Possible Origin of Ferromagnetism in Transition Metal Doped Zirconia

We have studied the electronic structure and magnetic properties of cubic zirconia (c-ZrO₂) with cobalt (Co) or nickel (Ni) doping using density functional theory (DFT) calculations. The pure c-ZrO₂ is a nonmagnetic insulator with a wide bandgap. The calculated results reveal that isolated Co or Ni atom can both produce the local magnetic moment in c-ZrO₂. And the isolated Co atom can introduce a magnetic moment of about 0.98 μ_B, while the Ni atom is 2.85 μ_B. The impurity peaks can be formed in the bandgap. Our studies show that the magnetic moments mainly result from d orbitals of the impurity atoms. And the spin-up electrons will be arranged in t_2g orbitals under the ligand field of O_h group in Co- or Ni-doped c-ZrO₂. Obviously, this will lead to a high-spin state (S =  1/2 or 1). The studies of magnetic coupling reveal that the two Co atoms in c-ZrO₂ are not always coupled ferromagnetically at different distances. And the system will be in a spin singlet state (S =  0) when the distance is 6.209 or 7.170 Å between two Co atoms. However, the two Ni atoms in c-ZrO₂ are always coupled ferromagnetically at all distances. So we can conclude that the Ni-doped c-ZrO₂ is more suitable for spintronic material than Co doping. These results are significant for spintronics.