Crystalstructures and magnetic anisotropy properties of Ni-Mn-Ga martensitic phases with giant magnetic-field-induced strain

摘要

Magnetic shape memory materials are expected to have potential in a variety of actuating devices and sensors. Magnetic-field-induced rearrangement of the crystallographic domains (twin variants) can produce a large strain similar to a stress-induced one. Several ferromagnetic materials exhibiting the large magnetic-field-induced strains have been found during last few years. The largest strain approximately 6% were achieved in NiMnGa system above room temperature due to efforts of several research groups. It was found that crystal structure of martensite in this case is nearly to tetragonal one with five-layer modulation along (11O)[11{top}(-)0]{sub}p system. Practically, observed 6% strain is very close to the maximal twinning strain value (1 - c/a) that can be expected for the tetragonal martensite crystal lattice (a = b ≠ c, c/a <1) and corresponds to magnetic field-induced transformation between two single variants.