High moment epitaxial Fe-N thin films

High moment epitaxial Fe-N films were produced using reactive sputtering in an ultra clean sputtering system with in-situ RHEED, and the effects of nitrogen concentration and annealing on magnetic and structural properties were investigated. A sulfur-passivated GaAs substrate was annealed at 450°C to get a good RHEED pattern. A 1 nm thick Fe seed layer was then deposited to promote epitaxial growth of a 20 nm thick Ag(100) buffer layer. Fe-N films were grown on these Ag(100) buffer layers. Nitrogen partial pressure and annealing temperature was varied to obtain epitaxial high moment films. Epitaxial GaAs(001)/1 nm Fe/20 nm Ag(001)/40 nm Fe-N(001)/Ru 10 nm films with low nitrogen concentration exhibited an α´-FeN single phase with a magnetization of about 18 kG. Films with high nitrogen concentration exhibited a mixture of α´-FeN and γ´-Fe₄N phases, resulting in low magnetization. Post-annealing of films with low nitrogen concentration increased the magnetization up to 20 kG, but the post-annealing of films with high nitrogen concentration increased the amount of the γ´-Fe₄N phases, resulting in lower magnetization. For films with low nitrogen concentration, sharp RHEED streaks are observed and this is an indication of well-ordered smooth epitaxial films. For films with high nitrogen concentration RHEED streaks are broadened and the background increases which is indicative of an increasing amount of disorder and roughness or possibly a multiphase film. Rms surface roughness of the films was in the range of 0.2-0.6 nm