ORDERED NICKEL-IRON-NITROGEN PHASE PRODUCED BY ELEVATED-TEMPERATURE NITROGEN ION-IMPLANTATION

Implantation of 1 x 10(18)N2+/cm2 at 60 keV ion energy into pure bcc-F e held at 400-degrees-C during implantation yields the well-known ferr omagnetic gamma'-Fe4N ordered fcc compound with two inequivalent cryst allographic sites, one of which consists of two different magnetic sit es. These sites are readily identified via their hyperfine interaction parameters as detected by conversion electron Mossbauer spectroscopy of the near-surface layer. X-ray diffraction confirms the N sublattice ordering. Here, nitrogen implantation under identical conditions into a disordered fcc Ni0.8Fe0.2 alloy (permalloy) yields a paramagnetic p hase with only one site defined by a rather large quadrupole interacti on (1.15 mm/s). The X-ray pattern is clearly that of the ordered gamma '-(Ni0.8Fe0.2)4N structure so we conclude that the Fe atoms occupy onl y the face-centered lattice sites where each can bond with two nearest -neighbour N atoms on opposite sides. Thus, additional ordering within the Ni-Fe sublattice has been induced by the elevated temperature imp lantation process. Post-implantation annealing at 400-degrees-C decomp oses the gamma' phase.