On the mechanism of the paramagnetic-to-ferromagnetic transition in Fe-Al

Single crystals of Fe-40 at.% Al were cold rolled to a variety of strains up to 48%, when cracking occurred. The rolled crystals were heated at 10 K min−1 to 973 K in a differential scanning calorimeter, whereupon three exothermic peaks were observed. The cold rolling also induced a transition from paramagnetism to ferromagnetism. At room temperature, the ferromagnetism disappeared upon annealing above the lowest-temperature exothermic peak, but at temperatures below 225 K the annealed specimen still showed a larger magnetic susceptibility than the virgin single crystal. Analysis of the possible contributions to the ferromagnetic behaviour suggests that antiphase boundaries (APBs), principally in APB tubes, are the source.