Stable antiferromagnetic nanocrystals for room temperature applications: the case of iron nitride

We characterise the magnetism of self-assembled FenN nanocrystals, combining core level spectroscopy with first-principles theory. Not only ferromagnetic but also antiferromagnetic iron nitride nanocrystals are identified, exhibiting stable magnetic properties at room temperature. New stable magnetic phases are found, previously believed to order magnetically only well below room temperature. As determined by the growth conditions, several phases of magnetic FenN nanocrystals are identified in the near surface region of GaN based thin films, with typical dimensions from 50 to 100 nm, embedded in the (Ga,Fe)N lattice or residing on the GaN surface. We determine, at room temperature, Fe4N and Fe3N ferromagnetic nanocrystals, as well as Fe2N and FeN nanocrystals in an antiferromagnetic state, which is not stable at room temperature in their bulk phases.