First principles study of the magnetic properties and charge transfer of Ni-doped BiFeO3

Highlights: • The magnetic moment increases due to the ferrimagnetic order in Ni-O-Fe. • Charge transfer of Bi 6s → Ni 3d lead to Ni²⁺ oxidation state. • Ni²⁺ oxidation state is helpful for high Néel temperature. • The electronic states is Bi⁴⁺_xBi³⁺_1-xNi²⁺_xFe³⁺_1-xO₃ • The polarization of Bi 6s and O 2p states contributes to the magnetic moment. • An acceptor level is responsible for increase in leakage current. We present a first-principles study of electronic structures and magnetic properties in Ni-doped BiFeO₃ using the density functional theory + U methods. The BiNi_xFe_1-xO₃ (x = 0.125, 0.25, 0.5) multiferroic ceramics represent ferromagnetic properties due to the ferrimagnetic order in Ni-O-Fe, and the magnetic moment rises with increase in Ni doping concentration agreeing well with experimental results. Ni atoms prefer to occupy the diagonal positions in the quasi-plane Ni-O-Fe eight-membered ring. Charge transfer from Bi 6s state to Ni 3d state through O 2p orbital lead to the 2+ oxidation state of Ni, indicating high Néel temperatures of BiNi_xFe_1-xO₃, and the electronic state of the system can be described as Bi⁴⁺_xBi³⁺_1-xNi²⁺_xFe³⁺_1-xO₃. The spin polarization of Bi 6s state and O 2p state near the Fermi level contributes to the total magnetic moment. A spin-polarized acceptor level of about 0.4 eV constituted by Bi 6s state and O 2p state is found, which is responsible for the increase in leakage current of Ni-doped BiFeO₃.