Mössbauer study of fine structure features of equiatomic FePd alloy after severe plastic deformation and ordering annealing

Tracking of the Multimodal Ordering Process in FePd Alloy

“…Additionally, it is expected that the ordering process proceeds through several intermediate steps rather than a direct transition between the A1 and L1 0 phases. Previous studies have reported sequential transformations in FePd alloy between the disordered A1 phase and ordered L1 0 phase, involving various intermediate phases. − In our case, starting from the multilayered sample, the transformation occurs initially to a disordered A1 phase with locally varying Fe-to-Pd stoichiometry or to the L1 2 phase of the FePd 3 alloy. With the further prolongation of the annealing time, the transition progresses from cubic A1 and L1 2 phases to phases with tetragonal structures, such as A6, L1′, and finally to the L1 0 phase.…”

“…42,43 The remaining 48% of the iron atoms have lower magnetic hyperfine field values and can be interpreted as iron atoms mixed with palladium, forming the fcc FePd alloy with local variations in stoichiometry. 18,44 Within this component, around 31% of the iron atoms have a mean magnetic hyperfine field value of approximately 31.5 T, corresponding to the value expected for the A1 FePd alloy with an atomic ratio close to 1:1. Another subcomponent, with a mean <B hf > value of around 26.0 T, suggests a disordered alloy with a Fe 20−25 Pd 80−75 stoichiometry.…”

“…Additionally, the gray, red, and blue subcomponents could also represent the A1 phase with Fe concentrations of approximately 15, 25, and 40, respectively, while the green subcomponent represents clusters enriched with iron ( x > 50). For more information, please refer to Mössbauer spectroscopy references of bulk FePd alloy. , …”

“…Since such a shift would result in a deficiency of iron atoms, the narrowing of the P ( B hf ) distribution suggests the gradual formation of different FePd phases, including A6, L1 2 , and L1′. These phases exhibit lower magnetic hyperfine fields compared to the A1 phase with similar local Fe-to-Pd compositions. ,,, …”

“…The presence of various FePd phases within a similar concentration range and under specific thermodynamic conditions suggests that the phase transition between the A1 and L1 0 phases may not occur through a direct transformation but rather a cascade-type transformation involving multiple stages. − This cascade transformation is believed to involve the following stages: (i) initial decomposition of the cubic phase into other cubic phases with different atomic stoichiometries, (ii) a shear transition leading to the transformation into tetragonal structures, and (iii) atomic ordering of the tetragonal phases, ultimately resulting in the formation of the L1 0 phase. This behavior is likely due to the shift of the congruent point in the FePd phase diagram from the equiatomic composition to around 58 atom % of Pd and the appearance of intermediary stages, such as L1 2 , L1′, and A6 phases in this phase transition process.…”