Growth and Characterization of Ni2MnGa Single Crystals

Ni2MnGa is a magnetic shape memory alloy (MSMA) which changes its shape when exposed to a variable magnetic field. The shape change is achieved through the magnetic-field-induced motion of twin boundaries. Single crystals of Ni2MnGa demonstrate the highest strains. In this study, the Bridgman–Stockbarger technique was used to produce single crystals of Ni2MnGa. Single crystals were comprised of high purity elements that were melted and mixed in an induction furnace and then crushed into a fine powder. The powder was loaded onto a Ni2MnGa seed that was crystallographically oriented inside an alumina crucible. The powder was then driven into a tube furnace, melted down to the seed and then slowly drawn out of the furnace to solidify as a single crystal in the orientation dictated by the seed. The single crystals displayed severe chemical segregation inherent to this crystal growth technique. This study highlights the characterization techniques used to determine the change in composition which affects the crystallographic phase present at room temperature, phase transformation temperatures and the magnetic-field-induced strain.