Internal Magnetic Fields and the Saturation Magnetization of Iron—Aluminum Alloys

Abstract

Internal magnetic fields in several iron—aluminum alloys ranging in composition from 19 to 28 at. % aluminum have been measured in a Mössbauer absorption experiment. In the composition range 22% to 26% aluminum three distinct internal magnetic fields were observed. At 300°K the magnitudes of these fields are in the ratio 1.00:0.88:0.72. In a 19% alloy only the two larger fields were observed, while in a 28% alloy only the largest and smallest fields were seen. The largest and smallest fields are the previously observed internal magnetic fields at iron atoms having, respectively, 8 and 4 iron nearest neighbors in an Fe3Al structure. The 0.88 field is attributed to iron atoms surrounded by 5 iron nearest neighbors in an Fe13Al3 structure. Using the known relation between the internal magnetic field and the atomic moment and the supposition that an iron atom with 3 iron nearest neighbors has no aligned moment, saturation magnetization curves of the iron—aluminum system have been calculated on a statistical basis under various known ordering conditions. In the case of annealed alloys, this calculation yields a saturation magnetization curve which agrees with measurements within experimental accuracy. The measured differences between the saturation magnetization of quenched and annealed alloys are also reproduced in these calculations. In the case of cold-worked alloys, good agreement with experiment is similarly obtained.