Temperature dependent magnetostrains in polycrystalline magnetic shape memory Heusler alloys

The transformation-induced strains with and without applied magnetic field and magnetostriction loops at different temperatures have been measured for polycrystalline ferromagnetic and metamagnetic shape memory Heusler alloys such as NiMnGa, NiFe(Co)Ga and NiMnSn, respectively. The results evidence a magnetic field oriented growth of martensitic variants during the martensitic transformation in NiMnGa sample, whereas this effect is not evident in the other two alloys. In the NiMnSn alloy, the isotropic volume magnetostriction dominates the anisotropic domain magnetostriction.

► NiMnGa (A1),NiFe(Co)Ga (A2) and NiMnSn (A3) as FSMA and MMSMA, respectively.
► Magnetic field oriented growth of martensite during martensitic transformation was observed in A1 and A2 only.
► Magnetostriction shows predominance of anisotropic contribution in A1 and A2. This contribution was not found in A3.
► Magnetostriction shows only magnetovolume effects in the case of A3.
► Magnetostriction exhibits maximums near phase transitions in A1 and A3.