First-Principles Study of Magnetism in Transition Metal Doped Na_0.5Bi_0.5TiO₃ System

The origins of magnetism in transition-metal doped Na_0.5Bi_0.5TiO₃ system are investigated by ab initio calculations. The calculated results indicate that a transition-metal atom substitution for a Ti atom produces magnetic moments, which are due to the spin-polarization of transition-metal 3d electrons. The characteristics of exchange coupling are also calculated, which shows that in Cr-/Mn-/Fe-/Co-doped Na_0.5Bi_0.5TiO₃ system, the antiferromagnetic coupling is favorable. The results can successfully explain the experimental phenomenon that, in Mn-/Fe-doped Na_0.5Bi_0.5TiO₃ system, the ferromagnetism disappears at low temperature and the paramagnetic component becomes stronger with the increase of doping concentration of Mn/Fe/Co ions. Unexpectedly, we find the Na_0.5Bi_0.5Ti_0.67V_0.33iO₃ system with ferromagnetic coupling is favorable and produces a magnetic moment of 2.00 μB, which indicates that low temperature ferromagnetism materials could be made by introducing V atoms in Na_0.5Bi_0.5TiO₃. This may be a new way to produce low temperature multiferroic materials.