Concepts and Physical Phenomena in Magnetic Shape Memory Science

The magnetically weakly anisotropic cubic Ni-Mn-Ga Heusler alloys exhibit martensitic transformation resulting in martensitic phases with elastically soft crystal lattices and strong magnetocrystalline anisotropies. The magnetic state of these martensites is coupled with a highly mobile twin structure through the ordinary magnetoelastic interactions giving rise to a giant magnetic-field-induced-strain effect. This effect is the key ingredient of a new scientific field. In the present article, the basic phenomena and concepts of this field, such as lattice instability, soft-mode behavior, electron concentration, ferromagnetic shape memory effect, magnetic-field-induced superelasticity, twinning strain-induced change of magnetization, and magnetoelastic mechanism of magnetostress are briefly reviewed.