Al Hyperfine Fields in Ordered Fe–Al Alloys

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.