Effect of crystal structure on magnetic-field-induced strain in Ni-Mn-Ga

摘要

Magnetic shape memory materials are expected to have a high potential in practical applications. Several ferromagnetic materials exhibiting the large magnetic-field-induced strain have been found in recent years. The largest field-induced strain is observed in Ni-Mn-Ga system. The most important experimental results on crystal structure, magnetic anisotropy and twinning stress of martensitic phases in Ni-Mn-Ga having tetragonal five-layered, orthorhombic seven-layered and tetragonal non-layered crystal structures are reported. Depending on the martensite crystal structure Ni-Mn-Ga alloys are able to show a really giant strain response (approximately 6% in tetragonal five-layered or 10% in orthorhombic seven-layered martensitic phase) in a magnetic field less than 1 T. Contrary to these two phases, a detectable field-induced strain is not observed in non-layered tetragonal martensitic phase in Ni-Mn-Ga system. Effect of crystal structure is in a good agreement with calculation of the magnetic-field-induced strain based on the model developed by authors. The effect of composition on appearance of undesirable non-layered tetragonal martensitic phase in Ni-Mn-Ga system is discussed based on the new experimental results.