Speaker
Description
High-energy synchrotron X-ray diffraction and $^{57}$Fe Mössbauer spectroscopy were combined to resolve the phase evolution and local magnetic environments in mechanically alloyed Fe$_{73.5-x}$Mn$_{x}$Cu$_{1}$Nb$_{3}$Si$_{13.5}$B$_{9}$ with ($x$ = 2, 4, 6, 8, 10 at.%) powders. Elemental mixtures were dry-milled for 30 h in a RETSCH PM400 planetary ball mill at 250 rpm using a ball-to-powder ratio of 40:1. High-energy diffraction measurements were performed at the I12 beamline of Diamond Light Source, and room-temperature Mössbauer spectra were evaluated using hyperfine magnetic-field distributions.
Synchrotron diffraction revealed progressive suppression of the bcc-Fe reflections with increasing Mn content. The powders with $x \leq 6$ consist of nanocrystalline bcc Fe embedded in an amorphous matrix, whereas the $x$ = 10 composition exhibits a fully amorphous diffraction pattern. Consistently, the Mössbauer spectra are dominated by broad magnetic-field distributions characteristic of structurally disordered Fe environments. A relatively narrow Fe-rich high-field contribution with a mean hyperfine field close to 30 T is present for $x$ = 2,4,6 and becomes nearly negligible at $x = 8$ and is absent at $x$ = 10. A pure $\alpha$-Fe component could be fitted only for $x$ = 2, with a relative spectral area below approximately 1%, preventing its unambiguous identification. The mean hyperfine field of the amorphous contribution decreases from 2.5 T at $x$ = 2 to 7.9 T at $x$ = 10, with the largest change occurring between $x$ = 6 and $x$ = 8. The accompanying decrease in the mean isomer shift from 0.08 to 0.02 mm/s demonstrates a systematic modification of the local electronic environment of Fe. The bimodal field distributions indicate the coexistence of Fe-rich regions and Mn-enriched or more strongly disordered environments. Together, these complementary local and long-range probes demonstrate that Mn simultaneously stabilizes the amorphous structure and weakens local magnetic ordering, identifying the $x$ = 10 alloy as the most completely amorphous composition within the investigated series.
Acknowledgment
This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034. Support from the project VEGA 1/0638/24 is also acknowledged.
