Investigation of dilute ferromagnetism induced at room temperature in undoped crystalline AlN thin film after isothermal annealing in a controlled oxygen environment

The crystalline aluminium nitride (AlN) thin films were isothermally annealed at 850 & DEG;C in a controlled oxygen environment. The oxidation process has led to significant enhancement in lattice parameters and degradation in the crystallinity of as-grown AlN film. The AlN bonding at the film's surface was systematically reduced and finally vanished when the film was annealed at 20% oxygen mixed with an argon environment. During annealing, nitrogen in AlN is replaced by oxygen, and a fraction of replaced nitrogen is trapped at the interstitial sites in AlN, which systematically enhances with an increment in oxygen content. Magnetic measurements exhibit dilute ferromagnetism induced in as-grown AlN film at 300 K after annealing. Density functional theory (DFT) calculation reveals interaction between N 2p orbitals of interstitial nitrogen and first neighbouring nitrogen atoms contributing to observed magnetic properties.