Zero-field ferroelectric state and magnetoelectric coupling in antiferromagnetic Fe4Nb2O9 single crystal

Abstract High quality Fe4Nb2O9 single crystal was grown by optical floating zone method. The magnetization-temperature(M-T) curves, isothermal magnetization curves(M-H) and pyroelectric current-temperature curves of the single crystal along different crystallographic directions were measured. The results of magnetization measurements which shows the Neel temperature TN of around 90 K and the in-plane magnetic structure of Fe4Nb2O9 are very consistent with the reported magnetic structure obtained by neutron diffraction. The isothermal magnetization curves along [210] direction show spin flop phase transition and a local ferromagnetic loop under 50 K. The critical field HC of spin flop phase transition is found to be 94 kOe. Pyroelectric current-temperature curves show ferroelectric polarization below about 90 K under zero magnetic field, which has not been reported before in single crystal Fe4Nb2O9. At the same time, Fe4Nb2O9 shows magnetoelectric coupling effect. With the increase of magnetic field, the polarization increases to over 300 μC/m2 along a axis under applied magnetic field of 70 kOe.