Annealing effects on the structural and magnetic properties of off-stoichiometric Fe-Mn-Ga ferromagnetic shape memory alloys

• Neutron diffraction determines the crystal structure and atomic occupancies of annealed Fe-Mn-Ga shape memory alloy.
• Cryo neutron diffraction visualizes the martensitic transformation that is correlated to the thermomagnetization behaviors.
• The formation of the ɣ phase alters the martensitic transformation temperature and magnetic properties of Fe-Mn-Ga alloys.
• Fe45Mn26Ga29 annealing at 773 K leads to the phase segregation into Fe-rich and Ga-rich cubic phases.

Annealing plays an important role in modifying structures and properties of ferromagnetic shape memory alloys (FSMAs). The annealing effect on the structures and magnetic properties of off-stoichiometric Fe45Mn26Ga29 FSMA has been investigated at different elevated temperatures. Rietveld refinements of neutron diffraction patterns display that the formation of the ɣ phase in Fe45Mn26Ga29 annealed at 1073 K increases the martensitic transformation temperature and reduces the thermal hysteresis in comparison to the homogenized sample. The phase segregation of a Fe-rich cubic phase and a Ga-rich cubic phase occurs at the annealing temperature of 773 K. The atomic occupancies of the alloys are determined thanks to the neutron's capability of differentiating transition metals. The annealing effects at different temperatures introduce a different magnetic characteristic that is associated with distinctive structural changes in the crystal.

Figure optionsDownload as PowerPoint slide