Plastic deformation inducing ferromagnetism in Fe2MnAl: Probing Fe magnetism

Structural and magnetic properties of the disordered and ordered Fe2MnAl Heusler alloys have systematically been investigated by local and bulk experimental methods. Plastic deformation, induced by cold-work, leads to a structural phase transformation from the ordered L21 to a disordered A2-structure, concomitantly with a change from paramagnetic PM to ferromagnetic FM state; an effect attributed to the strain-induced ferromagnetism. This transition is explained assuming a gradual transformation of the L21-structure to the anti-phase boundary APB tubes, which result in Fe-cluster formation. Plastic deformed ribbon annealed at low temperatures (Tan < 673 K) favors stabilization of L21-structure with (4 0 0) preferential orientation and magnetic ordering temperature of about 120 K. Considering that Fe atoms order magnetically at 120 K, as seen by Mössbauer, and the measured reduction of total magnetization for temperatures below 50 K, one proposes that Mn and Fe sublattices interact magnetically in a non-collinear magnetic structure that is established due to Fe-Fe, Mn-Mn and Fe-Mn frustrated magnetic couplings. High temperature annealing (Tan > 673 K) favors a strong Mn segregation, concomitantly with formation of disordered Fe-Mn-Al alloys that also have magnetic ordering temperature approaching to 300 K.