Single-crystal growth of NiMnGa magnetic shape memory alloys

The crystal growth of NiMnGa magnetic shape memory alloys was investigated by the optical zone melting method. Slightly macroscopic convex and planar solid-liquid interfaces were achieved by controlling the molten zone morphologies. Single crystals were successfully prepared in three typical series of NiMnGa magnetic shape memory alloys, including stoichiometric Ni₅₀Mn₂₅Ga₂₅, Ni-rich NiMnGa and Mn-rich NiMnGa alloys. Studies on the solute partition during crystal growth revealed the enrichment of Mn and deficiency of both Ni and Ga in front of the solid-liquid interface for both stoichiometric and Mn-rich NiMnGa alloys, while a slight enrichment of Ni for Ni-rich NiMnGa alloys. An initial transient stage was determined to be about 20 mm, and a uniform composition distribution existed along the axis of the crystals in the stable growth parts, which matches well with the proposed mathematic model.