Anomalous structural transformation and magnetism of Fe-Ga alloys

We have investigated the thermal expansion properties, crystal structures, and magnetism of Fe_1-XGa_X alloys with 27.5<X<37.5. Fe-Ga alloys with BCC structures can be obtained by quenching from high temperatures, and these alloys exhibit ferromagnetism. As the temperature increases, BCC Fe-Ga alloys undergo crystal structural transformation from the BCC to the FCC structure, accompanied by volume expansion. With a further increase in temperature, these alloys undergo structural transformation from the FCC to a hexagonal phase (D0₁₉). The transformation from the FCC to the D0₁₉ phase is accompanied by a decrease in volume per atom of the alloys, in spite of an increase in the temperature. The Curie temperature of FCC Fe-Ga alloys is higher than that of BCC Fe-Ga alloys, and D0₁₉ show the non-magnetic in present work. Considering from the above-mentioned results, the anomalous volume behavior accompanying the crystal structure transformation can be related to the contribution of magnetism in FCC Fe-Ga alloys. In a previous report, an FCC structure was obtained by carrying out long-time annealing at 550 °C. However, in this study, the FCC structure is obtained from the BCC structure as the temperature increases smoothly at a rate of 5 °C/min. Moreover, the Fe_62.5Ga_37.5 alloy undergoes a structural transformation from the BCC to an unknown high-temperature phase.