Synthesis of α″-Fe16N2 iron nitride by means of nitrogen-ion implantation into iron thin films

Abstract

Nitrogen ions were implanted into [1 0 0] oriented α-Fe thin films on MgO (1 0 0) substrates at room temperature. The films were annealed at a low temperature of 473 K. α″-Fe16N2 and α′-martensite phases were formed and the volume fractions of these nitride phases were estimated from the X-ray diffraction patterns. When the film thickness was 250 nm, α″-Fe16N2 was formed directly by ion implantation and the maximum volume fraction was about 12%. For the case of 50 nm thick films, no α″-Fe16N2 but α′-martensite was formed after nitrogen-ion implantation, and the volume fraction of the martensite exceeded 90%. By post annealing at 473 K, α″-Fe16N2 was formed, when the implanted specimens were coated with gold or copper films. The volume fraction of α″-Fe16N2 reached about 36%. A SQUID magnetic measurement showed that the saturation magnetization of the nitrogen-implanted 250 nm thick iron films was a few per cent larger than that of unimplanted iron films.