Large magnetization induced in single crystalline iron films by high-dose nitrogen implantation

Nitrogen ions were implanted in 200-nm-thick single crystalline iron films for a stoichiometric concentration of Fe16 N2 (11.1 at. %) by way of a multiple implantation. X-ray diffraction revealed that the as-implanted films were composed of 70% nitrogen martensite and 30% residual α-Fe. A slight amount of α″-martensite, that is, Fe16 N2, was detected but the principal constituent of the nitrogen martensite was α′-martensite. The saturation magnetic moment increased by 13.4 % with the implantation. Annealing the implanted films at 150 °C for 2 h in vacuum resulted in an increase in a constituent of the α″ phase, but affected the magnetic moment only slightly. It was deduced that the saturation magnetization of the nitrogen martensite is ∼257 emu/g at room temperature. It was also found that the implantation induced a perpendicular magnetic anisotropy due to the characteristics of the nitrogen martensite.