Ferromagnetic shape memory alloys

MSM in NiMnGa

The magnetic shape memory effect was discovered in 1996. The principle of this effect is twin boundary motion in a magnetic field. Our aim is to achieve large magnetic-field-induced strain (MFIS) in polycrystalline off-stoichiometric Heusler alloy Ni50Mn30Ga20. This alloy has a large martensitic transformation temperture of 80°C - 100°C. To show MFIS, structure and microstructure need to be precisely controlled. Therfore we chose the preparation by stationary casting and following thermal treatment. One of the suitable structures is to be seen in the figure (below/ on the right / left). Once a microstructure is given to sample by casting it is furher optimised by thermomechanical and mechanical training. For characterization DSC, XRD, dilatometry, magnetometry and magneto-mechanical testing are used.

Fig. 1: Atomic sheme of the suitable 7M-structure.