First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe2O4

• Bulk NiFe2O4 with P4122P4122 or Imma space group in inverse spinel structure was considered.
• GGA + U method with U=4.5,3.24 eVU=4.5,3.24 eV and J=0.79J=0.79, 1 eV for Fe, Ni was applied.
• In Imma phase the spontaneous polarization was calculated to be zero.
• In P4122P4122 phase ionic and electronic contributions to the polarization were zero and 23 μC/cm2.
• The polarization originates from Fe 3d–O 2p states hybridization induced by Jahn–Teller effect.

We investigate the ferrimagnetism and ferroelectricity of bulk NiFe2O4 with tetragonal P4122P4122 symmetry by means of density functional theory calculations using generalized gradient approximation + Hubbard U approach. Special attention is paid to finding the most energetically favorable configuration on magnetic ordering and further calculating the reliable spontaneous electric polarization. With the fully optimized crystalline structure of the most stable configuration, the spontaneous polarization is obtained to be 23 μC/cm2 along the z direction, which originates from the hybridization between the 3d states of the Fe3+ cation and the 2p states of oxygen induced by Jahn–Teller effect.