Shape memory effect and magnetostriction in polycrystalline Ni–Mn–Ga thin film microactuators

Ni–Mn–Ga cantilever and tensile microactuators are investigated with respect to their thermoelastic and magnetomechanical characteristics. The base materials are either single-layer Ni–Mn–Ga thin films or Ni–Mn–Ga/Mo thin film composites with different compositions and thicknesses up to 10 μm, which have been fabricated by magnetron sputtering. Differential scanning calorimetry measurements of the thin films show the characteristic features of ferromagnetic Heusler alloys exhibiting a martensitic transformation and a ferromagnetic transition well above room temperature. A pronounced temperature-induced shape memory effect is observed in deflection measurements of the microactuators. The maximum recoverable strain is about 0.8%. Magnetostriction measurements of cantilever actuators consisting of Ni–Mn–Ga/Mo thin film composites show a large increase of magnetostrain for decreasing Ni–Mn–Ga film thickness in the submicrometer range.