Al Hyperfine Fields in Ordered Fe–Al Alloys

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Abstract
In the Fe–Al system a number of ordered phases are possible for compositions between 10 and 30 at.% Al. Since the aluminum site is essentially nonmagnetic, measurements of the hyperfine interaction ought to yield sensitive and detailed information about the conduction electron polarization and its dependence on long‐range crystallographic order. We have studied the Al resonance in alloys containing between 14 and 28 at.% Al by NMR spin‐echo spectroscopy at 4.2°K. For all compositions, the spectra of alloys which have been subjected to cold work are similar and show a single broad asymmetric distribution with a maximum at about 58 MHz which extends to 30 MHz on the low‐frequency side for the higher concentrations. In the 23 to 28 at.% Al region the spectra of annealed alloys are very different having strong sharp lines at 29 and 33 MHz and a broad distribution around 58 MHz which decreases in amplitude with increasing Al content. These spectra seem to be characteristic of Fe3Al order. Since Al sites with 8 Fe nn should be in the majority, it appears that there is a large shift in the Al resonance when the alloy orders similar to the shift in the Si resonance in the Fe–Si system.

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