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First-principles calculations are performed to comparatively study the structural, electronic structures and magnetic properties of Mo doped AlN, GaN and InN monolayers (MLs). After Mo atom doping, the semiconducting GaN and InN MLs transform to metal, while the AlN ML keeps semiconducting with a reduced gap. Total magnetic moments of 1.0 and 0.54 µ B , which mainly arising from the localized Mo 4d states, are induced by doping in AlN and InN MLs, respectively, while the doped GaN ML is still nonmagnetic. Nevertheless, the excessive localization and strongly ionic character of the Mo-4d states in AlN ML directly impedes the magnetic coupling, leading to a paramagnetic ground states. A similar case is observed in Mo atoms doped InN ML. The firm N-Mo interaction prevent the impurity states permeating out the range of N-Mo pair, resulting in a quick vanishing of ferromagnetic coupling as the distance between two Mo atoms increasing. All configurations of Mo atoms doped GaN ML in this paper are room temperature ferromagnetic. Spin polarized itinerant electrons mediate the magnetic interaction between two Mo atoms. Increasing the Mo concentration may stabilize the FM state and produce a higher Curie temperature. Our calculations show that GaN nanosheets with Mo atoms doped may be a nice candidate for future spintronic devices. And we conclude that a appropriate magnitude of localization (or delocalization) is what the key point to produce room temperature ferromagnetism from this comparative study.

The electronic, structural, and magnetic properties of the perovskite Co-doped BiFeO 3 have been investigated using density functional theory within the generalized gradient approximation plus Hubbard U correction (GGA+ U ). We discuss the changes that occur in the structural parameters, electronic structure, and magnetic properties of the Co-doped BiFeO 3 under the consideration of the impact of the 3 d electrons. The results show that a substitutional Co for Fe in BiFeO 3 produces a magnetic moment of − 1.0 μ B and a half-metallic property emerges. The ferromagnetic (FM) coupling is more stable and still presents a half-metallic property when two Co atoms substitute for Fe atoms in BiFeO 3 .