Thin film phase diagram of iron nitrides grown by molecular beam epitaxy

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A low-temperature thin film phase diagram of the iron nitride system is established for the case of thin films grown by molecular beam epitaxy and nitrided by a nitrogen radical source. A fine-tuning of the nitridation conditions allows for growth of α′-Fe8Nx with increasing c/a-ratio and magnetic anisotropy with increasing x until almost phase pure α′-Fe8N1 thin films are obtained. A further increase of nitrogen content below the phase decomposition temperature of α′-Fe8N (180°C) leads to a mixture of several phases that is also affected by the choice of substrate material and symmetry. At higher temperatures (350°C), phase pure γ′-Fe4N is the most stable phase.