DOUBLE CURIE-POINT PHENOMENON IN FE-AL ALLOYS

The magnetic behavior of Fe-Al alloys with 21 to 26 at. % Al was investigated by magnetic measurements and Moessbauer spectroscopy. Magnetic anomalies observed could be interpreted on the basis of phase relationships. The variation in magnetization with quenching temperature shows a rapid increase in the intermediate temperature range owing to the appearance of a ferromagnetic disordered alpha phase. There are two different origins of the so-called ″double Curie point″ phenomenon. The first at the lower Al concentrations, is caused by the magnetic transformations of ordered DO//3 and disordered alpha phases. The second, in the higher Al alloys, is caused by the magnetic transformation of the ordered DO//3 phase and the transformation of the mixed phase, disordered alpha and ordered B2, to the ordered B2 single phase. The ratio of the phases, ferromagnetic alpha to paramagnetic B2, determines the magnetic intensity of the alloy depending on composition and cooling rate.