Synthesis of Fe₁₆N₂ compound films by reactive sputtering

Fe₁₆N₂ films (of thickness 3000 angstroms) were fabricated on MgO (001) substrates by the conventional dc facing target sputtering method using a controlled reactive plasma, at an electron temperature of T_e = 0.3 eV, an electron density of N_e = 1×10¹⁰ cm^-3, a deposition rate of 200 angstroms/min and an N₂ flow ratio ranging from 10% to 20%. In the as-deposited state, single α′ phases with various nitrogen contents were formed. After annealing at 150 °C for two hours, an α″ phase (≅11 at% N) and an α′ phase (11.1 at% N and 1 to 2 at% N) were formed. The M_s value was nearly the same as for α-Fe (2.2 T), despite the existence of the α″ phase. The lattice constant c of the α″ phase in these films agreed well with the value reported by Jack, but lattice constant a values were about 1 to 3% smaller than Jack's value. The unit cell volumes of the α″ phase in these films were between 192.5 and 202.6 angstroms³, from 1.4 to 6.3% less than Jack's value of 205.5 angstroms³.