Ordered nickel-iron-nitrogen phase produced by elevated temperature nitrogen ion implantation

Abstract

Implantation of 1×1018N2+/cm2 at 60 keV ion energy into pure bcc-Fe held at 400°C during implantation yields the well-known ferromagnetic γ'-Fe4N ordered fcc compound with two inequivalent crystallographic sites, one of which consists of two different magnetic sites. 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 phase with only one site defined by a rather large quadrupole interaction (1.15 mm/s). The X-ray pattern is clearly that of the ordered γ'-(Ni0.8Fe0.2)4N structure so we conclude that the Fe atoms occupy only 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 implantation process. Post-implantation annealing at 400°C decomposes the γ' phase.