A microscopic approach to the magnetic-field-induced deformation of martensite (magnetoplasticity)

Deformation experiments were performed in uniaxial compression with a Ni–Mn–Ga single crystal subjected to a magnetic field perpendicular to the stress axis. Depending on the field strength, different stress–strain curves for loading and unloading were obtained. The magnetic-field-induced stress (magneto-stress) and the work done by the corresponding magnetic force were evaluated. In order to understand the relationship between the magneto-mechanical properties and the microstructure, the microscopic processes occurring during magnetic-field-induced deformation are discussed in detail. It turns out that the magnetic work per unit volume and, to some extent, the macroscopic magneto-stress depend on the microstructure, i.e. the spatial distribution of martensite domains. The magnetic threshold field required for triggering magnetoplasticity depends on the twin thickness and is controlled by the mutual interaction of twinning dislocations and their interaction with interfaces. The threshold field can be entirely described within this microscopic approach, taking into account the elementary carrier of magnetoplasticity, which is the twinning dislocation.