Ferroelectric order associated with ordered occupancy at the octahedral site of the inverse spinel structure of multiferroic NiFe_2O_4

摘要

We report a ferroelectric order at similar to 98 K for NiFe2O4, which carries an inverse spinel structure with a centrosymmetric F d (3) over barm structure at room temperature. The value of spontaneous electric polarization is considerably high as similar to 0.29 mu C/cm(2) for 5 kV/cm poling field. The electric polarization decreases considerably (similar to 17%) around the liquid-nitrogen temperature upon application of 50 kOe field, proposing a significant magnetoelectric coupling. The synchrotron diffraction studies confirm a structural transition at similar to 98 K to a noncentrosymmetric structure of P4(1)22 space group. The occurrence of polar order is associated with an ordered occupancy of Ni and Fe atoms at the octahedral sites of the P4(1)22 structure, instead of random occupancies at the octahedral site of the inverse spinel structure. The results propose that NiFe2O4 is a member in the type-II multiferroics.