Two-way Shape Memory Behavior of Sputter-deposited Ni-rich Ni2MnGa Films

The properties of the Ni-rich Ni ₂ MnGa films and their shape memory behavior are investigated with respect to various sputtering conditions. The films are deposited on a poly-vinyl alcohol substrate with a radio-frequency magnetron sputtering apparatus using Ni ₅₀ Mn ₂₅ Ga ₂₅ and Ni ₅₂ Mn ₂₄ Ga ₂₄ targets. The sputtering power is in the range of 50–400 W. After separating from the substrate, the films are vacuum-annealed at 1073 K for 3.6 ks. The chemical composition of the films depends on the sputtering power. The martensitic transformation temperature increases with the valence electron density of the films, while the Curie temperature slightly decreases. The film obtained with 50 W using the Ni ₅₀ Mn ₂₅ Ga ₂₅ target after heat treatment at 1073 K shows a two-way shape memory effect through the martensitic transformation and its reversion.