Ferroelastic domains and phases in ferromagnetic nanostructured FePd alloy

Polarization optical, electron microscopic, and thermomagnetic investigations of FePd single crystals undergoing an A1 → L1₀ phase transformation have been carried out. The results obtained have been analyzed proceeding from the concept of ferroelasticity and the experimental criteria of its existence. The features of phase transformations in equiatomic FePt and FePd alloys have been compared. A conclusion has been drawn that the atomic ordering in the FePd alloy is preceded by the formation of a ferroelastic lowsymmetry disordered (BCT) phase, and the A1 → L1₀ phase transformation presents a combination of different types of phase transitions such as cooperative displacement and ordering of atoms.