Influence of Si-N interlayer on the microstructure and magnetic properties of γ′-Fe4N films

The (γ′-Fe4N/Si-N)n (n: number of layers) multilayer films and γ′-Fe4N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe4N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe4N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe4N to ɛ-Fe3N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ɛ-Fe3N transformed back into γ′-Fe4N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe4N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ɛ-Fe3N.