Large magnetic-field-induced deformation and magneto-mechanical fatigue of ferromagnetic Ni-Mn-Ga martensites

Cyclic magneto-mechanical experiments were performed with both tetragonal and orthorhombic ferromagnetic martensites formed in two different Ni-Mn-Ga single crystals. Depending on the structure and the thermo-magneto-mechanical history, the magneto-mechanical response (i.e. the magnetic-field-induced strain) to cyclic magneto-mechanical actuation is constant, increases to saturation at nearly the theoretical limit, or decays. Saturation of the magnetic-field-induced strain is obtained when the local and global preferred orientations of martensite domains coincide. The magnetic-field-induced strain decays if the local preferred state differs from the global preferred state.