Magnetization curves for tetragonal martensites: Experiments and modeling

In the absence of twin boundary motion, the magnetization curves of tetragonal martensites depend on the relative orientation of crystal axes, the shape anisotropy, and the applied field. Two tetragonal martensites with the lattice parameters ratio c∕a1 (easy axis) and c∕a1 (easy plane) exist in Ni–Mn–Ga alloys. The magnetization curves of rods and plates of both types of martensite, chosen for their immobile twin boundaries, have been measured at room temperature. The M(H) curves are well described by a theory including magnetocrystalline anisotropy and magnetostatic energy. The results can indicate the variant distribution in each of the samples.