Microstructure and nanomechanical properties of Mn-rich Ni-Mn-Ga thin films

We report the effect of post-annealing on the crystalline phase, grain growth, magnetic and mechanical properties of Ni-Mn-Ga thin films deposited at room temperature followed by post-annealing at different temperatures. The phase and microstructural analysis reveal that amorphous to crystalline transformation occurs in as-deposited films after post-annealing above 873 K. The transformation of disordered phase into nanocrystalline phase by the influence of annealing has been confirmed by transmission electron microscopy. The crystalline films exhibit soft magnetic behavior with the Curie temperature of 314 K, while the amorphous films exhibit the Pauli-paramagnetic behavior even down to 4 K. The mechanical properties like hardness and elastic modulus of the films also show a strong dependence on the annealing temperature with crystalline film exhibiting maximum values of 6 GPa and 103 GPa, respectively. The Ni-Mn-Ga film annealed at 873 K exhibits enhanced nanomechanical properties and room temperature ferromagnetism which make this a potential candidate for use in MEMS devices.