Thermal stability of Fe₁₆N₂ thin film on GaAs (0 0 1) substrate

There is a major need for a high performance magnetic system for high temperature applications. One propitious low cost permanent magnet candidate is Fe₁₆N₂, with its giant magnetic moment predicted to be above other materials from conventional first principles calculations. Here we report on a comprehensive study of the thermal stability of Fe₁₆N₂ thin films on GaAs (0 0 1) substrate. Using polarized neutron reflectometry (PNR), the saturation magnetization depth profile (Ms) of the films and its modification with temperature is directly measured at various thermal conditions. The structural modifications probed by x-ray diffraction (XRD) unravel that above 250 °C the Fe₁₆N₂ thin films decompose into α-Fe and γ′-Fe₄N phases. An influence of the strain effect is investigated by grazing incidence x-ray diffraction (GIXRD). We reveal that despite a large Fe₁₆N₂ in-plane lattice constant of ∼5.88 å and different strains from substrate or seed layer (up to 2.8% tensile strain), Fe₁₆N₂ thin films have the same thermal stability. Our results demonstrate that the high thermal stability of partially order Fe₁₆N₂ thin films makes them very promising candidates for spintronics and permanent magnet applications.