Origin of ferroelectric order in multiferroic RFe2O4

The series of spinel ferrites, RFe2O4 has attracted the community for the similar structural and physical properties of magnetite (Fe3O4). Analogous to Fe3O4, NiFe2O4 recently shows the ferroelectric order around ~ 98 K. Although a possible ordered occupancy of Ni2+ and Fe3+ atoms at the octahedral sites of the P4122 structure has been correlated to the ferroelectricity, the possible modulation of the magnetic structure still remains unexplored. Our recent measurements also confirm a ferroelectric order around 40 K for CuFe2O4 system, where we also observe a sharp change in magnetization, indicating a strong magnetoelectric coupling. Our interest is to understand the possible origin of ferroelectric order by investigating the exchange interactions in CuFe2O4. We therefore propose here to investigate temperature dependence of spin wave excitations using neutron inelastic scattering.