Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

Abstract—New data on the phase compositions and structural transformations in a number of Fe₈₁Ga₁₉ alloys doped with trace amounts (≤0.2 at %) of rare earth elements are presented. The data were obtained in neutron diffraction experiments performed with high resolution and in a continuous temperature scanning mode under heating to 900°C and subsequent cooling. It has been established that structural rearrangements generally proceed in an identical manner both in the original Fe₈₁Ga₁₉ alloy and in its doped analogues. Slow heating and subsequent cooling of the alloys (at a rate of ±2°C/min) leads to the formation of clusters of the D0₃ phase with sizes in the range of 200–300 Å in the matrix of the disordered A2 phase. The sizes and volume fraction of clusters (~0.3 of the sample volume) weakly depend on a specific composition. The degree of ordering of the atomic structure of clusters changes with temperature according to a phase transition of the second kind and is close to unity at room temperature. The search for structural ordering corresponding to the modified D0₃ phase, which was discovered in a number of electron-diffraction studies, did not lead to a positive result.