Magnetic and structural properties of nitrided Fe and FeTi thin films
This thesis investigates the magnetic and structural properties of Fe and Fe$STi1s thin films nitrided using a nitrogen atom source. In this novel technique, the atom source produces an atomic nitrogen beam for which multilayer samples with bilayers of the form Fe/FeN or FeTi/FeTiN were synthesized by varying the thickness of the Fe or FeTi exposed to the nitrogen beam. The samples studied here are all in the as-deposited state. X-Ray reflectivity confirms the presence of a multilayer structure showing sharp multilayer peaks indicative of good quality interfaces. The electron diffraction data shows a variation of nitride phases as the thickness of the Fe layer was varied. Fe2N was present when the bilayer was 7A thick. Increasing the bilayer thickness led to a bilayer consisting of two different nitride phases until the Fe layer was 42A thick and the bilayer consisted of a-Fe and Fe4N. In contrast, when Ti was present the phase was body centred cubic for all but the thinnest bilayers considered in this thesis. The grain structure of the two systems was also quite different. The Fe/FeN grain sizes ranged from 50 to 1000A in diameter as the bilayer was varied. In the FeTi/FeTiN sample set the grain growth was inhibited with no noticeable increase with nitriding. Despite these structural differences the magnetic character of the two series of samples were consistent. The samples ranged from nonferromagnetic to ferromagnetic with the presence of weak perpendicular anisotropy occurring as the bilayer thickness increased. As the bilayer thickness was increased there was an asymptotic approach of the magnetization to the level of the unexposed materials. The presence of the perpendicular anisotropy was maintained for a larger parameter space. In both series the anisotropy is attributed to stress induced by the substrate. Nitriding Fe and FeTi using the aforementioned technique provides a controlled and viable way to alter the magnetic and structural properties.