Interpretation of Fe-rich part of Fe–Al phase diagram from magnetic properties of A2-, B2-, and DO3-phases

Abstract

Iron-rich Fe–Al binary phase diagram in the composition range of 23–26 at% Al shows a complex structure partly due to magnetic properties of the disordered A2-phase, the ordered B2-phase and the ordered DO 3 -phase. In this study, the disorder-order transformations between the constituent phases have been investigated through magnetization measurements of Fe- x Al alloys ( x = 22.0, 24.0, 24.3, 24.7, 26.5 at%). It is found that spontaneous magnetization of the B2-phase is larger than that of the DO 3 -phase and smaller than that of the A2-phase. The former relation disagree with previous reports but was further confirmed as the decrease of the B2-DO 3 transformation temperature under magnetic field (−1.58 K/T). It is also found that the Curie temperature of the B2-phase (836 K for Fe-24.7 at%Al alloy) coincides with that of the A2-phase; furthermore, these temperatures agree with the phase boundary between B2-region and (A2+B2)-region. • Temperature dependence of spontaneous magnetization was evaluated for the A2-, B2- and DO3-phases of Fe24.7at%Al alloy, and found that the value decreases in this order at any temperature. • Magnetic field dependence of B2-DO3 transformation temperature was evaluated for several Fe-Al alloys, and confirmed that it decreases as magnetic field increases. • Critical behavior for the magnetic transition was analyzed for several Fe-Al alloys and revealed that Curie temperature of the B2-phase almost coincides with that of the A2-phase.