Abstract: The effect of heat treatment on the properties of Ni-Mn-Ga films
such as chemical composition, crystal structure, microstructure and
transformation temperature were investigated with respect to various sputtering
conditions. Ni-Mn-Ga films were 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. After separating from the substrates, the films were annealed at
temperatures between 873 and 1273 K for 3.6 ks. The chemical composition of the
films depended on the sputtering power, but there was no dependence on the heat
treatment temperature. Each deposited film had a columnar grain structure.
After the heat treatment, the width of the columnar grains increased and then
became indistinct with increasing heat treatment temperature. The martensitic
transformation temperature increased with increasing nickel content of the
films, while the Curie temperature decreased. The film heat-treated at 1073 K
showed a two-way shape memory effect through the martensitic transformation and
its reversion.
