The depth and lateral distribution of the magnetized regions at the nanoscale were observed by magnetic flux lines which became apparent via the phase shift of the scattered electrons. By means of X-ray magnetic circular dichroism (XMCD) and analysis of extended X-ray absorption fine structure (EXAFS) measurements, performed on beamline ID12 at the European Synchrotron (ESRF), it was shown that an increase in the irradiation fluence provided a progressive rise in the Fe magnetic moment, revealing the occurrence of a change in the chemical disorder in the Fe 60 Al 40 alloy (La Torre et al, 2018). Recent XMCD results obtained with soft X-rays at the Helmholtz-Zentrum Berlin (HZB) have confirmed these findings (Smekhova et al, 2021).…”