Phase structure and magnetic properties of the annealed Mn-rich Ni–Mn–Ga ferromagnetic shape memory thin films

The phase structure and magnetic behavior of sputter deposited and annealed Ni–Mn–Ga thin films of varying thickness have been studied. The as-deposited films exhibited quasi-amorphous structure having paramagnetic nature at room temperature. After annealing at 873 K for 30 min ferromagnetic ordering is recovered and the quasi-amorphous structure has changed to nanocrystalline structure. At low film thickness (<300 nm), the annealed films exhibited a mixture of cubic austenite (L21) and martensite phases while at thickness greater than 1000 nm ordered L12 phase was observed. The magnetic properties were found to strongly depend on the structure of the constituent phases in the films.