ИСТИНА

The progress in magnetic patterning of Fe60Al40 thin films with ion-irradiation [1, 2] stimulates the structural and magnetic studies of this system on the local scale that could provide more insights on the formation mechanism of a long-range ferromagnetic order induced by ions. In our work the evolution of the local environment and development of Fe magnetic polarizations in thin films of transition metal aluminide Fe60Al40 of 40 nm thickness have been probed by element-specific hard- and soft- X-ray absorption spectroscopy through the order-disorder (B2 → A2) phase transition initiated by 20keV Ne+ ion irradiation with low fluences (~1014 ions·cm-2). Extended X-ray absorption fine structure (EXAFS) spectra measured at the Fe K edge at room temperature have shown consequential changes in the local environment of Fe absorbers in a course of the transition. The analysis established a number of Fe-Fe nearest-neighbours as 3.47(7) and 5.0(1) for the ordered B2 and the fully disordered A2 state, correspondingly, and ∼ 1% of the unit cell volume expansion [3]. The visualization of the rearrangement of Fe and Al nearest-neighbours was done with wavelet transformations. The observed structural changes were followed by increased net magnetic moments of iron atoms: X-ray magnetic circular dichroism (XMCD) spectra measured either at the Fe K edge or L2,3 edges showed a strong rise of Fe 4p orbital and 3d spin net magnetic polarizations with fluence, respectively. The sum rule analysis revealed a characteristic S-shape dependence of iron 3d magnetic moments on fluence as it was previously found by macroscopic magneto-optical Kerr effect (MOKE) measurements [2] in spite of a presence of the top oxide layer. The strength of Fe 4p-3d hybridization for the fully disordered A2 state was found to be the largest among the studied B2 and intermediate A2 states. Self-consistent DFT calculations performed by the VASP program package for relaxed model systems in both phases have shown a clear variation of local configurations and changes in spin-resolved iron DOS. XANES spectra recorded at the Al K edge at low temperature have shown a distinct change in coordination of Al atoms for B2 and A2 phases. The work was partially funded by Helmholtz Association (Young Investigator’s Group “Borderline Magnetism”, VH-NG-1031). [1] J. Fassbender, M. O. Liedke, T. Strache et al., Phys. Rev. B, 77 (2008) 174430. [2] R. Bali, S. Wintz, F. Meutzner et al., Nanoletters, 14 (2014) 435-441. [3] E. La Torre, A. Smekhova, C. Schmitz-Antoniak et al., submitted to Phys. Rev. B (2017).