The electronic structures and magnetic properties of N-doped CeO _2 crystals have been investigated by first-principles calculations based on density functional theory with and without U. The results demonstrate a magnetic moment of 1.00μ_B per N obtained from all schemes. Predictions based on both LSDA and GGA calculations with and without U capture a half-metallic ground state for the N-doped CeO_2 system. Several doped configurations calculations within LSDA demonstrate that there exist robust ferromagnetic couplings between these local magnetic moments, which mainly stem from Hund's rule coupling. The hole-mediated long-range double exchange mechanism is responsible for the predicted ferromagnetism. It turns out that the percolation concentration needed to establish the collective ferromagnetism is at a few percent. However, further test calculations show that a weakly half-metallic ground state is predicted by GGAU for this system.
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