Double Curie Point Phenomenon in Fe–Al Alloys

Abstract

Magnetic behavior of Fe–Al alloys with compositions in the neighborhood of 25 at% Al has been investigated by means of magnetic measurement and Mössbauer spectroscopy. A reliable phase constitution is determined for the atomic and magnetic ordering. Magnetic anomalies observed in this system can be satisfactorily interpreted on the basis of our phase relationship. The variation in magnetization with quenching temperature shows a rapid increase in the intermediate temperature range owing to the appearance of a ferromagnetic disordered α phase. There are two different origins of the so-called “double Curie point” phenomenon. The first case occurs in the lower Al concentration, and is caused by the magnetic transformations of ordered DO₃ and disordered α phases. The second case occurs in the higher Al, and is caused by the magnetic transformation of the ordered DO₃ phase and the phase transformation of the mixed phase, disordered α and ordered B2, to the ordered B2 single phase. The ratio of the phases, ferromagnetic α to paramagnetic B2, determines the magnetic intensity of the alloy depending on composition and cooling rate.