Epitaxial growth and magnetic characterization of γ´-Fe4N thin films

Owing to their giant value of magnetic moment under specific conditions, certain phases of iron nitride have received considerable attention of the scientific community worldwide. In particular, α”-Fe₁₆N₂ and γ´-Fe₄N phases have been studied extensively due to their excellent ferromagnetic characteristics. The former being thermally less stable so γ´-Fe₄N appears as strong candidate for applications where high saturation magnetization (M_s), low coercivity (H_c) and better chemical stability is required . For instance, all nitride magnetic tunnel junctions (MTJs) using Cu₃N as insulating layer between γ´-Fe₄N electrodes and current perpendicular-to-plane (CPP) devices could greatly benefit from these materials. However, high value of magnetic moment in these types of materials could only be achieved in epitaxial thin films. In this context, we optimized the conditions for epitaxial growth of γ´-Fe₄N thin films by controlling the deposition temperature and post annealing time. 55 nm thick films were directly deposited on single crystal MgO(100) substrate using dc magnetron sputtering at a base pressure better than 2 x 10^-6 Torr . A mixture of pure Ar and N at a ratio of 10:1 was injected into the chamber at 5 .5 mTorr . 2” diameter thick target of highly pure α-Fe was sputtered at 30 W . The substrate temperature was varied from 200 to 500 °C and the films were in-situ annealed from 10 to 40 min .