Low Temperature Deposition of Ferromagnetic Ni-Mn-Ga Thin Films From Two Different Targets via rf Magnetron Sputtering

Low temperature (400°C) deposition of ferromagnetic Ni-Mn-Ga thin films is successfully performed via rf magnetron sputtering technique using co-deposition of two targets Ni50Mn50 and Ni50Ga50 on sapphire (0001) and Si (100) substrates. The films are in part amorphous with significant degree of crystallinity. The obtained crystallographic structure is shown to be substrate-dependent. Films on both substrates are ferromagnetic at room temperature (Curie temperature ∼ 332.5K) with well-defined hysteresis loops, low coercivity (∼ 100 Oe) and a saturation magnetization of ∼ 200 emu/cc. At low temperature (5 K), both films show increased magnetization value with wider hysteresis loops having higher coercivity and remanent magnetization. The process is therefore effective in achieving the appropriate thermodynamic conditions to deposit thin films of the Ni-Mn-Ga austenitic phase (highly magnetic at room temperature) at relatively low substrate temperature without the need for post-deposition annealing or further thermal treatment, which is prerequisite for the device fabrication.